EVALUATION OF TWO GENERATIONS OF COLD TOLERANT SORGHUM HYBRIDS AND PARENTAL LINES. II: COMBINING ABILITY, HETEROSIS AND HETEROBELTIOSIS

Two generations of cold tolerant sorghum [Sorghum bicolor (L.) Moench] experimental hybrids and parental lines adapted to the Mexican High Central Valleys were developed at the Colegio de Postgraduados, Mexico. In 1996, five experiments were set up (three irrigated and two rain fed), at 2250 in of altitude, to estimate the general combining ability (GCA) of the lines, as well as the heterosis and heterobeltiosis of the hybrids for grain yield, seed weight and seed number; and to compare the per se response vs. the GCA of the lines. Each experiment included 12 first generation hybrids, 80 from the second and their corresponding parents, in addition to four testers, in an 11x11 square lattice design with four repetitions. Plots had two rows (3.0 m long and 0.7 m wide) with one plant each 10 cm. Among the two sorghum generations, under both irrigated and rain fed conditions, the GCA for grain yield and seed weight of the 2(nd) generation of B- and R- lines was higher. In the irrigated condition, the greatest GCA for grain yield was that of B- lines numbered as 9, 11, 1 and 7, and R lines numbered as 22, 17 and 19; while in rain fed, it was that of B- lines 6, 3, 5 and 1, and R-lines 20, 22, 14 and 16. Under irrigation, the grain yield per se of both types of lines was a good estimate of the GCA. The 2(nd) generation hybrids showed greater heterosis and heterobeltiosis, for the three variables, in both moisture conditions. Under irrigation, the yield of the best four hybrids varied from 53 to 58 g/plant, their heterosis from 80 to 91 % and their heterobeltiosis from 47 to 77 %, while under rain fed the respective variations were from 16 to 19 g/plant, 127 to 148 %, and 109 to 146 %.