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Poster: Biology & Disease Mgmt: Oomycetes


Identification and characterization of potential oomycete pathogens from the University Agricultural Laboratory in Fresno, California
M. ELLIS (1), H. Deniston-Sheets (1), D. Sieperda (2), J. Bushoven (1) (1) Plant Science Department, California State University, Fresno, U.S.A.; (2) California State University, Fresno, U.S.A.

The University Agricultural Laboratory (UAL) at California State University, Fresno is a 1000-acre farm that grows a wide range of fruit, nut, vegetable, and field crops. Many of the crops grown on the UAL are negatively impacted by oomycetes; however, identification of pathogenic species has not been determined. Therefore, the goal of this research was to identify and characterize potential sources of oomycete pathogens from soil and irrigation reservoirs on the UAL. Oomycetes were baited over a 5-day period using pears or cucumbers as bait. Symptomatic fruit tissue was excised and plated on the oomycete selective medium PARP. Isolates were then characterized using morphology and DNA sequencing of the internal transcribed spacer region. Forty-four isolates of Pythium spp., 6 isolates of Phytophthora spp., 4 isolates of Phytopythium spp., and 1 isolate of a Pythiogeton sp. were identified. Pythium spp. (86%), Phytophthora spp. (11%), and Phytopythium spp. (3%) were identified from the irrigation reservoir. The most common species isolated from irrigation water were Pythium oopapillum (54%) and Pythium dissotocum (25%). Of the isolates baited from soil 75% were Pythium spp., while 13%, 8%, and 4% were Phytopythium spp., Phytophthora spp., and a Pythiogeton sp. respectively. These results suggest that the UAL has a diverse number of potential oomycete pathogens and that irrigation reservoirs may act as a source for potential inoculum in farming operations.