Optimal treatment against Athelia rolfsii rot in processing tomatoes using pesticide and rootstock against key stages of the disease

Abstract

The soilborne fungus Athelia rolfsii (synonym Sclerotium rolfsii) causes stem or collar rot in tomato (Lycopersicon esculentum Mill.). We aimed to develop an optimal treatment for A. rolfsii in processing tomatoes in Israel through an understanding of the key developmental stages of the plant that are susceptible to disease development. We tested two approaches: best timing for pesticide application, and grafting onto a tolerant rootstock. The fungus attacked processing tomatoes at two stages: (i) immediately after planting, when the root neck is attacked and the young plant wilts, and (ii) in the last month of growth, when the humidity under the foliage increases, temperatures are high, and the root neck, shoot and fruit, which are lying on the ground, are susceptible to pathogen attack. The number of infected plants was significantly reduced after incorporating azoxystrobin at 2.5 and 5 L a. i./ha in the soil preplanting, and applying the combination fungicide Nativo (a.i. tebuconazole and trifloxystrobin) at 0.75 kg/ha in the drip-irrigation system (chemigation) once, 60–90 days after planting. This treatment enhanced total yield by up to 35.2% and marketable yield by up to 33.7% relative to untreated plots. Grafting to a resistant rootstock significantly reduced plant wilting in the first weeks of growth to less than 1% of the plants, and enhanced fruit yield up to four fold. In soil with a history of infestation, A. rolfsii infection should be treated during the plants’ susceptible stages: preventive azoxystrobin treatment preplanting, and a single treatment of Nativo later on to prevent infection and decay, especially for late harvest; grafting to a resistant rootstock can also reduce infection in the early stages of growth and enhance yield. In this study, we show for the first time that A. rolfsii infection in processing tomato can be dramatically decreased with minimal pesticide application against key stages of the disease and rootstocks.