Heterosis, backcross analysis, and breeding potential of one exotic cultivar for grain yield in sorghum (Sorghum bicolor (L.) Moench)

Lian Tang Ai, a Chinese landrace cultivar donor parent and Tx2783, an elite US restorer parental line and, the recurrent parent, were used to develop BC2 derived lines which were evaluated for grain yield potential. The hypothesis of this research was that some of the BC2 derived lines themselves could have higher grain yield potential in BC2F2 and in hybrid combination with ATx623, respectively, than Tx2783 and the hybrid of ATx623xRTx2783. Grain yield of the derived lines and their hybrids grain yield was normally distributed. Five (3.7%) and 46(32.4%) derived lines (P=0.05) produced significantly higher grain yield than the recurrent parent in limited and fully irrigated combined analysis trials, respectively. In the combined analysis of fully irrigated trials, 132(89.2%) hybrids produced significantly higher grain yield than the recurrent parent hybrid. In the combined full irrigation trials, the average heterosis values was 50% over the midparent, heterosis of the best hybrid over the best parent was 60.2%, the best parent over the mid-parent was 78.0% and the worst hybrid had 23.3% over the mid-parent. Highest heterosis of the best hybrid over the best parent was 90.5% at Halfway 2001. Under full irrigation trials, five, four and nine derived lines, respectively, from Lubbock 2000, 2001 and Halfway 2001, were among the top 10% highest grain producing derived lines while four hybrids from Lubbock 2000, 2001 and Halfway 2001 were consistent in producing high grain yield across environments. Across irrigation levels, four derived lines and two hybrids produced consistently and significantly higher grain yield than the recurrent parent and its hybrid. Three high grain yielding derived lines produced high grain yield in hybrids and were significantly superior to the recurrent parent and its hybrids. Five hybrids from the combined limited trials and 7 hybrids from Lubbock 200l fully irrigated trial produced significantly higher grain yield than the standard commercial hybrid check. When using fully irrigated combined analysis, however, no hybrid produced significantly more grain than the standard commercial hybrid. Other derived lines and hybrids had erratic grain yield distribution. Higher grain yield was expressed at Halfway than at Lubbock. There was a significant low and negative correlation between grain yield and maturity in general. Grain yield of derived lines did not accurately predict well their respective hybrid grain yield in individual environments (trials). However, across environments in full irrigation combined trials, grain yield of derived lines was positively and highly correlated to grain yield of hybrids (r=0.419). Introgression of useful yield genes from Lian Tang Ai into Tx2783 was a success. However, genotype by environment interaction made the selection for high yielding and widely adapted derived lines for hybrid productivity a difficult task.