Improving Biopesticide Efficacy of Apple Diseases through Co-application with Natural Products

Progress report for GNE19-198

Project Type: Graduate Student
Funds awarded in 2019: $14,685.00
Projected End Date: 10/31/2022
Grant Recipient: University of New Hampshire
Region: Northeast
State: New Hampshire
Graduate Student:
Faculty Advisor:
Anissa Poleatewich
University of New Hampshire
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Project Information

Project Objectives:

The overall goal of this research is to improve biopesticide efficacy in suppressing apple scab through finding synergisms with the natural product, chitosan. Reaching this goal will help farmers to reduce losses, decrease reliance on fungicides, and improve overall yield. The specific objectives are to;

1. Compare reagent grade and commercial chitosan formulations and rates for inhibition of Venturia inaequalis in-vitro.

2. Investigate synergisms between chitosan-based treatments and microbial biopesticides for suppression of apple scab.

3. Investigate the potential for chitosan formulations to reduce overwintering inoculum of Venturia inaequalis in orchard leaf litter.

Introduction:

Apple scab, caused by the fungus Venturia inaequalis (Cke.) Wint., is the most destructive disease of apples in the Northeast U.S. where warm, moist conditions can cause severe infections and devastating crop losses to farmers (MacHardy, 1996). Apple scab can cause up to 100% crop loss and significant reduction in fruit marketability due to consumers’ low threshold for imperfection on their apples (Vaillancourt and Hartman, 2000). Apple growers rely on multiple fungicides applications per season to manage apple scab (MacHardy, 1996). The development of fungicide resistance (the ability to survive when exposed to a chemical) by V. inaequalis is of large concern and several classes of fungicides, such as benzimidazole and demethylation inhibitors, have already lost their effectiveness (Holb, 2009; Ma and Michailides, 2005). Thus, alternative practices that can be incorporated with sanitation, fungicides, and other IPM strategies are critical to manage apple scab in New England.

One way that farmers are reducing their use of chemical pesticides is by utilizing naturally occurring compounds that can promote plant health and suppress disease. One strategy is to use beneficial microbes (biopesticides) to suppress disease. Many growers have incorporated biopesticides into their spray programs with mixed success. These inconsistencies in performance remain a barrier to broad adoption. However, biopesticide may be more effective at reducing disease through synergisms with natural compounds. A promising natural compound, chitosan, a deacetylated derivative of chitin, has been documented to have antifungal properties and promote plant growth (Zhang et al., 2011). Other benefits include enhanced photosynthesis, resistance to abiotic and biotic stress, and increased plant growth and yield (Reddy et al., 2000). Chitosan is an approved food additive in the U.S. and has been used effectively as a postharvest application to prevent disease and extend shelf life of perishable fruits and vegetables (Pichyangkura and Chadchawan, 2015; Romanazzi et al., 2018). There are limited examples of research evaluating preharvest application of chitosan on tree fruits. However, success in vegetable crops to promote plant health and suppress disease suggests that chitosan may have broader applications in agriculture (El-ghaouth et al., 2000).

Most fungi, including V. inaequalis, contain cell walls composed of chitin (Jerome, 1965). Chitinase is an enzyme that denatures cell walls, effectively degrading the fungi (Boller, 1993). El-Ghaoth et al. (1994) found that chitosan amended soil controlled Pythium root rot on cucumbers and triggered the production of chitinase and other anti-fungal compounds by the host. An application of chitosan acts as a microbial food source and can stimulate production of chitinase enzymes. Researchers have investigated potential synergisms between beneficial microbes and natural products and the implications for disease management. For example, Kokalis-burelle et al. (Kokalis-burelle et al., 1992) reported a 60% reduction in early leafspot of peanut when plants were treated with Bacillus cereus and chitin. It was hypothesized that the chitin stimulated production of anti-fungal enzymes and helped the beneficial microbe persist long enough to compete with the pathogen. These studies suggest that finding synergisms between biopesticides and chitosan has great potential to improve biopesticide efficacy in suppressing diseases. Although there is significant research on chitosan in the literature documenting its potential (Zhang et al., 2011), research is needed to bring best practices to growers and facilitate adoption. The overall goal of this research was to improve biopesticide efficacy in suppressing apple scab in northeastern orchards through finding synergism with the natural product, chitosan. Reaching this goal will help farmers to reduce losses, decrease reliance on fungicides, and improve overall yields.

