Analytical studies on high yielding ability of hybrid maize [Zea mays] from the standing point of developmental morphology.

In order to elucidate the mechanisms of high yielding ability in hybrid maize from the standing point of developmental morphology, growth phases, leaf and stalk morphology and yield components of hybrids were compared with those of their parents, and the relationships between yield components and developmental morphology were discussed. The results obtained are summarized as follows: (1) Hybrids required less days (degree days) than parents from sowing to tasselinitiation and from silk-elongation to silking. The former change prolonged reproductive phase and the latter made rapid escape from mutual shading and kept large leaf area in hybrids through rapid stalk-elongation and leaf-expansion. In contrast, hybrids required more days (degree days) than parents in the period from ear-initiation to silk-elongation, which was ear-floret-differentiation phase. The prolongation of this phase increased number of florets per ear. (2) Morphological changes and heterosis in leaf area and stalk-volume were observed in hybrids. The leaves and internodes were divided into four groups according to their growth phases. Leaf area and internode-volume in the third (part from the leaf fully expanded at ear-initiation to ear-born leaf) and the fourth (part above ear-born leaf) group were remarkably increased, which corresponded to ear-floret-differentiation phase and grain-filling phase, respectively. Therefore, it was thought that the increase of number of florets per ear and high percentage of ripened grain resulted from expansion of the third and the fourth group. (3) Heterosis in grain yield resulted from increase of number of grains per ear, which consisted of remarkable increase of number of florets per ear and high percentage of ripened grain. (4) Leaf area and internode-volume in the third and the fourth group showed positive correlation with grain yield and number of grains per ear, but those in the first and the second group showed negative ones with number of grains per ear. These results explicated the relationships between high yielding ability and the developmental and morphological changes in hybrid maize.