Integrated Use of Grafting Technology to Improve Disease Resistance and Fruit Yield in Specialty Melon Production

Final Report for LS10-233

Project Type: Research and Education
Funds awarded in 2010: $223,000.00
Projected End Date: 12/31/2014
Region: Southern
State: Florida
Principal Investigator:
Dr. Xin Zhao
University of Florida
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Project Information

Abstract:

This multidisciplinary project was focused on integrating the grafting technology into specialty melon production for disease management and yield improvement. Different grafting methods were evaluated and a new method for cucurbit rootstock treatment was developed to enhance grafting efficiency. Rootstocks were screened and tested for effective control of Fusarium wilt in grafted specialty melon production. The Cucumis metulifer rootstocks with good graft compatibility were also identified for successfully managing root-knot nematodes in specialty melons. Significant rootstock-scion interaction effects on specialty melon fruit quality were observed. Given the high cost of grafted transplants, economic feasibility of grafted melon production needs to be determined based on site-specific conditions. 

Project Objectives:

Objective 1. Identify effective rootstocks for managing Fusarium wilt and root-knot nematodes in grafted specialty melon production in the Southeastern US.
  

Objective 2. Examine new grafting methods to reduce labor and increase production efficiency. 

Objective 3. Assess the growth promotion, yield increase, and fruit quality in grafted melon production beyond disease resistance. 

Objective 4. Analyze the economic costs and returns of field production of grafted melon. 

Objective 5. Develop education and outreach programs on integrated use of grafting in sustainable production of specialty melon.

Introduction:

The purpose of this project is to study the benefits of grafting to improve disease resistance and productivity of specialty melons and the feasibility for its implementation as an economically-viable practice in sustainable vegetable production. Specialty melon (Cucumis melo L.) varieties, e.g., galia-type muskmelons and honeydew melons, have been grown increasingly by small growers in the Southeastern U.S. The superior flavor and outstanding eating quality makes specialty melons a high premium produce especially for the local markets. However, many specialty melon cultivars with excellent sensory and nutritional quality attributes appear to be more susceptible to soilborne diseases. The problem of vine decline due to soilborne pests is emerging as one of the most serious threats to sustainable production of specialty melons in the Southeastern U.S. where light soils and warm humid climatic conditions tend to favor such pest populations. The lack of varietal disease resistance also limits the selection and adoption of desirable specialty melon cultivars in sustainable farming systems. Among many other soilborne pests, the devastating soilborne disease Fusarium wilt and/or destructive root-knot nematode infestation have been identified as the major obstacles to successful cultivation of specialty melons by growers in Florida, South Carolina, and Kentucky.

Fusarium wilt of melon is caused by the soilborne pathogen Fusarium oxysporum f. sp. melonis (Fom). There are four typical races of Fom: 0, 1, 2, and 1,2. Control of Fom races 0, 1, and 2 has traditionally been accomplished using host plant resistance or resistant cultivars (Yoshioka, 2001). However, with the increased prevalence of Fom race 1,2 and lack of cultivars with resistance, genetic improvement of current melon varieties remains a challenging task (Oumouloud et al., 2009). With respect to specialty melons, breeding new cultivars with complete resistance may be even more challenging as focusing on disease resistance might compromise their superior sensory qualities. On the other hand, the cultural control measures such as crop rotation and cover crops are also used for management of Fusarium wilt. Nevertheless, the effectiveness of these cultural practices turns out to be less satisfactory due to the long-term survival and persistence of chlamydospores in the soil (Zitter, 1998). Thriving in warm weather and moist sandy soils, root-knot nematodes (Meloidogyne spp.) can cause considerable galling on the roots of melon and even low initial populations may result in substantial yield loss. Root-knot nematode resistance has not been identified in Cucumis melo whereas incorporation of resistance genes from other related species like Cucumis metulifer into C. melo cultivars have been shown to be rather difficult (Sigüenza, et al. 2005). Solarization and crop rotation (e.g., with rye or other cover crops) are commonly employed to control root-knot nematodes on site, however, success of general cultural management can be restricted by the extensive host range of root-knot nematodes. 

Vegetable grafting follows the same principles applied to fruit tree grafting. A new grafted plant with combined desirable traits can be created through a physical union of a rootstock plant and a scion plant. This technique may be complementary to breeding in uniting positive genetic and physiological traits that confer elevated vigor and productivity to the resulting plant. Vegetable grafting has been successfully practiced in Asia and Europe as a unique component in sustainable vegetable production, reducing substantially the use of pesticides and realizing great gains in disease management and yield increase on solanaceous and cucurbitaceous vegetables (Lee, 2003, 2010; Leonardi and Romano, 2004). Research took place recently in the US to explore the use of grafting as a potential alternative to methyl bromide soil fumigant in open field production of fruiting vegetables (Kubota et al., 2008). 

Using resistant rootstocks to graft susceptible scion varieties has been demonstrated to effectively control Fusarium wilt and nematodes in cucurbits. Grafting for fusarium resistance began in Japan in the 1920s to control F. oxysporum f. sp. niveum in watermelon with Cucurbita moschata as the rootstock. C. moschata and C. maxima × C. moschata rootstocks were later used in melon production to battle Fusarium wilt (Sakata et al, 2008). Other germplasm materials conferring high levels of Fusarium resistance have also been evaluated for their application as potential rootstocks, including Citrullus spp. (Huh et al., 2002) and several different Cucumis spp. and Cucurbita spp. (Igarashi et al., 1987; Trionfetti-Nisini et al., 1999; Hirai et al., 2002). In addition, galia-type melons grafted with the Cucurbita rootstock showed certain resistance to sudden wilt caused by Monosporascus cannonballus. Recent studies demonstrated that using interspecific rootstocks (C. maxima × C. moschata) can provide resistance not only to Fusarium wilt (Fom race 1,2) but also to gummy stem blight caused by Didymella bryoniae (Crino et al., 2007). Grafting with C. metulifer rootstocks has been shown to significantly reduce levels of root galling and root-knot nematode buildup at harvest for melon production in M. incognita-infested soil (Siguenza et al., 2005). In some cases, the rootstocks appear to provide tolerance by providing a more extensive root area and vigor (Giannakou and Karpouzas, 2003). In addition to improved disease resistance, increased efficiency of nutrient and water absorption has been observed on grafted vegetables, which is often attributed to the vigorous root systems of rootstocks (Lee, 1994; Passam et al., 2005). Grafting with some C. maxima × C. moschata rootstocks enhanced N utilization and assimilation in melon plants and resulted in higher yields (Ruiz et al., 1999). Moreover, plants grafted onto certain rootstocks have demonstrated improvement of tolerance to environmental stresses such as drought, salinity, and low temperature (Davis et al., 2008; Lee, 2003, 2010). 

The adoption of grafted plants for commercial use requires not only successful performance in the field but also consideration of the quality characteristics of the harvested product for successful marketing. Analysis of quality of melon fruits from grafted plants has revealed variable results. The galia-type melon (C. melo) grafted onto Fom resistant squash rootstocks had larger fruit size and higher total soluble solids compared with non-grafted controls (Bletsos, 2005). In contrast, melon grafted onto several C. maxima × C. moschata rootstocks showed no change in fruit dry matter, total soluble solids, fruit firmness, and color (Crino et al., 2007), while grafted melon using winter squash rootstock (C. moschata) exhibited inferior textural properties (Traka-Mavrona et al., 2000). Give the concerns about possible negative effects of rootstocks on the quality of melon including shape, size, texture, total soluble solids, and flavor, analysis of fruit quality will be performed in our evaluation of rootstocks. 

