Characterization of Photothermal Flowering Responses in Maturity Isolines of Soyabean [Glycine max (L.) Merrill] cv. Clark

All eight isolines of three maturity genes (E₁/e₁, E₂ /e₂, andE₃ /e₃) of soyabean Glycine max (L.) Merrill] cv. Clark weregrown in widely different combinations of photoperiod and temperature.Under the more inductive conditions, i.e. in a warm mean temperature(30°C) when daylengths were less than the critical value(i.e. less than about 13 h), the isolines flowered at similartimes (23-24 d). The responses of all isolines to temperaturewere also similar, if not identical. Increase in daylength abovethe critical photoperiod progressively delayed flowering untilthe time taken to flower (f) reached a maximum at the ceilingphotoperiod. The relations between the rate of progress towardsflowering (1/f) and photoperiod (between the critical and ceilingvalues) were linear. The coefficient characterizing the slopeof the response (photoperiod sensitivity) varied amongst theisolines. These responses could be grouped into three categoriesof increasing sensitivity: (1) least sensitive, e₁e₂e₃ , e₁E₂e₃, e₁e₂E₃ ; (2) intermediate, E₁e₂e₃ , e₁E₂E₃ ; and (3) mostsensitive, E₁E₂e₃, E₁e₂E₃ , E₁E₂E₃ . Thus, in the Clark cultivargenetic background, E₁ induces greater photoperiod sensitivitybut neither E₂ nor E₃ on their own have any effect. However,both E₂ and E₃ together induce photoperiod sensitivity comparableto that induced by E₁ alone. Furthermore, in addition to thisepistasis, either E₂ or E₃ has considerable epistatic effecton E₁, further increasing photoperiod sensitivity. The effectsof these genes and their epistasis were also reflected in theextent of the maximum delays to flowering which occur when theceiling photoperiod is exceeded, and also possibly in earlinessin circumstances when photoperiods were below the critical value.Copyright1994, 1999 Academic Press Glycine max (L.) Merrill, soyabean, maturity genes, flowering, photoperiod, temperature