Comparative photoperiodic responses for several soya bean varieties of tropical and temperate origin

Abstract

Two experiments involving the testing of a number of soya bean varieties under a range of different photoperiods showed that all varieties were capable of flowering under all photoperiods tested, and appeared to be facultative short-day genotypes. Differential varietal responses were not obtained for flowering time at photoperiods of less than 12 hr per day, but the tropical varieties Mamloxi and Avoyelles differed markedly from the temperate variety Bienville in the flowering pattern under longer photoperiods. Other plant characters responded similarly to flowering time. Possible relationships of such responses to latitude of introduction, field adaptation in southeastern Queensland, and screening of varietal accessions are discussed. Uniform frequency distributions of an F2 population were obtained for most characters and photoperiods, which indicated a relatively complex form of inheritance. Skewness of some distributions, particularly in the longer photoperiods, suggested that the spectrum of action of genes determining these traits varied with photoperiod. Deviations from mid-parent values indicated dominance of low number of days to flowering, short node length, and high node number. Plant height approached that of the low parent in short photoperiods and the high parent in longer photoperiods. Transgressive segregation occurred for most traits, particularly in the longer photoperiods, and evidence of substantial genetic control of differences in photoperiodic response between varieties was found.