S14 - Session O6 - Strawberry cultivar responses to Fusarium oxysporum f. sp. fragariae density in soil

Authors: Oleg Daugovish *, Akif Eskalen, Karina Elfar Aedo, Ana Pastrana-Leon

Coastal California remains one of the world's primary strawberry growing regions with 13,000 ha annually in fruit production. Since the phase out of methyl bromide fumigation, soil-borne pathogens has been increasingly troublesome, causing strawberry mortality and yield losses. Genetic resistance to Fusarium oxysporum f. sp. fragariae has been linked to a dominant gene and recent breeding efforts focused on development of cultivars with reliable resistance. In 2019-2021 field trials in California fruit production regions we evaluated performance of short-day and day-neutral strawberry cultivars in soil inoculated with F. oxysporum f. sp. fragariae at five levels ranging from 0 to 2000 CFU/g soil applied as a mixture of infested sand with 1L of native soil from planting holes for bear-roots transplants. Fruit yields and plant mortality for cultivars Victor and Warrior at all pathogen levels were similar to soil without pathogen and showed no relationship with inoculum density on soil. Fruit yields of cultivars Albion and Monterey declined at moderate and high Fusarium densities and plant mortality was linearly related to increase in the pathogen density (R²= 0.7-0.9). End-season mortality for Monterey and Albion was proportional to CFU concentration in soil at that time. In 2020 cultivar Petaluma season-long fruit yields decreased 36% and mortality increased from 0 to 30% is soil with 2000 CFU compared to soil without the pathogen, while Victor and Warrior had neither significant yields losses nor mortality in response to pathogen inoculum levels. These results suggested that susceptible cultivars can be productive at low Fusarium levels in soil and newly developed resistant cultivars can be reliably productive in soils heavily infested with this soil-borne pathogen. Similar evaluations are being conducted for another troublesome soil-borne pathogen n Macrophomina phaseolina a causal agent of charcoal rot in strawberry.