Boller, T., 1993. Antimicrobial functions of the plant hydrolases, chitinases and 1,3 glucanases, in: Fritig, B., Legrand, M. (Eds.), Mechanisms of Plant Defense Responses. Kluwer Academic Press, Dordrecht, Netherlands, pp. 391–400.

El-Ghaouth, A., Arul, J., Grenier, J., Benhamou, N., Asselin, A., Belanger, R.R., 1994. Effect of chitosan on cucumber plants: Suppression of Pythium aphanidermatun and induction of defense reactions. Phytopathology 84, 313–320.

El-Ghaouth, A., Smilanick, J.L., Wilson, C.L., 2000. Enhancement of the performance of Candida saitoana by the addition of glycolchitosan for the control of postharvest decay of apple and citrus fruit. Post 19, 103–110.

Holb, I.J., 2009. Fungal Disease Management in Environmentally Friendly Apple Production – A Review. Sustain Agric. Rev. 2, 219–293.

Jerome, M., 1965. The cell wall, in: Ainsworth, G., Sussman, A. (Eds.), The Fungi: An Advanced Treatise. Academic Press, New York, pp. 49–76.

Kokalis-burelle, N., Backman, P.A., Rodriguez-kabana, R., Ploper, L.D., 1992. Potential for Biological Control of Early Leafspot of Peanut Using Bacillus cereus and Chitin as Foliar Amendments ’. Biol. Control 2, 321–328.

Ma, Z., Michailides, T.J., 2005. Advances in understanding molecular mechanisms of fungicide resistance and molecular detection of resistant genotypes in phytopathogenic fungi. Crop Prot. 24, 853–863. https://doi.org/10.1016/j.cropro.2005.01.011

MacHardy, W.E., 1996. Apple Scab: Biology, Epidemilogy and Management. American Phytopathological Society Press, St. Paul, MN.

Pichyangkura, R., Chadchawan, S., 2015. Biostimulant activity of chitosan in horticulture. Sci. Hortic. (Amsterdam). 196, 49–65. https://doi.org/10.1016/j.scienta.2015.09.031

Reddy, M.V.B., Belkacemi, K., Corcuff, R., Arul, J., 2000. Effect of pre-harvest chitosan sprays on post-harvest infection by Botrytis cinerea and quality of strawberry fruit. Postharvest Biol. Technol. 20, 39–51.

Romanazzi, G., Feliziani, E., Sivakumar, D., 2018. Chitosan, a Biopolymer With Triple Action on Postharvest Decay of Fruit and Vegetables: Eliciting, Antimicrobial and Film-Forming Properties. Front. Microbiol. 9, 1–9. https://doi.org/10.3389/fmicb.2018.02745

Vaillancourt, L.J., Hartman, J.R., 2000. Apple scab. Plant Heal. Instr. https://doi.org/10.1094/PHI-I-2000-1005-01

Zhang, H., Li, R., Liu, W., 2011. Effects of Chitin and Its Derivative Chitosan on Postharvest Decay of Fruits: A Review. Int. J. Mol. Sci. 12, 917–934. https://doi.org/10.3390/ijms12020917

Cooperators

Click linked name(s) to expand/collapse or show everyone's info
  • George Hamilton (Educator and Researcher)
  • Jeremy DeLisle (Educator and Researcher)
  • Dr. Kari Peter (Educator and Researcher)

Research

Materials and methods:

Chitosan Products:

Working 1 % (g/v) stock solutions of reagent grade low, medium, and high molecular weight chitosan (Sigma Aldrich, St. Louis, MO) were prepared by dissolving 5 g of chitosan in 200 mL of sterile MilliQ water with 5 mL of glacial acetic acid. The pH was adjusted to 5.0 by adding 1 M sodium hydroxide (NaOH). The stock solution was diluted with MilliQ water to prepare the concentrations for each trial. Glacial acetic acid (1% v/v) (pH 5.0) was included as a control. The commercial products used during these experiments were High Tide™, Tidal Grow™ 1%, Tidal Grow™ 2% obtained from Tidal Vision Inc and Armour Zen® 15% obtained from Botry-Zen Ltd.

Objective 1: Compare reagent grade and commercial chitosan formulations and rates for inhibition of Venturia inaequalis in-vitro.

