Genetic Variability and Agronomic Performance of Soybean Populations Developed from Plant Introductions

Plant introductions (Pl's) of soybean [Glycine max (L.) Merr.] may enhance genetic improvement for yield beyond the level possible with the domestic gene pool of cultivars and experimental lines. The genetic variability and agronomic performance of soybean populations with five different percentages of PI germplasm were evaluated. Forty PI's and 40 domestic cultivars and experimental lines were intermated systematically during four generations to form the populations AP10 (100% PI), APII (75% PI), API2 (50% PI), AP13 (25% PI), and (0% PI). In 1980, 200 random lines from each population with a restricted range in maturity were evaluated for seed yield and time of maturity at two locations in Iowa. In 1981, 60 of the highest-yielding lines from each population were evaluated for seed yield, time of maturity, plant height, and lodging at three Iowa locations. The genetic variability for seed yield among the 200 random lines was similar for API0 to API3 and about twice as large as the genetic variability for AP14. The mean yields of the random lines of 1980 and the selected lines of 1981 were greatest for AP14 and least for AP10. In the regression of mean yield of the populations in 1980 on percentage of PI germplasm in the populations, 73% of the variation was explained by the linear component. There was a similar decrease from API4 to API0 in the mean yields of the top 10 and 20 lines of each population that could be used as parents to form cycle 1 populations for recurrent selection. Lodging susceptibility of the populations decreased progressively from AP10 to AP14. The maximum difference in plant height among populations was only 8 cm. The use of PI germplasm for short-term improvement of yield is not likely to be as productive as selection in populations developed from domestic cultivars or experimental lines. Longterm recurrent selection studies will be required to determine the ultimate value of PI germplasm for yield improvement of soybean.