Abstract
Soybean (Glycine max (L.) Merrill) seed susceptibility to mechanical damage during harvesting, threshing, and storage operations has decreased seed quality by reducing seed germination ability and seedling vigour, mainly in tropical and subtropical environments. This research aimed at estimating the genetic variability of seed response to mechanical damage (MD), and its relationship to agronomic characters such as plant height at maturity (PHM) and seed yield (SY). The material included 10 early maturity parents and 45 diallel crosses among them and five experimental checks. Ten F 8:5 experimental lines from each cross were evaluated. The statistical and genetical analyses included estimates of phenotypic and genotypic correlations; relative contribution of genetic effects versus combined genetic and environmental effects; relationship between the genetical and experimental variation coefficients; coefficient of genotypic determination; expected and observed gain; and, correlated response to selection. The parents Parana, Hale-321, IAC-Foscarin-31 and Primavera, showed the same MD resistance levels as IAS-5 cultivar, a standard check for MD resistance. The parents Palmetto, Coker-136, FT-81-1835 and Forrest were MD susceptible; however, they were superior to the IAC-2 cultivar, a standard check for MD susceptibility. The coefficient of genotypic determination for MD was estimated in 0.739, indicating large possibility to select MD resistant inbred lines in a population represented by the 45 diallel crosses. Expected and observed genetic gains indicated the possibility of success in the selection for resistance to MD among and within crosses. Based on the low genetic correlations (<0.25) among MD, PHM, and SY, all possible combinations of these traits could be found in a same soybean plant, at least in the early maturity group.
Highlights
Soybean seeds are very sensitive to mechanical damage (MD)
This research aimed at estimating the genetic variability of seed response to mechanical damage (MD), and its relationship to agronomic characters such as plant height at maturity (PHM) and seed yield (SY)
The coefficient of genotypic determination for MD was estimated in 0.739, indicating large possibility to select MD resistant inbred lines in a population represented by the 45 diallel crosses
Summary
Soybean seeds are very sensitive to mechanical damage (MD). The vital parts of the embryonary axis (radicle, hypocotyl and plumule) are located under a very thin seed coat, which offers little protection (Copeland, 1972; Delouche, 1972; Gupta et al, 1973; França Neto and Henning, 1984; Costa et al, 1986). Dickson and Boettger (1977) have studied the genetical aspects of MD using Phaseolus vulgaris beans. Few papers deal with selection methods such as the drop test (Dickson and Boettger, 1977; Kueneman, 1989 and Carbonell et al, 1992), stationary threshers (Costa et al, 1987), the pendulum test (Carbonell, 1991) and the correlation between lignin content in the seed coat and its reaction to MD (Alvarez, 1994). They obtained heritability estimates from 22 to 73%. No report of MD heritability in soybeans was found in the literature
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