Low-input integrated management of tomato viruses in Hawaii

Final Report for SW12-040

Project Type: Research and Education
Funds awarded in 2012: $297,296.00
Projected End Date: 12/31/2015
Region: Western
State: Hawaii
Principal Investigator:
Dr. Mark Wright
University of Hawaii
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Project Information

Abstract:

Tomato production in Hawaii has been severely hampered by insect-vectored plant pathogenic viruses for decades. Varieties resistant to the historically major pathogen, Tomato Spotted Wilt Virus, have been used extensively to deal with this problem, and the industry has grown substantially in recent years. The recent advent of Tomato Yellow Curl Virus in Hawaii has set the tomato industry back to depending extensively on insecticides for virus vector management. There are currently no varieties with dual resistance to these viruses available for commercial production in Hawaii.

This project addressed this problem through screening tomato varieties with putative dual resistance to both of the above viruses to confirm resistance under local conditions and to determine their desirability for the local industry. We also tested the effectiveness of reflective mulches to deter the insects. A combination of tolerance or resistance with low-input insect suppression techniques will provide an effective and valuable tool that will enable farmers to continue producing tomatoes in Hawaii.

Project Objectives:
  1. Evaluation of resistant varieties.
  2. Evaluate effectiveness of reflective plastic mulch to suppress insect vectors and other insect pests.
  3. Conduct economic analysis of sustainable strategies to control TSWV and TYLCV in tomato in Hawaii.
  4. Disseminate research findings to tomato growers and agricultural professionals.

 

Introduction:

Tomato is an important crop in Hawaii’s diversified agriculture. Tomato local production and local consumption has risen over the last 15 years. In 2007, the last year that tomato production was reported, it was ranked as the 9th most important agricultural commodity in Hawaii (HASS, 2009). Among vegetable and melon crops, tomato also has the highest production at 14.3 million pounds and accounted for 27% of the revenue generated (HASS, 2009). There was a 264% increase in acreage and 267% increase in revenues from tomatoes over a 10-year span (http://www.nass.usda.gov/Statistics_by_State/Hawaii/index.asp). This dramatic increase can be attributed to the popularity of locally-grown tomatoes in Hawaii’s supermarkets and food industries. Early-picked tomatoes grown elsewhere and ripened in transit to Hawaii cannot compare to the high quality, freshly picked fruits grown in the islands (http://www.reeis.usda.gov/web/crisprojectpages/205465.html). Many farmers in Hawaii are currently struggling to meet the demands of local consumers as a result of the recent epidemics of Tomato Yellow Leaf Curl Virus (TYLCV), which together with Tomato Spotted Wilt Virus (TSWV, another viral disease that has hindered Hawaii’s tomato production for many years), has threatened tomato production (Melzer et al., 2009; http://www.hawaii.edu/news/article.php?aId=3320). Expeditiously developing sustainable control methods is imperative due to the importance of this crop in the daily diet of the local population, as well as importance of this crop in Hawaii’s diversified agriculture and economy.

Tomato spotted wilt virus (TSWV), vectored by many species of thrips, has been present in Hawaii since the 1920s. Production losses due to TSWV can be as high as 75-100% in Hawaii (Cho et al 1989). The recent introduction of Tomato yellow leaf curl virus (TYLCV), vectored by silverleaf whitefly (Bemisia argentifolii), has further threatened tomato production in Hawaii (Melzer et al. 2009). Current methods of control against insect vectors are heavily reliant upon insecticidal sprays. However, the use of insecticides is not always successful, and overdependence on insecticides could result in resistance built-up.