When we demonstrate the vegetable grafting technique to different groups of growers, they are always interested in learning how to conduct grafting themselves. Cleft, splicing, and hole insertion methods, which have high grafting positions, have been adapted to increase separation of scion from the ground in order to decreases the opportunity of scion adventitious roots contracting soilborne diseases. Achieving high survival rate of grafts is essential for profitable production of grafted vegetables. The survival rate of grafted plants depends on a variety of factors including compatibility between scion and rootstock, quality and age of seedlings, quality of the joined section, and post-grafting management. Through this project we expect to develop detailed guidelines for cost-effective production of grafted melon transplants at different scales. 

The cost of using grafted plants in commercial production is often perceived as an obstacle for the wide-spread adoption of this technique. Compared with traditional melon production, additional costs associated with grafted melon production are reflected mainly in producing grafted transplants, e.g., seeds, space, and labor for growing rootstock seedlings, tools, materials, space, and labor for making grafts, and care of grafts during healing process. Sometimes extra efforts are needed to remove rootstock suckers from grafted plants in the field. Obviously, high marketable yield and quality is the key to break-even and eventually making profitability in production of grafted specialty melons. In this project, we hope to provide research-based information on cost-return analysis for making site-specific recommendations for use of grafted plants in specialty melon production.

Cooperators

Click linked name(s) to expand
  • Dr. Zhifeng Gao
  • Dr. Richard Hassell
  • Dr. Mickie Swisher
  • Dr. Judy Thies
  • Dr. Danielle Treadwell
  • Dr. Patrick Wechter

Research

Materials and methods:

Specialty melon cultivar evaluation

With the purpose of determining the scion cultivars for the melon grafting studies, the specialty melon cultivar evaluation trials were conducted during spring 2011 in the certified organic (Quality Certification Services, Gainesville, FL) and conventional field plots at the University of Florida Plant Science Research and Education Unit (PSREU) in Citra, FL. Ten specialty melon cultivars (Cucumis melo) from five different types including ananas melon ‘Creme de la Creme’ and ‘San Juan’, canary melon ‘Brilliant’ and ‘Camposol’, asian melon ‘Ginkaku’  and ‘Sun Jewel’, galia melon ‘Arava’ and ‘Diplomat’, and honeydew melon ‘Honey Pearl’ and ‘Honey Yellow’ were evaluated. ‘Athena’ cantaloupe, one of the most popular muskmelon cultivars in the Southeastern United States, was included as a control. Both the organic and conventional field experiments were arranged in a randomized complete block design with four replications (blocks) and 10 plants for cultivar per replication. 

Anthesis dates, first harvest dates, and total and marketable fruit yields were recorded. Fruit quality attributes including fruit weight, size, soluble solids content (SSC), and flesh firmness were measured on four fruit from each cultivar per replication. Disease incidence and severity were recorded at both sites. In the conventional field, powdery mildew and downy mildew were the primary foliar diseases. In the organic field, gummy stem blight and root-knot nematode caused the major damage.

Evaluation of melon grafting methods

Greenhouse experiments were conducted at the University of Florida, Gainesville, FL to evaluate effects of grafting methods on plant early growth. The experiment was first conducted in spring 2011. Hole-insertion, one-cotyledon, and cotyledon-devoid (non-cotyledon) grafting methods were compared by grafting ‘Athena’ muskmelon onto three interspecific hybrid squash rootstocks ‘Strong Tosa’, ‘Tetsukabuto’, and ‘Just’ (Cucurbita maxima × Cucurbita moschata) as well as a melon rootstock ‘Dinero’ (C. melo). Non-grafted scions and rootstocks were used as controls. A completely randomized design with 12 plants per treatment was used. After post-graft healing, graft survival rate was recorded. Plant growth characteristics including scion leaf number, aboveground fresh weight, leaf area, chlorophyll content, and root fresh weight were measured at 22 days after grafting. 

Incorporating results from the first experiment, and adding tongue approach method and root excision treatment, a new practice in cucurbit grafting, two greenhouse experiments were performed during Nov. 2013 – March 2014. In these experiments, ‘Athena’ was grafted onto ‘Strong Tosa’ with four methods including hole insertion (HI), one-cotyledon (OC), non-cotyledon (NC), and tongue approach methods (TA). Non-grafted rootstock and scion plants were included as controls. Both grafted and non-grafted plants were examined with or without root excision. For the root excision treatment, plants were cut just above the root zone and replanted in pre-moistened soil. A randomized complete block design with three replications and 12 plants per treatment per replication was used in the grafting experiments. The numbers of healed grafts of each grafting treatment were recorded in the first experiment; while in the second experiment, a 0-10 scale was used to evaluate the quality of grafted plants at 16 days after grafting (DAG). For each treatment per replication, three randomly selected grafted plants were destructively measured at 4, 8, 12 and 16 DAG. Total root length and root surface area were evaluated using a root scanning apparatus. At 16 DAG, aboveground fresh weight and dry weight were measured. In order to further evaluate plant growth characteristics, six plants of each treatment were individually transplanted into 3.8 L pot. Plants were arranged in a completely randomized design with six plants serving as six replications in each treatment. Anthesis dates of plants were recorded. Plants were grown in the greenhouse until at least two female flowers bloomed in each plant. Aboveground growth characteristics including fresh weight, dry weight, leaf area, stem diameter, chlorophyll content, and stomatal conductance were measured. Root length and surface area of each plant were evaluated. 

Development of new grafting methods to eliminate rootstock meristems and prevent regrowth

Greenhouse studies were performed at Clemson University CREC, Charleston, SC in 2011 to evaluate available chemicals for prevention of rootstock meristem growth. Most compounds tested, including surflan and sulfuric acid, provided no control of rootstock meristematic growth. Maleic hydrazide (MH-30) controlled rootstock growth, but prevented graft healing. Fatty alcohol products controlled rootstock growth and allowed grafts to heal successfully. During 2012-2013, two experiments were conducted to 1) determine the optimal application rate and 2) determine the effect of time after application on rootstock size and carbohydrate content. In the first experiment, two fatty alcohol products (Fair 85® and Off-Shoot T®) at six concentrations (3.75, 5.0, 6.25, 7.5, 8.75, and 10% fatty alcohol) were applied to interspecific hybrid squash ‘Carnivor’ rootstock as the cotyledons unfolded. A water-only treatment was included as the control. On days 1, 7, 14, and 21 after application, rootstocks were individually rated for both damage and regrowth responses. In the second experiment, hypocotyl and cotyledons of both rootstocks were analyzed for size and carbohydrate content on days 1, 7, 14, and 21 after fatty alcohol treatment. Effects of rootstock age after fatty alcohol treatment on graft survival were also evaluated in 2013. Graft survival using one-cotyledon and hypocotyl-only (non-cotyledon) grafting methods was recorded using rootstocks at 1, 7, 14, and 21 days after treatment.