On-going and future work:

In-vitro assays will be used to determine if chitosan has direct antimicrobial activity against V. inaequalis. Reagent grade and commercial chitosan products will be spread onto ¼ strength PDA plates and left to dry for 24 hours. Four replicate plates per treatment will then be inoculated with a plug (5 mm) of V. inaequalis and incubated at 90% relative humidity and 22°C. Mycelium growth will be measured at 7, 14, and 21 days using a digital Vernier caliper. Each petri dish will be rinsed to dislodge the ascospores and the solution will be filtered through cheesecloth. Spore concentration will be enumerated using a hemocytometer. The experiment will be repeated twice.

Objective 2: Investigate synergisms between chitosan-based treatments and microbial biopesticides for suppression of apple scab.

Controlled environment evaluations.

Completed work:

Research has shown that chitosan efficacy is influenced by dose (% chitosan). However, higher doses can cause phytotoxicity. To determine a dose range for growth room and field trials, preliminary experiments were conducted to determine doses that can be applied to apple leaves without causing tissue damage. These experiments were conducted in a growth room using 'Macintosh' and ‘Golden Delicious’ seeds. Surface sterilized seeds were stratified in sterile sand at 4°C for 3 months. When germinated, the seedlings were transplanted into Ray Leach cone-tainers filled with peat (ProMix Bx) and placed in a walk-in growth room (22°C, 75% relative humidity, and a 12-hour photoperiod). While these seeds are genetically different due to pollination, this is an inexpensive way to develop methods prior to using grafted apple trees.

This experiment consisted of 7 treatments (Table 1) applied to 7 replicated plants. Apple seedlings were arranged in a completely randomized design. Once the apple seedlings had 6 true leaves, the chitosan treatments were sprayed onto plants until glisten. Plant height and SPAD measurements (leaf chlorophyll content) were measured prior to the chitosan application (day 0), 8 days, and 16 days post application to determine the effect of chitosan concentration on plant growth and photosynthesis.

Table 1. Chitosan treatments applied to apple seedlings in preliminary experiments to optimize chitosan dose.

Treatment

Application

1

Chitosan 1%

2

Chitosan 0.5%

3

Chitosan 0.25%

4

Chitosan 0.01%

5

Acetic Acid 1%

6

Milli Q Control

7

High Tide (0.5%)

A second experiment was conducted using low, medium, and high molecular weight chitosan. Solutions were prepared as described above with the addition of a nonionic surfactant, CapSil (0.4 mL/L). Five concentrations (2, 1.5, 1, 0.75, 0.5%) were applied to the apple seedlings. Additionally, three commercial products (Armour-Zen® 15%, Tidal Grow™ 1%, and Tidal Grow™ 2%) were evaluated. Application and data collection will be the same as previously described.

Ongoing and future work:

Chitosan and microbial biopesticides will be evaluated on apple plants in a controlled environment growth chamber. This experiment will consist of a 4 x 4 factorial with four chitosan treatments (3 chitosan formulations + water control) and four biopesticide treatments (3 commercial products + water control). Treatments will be arranged in a randomized complete block design with 10 replicate plants per treatment (160 plants total). In each treatment, half of the plants will be inoculated with V. inaequalis and half remained non-inoculated to observe the effects of the treatments on plant health and growth. The trial will be repeated twice.

Chitosan and biopesticide treatments will be applied to apple seedlings at the 3-leaf stage. Seven days later, the plants will be inoculated with V. inaequalis received from Dr. Kari Peter at Penn State University’s Fruit Research and Extension Center (FREC). To prepare inoculum, cultures will be maintained on ¼ PDA for 2-3 weeks. The isolate will be placed in a Filter Blender bag with sterile Milli-Q water and blended into a mycelial slurry. The resulting slurry will be filtered through cheesecloth and the concentration of the inoculum adjusted to 3.0 x 104 conidia mL-1 using a hemocytometer. One drop of Tween 20 will be added to minimize spore clumping. The spore suspension will then be sprayed on the plants to run-off. The control plants will be sprayed with sterile water. The plants will be placed in a humid chamber (18°C and 100% relative humidity) for 48 hours and then returned to the growth chamber. 

