Evaluating Peronospora Presence in Salinas Valley & Analyzing DNA Similarity in Downy Mildew Pathogens Affecting Spinach

Overview

Objectives/Goals Downy mildew is one of the most destructive plant pathogens across the globe, and the major production constraint on the $200,000,000 spinach industry in California, the majority of which is grown in the Salinas Valley. Fungicides are costly and time-consuming. They may also stain spinach leaves (copper residue) making even healthy plants unmarketable. Yet they are effective only when immediately applied. Though all downy mildew look exactly the same, only one species Peronospora effusa can infect spinach. 1. There is a need to be able to quickly accurately distinguish an unknown downy mildew to screen seeds and plants alike, and determine whether fungicides are necessary. 2. Understand how isolates Peronospora farinosa f.sp.betae and Peronospora farinosa f sp.cicla (found in Salinas Valley) are related to the rest of the Peronospora genus. 3. Assess whether Peronospora is a threat in the Salinas Valley. Analyze how it spreads, and propose solutions. Methods/Materials We screened crops and commercial seed for Peronospora using industry approved methods. We used E.Coli to clone the internal transcribed spacer (ITS) region, purified the DNA and sent it for Sanger sequencing to find genetic variations in Peronospora. Next, we created a phylogenetic tree to better understand how the species are related. Results Peronospora filaments were repeatedly found on commercial seed and on crops in the valley. Genetic variations were found between the isolates we sequenced and Peronospora effusa. Peronospora farinosa f. sp. betae and f. sp. cicla have the exact same ITS sequence. Interestingly they are more closely related to the P. effusa than they to other P. farinosa that attack the Chenopodiaceae family of plants. Conclusions/Discussion Genetic differences make it possible to identify unknown isolates and determine whether to use fungicides. Peronospora is systematically evading seed screening procedures, because spinach screening techniques involve culturing seed debris on agar from 20C-25C. Peronospora is an obligate parasite and cannot survive on agar. It prefers cool temperatures and degrades at these high temperatures. Seed debris should be cultured at about 13°C on spinach leaves, not agar.

Awards (1)

• Third Place

Competition history

• CSEF 2013 Plant Biology · Entry S1997

Resources

• CSEF project summary ↗

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