Identification of effective rootstocks for managing Fusarium wilt in grafted specialty melon production
Greenhouse studies were performed in 2011 at the U.S. Vegetable Laboratory in Charleston, SC to evaluate available rootstock material for resistance against the Fusarium wilt pathogen Fusarium oxysporum f. sp melonis (Fom). Fifteen rootstock lines were screened for Fusarium wilt resistance/susceptibility. Both race 1 and race 2 isolates of Fom were used for the screening study using a standard root-dip assay with a conidial concentration of 1 x 106 conidia per ml. The control plants ‘Ananas Yokneum’ (susceptible to race 1 &2) and ‘MR-1’ (resistant to both races) were included in each test. In the 2011 grafting experiment, melon grafted on 15 commercial rootstocks were evaluated for resistance to Fusarium wilt race 1 and 2. Studies were further conducted in 2013 to identify molecular markers linked to Fom resistance in melon. In addition, molecular markers linked to Alternaria leaf blight resistance and sulfur resistance were examined. Elemental sulfur is effective for controlling some important foliar diseases in cucurbits, whereas severe phytotoxicity may be developed.

Greenhouse evaluation of root-knot nematode resistance of grafted specialty melon

The greenhouse root-knot nematode (RKN) inoculation study was conducted at the University of Florida, Gainesville, FL during fall 2011. Honeydew melon ‘Honey Yellow’ was grafted onto Cucumis metulifer (African horned cucumber) rootstock. Non-grafted and self-grafted ‘Honey Yellow’, as well as non-grafted C. metulifer were included as controls. RKN (Meloidogyne incognita race 1) inoculum was used in this experiment. Grafting was conducted with one-cotyledon method. Grafted and non-grafted control plants were grown individually in 15-cm-diameter clay pots. Each plant was inoculated with 5,000 eggs of M. incognita race 1. Plants were grown in the shadehouse for 8 weeks with air temperatures ranging from 24 to 39 ºC. When the experiment was terminated, roots were washed gently and allowed to air dry. Then the roots were stained with 10% (v:v) solution of red food coloring to aid with an estimation of the amount of galling and egg masses based on a 0-5 scale. The number of eggs per root system was counted after their extraction using a 0.25% sodium hypochlorite solution and blender technique. Eggs were quantified with a nematode chamber counting slide under a 40× magnification microscope. Nematode reproduction factor (Rf) was calculated as the ratio of final eggs recovered to the initial inoculum number. 

Greenhouse studies were also conducted at the U.S. Vegetable Laboratory in Charleston, SC in 2011 to evaluate response of selected cucurbit lines against southern root-knot nematode (M. incognita) in order to identify additional potential RKN-resistant rootstocks for grafted melon. In the 2012 greenhouse test, forty-one accessions of C. metulifer were evaluated for reaction to root-knot nematodes. The most resistant accessions were selected for further evaluation as rootstocks for grafted melon. 

Field evaluation of root-knot nematode resistance and yield of grafted specialty melons

Two field experiments were conducted during spring 2012, including one trial in a certified organic field (Quality Certification Services, Gainesville, FL) that was naturally infested with RKN, and the other in a fumigated conventional field. Both fields were located at PSREU, Citra, FL. Honeydew melon ‘Honey Yellow’ and galia melon ‘Arava’ selected from the specialty melon cultivar evaluation trials were grafted onto C. metulifer rootstock, while self-grafted and non-grafted melon scions were included as controls. A randomized complete block design with five replications and eight plants per treatment per replication was used in both field trials. 

Melons were harvested 7 and 9 times in the organic and conventional fields, respectively. Immature melons were also harvested at the final harvest and separated from ripened fruit. Fruit were weighed individually. Small fruit (weighing less than 0.45 kg), immature, and misshapen fruit, and fruit with cracking and sunburn, as well as defective fruit with insect or disease damage were categorized as unmarketable fruit. 

After the final harvest of the organic field, the root systems of eight plants were dug and rated for RKN galling on a 0-10 scale. Soil cores (1.75-cm diameter × 20-cm depth) were collected in the root zone of six plants in the center of each plot. Each soil sample was thoroughly mixed and second-stage juveniles (J2) were extracted from 100-cm3 soil of each sample using a centrifugal-flotation method. RKN females were excised and identified to species using specific polymerase chain reaction primers. 

In the 2011 field trials at the U.S. Vegetable Laboratory in Charleston, SC, melon grafted onto ten selected C. metulifer rootstocks were evaluated for scion-rootstock compatibility. In the 2012 and 2013 experiments, ten selected C. metulifer breeding lines were evaluated as rootstocks for grafted melon in a root-knot nematode-infested field.

Planting density study of grafted specialty melons
The field experiment was conducted during spring 2012 at PSREU, Citra, FL. ‘Honey Yellow’ (HY) and ‘Arava’ (Ar) were grafted onto ‘Strong Tosa’ (St) and evaluated with two planting densities, i.e., 3 ft (0.91 m)  and 4 ft (1.22 m) in-row spacings, with a constant between-row spacing of 1.82 m (6 ft), corresponding to 2,420 and 1,815 plants per acre, respectively. The experiment was arranged in a split-plot design with fumigation as the main-plot factor, while grafted plants (Ar/St and HY/St) grown at standard (3 ft) and increased (4 ft) in-row spacings, and non-grafted control plants (NAr and NHY) grown at standard spacing were the subplot treatments. There were 8 plants per treatment per replication, 5 replications.

Fruit quality assessment of grafted specialty melons

Fruit quality assessments were conducted in the spring seasons of 2012 and 2013 at PSREU, Citra, FL, using melons harvested from field trials with different production systems. Melons harvested from the following production treatments were evaluated in 2012. 

Certified organic field: ‘Arava’ and ‘Honey Yellow’ grafted onto C. metulifer rootstock, non-grafted ‘Arava’ and ‘Honey Yellow’, as well as self-grafted ‘Arava’ and ‘Honey Yellow’. 

Non-fumigated conventional field: ‘Arava’ and ‘Honey Yellow’ grafted onto C. metulifer rootstock, ‘Arava’ and ‘Honey Yellow’ grafted onto ‘Strong Tosa’ rootstock, as well as non-grafted ‘Arava’ and ‘Honey Yellow’. 

Fumigated conventional field: ‘Arava’ and ‘Honey Yellow’ grafted onto ‘Strong Tosa’ rootstock, non-grafted ‘Arava’ and ‘Honey Yellow’, as well as self-grafted ‘Arava’ and ‘Honey Yellow’.   

In 2013, non-grafted ‘Arava’, ‘Arava’ grafted onto ‘Strong Tosa’ rootstock, and ‘Arava’ grafted onto ‘Carnivor’ rootstock were all produced from the fumigated conventional field. 

