Characterization of the apical ear mutant of maize: preliminary steps toward an ideotype

The present study was conducted in the context of ideotype breeding, and was pan of a major project which has as a main objective the development of a maize ideotype adapted to conditions of high temperature and low moisture. A previous research culminated in the description of the plant model; it called for important morphological modifications, but the most prominent involved the transfer of the site of grain production from a lateral position to the apex of the plant, associated with the complete suppression of the tassel. A mutant was also identified as a potential source to develop the ideotype. To decide on the suitability of this genetic material, several experiments were designed to characterize its morphology and to obtain information on the genetic nature of the different plant attributes associated with it;In average, the typical mutant plant was 85 cm tall, with 27 to 30 leaves from which 18 to 20 remained functional at maturity. It developed one or more apical female inflorescences; a tassel was usually present although suppressed at variable degrees. Ears were small, with few rows and gram. Gram yield per plain was low (+/-30 g). Lateral ear shoots frequently appeared. Little improvement in the level of expression of these plant attributes was accomplished after backcrossing, possibly because of an undesirable linkage between the presence of apical ears and a short, leafy plant;Preliminary evidence suggested that the apical ear characteristic may be a threshold trait. Generation mean analysis indicated that penetrance of the trait was controlled by additive, dominance, additive x additive and additive x dominance gene effects. Models including one to three digenic epistatic effects explained the inheritance of other plant attributes. Information from a biparental progenies experiment revealed that in the population derived from the maintenance of the mutant, genetic variation existed for most traits, although its magnitude was small;It is concluded that some selection could be practiced in the mutant population, but that the most recommendable course of action is to continue with the backcross process and to explore new germplasm sources