At 14 days post inoculation, plant disease severity will be measured using a five-point scale (0=no disease, 1=20%, 3=60%, 4=80%, and 5=100% or total plant collapse). Four leaves per plant will be evaluated for disease severity of apple scab using WinRHIZOTM (Regent Instruments, Quebec), a software which is an image analysis system which can be used for imaging leaves and calculating disease leaf area. Plant height, number of nodes per plant, and SPAD measurements (leaf chlorophyll content) will be measured for all non-inoculated treatments weekly to determine the effect of chitosan and biopesticides on plant growth and photosynthesis. At completion of the trial, plant dry biomass will be collected. Disease severity and plant health data will be analyzed for statistical significance using a Two-Way ANOVA in R studio. Statistical significance will be assessed at p < 0.05 and a Tukey HSD Post-hoc test will be used to separate the means.

In a third experiment, the three reagent grade chitosan formulations and the three commercial products (Table 2) will be applied on ‘Macintosh’ seedlings (rates will be based on the previous experiment) to evaluate disease suppression. This experiment will be set up as a randomized complete block design with 6 replicate plants per treatment. In each treatment, half of the plants will be inoculated with V. inaequalis and half will remain non-inoculated to observe the effects of the chitosan treatments on plant health and growth. The trial will be repeated twice.

Table 2. Chitosan treatment sprays applied to apple seedlings in the growth room

Treatment

Product

1

Low Molecular

2

Medium Molecular

3

High Molecular

4

Acetic Acid

5

Armour-Zen 15%

6

Tidal Grow 1%

7

Tidal Grow 2%

8

Milli Q + surfactant

9

Milli Q water control

 

Seven days after chitosan treatment application, the plants will be inoculated with V. inaequalis or water and maintained as described above.

At 14 days post inoculation, plant disease severity will be measured. Plant height, number of nodes per plant, and SPAD measurements (leaf chlorophyll content) will be measured for all treatments weekly to determine the effect of chitosan and biopesticide on plant growth and photosynthesis. At completion of the trial, plant dry biomass will be collected. Disease severity and plant health data will be analyzed for statistical significance using a One-Way Analysis of Variance (ANOVA) in R studio. Statistical significance will be assessed at p < 0.05 and a Tukey Honest Significant Difference (HSD) Post-hoc test will be used to separate the means. 

Field evaluation of disease suppression – Research Orchard.

Completed work:  

Chitosan and microbial biopesticide treatments were evaluated at Penn State’s FREC in an orchard of 6-year-old semi-dwarf apple cv. ‘Law Rome’ on M.7 rootstock in 2020 and 2021. In the 2020 season, treatments (Table 3) were applied to 4 replicate trees arranged in a randomized complete block design. Treatments were applied using a boom sprayer at 400 psi, delivering 100 gallon per acre. Treatment applications were made on 7-15 days intervals starting when trees reached tight cluster (mid-April).

Table 3. Treatment sprays for Penn State’s FREC Research Orchard, 2020

Treatment

Product

Rate per Acre

Water Control

Water Spray

--

Grower Standard

Manzate Pro-Stick

Captan Gold

3 lb

3 lb

Grower Standard + Chitosan

Manzate Pro-Stick

Captan Gold

Tidal Grow

3 lb

3 lb

150 mL*

Reduced Risk

Micothiol Disperss 10 lb (or 5lb)

Regalia

Nu-film P

10 lb (or 5lb)

2 qt

8 fl oz

Reduced Risk + Chitosan

Microthiol Disperss

Regalia

Nu-film P

Tidal Vision

10 lb (or 5 lb)

2 qt

8 fl oz

150 mL*

*Label Rate for Tidal Grow 2% on fruit trees

Trees were assessed in mid-June for foliar apple scab incidence. Disease incidence was determined by randomly selecting 10 terminal shoots per tree and counting the number of leaves with apple scab lesions. For apple scab severity, the number of scab lesions were counted on each leaf. Additionally, twenty-five apples per treatment per rep were evaluated for apple scab incidence.

In October, twenty-five fruit per tree per treatment were evaluated for apple scab incidence and severity. Apple scab incidence was measured by counting the number of fruits with apple scab and apple scab severity was measured by counting the number of lesions per fruit. Disease severity and incidence on leaves and fruit, and fruit quality will be analyzed for statistical significance using a One-Way Analysis ANOVA in R studio. Statistical significance will be assessed at p < 0.05 and a Tukey HSD Post-hoc test will be used to separate the means.

