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ARS Home » Pacific West Area » Salinas, California » Crop Improvement and Protection Research » Research » Publications at this Location » Publication #422102
Research Project: Disease Management and Improved Detection Systems for Control of Pathogens of Vegetables and Strawberries

Location: Crop Improvement and Protection Research

Title: Phenotypic and genotypic characterization of novel strains of spinach downy mildew pathogen

Author
item Feng, Chunda
item FICHEUX, PAULINE - University Of Arkansas
item VILLARROEL-ZEBALLOS, MARIA - University Of Arkansas
item CASTROAGUDIN, VANINA - University Of Arkansas
item ZIMA, HANNAH - University Of Arkansas
item LAMOUR, KURT - University Of Tennessee
item CLARK, KELLEY - University Of California
item Klosterman, Steven
item CORRELL, JAMES - University Of Arkansas

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/4/2025
Publication Date: 6/17/2025
Citation: Feng, C., Ficheux, P.F., Villarroel-Zeballos, M.I., Castroagudin, V.L., Zima, H.V., Lamour, K., Clark, K.J., Klosterman, S.J., Correll, J.C. 2025. Phenotypic and genotypic characterization of novel strains of spinach downy mildew pathogen. Plant Disease. https://doi.org/10.1094/PDIS-01-25-0064-RE.
DOI: https://doi.org/10.1094/PDIS-01-25-0064-RE

Interpretive Summary: Downy mildew disease on spinach is caused by a foliar plant pathogen known as Peronospora effusa. Downy mildew is the most widespread and destructive disease on spinach in the US and worldwide. Downy mildew is successfully managed with fungicides and resistant cultivars in conventional fields. However, only the use of resistant cultivars can be implemented for organic production, which represents about half of U.S. production. In this study, 70 different commercial spinach cultivars were examined for downy mildew disease incidence in response to 74 isolates of the pathogen, P. effusa. The results revealed 17 isolates of P. effusa with novel pathogenicity characteristics and three new races, while some cultivars of spinach exhibited to resistance to a range of the isolates tested. These results with these cultivars and the pathogen are informative in programs that aim to breed for plant resistance.

Technical Abstract: Downy mildew, caused by the obligate pathogen Peronospora effusa , has a devastating impact on spinach. Growing resistant cultivars is the most economical way to manage this disease, especially for organic spinach production. However, rapidly emerging new races or novel strains may result in a breakdown of the resistance deployed. It is therefore critical to monitor the dynamics of the population of P. effusa and to determine the disease reactions of newly released cultivars to the new races and novel strains. In this study, 74 isolates of P. effusa were examined for their reactions on differential host cultivars, resulting in the identification of three new races and 18 novel strains with unique virulence pathotypes. Race 19 of P. effusa could infect many currently wide-grown P. effusa 1-17 resistant cultivars. Targeted sequencing of DNA isolated from lesions of P. effusa 19 isolates revealed genetic variations among isolates of this race, and within isolates of P. effusa 19. The isolates showed either no genetic variation (only one genotype of multiple lesions of an isolate tested), limited, or abundant genetic variation (multiple genotypes within an isolate tested). Seventy spinach cultivars were tested for their reactions to two P. effusa races, 18 and 19, and four novel strains. The results of this study are helpful for growers to select suitable cultivars for their production, and for breeders to develop downy mildew resistant cultivars.