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Southern root-knot nematode [RKI; Meloidogyne incognita (Kofoid and White) Chitwood] is an important soybean [Glycine max (L.) Merr.] pest. When RKI resistance was introgressed from the highly resistant, gray pubescent breeding line G93-9009 into moderately resistant, tawny pubescent cultivars BoggsRR and BenningRR, higher than expected proportions of two advanced backcross populations had gray pubescence. Introgressing genes from unadapted breeding lines into cultivars may reduce seed yield or quality of the resulting lines. This study's objectives were to determine if (i) an RKI resistance quantitative trait locus (QTL) is linked to the T-locus conditioning pubescence color in G93-9009, and (ii) a yield or seed quality loss is associated with introgressing G93-9009 RKI resistance QTL into BenningRR and BoggsRR. Tawny and gray pubescent [F.sub.2:4] lines of BoggsRR(6) x G93-9009 and BenningRR(5) x G93-9009 were evaluated in greenhouse experiments for RKI resistance and in field experiments grown in four environments for seed yield and quality. Gray lines of both populations averaged 75% fewer RKI eggs per plant than tawny lines. There were no significant differences in seed yield. Differences in agronomic traits such as plant height, seed size, and oil and protein content were observed. These results suggest an RKI resistance QTL exists near the T-locus and the potential to introgress resistance from G93-9009 into other genetic backgrounds without a loss in yield or major impact on other agronomic traits.

Glyphosate application to glyphosate-tolerant soybean [Glycine max (L.) Merr.] cultivars expressing a CP4 EPSPS transgene has become the most common method of soybean weed control in the USA. The objectives of this research were (i) to determine whether atypical segregation ratios for glyphosate tolerance and glyphosate sensitivity in the progeny of hemizygous plants resulted from gametic selection caused by glyphosate applications, (ii) tn investigate the effects of different glyphosate application rates and timing of application on segregation ratios, and (iii) to determine whether male gametes, female gametes, or both were sensitive to the levels of glyphosate used. Segregation for glyphosate tolerance in a no-glyphosate control treatment fit the expected 3:1 segregation ratio, indicating segregation of a single transgene. Glyphosate applications at three stages of plant development (V3, V3 + 2 to 3 wk, V3 + 3 to 4 wk) eliminated the glyphosate-sensitive phenotypic class irrespective of plant maturation stage in a field experiment. Variations observed in the relative proportions of lines with either all-tolerant or segregating phenotypic classes depended on glyphosate dosage and stage of plant development at the time of application. Overall, the data suggest that glyphosate application to hemizygous plants shortly before the onset of flowering was lethal to male gametes that do not carry the glyphosate tolerance transgene., A GLYPHOSATE-TOLERANT (GT) soybean line, 40-3-2, was developed by the Monsanto Company (Padgette et al., 1995). Glyphosate [N-(phosponomethyl)-glycine] inhibits the activity of 5-enol-pyruvylshikimate-3-phosphate synthase (EPSPS), an enzyme crucial to biosynthesis [...]