2017 ASHS Annual Conference

Fresh market tomatoes have been increasingly grown in high tunnels because of the extended production season, higher yield and better fruit quality. Unfortunately, high tunnel production of tomatoes is often limited by the foliar disease leaf mold (Passalora fulva), which may cause defoliation of tomato plants. While some tomato varieties have resistance to leaf mold, growers often chose varieties based on consumers’ preference rather than the disease resistance. Grafting is becoming increasingly accepted among fresh market tomato growers because this technology is known to increase yields and offer resistance to soil borne diseases. Yet, it is unknown how grafting affects susceptibility to leaf mold. In this study, the leaf mold susceptible variety ‘Mountain Spring’ was grafted with tomato rootstock ‘Maxifort’. Non-grafted plants were used as controls. Six fungicide treatments, i.e. Dithane^® (mancozeb), Badge X₂^® (copper), InspireSuper^® (difenoconazole + cyprodinil), Serenade^® (Bacillus subtilis), Milstop^® (potassium bicarbonate) and an untreated control were applied weekly beginning 3 June when the leaf mold symptoms were first observed. The experimental design was split-plot design with fungicide as the whole-plot treatment and grafting as the sub-plot treatment. Leaf mold symptoms were evaluated using a Horsfall-Barratt scale; Area Under the Disease Progress Curve (AUDPC) were calculated. In addition, we recorded the number of leaf lesions on individual leaves. Tomato harvest started on 15 Jun. and ended on 7 Sep. The values of AUDPC were significantly lower for plants treated with Dithane^® and InspireSuper^® than other fungicide treatments and the untreated control. However, no significant differences in tomato yields were observed among the fungicide treatments. Grafted and non-grafted plants had similar AUDPC values. But more leaf mold lesions were observed on individual leaves of grafted plants. Grafting slightly delayed the early harvest of tomatoes in June, but it significantly increased tomato yield by 19% compared with non-grafted controls during the production season. Total soluble solids (TSS), pH, and titratable acidity of tomato fruit were evaluated on 5 July and 15 Aug. No significant differences in the quality attributes were observed in the first evaluation. But tomatoes harvested from plants treated with Dithane^® had significantly higher TSS compared with non-treated control, as well as plants treated with Serenade^®, Copper^® and Milstop^®. This study indicated that leaf mold can reduce fruit quality. Grafted tomatoes had increased yields, but were associated with increased lesion numbers on leaves.