Analyses of the two melon cultivars were conducted separately on different days. Each cultivar was analyzed twice in the 2012 harvest season. The day before the sensory analysis, melons were harvested and stored at 10 ºC overnight. Ten fully ripe melons were chosen from each treatment based on fruit size, i.e., approximately 1.5 kg per fruit, and absence of defects. Six treatments were included in each of the analyses. The first analysis of each melon cultivar included melons produced from the fumigated conventional field (i.e., fruit of non-grafted, self-grafted, and ‘Strong Tosa’ rootstock grafted melon plants) and the organic field (i.e., fruit of non-grafted, self-grafted, and C. metulifer rootstock grafted melon plants). The second analysis assessed melons from the fumigated and the non-fumigated conventional fields (i.e., fruit of non-grafted, and ‘Strong Tosa’ and C. metulifer rootstock grafted melon plants). In 2013, only one sensory analysis with three treatments, i.e., non-grafted ‘Arava’, ‘Arava’ grafted onto ‘Strong Tosa’ rootstock, and ‘Arava’ grafted onto ‘Carnivor’ rootstock, were conducted. 

On the day of consumer sensory analysis, melon fruits were washed in tap water and dried with paper towel. They were then cut longitudinally into halves. Half of the samples were used for sensory analysis while the remaining counterparts were used for instrumental measurements. Consumer sensory analyses were conducted at the University of Florida Sensory Analysis Lab in Gainesville, FL. Each of the consumer sensory tests had 96 – 100 panelists. Six samples with 2 melon cubes (3 cm × 3 cm × 3 cm) of each sample were randomly arranged and presented to consumers. Consumer panelists were first asked to answer demographic questions including gender, age, and melon consumption frequency. For each sample, consumers were asked to score overall acceptability, firmness liking, and flavor liking using a 1-9 hedonic scale (9 = like extremely, 5 = neither like nor dislike, 1 = dislike extremely). They were then asked to describe firmness and sweetness levels using a 1-5 just-about-right scale, e.g., 1= too soft, 2 = slightly too soft, 3 = just about right, 4 = slightly too firm, 5 = too firm. 

For the instrumental measurements, flesh firmness and SSC were measured in the 2012 samples, while flesh firmness, SSC, titratable acidity, and pH were measured in the 2013 samples. Flesh firmness was measured twice in the middle of the mesocarp of each melon half using a penetrometer with an 8-mm plunger. SSC was determined by a refractometer while titratable acidity and pH were measured using a 719 S Titrino. 

Exploring potential factors associated with fruit quality reduction in grafted galia melon
This field trial was conducted in spring 2013. Galia melon ‘Arava’ grafted onto hybrid squash rootstock ‘Strong Tosa’ exhibited fruit quality reduction in 2012 trials, which led us to investigate the potential factors associated with the decrease of fruit quality in grafted melon. Three treatments were included: ‘Arava’ grafted onto ‘Strong Tosa’, non-grafted ‘Arava’, and self-grafted ‘Arava’. The field experiment was arranged in a randomized complete block design with four replications and ten plants per treatment per replication. The anthesis dates of female flowers on each plant were recorded and labeled every day from 16 days after transplanting (DAT) to 41 DAT. The length of the longest vine was measured on three plants per treatment per replication at 36 DAT and 46 DAT. Melons were harvested seven times from 25 May to 10 June at the full-slip stage. The early (fruit from the first two harvests that occurred on 25 and 28 May, respectively) and total yields were recorded. The harvest dates of fruit developed from the labeled female flowers that were successfully fertilized were recorded, and the fruit development duration was calculated.

Research results and discussion:

Specialty melon cultivar evaluation

The cultivar evaluation trials identified early maturing specialty melons cultivars, such as ‘Honey Yellow’, ‘Honey Pearl’, ‘Sun Jewel’, and ‘Diplomat’. As the rainy season normally starts in May in north and central Florida, using early maturing cultivars may help to alleviate adverse impacts caused by warm and wet conditions.

Canary melon ‘Camposol’ consistently exhibited high fruit yields in both organic and conventional trials. On the other hand, differential performances of some cultivars between organic and conventional farming systems were observed, indicating the need for selecting promising specialty melon cultivars more adapted to the organic farming system. Asian melon ‘Ginkaku’ and honeydew melon ‘Honey Yellow’ in the conventional field showed an increase in marketable fruit weight by over 35% compared with melons in the organic field. Asian melon ‘Sun Jewel’, galia melon ‘Diplomat’, and ananas melon ‘San Juan’ had relatively high percentages of cull fruit, suggesting they might not be suitable cultivars for growing in Florida conditions that are known for high humidity and disease pressure.

Honeydew melon ‘Honey Yellow’ had the highest SSC of 15.3 and 15.6% in the organic and conventional fields, respectively. The flesh firmness of climacteric ‘Athena’ cantaloupe, ananas, and galia melons ranged from 5.1 to 10.0 N, significantly lower than that of non-climacteric canary and honeydew melons (flesh firmness ranged from 15.8 to 28.8 N).

Gummy stem blight and root-knot nematode were the primary diseases found in the organic field. Overall, canary melon ‘Camposol’, galia melon ‘Arava’ and ‘Diplomat’, and honeydew melon ‘Honey Pearl’ and ‘Honey Yellow’ showed less aboveground symptoms compared with other melon cultivars. Since ‘Honey Yellow’ and ‘Diplomat’ exhibited severe RKN galling, it might be possible that they carry some potential tolerance to RKN infestation. In the conventional field, powdery mildew and downy mildew caused the most severe damage. Honeydew melon ‘Honey Yellow’, canary melon ‘Brilliant’ and ‘Camposol’, and asian melon ‘Sun Jewel’ showed relatively good foliar disease performance with less than 40% defoliation.

Based on results of the cultivar evaluation trials, two specialty melon cultivars including honeydew melon ‘Honey Yellow’ and galia melon ‘Arava’ were identified as promising scions for the grafting experiments at the University of Florida. 

Evaluation of melon grafting methods

Survival rates of grafted plants were not significantly different among HI, OC, and NC grafting methods. Grafted plants with TA method without root excision achieved 83% survival rate, but the survival was lower than 50% when root excision was practiced. The highest survival rate (100%) was achieved in plants grafted with OC method. Rootstock regrowth (sucker) need to be removed, which requires extra labor. Grafted plants with HI and OC developed rootstock suckers even though the meristem tissues were carefully removed. TA and NC method completely eliminated rootstock sucker problems. 

Root regeneration was generally initiated on the root-excised plants at 4 days after grafting (DAG), which then developed similar root length and surface area as the plants with intact root at 16 DAG. Root length and surface area were similar among rootstock control, scion control, HI and OC grafted plants. NC grafted plants exhibited a root growth pattern different from that of other grafting treatments. The root excision treatment initiated new root growth at 8 DAG instead of 4 DAG, while the root length and surface area of the intact root system did not exhibit a significant increase during 16 DAG. As a result, the root length and surface area of NC grafted plants were significantly lower than other plants at 16 DAG. 

Quality of the NC grafted plants was significantly lower than HI and OC grafted plants. Although the majority of NC grafted plants healed initially, about one-third of the grafts exhibited slowed and stunted growth, and the rootstock hypocotyl declined and eventually died. Without the phytosynthates from rootstock cotyledons, insufficient nutrient reserved for rootstock growth may be one of the possible causes of rootstock hypocotyl deterioration. On the other hand, the decline of NC grafted plants after healing may be due to the inhibition of root growth as a result of removing rootstock cotyledons.