Cooperators

Click linked name(s) to expand
  • Dr. Leyla Kaufman
  • Dr. Mike Melzer

Research

Materials and methods:

 

  1. Evaluation of resistant varieties

The screening of resistant varieties was conducted at three sites (Waimanalo, Waialua and Kahuku) during 2013 and 2014. At each site we screened 10 – 14 varieties with either dual or single resistance to TYLCV and/or TSWV. The trials tested five different types of tomato variety types and two different growth forms (Table 1). Field trials were arranged in a completely randomized design, five replicates per variety and seven plants per replicate. The field plots were 90 by 90 feet, with 5 feet between rows and 2.5 feet within-row spacing. A weed mat 4 feet in width was placed in-between rows for weed suppression. Tomato seeds were planted in plug trays and transplanted six weeks after seeding. Two weeks after transplanting, The Disease Severity Index (DSI) from (0-4) was used to assess weekly visual symptoms of TYLCV and TSWV, ranging from 0 having no symptoms to 4 having severe virus symptoms. Rating scales used were described by Friedmann et al. (1998) and Canady et al. (2001). DSI data collection ended once the harvest period began. A plant with a DSI rating of 2 and higher was classified as positive for TSWV or TYLCV infection respectively, based on specific symptoms. Percentage infected plants per variety was calculated.

During the harvest period, fruits were collected weekly from all replicates, sorted and weighed to assess yield of each variety. The field trial cropping durations, including transplanting-flowering, flowering, and harvest period for the Waialua and Kahuku trials are displayed in Figures 1 and 2, respectively. In both trials, smaller tomato varieties flowered two weeks before bigger tomato varieties, and, thus, fruit production and harvest occurred earlier. Harvest started at different times, but all varieties generally had a three-five week harvest period that varied among field trials due to seasonal differences.

Fruits were sorted into six different categories: Marketable or Damaged/Injured (Mite damage, Splotchy skin, Fruit Fly infested, and Hemiptera damaged) yield. Fruits were sorted into these six categories since these were the most common traits observed. Marketable fruit refers to saleable quality fruits, while Damaged/ Injured is not saleable, typically owing to aesthetic damage, of more serious injury, such as fruit fly infestation. The Splotchy category could indicate possible virus symptoms, by expressing splotchy patches on the fruit.

  1. Evaluate effectiveness of reflective plastic mulch to suppress insect vectors and other insect pests.

Fruits were sorted into six different categories: Marketable, Damaged/Injured, Mite, Splotchy, Fruit Fly, and Hemiptera yield. Fruits were sorted by these six categories since these were the most common traits observed, as described above.

  1. Conduct economic analysis of sustainable strategies to control TSWV and TYLCV in tomato in Hawaii.

This objective is still being addressed. Detailed management records have been kept for yield and costs of materials. All plot results will be converted into per acre values. Net return for the different varieties compared to standard susceptible varieties, and for different pest management options applied to susceptible varieties will be estimated and compared. Partial budgeting techniques will be used to quantify the economic impact of the various virus and vector management options. Among the most significant indicators that will be quantified are yield, costs of cultivation and production, net return and benefit-to-cost ratio. The procedures for quantification and interpretation of the economic indicators used will be based on Gajanana et al. (2006).

We will modify economical analysis spreadsheets developed specifically for tomato by the University of Hawaii, College of Tropical Ag and Human Resources (www.ctahr.hawaii.edu/oc/freepubs/spreads/tomato$.xls).

 4. Disseminate research findings to tomato growers and agricultural professionals.

A continuous commitment has been made to disseminate research findings in order to encourage the adoption of these sustainable pest management strategies. Field days, handouts and articles were developed during the project. Extension publications and peer-reviewed publications are still in preparation.

Research results and discussion:

Hathor and Rona were the two varieties that produced the highest marketable yield throughout both trials (Figure 1). These two varieties, along with the remaining smaller tomato varieties 72618, Sarina, and 75125, generally had higher yields than the bigger tomato varieties: Katya, Shanty, Matty, 72103, V3051, 72061, 74956, Indigo Rose, Inbar, and Kewalo. In the Waialua trial Katya, Shanty, and Matty were the highest yielding bigger tomato varieties. Unfortunately the Kahuku trial was infected with late blight (Phytophthora infestans) in the middle of the cropping season, and even though plants were treated, it caused a decline in tomato production for these varieties. Big tomato varieties 72103 and V3051 were globe and roma types that generally had the same marketable yield in both trials, despite late blight infection. Even though variety V3051 showed late blight resistance, it did have the highest unmarketable yield due to other factors in both trials (Figure 2 & 3). Kewalo, which was susceptible to TYLCV only, was the lowest yielding tomato variety in both trials. The susceptible control Indigo Rose generally had a lower yield than the other tomato varieties.

