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ARS Home » Pacific West Area » Salinas, California » Crop Improvement and Protection Research » Research » Publications at this Location » Publication #315453

Title: Detection of spinach downy mildew during latent infection

item SUBBARAO, CHAITRA - Non ARS Employee
item Anchieta, Amy
item SUBBARAO, KRISHNA - University Of California
item Klosterman, Steven

Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: 3/21/2015
Publication Date: 8/1/2015
Citation: Subbarao, C., Anchieta, A.G., Subbarao, K.V., Klosterman, S.J. 2015. Detection of spinach downy mildew during latent infection. Phytopathology. Available:

Interpretive Summary:

Technical Abstract: Downy mildew of spinach is caused by the plant pathogenic microorganism Peronospora effusa. In California, where nearly 75% of the US fresh spinach crop is grown, downy mildew causes millions of dollars in losses annually. The disease is currently controlled by fungicide applications in conventional production, and some of these fungicides are applied whether or not infection has occurred on spinach because of the explosive nature of these epidemics. It was, therefore, hypothesized that if downy mildew infection could be detected during the latent period, before symptoms appeared, fungicide applications could be targeted only when and where the pathogen was present. In turn, this may prevent epidemics from developing. Polymerase chain reactions (PCR) with P. effusa-specific primers were used to detect the pathogen DNA from potential infections on 50 samples weekly for six weeks. Spinach plants were randomly sampled every 3 m within the beds, from a 36 m plot, consisting of four beds. Only a few of the 50 samples (usually in clusters throughout the plot) provided Peronospora-specific amplicons in the initial four weeks. However, a few weeks later, about 90% of the samples were positive. Initial samples were asymptomatic and yet the PCR detected P. effusa, confirming detection in a latent period. In conclusion, using PCR, downy mildew pathogen DNA was detected on symptomless spinach plants, and application of fungicides on plants within the field and nearby is expected to prevent further downy mildew development. The approach requires additional validation in larger commercial fields.