ENVIRONMENTAL AND GENETIC-REGULATION OF FLOWERING OF TROPICAL ANNUAL CROPS

Phenology (i.e. the influence of environment on ontogeny) is the most important single factor influencing crop adaptation. The timing of flo wering is particularly important since it largely determines when annu al cereal, pulse and oilseed crops will subsequently be ripe for harve st. Two environmental factors are of overriding importance in the indu ction of flowering - photoperiod (daylength) and temperature. In seeki ng to predict times from sowing to flowering, f, it has proved profita ble to analyse photothermal responses in terms of the rate of progress from sowing to flowering, 1/f. This paper summarises the advantages o f a model based on rates rather than the traditional approach based on f. Over a wide range of photothermal regimes, the model involves just six coefficients, all of which (and their derivatives) have clearly d efined biological meaning. Of paramount importance too is that the coe fficients are not affected by the environment; they are genetic charac ters which determine phenotypic responses to the environment in a quan titative and predictable way.