In the 2021 season, treatments (Table 4) were applied to 6 replicate trees arranged in a randomized complete block design. Treatments were applied using a boom sprayer at 400 psi, delivering 100 gallon per acre. Treatment applications were made on 7-15 days intervals starting when trees reached tight cluster (mid-April). 

Table 4. Treatment sprays for Penn State’s FREC Research Orchard, Season 2021

Treatment

Product

Rate per Acre

Water Control

Water Spray

--

Grower Standard

Manzate Pro-Stick

Captan Gold

Luna Sensation

Inspire Supre

LI 700

3 lb

2.5 lb

5 fl oz

12 fl oz

1 pt

Chitosan

Tidal Grow 2%

473 mL

Reduced Risk

Micothiol Disperss

Serenade ASO

10 lb

4 qt

Reduced Risk + Chitosan

Microthiol Disperss

Serenade ASO

Tidal Vision 2%

10 lb

4 qt

473 mL

Trees were assessed in mid-June for foliar and fruit apple scab incidence. Disease incidence was determined as described for 2020.

In October, twenty-five fruit per tree per treatment were evaluated for apple scab incidence and severity using a 0-to-6 rating scale as described by Poleatewich et al. (2012). Then, twelve fruit per treatment were randomly sampled to measure starch pattern iodine index (starch content) and Brix (total soluble solids) (Ewing et al., 2019). The starch index was measured using the Cornell Starch-Iodine Index 1-8 scale (1 = fully green fruit (low starch degradation) and 8 = fruit with a high degree of maturation (high starch degradation)). The other half of the cut fruit were used to measure brix (total soluble solids) for sugar content using the Hanna digital refractometer (model H196801) (Hanna® Instruments, Woonsocket, RI). Two Brix measurements were taken per fruit, representing subsample measurements. A garlic press was used to juice the fruit pieces onto the digital refractometer and the refractometer was cleaned after every sample.

Disease severity and incidence on leaves and fruit, and fruit quality will be analyzed for statistical significance using a One-Way Analysis ANOVA in R studio. Statistical significance will be assessed at p < 0.05 and a Tukey HSD Post-hoc test will be used to separate the means.

Ongoing and Future work:

Field evaluation of disease suppression – NH On-farm trials. On-farm trials will be established through the assistance of our UNH Extension collaborators, George Hamilton and Jeremy DeLisle. Weather stations connected to the Network for Environmental and Weather Applications (NEWA) will be used to collect climate data (temperature, precipitation, leaf wetness, degree days, etc.) during these trials.

These field trials  consist of four treatments (grower standard alone, chitosan, reduced risk, or reduced risk + chitosan. Each treatment will be applied to two apple cultivars (one susceptible to apple scab and one moderately susceptible). Each treatment will be applied to five replicates of 3-4 dwarf/semi-dwarf trees. The chitosan/biopesticide treatments will be applied using a backpack sprayer at bloom (early May) and again in mid-June. The trials will rely on natural apple scab inoculum present in the grower’s orchard.

The middle 1-2 trees in a replication will be assessed at three time points during the season (June, July, and September). Disease incidence and overall plant disease ratings will be collected on ten random shoots per replication. Six leaves per replicate tree will be collected at each sampling time to measure percent leaf area affected by apple scab using WinRHIZOTM as described above.

Fifty fruit per treatment will be randomly collected (200 fruit per cultivar) (prior to normal harvest in September and October). Fruit will be evaluated for fruit scab incidence and severity using a 0-to-6 rating scale as described by Poleatewich et al. (2012). Then, fifteen fruit per treatment will be randomly sampled to measure fruit weight and quality as described above.

Disease severity on leaves and fruit, fruit weight, and fruit quality for each farm will be analyzed for statistical significance using a Two-Way Analysis ANOVA in R studio. Statistical significance will be assessed at p < 0.05 and a Tukey HSD Post-hoc test will be used to separate the means.

Objective 3: Investigate the potential for chitosan formulations to reduce viability of overwintering spores of Venturia inaequalis in leaf litter.

