AGRONOMIC VARIATION IN A BACKCROSS SOYBEAN POPULATION RESISTANT TO PHYTOPHTHORA ROOT ROT

ERVIN HENRY MUELLER, Purdue University

Abstract

The soybean (Glycine max (L.) Merrill) cultivar Wells II was developed for resistance to most of the newer physiologic races of Phytophthora megasperma Drechs. var. sojae A. A. Hildeb. that have been causing yield losses in northern Indiana. Wells II was a composite of all the seed from each of 72 homozygous resistant lines selected in the F(,3) generation from the backcross Wells('7) x (Wells x Arksoy). The dominant gene Rps(,1)('c) from Arksoy conveys resistance to races 1, 2, 3, 6, 7, 8, and 9, whereas the gene Rps(,1) in Wells controls resistance to only races 1 and 2. The hypocotyl-inoculation tests conducted to identify the homozygous resistant lines in the population, also identified 17 backcross derived lines that were homozygous susceptible to race 3 (Rps(,1)). Each of the susceptible lines originated from the same F(,2) plant as had one of the resistant lines. These sibling-pairs were nearly-isogenic except for the genes Rps(,1) and Rps(,1)('c). Fourteen sibling-pairs and a check pair consisting of the recurrent parent Wells and the BC7 Composite made from equal numbers of seed of each resistant selection were tested for two years in the absence of the disease to ascertain if these genes had any effect other than disease reaction. The data indicated no effect or an equal effect for these genes on yield. There was a trend for the Rps(,1) sibling in most pairs to be taller and to lodge more than the Rps(,1)('c) sibling. The BC7 Composite and Wells II did not differ in yield, seedling emergence, maturity, lodging, height, seed size, protein and oil content, or germination. The results indicated no advantage for using equal numbers of seed from each BC7 selection to be composited into a new cultivar for disease resistance. The data from two years of testing the 72 resistant selections, Wells, Wells II, and the BC7 Composite indicated that only one selection was significantly lower in yield than the recurrent parent Wells, and this selection was also earlier, shorter, and had smaller seeds than Wells. A few other selections were different than Wells for maturity, seed size, height, and oil content, but none differed for seedling emergence, lodging, protein content, or germination. Significant variation was present among the resistant selections for yield, seedling emergence, maturity, height, seed size, protein and oil content, and germination in the two-year test. A single line was consistently identified as a high yielding entry and was significantly higher in yield than 31 of the other selections, and Wells II, but was not significantly different than Wells in the two year test. A composite made up of the top three yielding lines in 1978 did not yield significantly different than any of the trial entries in 1979, and was below the average yield of its three components. This emphasized the need for more than one year a consistently select the highest yielding line. The earliest possible release of a cultivar consisting of all available seed of the homozygous resistant selections derived from backcrossing would provide an immediate yield advantage in the area of disease induced losses. Additional testing of the resistant lines to identify the highest yielding line for subsequent release would impart the greatest yield advantage. The cost of additional testing would be justified if the new cultivar was projected to occupy a large acreage or to have a long life expectancy.

Degree

Ph.D.

Subject Area

Agronomy

Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server
.

Share

COinS