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United States Department of Agriculture

Agricultural Research Service


item Wilcox, James
item St. Martin, Steven

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/20/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: Phytophthora rot is a destructive disease of soybean in the U.S. Genetic resistance has limited disease losses, but is not always available in high-yielding varieties. Blends of equal numbers of seed of soybean strains resistant and susceptible to the pathogen produced seed yields equal or nearly equal to yields of resistant varieties. The high yield of the blends can be attributed to resistant plants in the blend producing more seed per plant than would be expected. The higher-than-normal seed production of the resistant plants is due to their effective utilization of space, nutrients, and soil moisture that was not being utilized by the weakened, susceptible plants in the blend. The information provides a management strategy that will be useful in minimizing disease losses associated with new races of the pathogen where resistance is not available in high-yielding varieties. Blends of high-yielding, susceptible evarieties and lower-yielding, resistant varieties may provide the best opportunity to optimize seed yield. In environments where disease pressure is nonexistent or minimal, the high-yielding, susceptible component could compensate for the lower-yielding resistant component of the blend. Where prevalent races of the pathogen reduced yields of the susceptible component, the resistant component of the blend could partially compensate for these yield reductions.

Technical Abstract: Isolines, differing in seedcoat color and in resistance to Phytophthora sojae, of three soybean cultivars were grown in replicated tests at three Indiana locations and one location in Ohio for three years. Isolines of Beeson and Century, with the Rps1-a allele, and Williams, with the rps allele, were susceptible to prevalent races of P. sojae, and all had black seed coats as a marker trait. Beeson 80, with the Rps1-c allele, and Century 84 and Williams 82, with the Rps 1-k allele, were resistant to prevalent races of the pathogen and had yellow seed coats. Blends of each cultivar were seeded with equal numbers of seed with black and yellow seed coats. In six environments, isolines susceptible to prevalent races of the pathogen produced seed yields from 65 to 93 percent of the yields of isolines resistant to these races. In these environments, blends produced yields similar or equal to yields of the resistant isoline. Yellow seeds of the resistant isoline in the blend contributed from 10 to 33 percent more seed than would be expected if resistant and susceptible isolines contributed equally to seed yield. The data demonstrate that plants of the resistant isoline in the blend were compensating for reduced productivity of the susceptible plants in the blend.

Last Modified: 10/18/2017
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