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United States Department of Agriculture

Agricultural Research Service

Title: Screening for Resistance to Stemphylium Leaf Spot of Spinach

Authors
item MOU, BEIQUAN
item Koike, Steven - UC COOP. EXT.
item Du Toit, Lindsey - WASHINGTON STATE UNIV.

Submitted to: Proceedings of the 2006 International Spinach Conference
Publication Type: Proceedings
Publication Acceptance Date: July 12, 2006
Publication Date: July 13, 2006
Citation: Mou, B., Koike, S., Du Toit, L. 2006. Screening for resistance to stemphylium leaf spot of spinach. Proceedings of the 2006 International Spinach Conference. July 13-14, La Conner, WA.

Interpretive Summary: In 1997, a new leaf spot disease was found in spinach fields in California. The pathogen was identified as Stemphylium botryosum. S. botryosum has since been reported as a foliar pathogen of spinach in Arizona, Delaware, Florida, Maryland, Oregon, Washington, and Quebec, Canada. Quality standards for fresh market spinach are extremely high, so this emerging disease poses another challenge for spinach growers to produce high quality, defect-free products. Resistance to Stemphylium leaf spot in spinach has not been reported. The entire USDA spinach germplasm collection (338 accessions) as well as 148 cultivars or breeding lines from seed companies were evaluated for their response to the disease in inoculated tests in a greenhouse. No genotype was completely immune to the disease. However, there were significant differences in the number of leaf spots among the genotypes tested. Two accessions from Turkey, PI 169685 and PI 173809, consistently had low disease incidence (% diseased plants) and severity (% diseased leaf area) ratings. Although the order in which entries from seed companies were ranked for severity of leaf spot differed between two tests, the screens identified entries that are highly susceptible to S. botryosum, and entries with putative resistance to this pathogen. Further screening under field conditions is needed. Resistance (or susceptibility) information of spinach germplasm should be useful for plant breeders to develop leafspot-resistant cultivars.

Technical Abstract: Leaf spot disease of spinach (Spinacia oleracea L.) caused by Stemphylium botryosum has continued to occur in California and six other states since 1997, posing another challenge for growers to produce high quality and defect-free products. No resistance to the pathogen has been reported in spinach. The entire USDA spinach germplasm collection (338 accessions) as well as 148 cultivars or breeding lines from seed companies were evaluated for their response to the disease in inoculated tests in a greenhouse. No genotype was completely immune to the disease. However, there were significant differences in the number of leaf spots among the genotypes tested. Two accessions from Turkey, PI 169685 and PI 173809, consistently had low disease incidence (% diseased plants) and severity (% diseased leaf area) ratings. No correlation between disease incidence/severity and leaf type was observed. S. botryosum fungi were consistently isolated from the leaf spots. None of the control plants treated with sterile distilled water developed symptoms. Although the order in which entries from seed companies were ranked for severity of leaf spot differed between two tests, the screens identified entries that are highly susceptible to S. botryosum, and entries with putative resistance to this pathogen. Further screening under field conditions is needed. Resistance (or susceptibility) information of spinach germplasm should be useful for plant breeders to develop leafspot-resistant cultivars.

Last Modified: 9/10/2014
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