No significant difference in plant growth characteristics was observed among HI, OC, and TA grafted plants. Grafted plans with root excision performed similarly as plants with intact root systems. The experiments demonstrated that without root excision, plants grafted with hole insertion, one-cotyledon, and tongue approach methods performed similarly regarding graft quality and growth characteristics; however, non-cotyledon method resulted in quality reduction of the grafted plants. Root excision was unsuccessful with tongue approach method, while it did not exhibit significant impacts on graft quality and growth of plants grafted with one-cotyledon and hole insertion methods.

Development of new grafting methods to eliminate rootstock meristems and prevent regrowth 

Rootstock regrowth is a major problem in cucurbit grafting, and the cost of regrowth control is a major reason for the lack of grafted transplants in U.S. melon production. Fatty alcohol products were found to effectively control rootstock growth without affecting graft survival. Rootstock damage increased and regrowth decreased with increasing rates of fatty alcohol compound. Results showed a significant decrease in regrowth as concentration increased up to 7.5% fatty alcohol, while damage increased significantly at fatty alcohol concentrations of 6.25% and above. The optimal treatment rate, which controlled at least 95% of regrowth with less than 10% damage, was found to be between a 5% (Off-Shoot T®) and 6.25% (Fair 85®) fatty alcohol application. The optimal treatment rate did not exhibit any adverse effects on grafting success. 

Two commercial rootstock seedlings were harvested weekly up to 3 weeks after treatment and analyzed to verify size changes and carbohydrate content. Rootstock hypocotyls and cotyledons increased significantly in fresh and dry weight and hypocotyl width over 21 days after fatty alcohol treatment. Rootstock hypocotyls and cotyledons also increased significantly in carbohydrate content, most notably starch. Starch content increased 194-fold in ‘Carnivor’ rootstock hypocotyls, and 109-fold in ‘Emphasis’ cotyledons. 

Graft survival using the one-cotyledon method, an industry standard, remained at or above 90% for 14 and 21 days after rootstock treatment for ‘Carnivor’ and ‘Emphasis’ rootstocks, respectively. Graft survival using the hypocotyl-only (non-cotyledon) graft method, one that has not yet been successful in industry practices, increased significantly at 7 and 14 days for ‘Carnivor’ and ‘Emphasis’ rootstock, respectively.   

Grafting for managing Fusarium wilt and root-knot nematodes in grafted specialty melon production

In the rootstock screening study, nearly all the test rootstock lines were found to be resistant to Fom, this is expected as many of these are not C. melo (melon) and thus are not a host to this pathogen. Results of the race 1 test showed that all the rootstock lines tested were resistant, including the ‘Dinero’ (C. melo).  In the race 2 test, all lines except for ‘Dinero’ were found to be resistant. In this test, 30% of the ‘Dinero’ plants were found to have wilt symptoms. In the grafted melon experiment, fourteen of the fifteen rootstock / scion grafted tests were found to be healthy 30 days post inoculation with the pathogen, while the 80% and 70% of the grafted plants using “Dinero” as the rootstock were dead or wilted when challenged with race 1 or 2 of Fom, respectively. In the follow-up studies of molecular markers linked to Fom resistance in melon, quantitative trait loci (QTLs) were identified in race 1 and race 2 resistant lines from a recombinant inbred line (RIL) derived from the multi-resistant melon ‘MR-1’ and the susceptible ‘Ananas Yokneum’. QTLs were also identified in Alternaria leaf blight resistant lines as well as in sulfur resistant lines.

In the greenhouse inoculation study for RKN control, ‘Honey Yellow’ grafted onto C. metulifer exhibited significantly lower root gall index, egg mass index, and reproduction factor than non-grafted and self-grafted ‘Honey Yellow’, indicating that grafting RKN susceptible melon onto C. metulifer was effective in reducing RKN reproduction. 

In the field evaluation, the RKN species in the naturally infested organic field was identified as M. javanica. Both non-grafted and self-grafted ‘Honey Yellow’ and ‘Arava’ plants exhibited severe galling (GI > 4). Root galling was significantly reduced on ‘Honey Yellow’ and ‘Arava’ grafted onto C. metulifer (GI < 1). Grafting with C. metulifer rootstock also reduced J2 numbers in the soil compared with non-grafted melon plants, suggesting that grafting RKN susceptible specialty melon cultivars onto C. metulifer could be an effective approach in reducing RKN damage and decreasing nematode population densities in the soil. 

In the organic field experiment, despite the improved RKN management, no significant differences in total and marketable yields were observed when comparing ‘Honey Yellow’ and ‘Arava’ grafted onto C. metulifer with non-grafted and self-grafted melon plants. Relatively low disease pressure may be part of the reason. In the conventional field, no significant differences in total and marketable yields were observed between non-grafted ‘Arava’ and ‘Arava’ grafted onto C. metulifer rootstock. However, total yield (but not marketable yield) of ‘Honey Yellow’ grafted onto C. metulifer was significantly lower than that of non-grafted ‘Honey Yellow’ in the conventional field. The smaller stem diameter below the graft union was observed in contrast to that above the graft union. The growth vigor of C. metulifer as a potential rootstock deserves more investigations with respect to its impact on growth and development of the grafted melon plants. 

Compared with non-grafted and self-grafted plants, specialty melons grafted onto C. metulifer exhibited less root galling and reduced RKN population densities in the root zone. Although fruit yield was not improved by grafting, incorporating specialty melons grafted onto C. metulifer into a double-cropping system with RKN susceptible vegetables may be an alternative approach to manage Meloidogyne spp. and enhance production of high-value vegetables in RKN infested fields.

Greenhouse studies conducted at the U.S. Vegetable Laboratory in Charleston, SC identified several accessions of C. metulifer with moderate to high resistance to M. incognita. All other cucurbit species evaluated were highly susceptible to M. incognita. The scion-rootstock compatibility experiments showed that a number of the selected C. metulifer rootstocks were highly compatible with melon. The grafted melon trials in the root-knot nematode-infested field at the U.S. Vegetable Laboratory in Charleston, SC demonstrated that all ten rootstocks were highly compatible with melon and nine of ten C. metulifer rootstocks were moderately to highly resistant to root-knot nematodes in both 2012 and 2013. ‘Athena’ melon grafted on root-knot nematode-resistant C. metulifer rootstocks produced significantly higher yields than ‘Athena’ cantaloupe (non-grafted and self-grafted) and ‘Athena’ grafted onto ‘Carnivor’ squash hybrid rootstock. The C. metulifer rootstocks also had significantly lower root-knot nematode reproduction than ‘Athena’ cantaloupe and ‘Carnivor’ rootstock, which should result in reduced soil populations of root-knot nematodes and reduced damage in subsequently planted susceptible vegetable crops.

Planting density study of grafted specialty melons
‘Honey Yellow’ grafted onto ‘Strong Tosa’ with the reduced planting density had lower total yield compared with non-grafted ‘Honey Yellow’ and ‘Honey Yellow’ grafted onto ‘Strong Tosa’ with the standard in-row spacing. However, total and marketable yields did not differ significantly between grafted ‘Arava’ with ‘Strong Tosa’ rootstock under the reduced planting density and grafted and non-grafted plants grown with the standard in-row spacing. The results indicated that using grafted plants could reduce planting density of ‘Arava’ from 2,420 per acre to 1,815 per acre, while still maintaining fruit yield comparable to non-grafted plants. 