For the smaller tomato varieties such as Hathor, Rona, 72618, 75125, and Sarina, the marketable yield was generally greater than the unmarketable yield for both Waialua and Kahuku trials (Figure 2 and 3, respectively). For the bigger tomato varieties the opposite trend was observed; the unmarketable yield was generally greater than the marketable yield (Figure 2 and 3). The categories Mite, Fruit Fly, and Hemiptera (Figure 4 and 5), were the most important unmarketable categories. A regular commercial treatment for the damaging pests can potentially reduce the unmarketable yield in these categories.

Results of the reflective mulch trial showed dramatic differences between the two types of mulch (reflective and standard black plastic mulch). Plants growing in the reflective mulch grew faster and more vigorously compared to plants in the black plastic mulch (Fig. 6). Plants in the reflective mulch flowered and set fruit two weeks earlier than plants growing in the black mulch. Pest densities were significantly lower in plants growing in the reflective mulch compared to plants growing in the black mulch.

The reflective mulch did not prevent the transmission and spread of TYLCV in the susceptible variety (Shiren). At the end of the trial all plants of the susceptible variety showed symptoms of TYLCV. Plants of both varieties had significantly more marketable yield when growing in the reflective mulch treatment compared to the black mulch (Fig. 7).

Figures 1 to 10 Table 1

Research conclusions:

Results from the variety testing are providing farmers with options to deal with main viruses that impact tomato production in Hawaii. Even though it is difficult for some of farmers to transition to a new variety (they are used to growing their old varieties), increased problems with viruses and dependence on pesticides, all addressed by the development of appropriate extension material, will facilitate this transition.

The reflective mulch tested in this trial showed promising results. Farmers, extension agents, agricultural professionals, and agricultural providers that attended the field day were very impressed with the difference in performance (reflective vs. black plastic mulch). The reflective mulch used in our trials was obtained from a mainland provider. After the field demonstration, a local provider is making the reflective mulch available for Hawaii farmers.

Participation Summary

Educational & Outreach Activities

Participation Summary

Education/outreach description:

During the course of the project we have been able to provide outreach to farmers, extension agents and agricultural professionals. A field day was organized during the second year of the variety field trials. Attendants were able to see first-hand the varieties in the field and taste test fruits in the field. During the third year of the project we conducted another field day to show case the performance of the reflective plastic mulch. Farmers were able to see differences in plant growth, plant health and yield between the standard practice (black plastic mulch) and the reflective mulch. We have developed handouts and extension articles that are available in the CTAHR Sustainable Agriculture website.

Since this final report is submitted at the end of the last round of field trials, we are in the process of preparing the publications for this project. At the moment we are preparing one extension publication and two peer review publications based on the findings of the project.

Tomato and Mulch-2 V22-Tateno-tomato-5 Field day handout_last version 

Project Outcomes

Project outcomes:

Did not complete.

Farmer Adoption

All participating farmers have seen first-hand the performance of tomato varieties included in the variety trial. Some farmers have been adopting these new varieties and extension agents are recommending varieties that had the least incidence of virus and that had the greatest yield. We are in the process of developing more outreach material and expect that this will increase the adoption varieties and IPM approaches developed in this project.

Recommendations:

Areas needing additional study

The effect of the reflective plastic mulch was more distinct at the beginning of the cropping season. As the plants start to grow and shade the plastic mulch, there is an increase in incidence of pests such as mites. Future work on modified spacing between plants and rows could potentially increase effect of the reflective material and provide optimal yields. We also observe differences in performance of the reflective mulch between summer and winter production (winter production data is still being processed as field trial is fishing at the time this report is due). During summer months we observed more pest damage by mites and leafminers. More research on the seasonal differences would be helpful.

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.