Evaluation of backcross progenies and recombinant inbred line populations of sorghum (Sorghum bicolor (L.) Moench)

In the past, breeding sorghum for resistance to greenbugs and drought has used traditional breeding methodology. Marker-assisted selection has been used to accelerate the recovery of the recurrent parent genome in backcross breeding and to transfer desirable traits such as post-flowering drought resistance trait known as stay-green into greenbug resistant and elite lines of sorghum. The objectives of the study were to:

1. Evaluate under post-flowering drought stress the performance of the backcross generations from the Introgresslon of stay-green Into greenbug resistant and elite lines of sorghum.
2. Evaluate under stress and non-stress environments the recombinant inbred lines derived from a cross between B35 and Tx7000.
3. Identify quantitative traits loci affecting grain yield in stress and nonstress environments.

In the introgresslon of stay-green Into greenbug resistant lines study, 217 backcross lines ranging from BC2 to BC4 generations and derived from 9 populations were evaluated under post-flowering drought stress along with 15 parental lines used as checks at the Texas A&M University Agricultural Research and Extension Center, Lubbock, during the summer of 2001. Four backcross progenies rating between 2.5 and 2.9 could be classified as post-flowering drought stress resistant. The progeny P8-01PR1057-4 (4568 kg ha"^) had significantly 77% and 50% higher grain yield than B35 and Tx7000, respectively. Overall, the populations generally produced more grain yield than the parental lines. In general, progenies or parental lines with multiple QTLs were resistant to moderately resistant to both greenbug biotypes E and I.

In the introgression of stay-green into elite lines study, 150 BC2 to BC4 progenies from 5 populations and 15 parental lines used as checks were evaluated under post-flowering drought stress conditions at Texas A&M University Agricultural Research and Extension Center, Lubbock, during the 2001 summer. Results indicated that only P5-01PR151-1 would be classified as postflowering drought resistant as B35 (rating 1.6) the resistant check based on the stay-green rating 2.2. Although some progenies were carrying stay-green QTLs, they were considered as post-flowering drought susceptible. The elite line B1 significantly produced more grain yield (5283 kg ha'^) than most of the progenies.

Grain yield is a complex trait that is influenced by genetic and environmental factors. Severe losses can be caused by drought, a common stress in most sorghum growing regions. Two hundred seventy-four Restriction Fragment Length Polymorphic markers covering the sorghum genome were used to identify the main-effect QTLs in the 98 recombinant inbred lines evaluated under water stress conditions at Lubbock during 1993 and 1994, and under stress and no-stress conditions in Halfway during 1994. Significant (P<0.05) differences were detected between the parents B35 and Tx7000 and among the RILs for all phenotypic traits measured. The analysis detected 7 main-effect QTLs for grain yield under stress and non-stress conditions in Lubbock and Halfway. Under stress, 3 main-effect QTLs collectively explained 52.3% of the phenotypic variation with significant allelic effects for 2 QTLs from Tx7000.