Genetics of Maturity and Photoperiod Sensitivity in Maize

Ninety tropical-adapted maize inbreds were evaluated for maturity and photoperiod sensitivity under short daylength (SD) environment in Hawaii, and under long daylength (LD) environments in Iowa, and Korea. Extensive genotypic variations were observed for the two traits among these inbreds. There was no single inbred classified as strictly day-neutral. Inbreds that exhibited early maturity and low photoperiod sensitivity were mostly temperate-derived, while those that exhibited late maturity and high photoperiod sensitivity were exclusively tropical-derived. Diallel analysis (Analysis III of Gardner and Eberhart, 1966) revealed that variations among general combining ability (GCA) estimates were much larger than variations among specific combining ability (SCA) estimates for days to anthesis, silking, blacklayer formation, and their respective delays. GCA and SCA variations contributed more or less equally to the expression of anthesis to silking interval, and grain filling period. High GCA/SCA ratios indicated large additive genetic variation for maturity and photoperiod sensitivity traits. Estimates of heterosis included in the model, however, were high in most cases which suggested that non-additive genetic variation was also important in the inheritance of these traits. Generation mean analyses showed that additive and dominance gene effects were highly significant in a majority of the crosses. Magnitude of estimates varied with types of crosses, but in general, dominance gene effects had greater magnitude than additive gene effects for maturity and photoperiod sensitivity. Significant amounts of epistatic gene effects were detected, but they seemed to cancel each other, thus leaving dominance gene effects as the main contributors to the inheritance of the two traits. Maturity appeared to be controlled by few genes (between two and four). Three cycles of divergent mass selection for silking dates of two tropical maize composites were evaluated under SD environments in Waimanalo and Kauai and under extended daylength in Waimanalo. Selection was effective in diverging silking dates in both populations. Selection for early and late silking resulted in decreased and increased photoperiod sensitivity, respectively. The strong correlated effects of selection on photoperiod sensitivity suggested that short-day maturity and photoperiod sensitivity were under common genetic control. Pleiotropic effects of genes were most likely behind this relationship