Abstract
The objective of this work was to validate microsatellite markers associated with resistance to soybean cyst nematode (Heterodera glycines Ichinohe) races 3 and 14, in soybean (Glycine max L.) genotypes, for use in marker-assisted selection (MAS) programs. Microsatellites of soybean linkage groups A2, D2 and G were tested in two populations, and their selection efficiencies were determined. The populations were 65 F2:3 families from Msoy8001 (resistant) x Conquista (susceptible) cross, and 66 F2:3 families of S5995 (resistant) x Renascença (susceptible) cross, evaluated for resistance to races 3 and 14, respectively. Families with female index up to 30% were considered moderately resistant. Markers of A2 and G linkage groups were associated with resistance to race 3. Markers Satt309 and GMENOD2B explained the greatest proportion of phenotypic variance in the different groups. The combinations Satt309+GMENOD2B and Satt309+Satt187 presented 100% selection efficiency. Resistance to race 14 was associated with markers of G linkage group, and selection efficiency in the Satt309+Satt356 combination was 100%. The selection differential obtained by phenotypic and marker assisted selection showed that both can result in similar gains.
Highlights
One of the great limitations in developing soybean cultivars resistant to soybean cyst nematode (SCN) is phenotypic evaluation, because it is time consuming, expensive and influenced by the environment, restricting the number of plants to be assessed
The genetic variability in Msoy8001 x Conquista population, for resistance to race 3, was shown by the high variation in the mean number of cysts detected between parents, and by the finding of transgressive segregation in the mean number of cysts in the families in the population
The high value of the mean number of cysts, found in the resistant S5995 parent, showed that genes were segregating in this population, which conferred moderate resistance to SCN race 14
Summary
One of the great limitations in developing soybean cultivars resistant to soybean cyst nematode (SCN) is phenotypic evaluation, because it is time consuming, expensive and influenced by the environment, restricting the number of plants to be assessed. Two regions on the soybean genome are very important for wide resistance to SCN, the regions of the rhg gene (LG G) and the Rhg gene (LG A2). These two loci account for almost all the variability in soybean for resistance to SCN race 3 (Weisemann et al, 1992; Webb et al, 1995) and a great part of the variability for the other races (Concibido et al, 1997, 2004; Wang et al, 2004; Guo et al, 2005, 2006). It is suggested that the minor genes reported in other LG may be involved in race specificity, but they need to be validated
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