Here’s an update on the Cal Poly Strawberry Center’s Disease Diagnostics. A total of 16 samples have been submitted so far of which 11 have been diagnosed with the pathogens in (see Table below). Relative to this time last year we are seeing more samples positive for Phytophthora spp. and Pythium spp. These two soil-borne pathogens are not true fungi but are Oomycetes. They produce survival structures that can withstand harsh conditions in soil and those would produce sporangia which release zoospores (see Figure below) that can swim around and find new strawberry roots and infect. The increased prevalence of Phytophthora crown rot can be linked to rains we got in the winter. Pythium spp. is part of the black root rot complex that consists of Illyonectria spp. Rhizoctonia fragariae, and Fusarium spp. We are working on a research project to determine the role of Pythium on plant mortality using isolates obtained from these plant samples. The first Fusarium wilt and Verticillium wilt samples of the year were also found in this quarter.

Table: Summary of diagnostic service activity

Figure: Phytophthora oospore, sporangium and zoospores.