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ARS Home » Pacific West Area » Salinas, California » Crop Improvement and Protection Research » Research » Publications at this Location » Publication #403482
Research Project: Disease Management and Improved Detection Systems for Control of Pathogens of Vegetables and Strawberries

Location: Crop Improvement and Protection Research

Title: Evaluation of spinach cultivars for downy mildew resistance in San Juan Bautista, CA 2022

Author
item ZIMA, HANNA - University Of Arkansas
item Clark, Kelley
item Klosterman, Steven
item WANG, YU-CHEN - University Of Arkansas
item CORRELL, JIM - University Of Arkansas

Submitted to: Plant Disease Management Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/30/2023
Publication Date: 8/30/2023
Citation: Zima, H.V., Clark, K.J., Klosterman, S.J., Wang, Y., Correll, J.C. 2023. Evaluation of spinach cultivars for downy mildew resistance in San Juan Bautista, CA 2022. Plant Disease Management Reports. 17. Article V154.

Interpretive Summary: Downy mildew disease on spinach is caused by a microscopic pathogen known as Peronospora effusa. The pathogen can produce wind-dispersed spores, and requires cool, wet conditions for infection. Due to the increased canopy density that spinach is planted, low levels of disease incidence can lead to unmarketable spinach because of the rapid establishment and spread of the disease. Downy mildew is successfully managed with fungicides and resistant cultivars in conventional fields, but only the latter is implemented for organic production, which represents about half of U.S. production. In this study, commercial spinach cultivars were examined for downy mildew disease incidence under field conditions near San Juan Buatista, CA. The amount of disease appearing on susceptible plants in the experiment was adequate to evaluate resistance in cultivars Some cultivars showed reduced disease incidence and thus some of these cultivars may be informative in programs that aim to breed for plant resistance.

Technical Abstract: Downy mildew (Peronospora effusa) is a major constraint to spinach production. The pathogen can produce wind-dispersed spores, and requires cool, wet conditions for infection. Increased canopy density and overhead irrigation create optimal conditions for the pathogen and subsequent spread of the disease. Management strategies in conventional fields consist of fungicide applications and resistant cultivars. Host resistance in spinach is the only effective management strategy for organic production, which represents about half of U.S. production. At present, there are 19 described races of P. effusa, as well as isolates with novel virulence patterns on spinach differentials. The purpose of this study was to assess resistance to P. effusa among commercial spinach cultivars, with a total of 70 cultivars that were rated at the Enza Zaden Research Institute in San Juan Bautista, CA, between 20 Oct-17 Nov 2022. Seed was sown on 14-16 Sept. The “wet-date” was 19 Sept. The plots were 15 ft by 6 ft and seed was planted at a density of 4 million seed/A, and beds were 600 ft in length with three separated replications. Each replication consisted of rows with 10 cultivars per row. The plot was set up as a completely randomized block design. The trial was flanked by a single bed of the cultivar Woodpecker and a single bed of a mixture of cultivars. Maximum air temperature ranged from 65-95°F and minimum from 36-58°F, cumulative rainfall was 0.00 in., and the maximum wind peak was 4 mph. Plants were watered with overhead sprinklers 2-3 times per week for the duration of the experiment. Downy mildew incidence was rated by visually estimating the percentage of plants showing downy mildew symptoms for each of the three replicate plots per cultivar. Mean disease incidence was calculated by averaging the three replications.