FLOWERING OF DIVERSE MAIZE CULTIVARS IN RELATION TO TEMPERATURE AND PHOTOPERIOD IN MULTILOCATION FIELD TRIALS

The accurate prediction of time to flower is important for the efficie nt exchange of genetic material among environments. The objective of t his research was to evaluate methods of calculating thermal time for t he sowing-silking interval (SSI) in a diverse group of 18 maize (Zea m ays L.) cultivars, which were sown in a multilocation field trial at 5 3 planting date-location combinations. These ranged in mean temperatur e from 13.2 to 29.4 degrees C during the SSI, and in photoperiod at ta ssel initiation from 11.7 to 19.5 h. Thermal time computed from daily maximum (TX) and minimum temperatures with a base of 6 degrees C, an o ptimum temperature (T,) of 30 degrees C, and a linear adjustment for s upra optimal values of TX such that TX = 30 - (TX - T-degrees), result ed in a lower coefficient of variation (CV) for thermal time across si tes and cultivars (10.9%) than did other methods, though several of th ese methods gave similar results. The CVs for thermal duration of the SSI for cultivars adapted to temperate, lowland tropical and highland tropical environments averaged 7.8, 11.5, and 15.4% respectively. For tropically-adapted cultivars, the increase in the sowing-anthesis inte rval in day lengths >13 h averaged 47 degrees Cd h(-1) (range 24-100 d egrees Cd h(-1)), while temperate cultivars were virtually photoperiod insensitive. Photoperiod sensitivity was positively correlated with t he anthesis-silking interval [r = 0.62 (P = 0.01), 16 df]. This study confirms the need to determine photoperiod sensitivity and optimum tem peratures for development of tropical cultivars if precise estimates o f thermal time to flowering and maturity at sites with photoperiods >1 3 h are required.