[The number of ears per plant for selecting Zea mays ideotypes]

Inglés. The number of ears per plant (prolificacy) is an inheritable component of grain yield, which might be a desirable criterion for selecting maize (Zea mays L.) ideotypes. To study the importance of this trait, 17 pairs of maize lines, quasi-isogenic for number of young ears per plant at silking, were formed; in each pair, lines were highly related in genotype and very similar in phenotype, but contrasting from 30 to 100 in their prolificacy degree. The 17 pairs of lines were evaluated in three population densities (40, 80 and 120 thousand plants/ha), in Montecillo, Mexico. Results showed that only in six pairs the prolific lines produced statistically more mature ears/plant, and that only in three of these pairs the prolific lines had a higher grain yield and a higher grain number per plant, than their corresponding non-prolific lines. It was inferred that prolificacy (as mature ears per plant) should be higher than 25 in order to produce significant grain yield increases. In the other three pairs, the prolific lines suffered a reduction in their main ear size; therefore, selection by prolificacy must be accompanied by maintenance of the ear size. It was also concluded that prolificacy is not associated to other traits, such as plant height, grain size, leaf area

Español; castellano. El numero de mazorcas por planta (prolificacion) es un componente heredable del rendimiento de grano, que puede ser un criterio de seleccion deseable en la formacion de arquetipos de maiz (Zea mays L.). Para estudiar la importancia de este caracter se formaron 17 pares de lineas cuasi-isogenicas en cuanto a numero de jilotes por planta; en cada par, las lineas eran fenotipicamente similares por estar altamente emparentadas entre si, pero en su grado de prolificacion en jilotes contrastaban de 30 a 100. Los 17 pares se evaluaron en tres densidades de poblacion (40, 80 y 120 mil plantas/ha), en Montecillo, Mex. Se encontro que el grado de prolificacion medido en mazorcas/planta resulto significativamente diferente entre lineas solo en seis pares; solamente en tres de estos las lineas prolificas superaron estadisticamente a sus contrapartes no prolificas en numero de granos/planta y rendimiento de grano; de ello se deduce que para mejorar el rendimiento mediante este caracter, la parte prolifica debe superar a la no prolifica en mas del 25 respecto al numero de mazorcas/plantas. En los otros tres pares cuasi-isogenicos, la linea prolifica sufrio reducciones en el tamano de la mazorca principal; por tanto, al seleccionar por prolificacion se debe tener cuidado en mantener el tamano de dicha mazorca. Tambien se observo que el numero de mazorcas/planta es un caracter independiente de otros, como altura de planta, tamano del grano, area foliar y precocidad, lo que permite formar arquetipos prolificos de maiz de diferente morfologia y fenologia.