Fifty years of recurrent selection in the Iowa stiff stalk synthetic maize population

Abstract

<p>Recurrent selection is a breeding procedure designed to increase the frequency of favorable alleles in a population. Increasing the frequency of favorable alleles will increase the probability of obtaining surerior inbred line.s for use in hybrids. The Iowa Stiff Stalk Synthetic (BSSS) maize (£ea mays I..) population has been involved in continuous recurrent selection since 1939. Thirteen cycles of selection have been completed . The first seven cycles were half-sib selection using the double-cross lowa 13 as a tester. After completion of seven cycles of half-sih selection, the population was renamed BSU and six cycles of S2-progeny selection were completed. The objective of this study was to evaluate the responses of the populations per se to 1:3 cycles of recurrent selection. The CO to C7 of half-sib selection and the CO to C6 fo S2-progeny selection were evaluated at ti >ur Iowa locations in 198'-J and 1990. The average rate of response for yield after seven cycles of halt~ sih selection was 1.64** q h-1- I cycle-1 (3.9101 cycle-I). Changes in other traits were generally in the desired direction, except for grain moisture and root lodging for which the responses were positive:, but relatively smalll. Unlike halt~ sib selection, six cycles of S2-progeny selection did not significantly improve yield of the population per se, changes in other traits were generally small and not agronomically important. Theoretically, the lack of population per se improvement following S2-progeny selection is an unexpected result, because in the absence of overdominance, S2-progeny selection is expected to he superior to other methods of recurrent selection. Empirical data from this and other studies do not support the theoretical superiority of inbred progeny selection over other types of recurrent selection.</p>