Fruit quality assessment of grafted specialty melons 

Consistent among all the production conditions evaluated in 2012 and 2013, the ‘Arava’ scion grafted onto ‘Strong Tosa’ rootstock (Ar/ST) reduced consumer rated overall acceptability and flavor liking compared with non-grafted ‘Arava’ (NGAr). Results from ‘just-about-right’ questions indicated that consumer preference for Ar/ST melons was decreased because they were not sweet enough. This was further confirmed by the instrumental measurement. SSC that reflects the sugar content showed a significantly lower value in the melon flesh of Ar/ST than NGAr. 

Organically produced ‘Arava’ grafted onto C. metulifer (Ar/Cm) decreased overall acceptability and flavor liking compared with NGAr. However, the negative rootstock effects on sensory properties were not detected when plants were grown in the non-fumigated conventional field. No differences in SSC and flesh firmness between NGAr and Ar/Cm were detected under either of the production conditions. C. metulifer rootstock did not affect SSC and flesh firmness, indicating that its effects on sensory properties might be attributed to quality attributes other than sweetness and firmness. 

Regardless of the production conditions and the rootstock selection, grafted ‘Honey Yellow’ melon did not exhibit any significant differences in sensory properties (overall acceptability, flavor liking, and firmness liking), SSC, and flesh firmness in comparison with non-grafted ‘Honey Yellow’ fruit. 

A distinct difference in grafting effect on fruit quality was observed in the two specialty melon cultivars. One of the fundamental differences between the two melon cultivars is the fruit ripening pattern. Galia melon ‘Arava’ produces climacteric fruit that exhibits an autocatalytic ethylene production peak during fruit ripening, while the ethylene production peak was not observed in non-climacteric honeydew melons. As many aroma compounds are only produced through ethylene-dependent pathways, climacteric melons generally have higher aroma levels than non-climacteric fruit. Because climacteric galia melons are rich in aroma components, their sensory properties perceived by consumers might be more likely to be affected by grafting practice than honeydew melons. 

Exploring potential factors associated with fruit quality reduction in grafted galia melon
The first female flower of the self-grafted and non-grafted ‘Arava’ plants bloomed around 29 and 30 DAT, respectively, 8 to 9 days earlier than that of ‘Arava’ grafted onto ‘Strong Tosa’ rootstock. Although grafting with ‘Strong Tosa’ delayed the appearance of female flowers, the first harvest dates were not affected as shown in our study, while the early and total yields did not differ significantly between the grafted and non-grafted plants. On average, the length of fruit development period from anthesis to full-slip for ‘Arava’ grafted with ‘Strong Tosa’ was 34 days, significantly shorter than that of non-grafted and self-grafted ‘Arava’. As fruit sugar content is correlated with the fruit development duration, the shorter fruit development period observed in the grafted plants may partially explain the reduced fruit SSC. About 27% of grafted plants with ‘Strong Tosa’ wilted during the late fruit development stage, and eventually died at the end of the season. Analysis of these plants indicated that it was not caused by pathogens. Plant decline during the late harvest might also partially explain the reduced fruit quality.

Participation Summary

Educational & Outreach Activities

Participation Summary

Education/outreach description:

Refereed Publications 

Guan, W., X. Zhao, D.J. Huber, and C.A. Sims. 2015. Instrumental and sensory analyses of quality attributes of grafted specialty melons. Journal of the Science of Food and Agriculture. In press. 

Daley, S. and R.L. Hassell. 2014. Fatty alcohol application to control meristematic regrowth in bottle gourd and interspecific hybrid squash rootstocks used for grafting watermelon.  HortScience 49:206-264. 

Daley, S., J. Adelberg, and R.L. Hassell. 2014. Improvement of grafted watermelon transplant survival as a result of size and starch increases over time caused by rootstock fatty alcohol treatment. Part I. HortTechnology 24:343-349. 

Daley, S., W.P. Wechter, and R.L. Hassell. 2014. Improvement of grafted watermelon transplant survival as a result of size and starch increases over time caused by rootstock fatty alcohol treatment. Part II. HortTechnology 24:350-354. 

Guan, W., X. Zhao, D.W. Dickson, M.L. Mendes, and J.A. Thies. 2014. Root-knot nematode resistance, yield, and fruit quality of specialty melons grafted onto Cucumis metulifer. HortScience 49:1046-1051. 

Guan, W., X. Zhao, D.D. Treadwell, M.R. Alligood, D.J. Huber, and N.S. Dufault. 2013. Specialty melon cultivar evaluation under organic and conventional production in Florida. HortTechonology 23:905-912.

Guan, W., X. Zhao, R. Hassell, and J. Thies. 2012. Defense Mechanisms involved in disease resistance of grafted vegetables. HortScience 47:164-170.

Book Chapters 

Zhao, X., W. Guan, and D.J. Huber. 2015. Melon grafting. In: M. Pessarakli (Ed.), Handbook of Cucurbits: Growth, Cultural Practices, and Physiology. CRC Press, Boca Raton, FL. In review.

Theses and Dissertations 

Guan, W. 2014. Integrated use of grafting technology in specialty melon production: Grafting
techniques, root-knot nematode management and fruit quality. Doctoral dissertation, University
of Florida, Gainesville, FL.

Non-Refereed Publications 

Guan, W. and X. Zhao. 2014. Techniques for melon grafting.  <http://edis.ifas.ufl.edu/pdffiles/HS/HS125700.pdf>. UF/IFAS Extension EDIS publication HS1257.

Grafting Workshops and Exhibits Organized

2014: 

Root-knot Nematodes and Grafting Workshop, 17th Annual Georgia Organics Conference & Expo, Jekyll Island, GA.

Vegetable Grafting Workshop, Small Farm Academy Education Program at the Suwannee Valley Agricultural Extension Center, Live Oak, FL. 

2013: 

Vegetable Grafting Exhibit, Florida Small Farms and Alternative Enterprises Conference, Kissimmee, FL. 

2012: 

Vegetable Grafting Exhibit, Florida Small Farms and Alternative Enterprises Conference, Kissimmee, FL. 

Conference Presentations

Daley, S., and R.L. Hassell. 2014. Fatty alcohol rootstock treatment: An overview of a new approach to cucurbit grafting. 1st ISHS International Vegetable Grafting Symposium, Wuhan, China.  

Guan, W. and X. Zhao. 2014. Effects of grafting methods and re-rooting on the growth characteristics of grafted muskmelon plants. American Society for Horticultural Science Annual Conference, Orlando, FL.  

Guan, W. and X. Zhao. 2014. Physiological changes in grafted melon plants with a hybrid squash rootstock. 1st ISHS International Symposium on Vegetable Grafting, Wuhan, China. 

Daley, J., R.L. Hassell, and W.P. Wechter. 2013. Mapping Alternaria cucumerina resistance in Cucumis melo. American Phytopathological Society Annual Meeting, Austin, TX. 

Daley, J., R.L. Hassell, and W.P. Wechter. 2013. Mapping Alternaria cucumerina and sulfur resistance in Cucumis melo. American Society for Horticultural Science Annual Conference, Palm Desert, CA.
Daley, S. and R.L. Hassell. 2013. The Effect of rootstock age on grafting ability, re-rooting, and field performance of grafted watermelon transplants. American Society for Horticultural Science Annual Conference, Palm Desert, CA.  

