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Responses to a Modified Reciprocal Recurrent Selection in Two Maize Synthetics

Dep. of Agronomy, Univ. of Bologna, via Filippo Re 6–8, 40126 Bologna, Italy

^* Corresponding author (tz4bot61{at}cine88.cineca.it).

The early genotypes of maize (Zea mays L.) selected for the northern Corn Belt regions can perform poorly when grown as a delayed-sowing crop in warmer regions. Two early synthetics, A and B, were developed and two cycles of a modified reciprocal recurrent selection were conducted in a delayed-sowing crop by using A632 as a tester for Synthetic A and W117 as a tester for Synthetic B. Selection was based on a multitrait index involving grain yield, percent erect plants, and grain moisture. This study was conducted in three environments to evaluate the effects of selection. The source and selected populations of the two synthetics were tested per se and in hybrid combination to each other, to their inbred tester, and to the unrelated hybrid, A188 x W64A. The gain in the cross between the two synthetics was 4.9% cycle^–1 (P 0.01) for the performance index (calculated similarly to the selection index), and this was mainly due to the gain in grain yield (12.2% cycle^–1). However, undesired increases were found for grain moisture and silking date. The gains for performance index and grain yield were due to a balanced contribution of both changes per cycle of populations per se and of heterosis. Synthetic B contributed more than Synthetic A to the gain in the population cross for performance index, grain yield, and to the loss of earliness. Population crosses of both synthetics with corresponding testers and A188 x W64A showed a positive response for performance index and grain yield, and a loss of earliness for Synthetic B. The results indicated that the selection procedure was effective in improving the performance index of the two synthetics both per se and in hybrid combinations.

Received for publication May 31, 1994.