Submitted to: Plant Disease
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/2/1998
Publication Date: N/A
Citation: Interpretive Summary: Phytophthora rot is a major disease in many soybean growing areas of the U.S. Although there are many known genes for resistance currently available, there are known strains of the pathogen causing Phytophthora rot, Phytophthora sojae, that can attack all known sources of resistance. Finding new sources of resistance is critical to maintaining soybean production in P. sojae infested areas. The USDA Soybean Germplasm Collection has acquired soybean germplasm from provinces in China not previously represented in the Collection. These accessions are ideal candidates for screening for new sources of disease resistance. Over 600 accessions from 7 provinces of southern China were evaluated for reaction to 10 races of P. sojae. Eighteen accessions were found that were resistant to all ten races and 11 of those accessions came from a single province, Jiangsu. Over 80 accessions were resistant to 8 or more races of the pathogen. Of the 14 reaction patterns with resistance to 8 or more races, only 1 could be explained by a single known gene and combinations of 2 known genes would account for only 8 more patterns. This research has identified over 500 new accessions of soybean with resistance to at least one race of P. sojae and 18 accessions with resistance to all ten races used in this work. Based on reaction patterns of known genes, many new genes for resistance will likely be identified among these accessions. These accessions are already being crossed with adapted varieties to develop new cultivars with resistance to a broader spectrum of P. sojae races to help keep soybean production profitable. The identification of areas of China with high levels of resistance is useful in guiding future collection and evaluation.
Technical Abstract: Phytophthora rot, caused by Phytophthora sojae, is a damaging disease of soybean [Glycine max (L.) Merr.] throughout the soybean producing regions of the world. New races of the pathogen have been discovered which are capable of causing susceptible reactions on cultivars with commonly used resistance genes. The discovery of new sources of resistance in soybean is vital in maintaining control of Phytophthora rot. The objectives of this study were to investigate the distribution and diversity of Phytophthora resistance in 628 accessions of soybean from southern China and identify sources which confer resistance to multiple races for implementation into breeding programs. Soybean accessions were evaluated for their response to races 1, 3, 4, 5, 7, 10, 12, 17, 20, and 25 of P. sojae using the hypocotyl inoculation technique in the greenhouse at Urbana, IL in 1996 and 1997. Accessions were identified that confer resistant responses to multiple races. These accessions may provide sources of resistance for control of Phytophthora rot of soybean in the future. Accessions were identified with resistance to all ten races of P. sojae. The majority of the accessions with resistance to eight or more of the ten races used for evaluation were from the provinces of Hubei, Jiangsu, and Sichuan in southern China. Based on the evaluated accessions, these provinces appear to be valuable sources for collecting Phytophthora resistant soybean in China.