Daley, S. and R.L. Hassell. 2013. Rootstock age affects grafting ability and rootstock re-rooting of grafted watermelon transplants. American Society for Horticultural Science Annual Conference, Palm Desert, CA. 

Daley, S. and R.L. Hassell. 2013. A new grafting procedure decreases grafting cost and increases grafting efficiency by eliminating rootstock re-growth in watermelon. Southern Region American Society for Horticultural Science Annual Meeting, Orlando, FL.   

Daley, S., and R.L. Hassell. 2013. Fatty alcohol treatments control rootstock regrowth in grafted watermelon. Southern Region American Society for Horticultural Science Annual Meeting, Orlando, FL.  

Guan, W., X. Zhao, and C.A. Sims. 2013. Studying quality attributes of grafted specialty melons using both consumer sensory analysis and instrumental measurements. American Society for Horticultural Science Annual Conference, Palm Desert, CA.  

Guan, W., X. Zhao, D.W. Dickson, and J. Thies. 2013. Grafting specialty melons for root-knot nematode management. Southern Region American Society for Horticultural Science Annual Meeting, Orlando, FL.  

Nguyen, N., X. Zhao, W. Guan, and R.L. Hassell. 2013. Assessing root characteristics of cucurbit rootstocks using a simple germination test. American Society for Horticultural Science Annual Conference, Palm Desert, CA.  

Thies, J.A., J.J. Ariss, S. Buckner, R.L. Hassell, and A. Levi. 2013. Response of cucurbit rootstocks for grafted melon (Cucumis melo) to Southern root-knot nematode, Meloidogyne incognita. Society of Nematologists Annual Meeting, Knoxville, TN.  

Thies, J.A., J.J. Ariss, S. Buckner, R.L. Hassell, and A. Levi. 2013. Response of African horned cucumber, (Cucumis metulifer) to Southern root-knot nematode, Meloidogyne incognita.  American Phytopathological Society Annual Meeting, Austin, TX.  

Zhao, X. and J.K. Brecht. 2013. The influence of grafting on fruit quality: A research update on grafted tomato and melon. Vegetable Grafting Symposium at Annual International Research Conference on Methyl Bromide Alternatives and Emissions Reductions, San Diego, CA.  

Zhao, X., C.A. Sims, C.E. Barrett, and E.Q. Dreyer. 2013. Sensory attributes of tomato and muskmelon fruits as affected by grafting. Southern Region American Society for Horticultural Science Annual Meeting, Orlando, FL.  

Guan, W. and X. Zhao. 2012. Effects of grafting on yield and fruit quality of specialty melons (Cucumis melo). Vegetable Grafting Symposium at Annual International Research Conference on Methyl Bromide Alternatives and Emissions Reductions, Orlando, FL.  

Guan, W., X. Zhao, D.W. Dickson, M.L. Mendes, and J. Thies. 2012. Rootstock assessment for root-knot nematode management in grafted honeydew melon. American Society for Horticultural Science Annual Conference, Miami, FL.  

Guan, W., X. Zhao, D.D. Treadwell, M. Alligood, D. Huber, and N. Dufault. 2012. Specialty melon cultivar evaluation under organic and conventional production in Florida. American Society for Horticultural Science Annual Conference, Miami, FL.

Thies, J.A., J.J. Ariss, R.L. Hassell, and A. Levi. 2012. Resistant rootstocks for managing root-knot nematodes in grafted melon. Vegetable Grafting Symposium at Annual International Research Conference on Methyl Bromide Alternatives and Emissions Reductions, Orlando, FL.  

Thies, J.A., J.J. Ariss, R.L. Hassell, and A. Levi. 2012. Resistant rootstocks for managing root-knot nematodes in grafted watermelon and melon. Cucurbitaceae Conference, Antalya, Turkey. 

Project Outcomes

Project outcomes:

Project impacts and outcomes

Cucurbit grafting is used throughout the world to provide control of soilborne diseases, but the technology has not been accepted commercially in the U.S. Much of the reason of this is the increased cost associated with the increased amount of labor required for grafting. Much of the labor required is a result of rootstock regrowth, which traditionally requires hand removal for control. Rootstock fatty alcohol treatments can be used to destroy the axillary meristem and prevent regrowth for grafting. Treatments can also improve the efficiency of grafting, as a result of the increased carbohydrates accumulated over time in treated rootstocks. In addition, accumulated carbohydrates increase the window in which rootstocks can successfully be grafted from 2-3 days to 2-3 weeks. Increased carbohydrates also provide energy for successfully grafting below the rootstock cotyledons. This new method, which previously has not been a possibility in cucurbits because of the dependence of cucurbits on the energy provided by the cotyledon for growth, can now be used by commercial grafting operations to save space and decrease chances for disease by grafting below the cotyledons. Results from the examination of hole-insertion and one-cotyledon grafting methods together with root excision provided useful practical information for growers and propagators interested in melon grafting with respect to plant growth characteristics as affected by different grafting practices. 

Grafting of specialty melons onto non-C. melo rootstocks was found to control the effects of the Fusarium wilt pathogen on the Fom-susceptible melon scions. The use of non-C. melo rootstocks for grafting Fom-susceptible melon cultivars should be useful for control of Fusarium wilt in fields infested with race 1 or 2 of the melon pathogen Fusarium oxysporum f. sp. melonis. C. melo RILs derived from ‘MR-1’ and confirmed by the use of molecular markers from this study to possess resistance to both race 1 and race 2 of Fom, Alternaria leaf blight, and sulfur may be useful as resistant C. melo rootstocks. Molecular markers identified in this work will be useful for C. melo rootstock breeding programs for introgression of resistance genes into existing rootstock material. 

Results from both greenhouse and field studies demonstrated the effectiveness of grafting with root-knot nematode-resistant C. metulifer rootstocks for managing root-knot nematodes in melon production in the Southeastern U.S. Although the improvement of root-knot nematode resistance did not translate into yield enhancement, the reduction in soil root-knot nematode population densities could make grafting a viable rotational tool for organic and conventional specialty melon growers. Grafting as a cultural practice may also be considered a partial alternative to soil fumigation for controlling soilborne pathogens. The scion-rootstock interaction effect on fruit quality is rather complex, which is dependent upon the types of melon scions and rootstocks as well as the production systems and environmental conditions. Consumer perceived sensory properties of melon fruit from grafted plants deserve more comprehensive studies. In the development and test of disease-resistant rootstocks for grafted melon production, the rootstock impacts on fruit development and quality attributes should not be overlooked. 

Based on the project results, research publications and an extension publication on techniques for melon grafting have been produced. We organized vegetable grafting workshops to disseminate project findings. Our vegetable grafting exhibit attracted tremendous interest at the Florida Small Farms and Alternative Enterprises Conference in 2012 and 2013. A diverse group of conference participants consisting of small growers, organic producers, extension agents, home gardeners, nursery managers, school teachers, and college students greatly enjoyed the interactive hands-on demonstration to learn the basics of grafting practices. One Ph.D. student and two M.S. students participated in this research and education project. Through hands-on activities, melon grafting techniques were also introduced to undergraduate students in the courses of horticultural crop production, greenhouse and protected crop production, as well organic and sustainable crop production at the University of Florida.

