Daylength and Temperature Effects on Days to Flowering of Early and Late Maturing Beans (Phaseolus vulgaris L.)1

Abstract

Starting from daylength (DL) × temperature (T) environments combining short or intermediate DL with low or intermediate T, days to first flower (FF) of beans was progressively decreased as the duration of T was extended and/or as T was raised to intermediate levels. This universal temperature response caused 13 to 22 day decreases, under both 3° and 6°C night temperature/day temperature (NT/DT) difference, for both early and late maturing lines. The decrease in days to FF that appeared to result from extending DL was due to the attendant and simultaneous extending of the duration of DT and decreasing of the duration of NT. Starting from environments combining intermediate to longest DLs with intermediate to highest Ts, which environments had the fewest days to FF, on the contrary, increases in days to FF occurred as DL was further extended and/or as T was further raised. This photoperiod-temperature response (Pp-T response) caused 2 to 5 day increases in days to FF for early-maturing photoperiod-insensitive lines, and 10 fold larger increases of 40 to 53 days for late-maturing, photoperiod-sensitive lines. The gene(s) conditioning the late-maturing, photoperiod-sensitive phenotype, therefore, caused a 10-fold increase in the days of delay to FF, i.e. of a Pp-T response that is weakly expressed in the early-maturing photoperiod-insensitive genotype. The Pp-T responses of the photoperiod insensitive and sensitive genotypes were both half as large, 0 to 4 and 17 to 29 days, respectively, when the NT/DT difference was 3° rather than 6°C; there was also a requirement for a higher T to activate the Pp-T response. This commonly called photoperiod response , was called the Pp-T response because it was altered as much by T as by DL.