The Inheritance of Photoperiodism in Snap Bean (Phaseolus Vulgaris)

Tsao, Shing-Jy J.
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The heredity of photoperiodic response of flowering in Phaseolus vulgaris was studied. The parents were classified into three types according to their photoperiod sensitivity— day-neutral (flower at any daylength), intermediate (require a night longer than 11.5 hours), and sensitive (require a night longer than 12 hours). Crosses between parents of the same phenotype generally produced F1 and F2 progenies which showed no segregation. The segregation patterns for photoperiodic response were determined for larger numbers of individuals by planting during the summer when days are too long for floral induction and assuming that each plant begins to flower when the daylength has shortened to the critical length required by that plant. Temperatures within the range experienced in the field were found to have an insignificant effect. It is postulated that the inheritance of the photoperiodic response in these lines is determined by at least four major gene loci with dominance, epistasis, and independent segregation. A dominant N gene is postulated that permits flowering at any daylength. If the recessive n gene or a dominant inhibitor of the N gene, IN , are present, there is an intermediate daylength requirement for flowering. A dominant Q gene which intensifies the short daylength requirement is also postulated. If the recessive q gene or a dominant inhibitor of the Q gene, IQ, are present, the daylength requirement again is of the intermediate type. The day-neutral and intermediate parents therefore differ by two genes (at the N and IN loci), and the intermediate and sensitive parents differ by another two genes (at the Q and IQ loci), so that the day-neutral and sensitive parents differ by a total of four genes. It is likely that additional genes with smaller effects may also be involved.
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