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United States Department of Agriculture

Agricultural Research Service

Title: Three New Races of the Spinach Downy Mildew Pathogen Identified by a Modified Set of Spinach Differentials

Authors
item Irish, Brian
item Correll, J. - UNIV. OF ARKANSAS
item Koike, S. - UNIV. OF CALIFORNIA
item Morelock, T. - UNIV. OF ARKANSAS

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 9, 2007
Publication Date: November 1, 2007
Citation: Irish, B.M., Correll, J.C., Koike, S.T., Morelock, T.E. 2007. Three new races of the spinach downy mildew pathogen identified by a modified set of spinach differentials. Plant Disease. 91(11):1392-1396.

Interpretive Summary: Spinach downy mildew is the most economically important disease of spinach worldwide. In the past few years, field observations indicated that spinach cultivars resistant to the previously described downy mildew races were heavily infected. Four downy mildew isolates were collected from California and the Netherlands and characterized for race on spinach differentials. The results led to the description of three new races of the downy mildew pathogen designated races 8, 9, and 10. Four differential spinach cultivars with resistance to the previous races were used to distinguish the three new races. The three new races also were used to evaluate the disease reactions of contemporary commercial spinach cultivars in greenhouse trials. In addition, a downy mildew isolate survey collected in California and Arizona between in 2004 and 2006 indicated that race the new race 10 predominated in the areas sampled. Characterizing downy mildew races and the subsequent identification of spinach cultivars with resistance to new races will provide producers the most efficient means for disease management.

Technical Abstract: Spinach downy mildew, caused by Peronospora farinosa f. sp. spinaciae, is the most economically important disease of spinach worldwide. In the past few years, field observations in both the United States and the European Union indicated that spinach cultivars resistant to the seven previously described races of P. farinosa f. sp. spinaciae were heavily infected with the downy mildew pathogen. Four new isolates of P. farinosa f. sp. spinaciae were collected from California and the Netherlands and characterized based on disease reactions on two modified sets of spinach differentials. The results led to the description of three new races of the downy mildew pathogen, designated races 8, 9, and 10. Four differential cultivars with resistance to races 1 to 7 were used to distinguish the three new races. Dolphin was susceptible to races 8 and 10 but resistant to race 9; Lion was susceptible to race 10, but resistant to races 8 and 9; Lazio was resistant to races 1 to 7 as well as races 8, 9, and 10 and Tarpy was susceptible to all three new races 8, 9, 10. The three new races also were used to evaluate the disease reactions on 43 contemporary commercial spinach cultivars in greenhouse trials. A survey of 58 isolates of P. farinosa f. sp. spinaciae collected in California and Arizona between in 2004 and 2006 indicated that race 10 predominated in the areas sampled.

Last Modified: 8/21/2014
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