|Gibbons, James - Gibbons Farm Organics|
|Roe, Nancy - Farming Systems Research, Inc|
Submitted to: Proceedings of International Research Conference on Methyl Bromide Alternatives
Publication Type: Proceedings
Publication Acceptance Date: 9/15/2012
Publication Date: 11/5/2012
Citation: Rosskopf, E.N., Burelle, N.K., Adkins, S.T., Hong, J.C., McKenzie, C.L., Gibbons, J., Roe, N. 2012. Grafting heirloom tomatoes for increased vigor and virus tolerance. Proceedings of International Research Conference on Methyl Bromide Alternatives. 55-1-55-2.
Interpretive Summary: In organic and transitional vegetable production, there are few options currently available to growers for virus management. Tomato yellow leaf curl virus (TYLCV) is a particularly difficult problem for tomato growers and can completely devastate crops, reducing yields to zero when early infection occurs. One on-farm field trials and one microplot trial were conducted in cooperation with grower cooperators and on a research farm in Florida to evaluate tomato rootstocks grafted to heirloom variety scions for effects on virus incidence and severity. Heirloom varieties with no tolerance to TYLCV were grafted onto the commercial tomato variety 'Tygress' as it has known TYLCV-tolerance, but does not produce fruit that are desired by consumers of heirloom tomatoes. After grafting and healing, grafted and ungrafted plants were either planted to the commercial field or were caged with viruliferous whiteflies and then planted to microplots for evaluation of symptom expression. In the field trial, virus infection was not significantly different when comparing treatments, due to the high level of variability between plots. Plants infection prior to planting showed significant differences in the final percentage of plants infected for two of the heirloom scions tested.
Technical Abstract: Previous work in vegetable grafting has shown promise for control of a variety of pathogens using soilborne pathogen-resistant rootstocks. Few studies have shown potential for management of viruses through the use of resistant rootstocks. A field trial and a research farm-microplot trial were conducted to evaluate heirloom tomatoes used as scions grafted to the commercial cultivar 'Tygress'. Heirloom variety tomato scions evaluated were ‘Purple Calabash’, ‘Black Prince’, and ‘Moskvich’. These varieties are highly susceptible to tomato yellow leaf curl virus (TYLCV) and early-season infection with this virus can completely eliminate crop yields. A small-fruited tomato, 'Matt's Wild Cherry' has been observed to also have tolerance to TYLCV. For the on-farm field trial, all three heirloom varieties were grafted onto each of the tolerant varieties used as rootstocks. All heirloom varieties were assessed on their own roots as ungrafted controls, as were the two rootstocks. Plants were produced in a commercial setting in protected, raised beds, according to USDA organic production standards typically utilized by the grower for tomato. Plants were infected by the native whitefly population. Virus infection was evaluated weekly for 12 weeks. Area under the disease progress curve (AUDPC) was calculated for each grafting treatment. Although there was a range of AUDPC values of 20.11 for Tygress alone to 60.55 for Moskvich ungrafted plants, the variability in the field resulted in no significant differences between treatments. However, in microplot studies conducted at the USDA-ARS farm, when plants were infected via viruliferous whiteflies prior to planting in the field, there were significant differences between final virus ratings for Black Prince ungrafted (87% of plants with visual symptoms) versus Black Prince grafted on Tygress (42% of plants with visual symptoms), and for Moskvich ungrafted (73%) and Moskvich grafted to Tygress (36%). Asymptomatic infection in some graft combinations was detected using tissue blot nucleic acid hybridization and interestingly, many grafted plants with severe symptoms showed virus infection of the tolerant Tygress used as the rootstock.