Submitted to: Plant Health Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/13/2011
Publication Date: 3/23/2011
Citation: Radwan, G.L., Isakeit, T., Magill, C.W., Perumal, R., Prom, L.K., Little, C.R. 2011. Screening exotic sorghum germplasm, hybrids and elite lines for resistance to a new virulent pathotype (P6) of Peronsclerospora sorghi causing downy mildew. Plant Health Progress. Available: doi:10.1094/PHP-2011-0323-01-RS. Interpretive Summary: In recent years, a new race of the sorghum downy mildew fungus was identified in Wharton County, Texas. As a result, sorghum lines from India, Kansas, and Texas were tested to identify new sources of resistance to this new race. Using the sandwich method of inoculation, plants were inoculated with the fungal spores in the greenhouse. Sixty-eight sorghum lines, including commercial hybrids, were found to be resistant to the downy mildew fungus. Thirteen of 24 elite breeding lines from Texas were also resistant. This work is significant because it has identified potential new sources of downy mildew resistance in sorghum that can be utilized by breeders to develop new lines and hybrids.
Technical Abstract: A recent outbreak of sorghum downy mildew (SDM) in Texas has led to the discovery of both metalaxyl fungicide resistance and a new pathotype, P6, in the causal organism Peronsclerospora sorghi. New and alternate sources of the host plant resistance are needed for successful management of SDM. To identify sources of resistance a total of 333 (242 minicore lines representing diverse germplasm from India, 67 commercial hybrids from Kansas, and 24 elite breeding lines from Texas) were inoculated in the greenhouse. Using an established sandwich inoculation technique, artificial inoculation of text lines with P. sorghi conidia, resulting in < 10% infection, were scored as “resistant.” Forty-eight minicore and 20 accessions from Kansas exhibited = 10% infection and were selected as resistant. Out of 48 resistant minicore accessions, 20 were photo-insensitive. Eleven of 20 commercial hybrids from Kansas showed zero percent infection. Thirteen of 24 elite breeding lines from Texas were also resistant. In this study, resistance sources for the new P6 SDM pathotype were identified. The diversity among these materials is expected to provide different single gene sources as well as quantitative sources of SDM resistance for use in breeding programs.