The apple scab pathogen, V. inaequalis survives from year-to-year on infected leaves that have fallen to the ground as leaf litter. New spores (ascospores) are released in the spring during periods of rain and high humidity. An important component of apple scab management is to reduce the amount of primary inoculum (ascospores) in an orchard (MacHardy, 1996). In this study we will investigate the effect of chitosan applications to the leaf litter on potential ascospore dose (PAD) and spore viability. These treatments will be compared to an application of urea, which is a common strategy to decrease primary inoculum of apple scab. 

Field study to determine the potential of chitosan to reduce spore production under natural conditions. These field trials were performed at Penn State’s FREC in the winter of 2021 and 2022. Apple leaves infected with V. inaequalis were collected from the research orchard at the end of each season. The collected leaves were placed into 9 replicate sachets per treatment and then sprayed with the treatments. This experiment consisted of three treatments (Tidal Grow™, 5% urea solution (42 lb/gallon), and a water control). For winter 2020/2021 trials a rate of 3 mL per gallon was used for Tidal Grow™. For the 2020/2021 trials a rate of 30 mL per gallon was used for Tidal Grow™. After treatment application, leaves were overwintered fixed to the research orchard floor. Starting at the end of March, three sachets per treatment were analyzed for ascospore production weekly. Sachets were soaked in sterile water for 1 minute to induce spore release. The sachets were then placed into a vacuum to pull the spores onto a microscope cover slide. The cover slide was placed onto a slide bottom with a drop of Lactophenol (blue dye). The number of ascospores were counted under a compound microscope. For each sachet, the area under the disease progress curve was calculated and analyzed using a One-Way ANOVA in R studio. Statistical significance was assessed at p < 0.05 and a Tukey HSD Post hoc test was used to separate the means.

References:

Benhamou, N., Theriault, G., 1992. Treatment with chitosan enhances resistance of tomato plants to the crown and root rot pathogen Fusarium oxysporum f. sp. radicis-lycopersici. Physiol. Mol. Plant Pathol. 41, 33–52.

Bhaskara Reddy, M. V, Belkacemi, K., Corcuff, R., Arul, J., 2000. Effect of pre-harvest chitosan sprays on post-harvest infection by Botrytis cinerea and quality of strawberry fruit. Postharvest Biol. Technol. 20, 39–51.

Boller, T., 1993. Antimicrobial functions of the plant hydrolases, chitinases and 1,3 glucanases, in: Fritig, B., Legrand, M. (Eds.), Mechanisms of Plant Defense Responses. Kluwer Academic Press, Dordrecht, Netherlands, pp. 391–400.

El-Ghaouth, A., Arul, J., Grenier, J., Benhamou, N., Asselin, A., Belanger, R.R., 1994. Effect of chitosan on cucumber plants: Suppression of Pythium aphanidermatun and induction of defense reactions. Phytopathology 84, 313–320.

El-Ghaouth, A., Smilanick, J.L., Wilson, C.L., 2000. Enhancement of the performance of Candida saitoana by the addition of glycolchitosan for the control of postharvest decay of apple and citrus fruit. Post 19, 103–110.

Ewing, B.L., Peck, G.M., Ma, S., Neilson, A.P., Stewart, A.C., 2019. Management of Apple Maturity and Postharvest Storage Conditions to Increase Polyphenols in Cider. HortScience 54, 143–148. https://doi.org/10.21273/HORTSCI13473-18

Holb, I.J., 2009. Fungal Disease Management in Environmentally Friendly Apple Production – A Review. Sustain Agric. Rev. 2, 219–293.

Jerome, M., 1965. The cell wall, in: Ainsworth, G., Sussman, A. (Eds.), The Fungi: An Advanced Treatise. Academic Press, New York, pp. 49–76.

Kokalis-burelle, N., Backman, P.A., Rodriguez-kabana, R., Ploper, L.D., 1992. Potential for Biological Control of Early Leafspot of Peanut Using Bacillus cereus and Chitin as Foliar Amendments ’. Biol. Control 2, 321–328.

Ma, Z., Michailides, T.J., 2005. Advances in understanding molecular mechanisms of fungicide resistance and molecular detection of resistant genotypes in phytopathogenic fungi. Crop Prot. 24, 853–863. https://doi.org/10.1016/j.cropro.2005.01.011

MacHardy, W.E., 1996. Apple Scab: Biology, Epidemilogy and Management. American Phytopathological Society Press, St. Paul, MN.

