Variation in the durations of the photoperiod-sensitive and photoperiod-insensitive phases of development to flowering among eight maturity isolines of soyabean [Glycine max (L.) Merrill].

In soyabean [Glycine max (L.) Merrill] the period between sowing and flowering is comprised of three successive developmental phases--pre-inductive, inductive and post-inductive--in which the rate of development is affected, respectively, by temperature only, by photoperiod and temperature, and then again by temperature only. A reciprocal-transfer experiment (carried out at a mean temperature of 25 degrees C) in which cohorts of plants were transferred successively between short and long photoperiods and vice-versa showed that eight combinations of three pairs of maturity alleles (E(1)/e(1), E(2)/e(2), E(3)/e(3)) had their greatest effect on the duration of the inductive phase in long days. This phase was increased with the increasing photoperiod sensitivity induced by the different gene combinations, and ranged from about 27 to 54 d according to genotype. In a short day regime (11.5 h d(-1)), less than the critical photoperiod, the duration of the inductive phase was brief-requiring about 11 photoperiodic cycles in the less photoperiod-sensitive genotypes and only about seven cycles in the more sensitive ones. The maturity genes also affected the duration of the two photoperiod-insensitive phases; these durations were positively correlated with the photoperiod-sensitivity potential of the gene combinations. The largest effect was on the pre-inductive phase which varied from 3 to 11 d, while the post-inductive phase varied from about 13 to 18 d. As a consequence of these nonphotoperiodic effects of the maturity genes, even in the most inductive regimes (daylengths less than the critical photoperiod) the time taken to flower by the less photoperiod-sensitive combinations of maturity genes was somewhat less than in the more sensitive combinations-ranging from about 28 to 34 d. The genetic and practical implications of these findings are discussed.