Soybean Cultivars Resulted from More Recombination Events Than Unselected Lines in the Same Population

The selection of superior adapted cultivars has contributed to the doubling of soybean [Glycine max (L.) Merr.] yields in the USA since 1930. Genetic variation was required for this selection to be effective. The objective of this study was to evaluate the importance of homologous chromosome meiotic recombination in the creation of soybean cultivars. A set of 10 adapted high-yielding cultivars selected from the cross ‘Williams’ × ‘Essex’ was com-pared with a set of 156 random recombinant inbred lines (RILs) from the same population. Crossover events were identified using 143 simple sequence repeat (SSR) markers span-ning all 20 soybean chromosomes. The recombination rates were standardized among chromosomes by dividing the realized crossovers by the potential crossovers. The stand-ardized recombination rate for the entire genome was significantly greater for the 10 culti-vars (0.34) than for the RILs (0.29). The cultivars had numerically higher standardized recombination rates for 17 of the 20 chromosomes, significantly higher on chromosomes defined by the molecular linkage groups C2, L, and M. The interaction of linkage groups with the two sets of lines was nonsignificant for standardized recombination. Soybean breeding progress has been accomplished in part by creating and capitalizing on new within-chromosome allele combinations

Registration of DT99-16864 Soybean Germplasm Line with Moderate Resistance to Charcoal Rot [\u3cem\u3eMacrophomina phaseolina\u3c/em\u3e (Tassi) Goid.]

Charcoal rot, caused by Macrophomina phaseolina (Tassi) Goid., is a disease that is a worldwide problem in soybean [Glycine max (L.) Merr.] production for which no highly resistant cultivars are currently available. It has been estimated that charcoal rot was among the most important diseases for suppressing yield of soybean in the USA from 1996 to 2007. Soybean breeding line DT99-16864 (Reg. No. GP-404, PI 675996), with moderate resistance to charcoal rot disease, was developed and released by the USDA-ARS, Stoneville, MS. DT99-16864 originated from a single F5 plant derived from a cross of ‘S59-60’ × ‘Bolivar’. The breeding population was advanced from the F2 to the F5 generation using the single-seed descent method. Colony-forming units, root and stem severity scores, and other rating methods indicated that DT99-16864 had significantly lower levels of M. phaseolina infection than susceptible checks in trials in Stoneville, MS, and Jackson, TN. In the Uniform Soybean Tests–Southern States, DT99-16864 was not significantly different from the check cultivars ’5002T’ and ’5601T’ for yield. DT99-16864 belongs to maturity group V and is later in maturity than DT97-4290, a moderately resistant charcoal rot line that is adapted to the midsouthern United States. The well-documented moderate resistance of DT99-16864 to M. phaseolina infestation, and good yield potential, will make this line useful for research and breeding

Performance of super hybrid rice cultivars grown under no-tillage and direct seeding

Good progress has been made in the super hybrid rice (Oryza sativa L.) breeding in China. However, rice yield not only depends on the genetic characteristics but also on the agronomic practices. No-tillage and direct seeding (NTDS) is a simplified cultivation technology that greatly simplifies both land preparation and crop establishment. Aiming to determine the grain yield performance of super hybrid rice under NTDS and to identify critical factors that determine grain yield, field experiments were conducted in Nanxian, Hunan Province, China in 2009 and 2010. Two super hybrid cultivars, Liangyoupeijiu and Y-liangyou 1, were grown under conventional tillage and transplanting (CTTP) and NTDS. Grain yield, yield components, biomass production, crop growth rate and biomass accumulation during sowing to heading (HD) and HD to maturity were measured for each cultivar. There was no difference in grain yield under NTDS and CTTP. However, grain yield differed with cultivar and year. Y-liangyou 1 produced 4 % higher grain yield than Liangyoupeijiu in 2009, whereas in 2010 both cultivars yielded similarly. Grain yields of both cultivars were higher in 2009 than in 2010. Higher grain yield of Y-liangyou 1 in 2009 was associated with higher spikelet filling (spikelet filling percentage and grain weight), which resulted from higher biomass production. Crop growth rate after HD was critical for biomass production by the super hybrid rice. We suggest that increasing the crop growth rate after HD is an effective approach to increase grain yield of super hybrid rice under NTDS