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ARS Home » Pacific West Area » Salinas, California » Crop Improvement and Protection Research » Research » Publications at this Location » Publication #223791
Title: Screening for Resistance to Leaf Spot Diseases of Spinach.

Author
item Mou, Beiquan
item KOIKE, STEVEN - UC, COOP. EXTENSION
item DU TOIT, LINDSEY - WASHINGTON STATE UNIV.

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/30/2008
Publication Date: 10/1/2008
Citation: Mou, B., Koike, S.T., Du Toit, L.J. Screening for Resistance to Leaf Spot Diseases of Spinach.. HortScience 43(6):1706-1710.2008.

Interpretive Summary: Leaf spot of spinach (Spinacia oleracea L.) caused by Stemphylium botryosum has continued to occur in California and at least six other states since 1997, posing yet another challenge for growers to produce high quality and defect-free products. Resistance to the pathogen has not been reported in spinach. The entire USDA spinach germplasm collection (338 accessions) and 22 commercial spinach cultivars were evaluated in a preliminary screening with two replications in a greenhouse. Putative resistant accessions that were identified, susceptible accessions that served as control treatments, and the 22 commercial cultivars were included in a second test with four replications to confirm the results. No genotype was immune to the disease. Two accessions from Turkey, PI 169685 and PI 173809, consistently had low disease incidence and severity ratings. None of the commercial cultivars tested consistently showed low disease incidence or severity. There was no significant correlation between disease incidence/severity and leaf type (smooth, semi-savoy, or savoy). In addition to the public germplasm evaluated, 138 proprietary spinach genotypes (breeding lines and cultivars) were obtained from seed companies and screened for resistance to Stemphylium leaf spot as well as Cladosporium leaf spot (caused by Cladosporium variabile) in a greenhouse in each of 2004 and 2005, along with 10 accessions from the USDA germplasm collection. Significant differences in severity of leaf spot were observed among the genotypes for both diseases. For each disease, there was a significant positive correlation in severity ratings of the genotypes between 2004 and 2005. Information on the relative resistance (or susceptibility) of the spinach germplasm evaluated in this study should be useful for plant breeders to develop leaf spot-resistant cultivars.

Technical Abstract: Leaf spot of spinach (Spinacia oleracea L.) caused by Stemphylium botryosum has continued to occur in California and at least six other states since 1997, posing yet another challenge for growers to produce high quality and defect-free products. Resistance to the pathogen has not been reported in spinach. The entire USDA spinach germplasm collection (338 accessions) and 22 commercial spinach cultivars were evaluated in a preliminary screening with two replications in a greenhouse. Putative resistant accessions that were identified, susceptible accessions that served as control treatments, and the 22 commercial cultivars were included in a second test with four replications to confirm the results. No genotype was immune to the disease. However, there were significant differences in disease incidence (% of plants with leaf spot) and severity (% total diseased leaf area per pot) among the genotypes tested. Two accessions from Turkey, PI 169685 and PI 173809, consistently had low disease incidence and severity ratings. The two Spinacia tetrandra and four Spinacia turkestanica accessions screened in these public germplasm tests were all susceptible. None of the commercial cultivars tested consistently showed low disease incidence or severity. There was no significant correlation between disease incidence/severity and leaf type (smooth, semi-savoy, or savoy). S. botryosum was consistently isolated from the leaf spots. None of the control plants treated with sterile distilled water developed symptoms. In addition to the public germplasm evaluated, 138 proprietary spinach genotypes (breeding lines and cultivars) were obtained from seed companies and screened for resistance to Stemphylium leaf spot as well as Cladosporium leaf spot (caused by Cladosporium variabile) in a greenhouse in each of 2004 and 2005, along with 10 accessions from the USDA germplasm collection. Significant differences in severity of leaf spot were observed among the genotypes for both diseases. For each disease, there was a significant positive correlation in severity ratings of the genotypes between 2004 and 2005. Information on the relative resistance (or susceptibility) of the spinach germplasm evaluated in this study should be useful for plant breeders to develop leaf spot-resistant cultivars.