Line × Tester Analysis in S1 top-crosses of Maize for Grain Yield and its Related Traits

The line × tester model was used to evaluate 243 top-crosses with their parents (81 S1 families and the three testers) of maize for general and specific combining abilities and to estimate the genetic components. Highly significant differences were found among crosses, lines (L), testers (T), and their interaction for grain yield/plot (GY/P), ear diameter (ED), number of kernels/row (NK/R) and days to 50% silking (SILK). The contribution of L vs. T interaction was higher than lines and testers indicating high estimates of variance due to specific combining ability for NK/R and GY/P. The general mean over all testers surpassed both S1 families and S1 top-crosses for GY/P (414.29 and 77.05%), and only S1 top-crosses for SILK (3.42%). Otherwise, the testers were less than S1 families for SILK (2.84%). Moreover, the S1 top-crosses exceeded the S1 families for GY/P (190.48%). The S1 top-crosses were earlier than both testers (-3.31%) and S1 families (-5.98%). 22, 28, and 26 S1 families possessed positive and significant GCA effects for GYP, ED, and NKR, respectively, and 16 lines with negative and significant GCA effects for SILK. Lines i.e., L26 and L33 had significant positive GCA effects for GY/P, ED, and NK/R, but negative effects for SILK. The tester T2 was a good combiner for GY/P, NK/R, and SILK, but T1 for ED.14, 46, 16, and 9 S1 top-crosses possessed significant SCA effects for GY/P, NK/R, ED and SILK (earliness), respectively. The earliness of S1 top-crosses depends on the specific combining between lines and testers.