Pichyangkura, R., Chadchawan, S., 2015. Biostimulant activity of chitosan in horticulture. Sci. Hortic. (Amsterdam). 196, 49–65. https://doi.org/10.1016/j.scienta.2015.09.031

Poleatewich, A.M., Ngugi, H.K., Backman, P.A., 2012. Assessment of Application Timing of Bacillus spp. to Suppress Pre- and Postharvest Diseases of Apple. Plant Dis. 96, 211–220. https://doi.org/10.1094/PDIS-05-11-0383

Romanazzi, G., Feliziani, E., Sivakumar, D., 2018. Chitosan, a Biopolymer With Triple Action on Postharvest Decay of Fruit and Vegetables: Eliciting, Antimicrobial and Film-Forming Properties. Front. Microbiol. 9, 1–9. https://doi.org/10.3389/fmicb.2018.02745

Vaillancourt, L.J., Hartman, J.R., 2000. Apple scab. Plant Heal. Instr. https://doi.org/10.1094/PHI-I-2000-1005-01

Zhang, H., Li, R., Liu, W., 2011. Effects of Chitin and Its Derivative Chitosan on Postharvest Decay of Fruits: A Review. Int. J. Mol. Sci. 12, 917–934. https://doi.org/10.3390/ijms12020917

Research results and discussion:

Objective 2: Investigate synergisms between chitosan-based treatments and microbial biopesticides for suppression of apple scab in laboratory and on-farm studies.

Controlled environment evaluations

In the preliminary growth room experiments, the apple seedlings did not exhibit phytotoxicity after being treated with chitosan treatments up to a concentration of 1% (w/v). Chitosan treatments did not have an effect on plant height or SPAD. 

Field evaluations of disease suppression – Research Trials

The research trial conducted at Penn State’s FREC during the 2020 season gave us insight on how to improve our experimental design for the 2021 season. All treatments significantly reduced apple scab incidence on leaves and fruit compared to the water control. However, there was no difference between the reduced risk+ chitosan and reduced risk without chitosan. We did not include a standalone chitosan treatment to compare against the reduced risk and reduced risk + chitosan. Thus, the reduction in apple scab compared to the water control could have been solely due to the efficacy of the reduced risk program. Further, the Tidal grow label rate of 150 mL per acre equals a chitosan dose of 0.000798%. Based on results published in the literature and our own observations, it is unlikely that this dose would reduce disease. We decided that the rate needed to be higher for the 2021 trials. Finally, for the 2021 trials, we decided to change the biopesticide used from Regalia to Serenade. This is because Serenade’s active ingredient is a Bacillus subtilis, which is more likely to have a synergistic effect with chitosan (Benhamou and Theriault, 1992; Kokalis-burelle et al., 1992).

The data analysis from this research trial is underway and will be completed in spring 2022.

Objective 3: Investigate the potential for chitosan formulations to reduce viability of overwintering spores of Venturia inaequalis in leaf litter.

In 2020/2021 overwintering experiment there was no significant difference in number of ascospores on leaves treated with chitosan application compared to the water control. The urea treatment resulted in significantly lower ascospore production than the chitosan and water treatments. However, the rate used for the chitosan application was the label rate of Tidal Grow™ of 3 mL per gallon which is 0.0015% chitosan. We hypothesize that this concentration is too low to have an affect. We decided that the rate needed to be higher for the 2021/2022 winter trials. Although the results were not what we expected, as the chitosan industry is still new and developing, narrowing in on the proper rates is crucial. Data collection for the 2021/2022 trial is ongoing.

Participation Summary
2 Farmers participating in research

Education & Outreach Activities and Participation Summary

2 Published press articles, newsletters

Participation Summary:

Education/outreach description:

This research was featured in a New Hampshire Agricultural Experiment Station article found here: https://www.colsa.unh.edu/nhaes/article/2020/08/applescab. Additionally, this work was featured in a Good Fruit Grower article found here: https://www.goodfruit.com/what-can-chitosan-do/.

 

UNH graduate student Liza will give a brief introduction to her work with chitosan during the Winter Webinar Series hosted by Northeast Extension Fruit Consortium on March 8th, 2022. Additionally, Liza will present this research to New Hampshire tree fruit growers at the annual NH Fruit Growers Association Meeting in early April.

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.