Evaluation of spinach cultivars for downy mildew resistance in Yuma, AZ 2020

Authors: CLARK, KELLEY - University Of Arkansas; FENG, CHUNDA - University Of Arkansas; BRAHAM, DHILLON - University Of Florida; Kandel, Shyam; POUDEL, BINDU - University Of Arizona; Mou, Beiquan; Klosterman, Steven; CORRELL, JAMES - University Of Arkansas

Submitted to: Plant Disease Management Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/12/2020
Publication Date: 8/25/2020
Citation: Clark, K.J., Feng, C., Dhillon, B., Kandel, S.L., Poudel, B., Mou, B., Klosterman, S.J., Correll, J.C. 2020. Evaluation of spinach cultivars for downy mildew resistance in Yuma, AZ 2020. Plant Disease Management Reports. 14. Article V146.

Interpretive Summary: Downy mildew, caused by Peronospora effusa, is responsible for high economic losses in spinach in the US and elsewhere. Host resistance remains the most effective and environment friendly approach for downy mildew management for conventional and organic production. A field experiment was conducted to assess the downy mildew resistance in 70 spinach cultivars at the University of Arizona, Yuma Agricultural Center from January 15 to March 5, 2020. We evaluated downy mildew incidence on Mar 5 (48 days after the initial irrigation) by evaluating the percent of infected plants of each cultivar. Information obtained in this study on the levels of resistance and susceptibility of spinach cultivars is useful for plant breeders to select cultivars with increased resistance to downy mildew.

Technical Abstract: Downy mildew disease, caused by Peronospora effusa, is responsible for high economic losses in spinach and the emergence of new P. effusa races continues to threaten the spinach industry. The use of resistant cultivars remains an effective strategy for disease management, especially since nearly 50% of the U.S. spinach production is organic. We assessed downy mildew resistance of 70 spinach cultivars in a replicated field test at the University of Arizona, Yuma Agricultural Center from 15 Jan to 5 Mar 2020. Downy mildew was first observed in the plots on 24 Feb 2020. The final evaluation for disease incidence was made on 5 Mar, 48 days from the initial irrigation on 17 Jan. Disease incidence was determined by evaluating the percent of infected plants from each spinach cultivar that showed the chlorosis on the adaxial leaf surfaces with sporulation on the abaxial side. No downy mildew infection was observed on 46 cultivars, and infection on the 24 susceptible cultivars ranged from 0.7% to 61.7%. The spinach cultivar SV2157VB was found to be most susceptible.