Developmental responses to temperature and photoperiod in ecotypes of Medicago polymorpha L. collected along an environmental gradient in central Chile

The phenological development of nine Chilean accessions of Medicago polymor pha, collected along a north-south aridity gradient, and of two commercial cultivars of the same species, were compared in 12 sequential outdoor sowin gs at Cauquenes (35 degrees 58'S, 72 degrees 17'W, elev. 177 m), in the sub -humid Mediterranean climate zone of Chile. A glasshouse experiment was als o conducted to evaluate the effect of photoperiod on phenophase timing. The re was a clear gradient in precocity among the Chilean accessions in both e xperiments: accessions MPO-9-88 and MPO-7-88, from the arid zone, were the earliest-flowering accessions, whereas MPO-36-88 from the humid Mediterrane an zone was the latest. Both experiments revealed significant variation amo ng the Chilean accessions in the response of flowering time to variation in photoperiod regime. Differences in days to flowering between the least- (8 h) and the most- (16 h) inductive photoperiods were lower in precocious ac cessions from arid and semi-arid zones, than in late-flowering accessions f rom more humid zones. Rate of progress to flowering, defined as the inverse of time from emergence to first flower appearance (1/f), was related to me an diurnal temperature, or to both mean diurnal temperature and mean photop eriod. In two early-flowering accessions from the arid zone, and in the Aus tralian cultivar 'Circle Valley', 1/f was affected significantly (P < 0.05) by both temperature and photoperiod. In the remaining accessions, no signi ficant responses to temperatures were detected; 1/f was influenced signific antly by photoperiod only. (C) 2000 Annals of Botany Company.