Survey of late-season soilborne pathogens infecting strawberry in Watsonville-Salinas, California

There are four major soilborne pathogens of strawberries in California, but their distribution and prevalence in the Watsonville-Salinas production district are unknown. To fill this knowledge gap, 74 symptomatic strawberry plant samples were collected from 69 fields in the Watsonville-Salinas growing district between 11 August and 15 October 2021. Each sample consisted of eight plants exhibiting moderate to severe plant collapse. Crown tissue from each plant was excised and pooled for recombinase polymerase amplification (RPA) to detect Macrophomina phaseolina, Fusarium oxysporum f. sp. fragariae, Verticillium dahliae, and Phytophthora spp. Root, petiole and crown tissue from plant samples in which no pathogens were detected by RPA was plated on semi-selective media to verify the absence of the four pathogens and screen for other pathogenic fungi. At least one of the four pathogens was detected in 55 of the 74 samples (74.3%). All four of the major soilborne pathogens are prevalent in this growing district, as F. oxysporum f. sp. fragariae, M. phaseolina, Phytophthora spp. and V. dahliae were detected in 23 samples (31.1%), 22 samples (29.7%), 18 samples (24.3%), and 16 samples (22.0%), respectively. No strong associations were found between the pathogens and growing practices.