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POSTERS: Cultural control

Effect of deficit irrigation on development of Fusarium wilt in processing tomato
Kelley Paugh - University of California, Davis. Cassandra Swett- University of California, Davis, Johanna Del Castillo Munera- University of California, Davis

Fusarium wilt of tomato, caused by Fusarium oxysporum f. sp. lycopersici race 3 (Fol3), is a major driver of yield losses in California processing tomatoes. In response to decreasing water availability, it is becoming more common to deficit irrigate processing tomatoes (a water stress-tolerant crop); however, this change in irrigation practice may influence Fusarium wilt (FW) risk. The effect of deficit irrigation on FW risk was examined in a 2018 field trial with four irrigation treatments [0, 25, 75, and 100% evapotranspiration (ET)] using a highly susceptible cultivar. In this preliminary study, there was a linear increase in incidence of mid-season FW, as water inputs decreased. By harvest, incidence increased in all deficit irrigation treatments compared to 100% ET. In a greenhouse trial, we evaluated whether the use of a FW-tolerant cultivar could mitigate effects of deficit irrigation on disease risk. When comparing full irrigation [45% soil volumetric water content (VWC)] to mild (35% VWC) and moderate (28% VWC) deficit in UC Mix, deficit irrigation did not influence disease development under variable inoculum densities (IDs) (0, 102, 104, or 106 spores/mL drench) of Fol3. Analysis of effects on colonization and IDs in substrate are underway. These results suggest that deficit irrigation influences disease risk, but that the use of FW-tolerant cultivars may allow growers to manage this disease while taking maximum possible advantage of deficit irrigation.