Vegetable grafting workshop evaluation

The project team organized a full-day vegetable grafting workshop at the Suwannee Valley Agricultural Extension Center, Live Oak, FL in April 2014. Eleven (out of more than 20 attendees) participants completed an evaluation after the training, including three service providers and eight producers. Participants were asked to rate their confidence in their ability to achieve the training objectives on a scale of one to four, where 1 = not at all confident and 4 = very confident. Almost all participants indicated they were ‘confident’ or ‘very confident’ in their ability to complete all of the training objectives after the workshop. The objectives were to: 1) explain how grafting can be used as an integrated disease management tool in vegetable production, 2) describe the effects of rootstocks on plant growth, fruit quality, water and fertilizer use, and tolerance to environmental stresses, 3) explain how grafting can help improve crop yield and profitability beyond disease control, 4) list the limitations of vegetable grafting and potential issues associated with grafting, 5) apply appropriate grafting methods to different types of vegetable crops, and 6) set up appropriate healing conditions to achieve high graft survival rate. Two participants indicated they were ‘not confident in their ability to complete objectives five and six. One participant was ‘not confident’ in their ability to accomplish objective three. Overall, the average level of confidence for all participants in their ability to achieve all objectives was ‘confident’. 

All of the service providers who attended indicated they intend to use the information provided in the training in newsletters or other media outlets, to answer client questions, and to conduct individual consultations in this area. They also all intend to incorporate some of the concepts from this training into their existing programs and/or deliver new programming in this area. Four of the producers who participated intend to share the information provided in this training with other producers or through newsletters or other media outlets. All of the participants except for two producers felt the training helped them identify new contacts and partners for their work. 

Participants were asked to indicate how good or poor the training was on several aspects using a scale of 1 = very poor and 5 = very good. Overall, the average rating for the training for all participants was ‘very good’ for the following aspects: 1) time spent on hands-on activities in the workshop, 2) opportunities for interaction with other participants, 3) opportunities for asking questions or comments, 4) activities that get them involved, and 5) answers to their questions. 

Next, participants rated the quality of instruction using the same scale used above, where 1 = very poor and 5 = very good. Instructional aspects rated included: 1) ease for them to understand the information, 2) quality of visual aids, 3) inclusion of the latest research findings, 4) degree to which the information was comprehensive, and 5) overall rating of the instructor. All participants rated the instruction as ‘good’ or ‘very good’ for all aspects. The average score for each participant was 5, indicating ‘very good’. 

Service providers were also asked the degree to which the workshop increased their competency related to their 1) mastery of the training’s information, 2) ability to teach clients on the topics, 3) use workshop activities in their own teaching, 4) design and lead a workshop on the topics, 5) collaborate with local organizations, and 6) address emerging issues in this area. They were asked to respond on a scale of one to four, 1 meaning not at all and 4 meaning a lot. Two of the three service providers who responded to the evaluation questions indicated their competency increased ‘a lot’ in the first four tasks and either ‘a lot’ or ‘some’ in tasks five and six. The third respondent indicated their competency increased ‘a lot’ for the first two tasks, ‘some’ for the third, ‘a little’ for tasks four and five, and ‘not at all’ for task six. Overall, the average level of increase for tasks one through three was ‘a lot’ and the average for tasks four through six was ‘some’.

Economic Analysis

Using the ‘Arava’ melon scion and the commercially available rootstock ‘RST-04-109-MW’, we estimated the costs of grafted and non-grafted melon plants based on our experimental conditions (Table 1). A considerable difference was revealed between grafted and non-grafted plants, with the estimated cost of $0.64/plant for grafted melon seedlings versus $0.10/plant for non-grafted melon seedlings. Although this cost difference may be reduced with the increase of production scale and decrease of rootstock seed price and labor cost, the overall increase of transplant cost in grafted melon production can be substantial. The enhanced return as a result of effective disease control and fruit yield and quality improvement would be essential for achieving profitable production using grafted plants. Hence, the production systems need to be carefully evaluated to determine the economic feasibility of melon grafting based on site-specific conditions. 

Farmer Adoption

On-farm demonstration trials with grafted melons were conducted at Jackson Farms in North Carolina and Fields Farms in South Carolina. The owner and grower of Possum Hollow Farm, Alachua, FL is focused on environmentally-friendly approaches in his farming practices and has expressed great interest grafted melon production. Given the root-knot nematode problem at the farm, an on-farm study of rootstock evaluation for root-knot nematode control was carried out at Possum Hollow Farm. Galia melon ‘Arava’ was grafted onto two interspecific hybrid squash rootstocks ‘Strong Tosa’ and ‘Tetsukabuto’ and the C. metulifer rootstocks. The root gall index was significantly lower in grafted ‘Arava’ with C. metulifer and ‘Strong Tosa’ rootstocks than that of non-grafted and ‘Tetsukabuto’ grafted ‘Arava’, while the root-knot nematode population in the soil was also reduced by 84% on average. Although the total fruit yield seemed to be numerically higher in ‘Arava’ grafted onto ‘Strong Tosa’ and C. metulifer rootstocks as compared with non-grafted ‘Arava’ and ‘Arava’ grafted onto ‘Tetsukabuto’, the difference was not statistically significant. 

Melon grafting is still considered a new practice to most growers in the Southeastern U.S. With the cost reduction in grafted transplant production and the increased grafting benefits in soilborne disease management and fruit yield and quality enhancement as the grafting technology advances, farmer adoption of grafted vegetable production under site-specific conditions for improved sustainability is expected.  

Recommendations:

Areas needing additional study

Optimizing grafting methods to produce high quality grafted plants is essential in implementing grafting technology in specialty melon production. In this project, the effects of grafting methods and root excision on the growth characteristics of grafted melons were evaluated under greenhouse conditions. Future field studies are needed to assess yield performance of grafted melons as affected by different grafting methods taking into consideration the economic analysis. The cucurbit rootstock treatments using fatty alcohol products also need to be evaluated in more field trials. 

This research demonstrated the effectiveness of RKN management by grafting ‘Honey Yellow’ and ‘Arava’ melons onto C. metulifer. Future breeding efforts could be directed to develop more vigorous C. metulifer rootstocks targeting fruit yield improvement. Currently, most cucurbit rootstocks with resistance to Fusarium wilt, especially the interspecific hybrid squash rootstocks, are often susceptible to RKN. More research is warranted to select and develop new rootstocks that are resistant to both Fom and RKN as well as other emerging soilborne diseases. Moreover, the grafting practice involving diverse types of specialty melon cultivars will need to be tested at locations with different levels of disease pressure and varying environmental conditions. 

The complex rootstock-scion interactions and adverse effects of hybrid squash rootstock on galia melon fruit quality were revealed in this project. More in-depth studies are warranted to understand nutrient and water uptake of grafted plants and the changes in fruit development and ripening as affected by grafting with different cucurbit rootstocks. Identification of long-distance signals and grafted plant modification at physiological and molecular levels are among hot topics of vegetable grafting. Breakthroughs in these areas will greatly advance our understanding of the rootstock-scion-environment interactions, leading to more effective and efficient use of grafting technology in sustainable agriculture.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.