PHOTOPERIOD AND VERNALIZATION RESPONSE OF MEDITERRANEAN WHEATS, AND IMPLICATIONS FOR ADAPTION (REPRINTED FROM WHEAT - PROSPECTS FOR GLOBAL IMPROVEMENT, 1998)

Hexaploid wheat has the largest cultivated area among crop plants due to its adaptability to different agroclimatic regions. A large part of this adaptability depends upon the variation in vernalisation and pho toperiod requirements. A better understanding of the genetic control o f flowering in wheat, as expressed by vernalisation requirements and p hotoperiod response, will guide breeders in targeting crosses of diffe rent types and will also improve our understanding of regional adaptat ion requirements. Characterisation of large numbers of breeding lines for photoperiod and vernalisation response in wheat is needed to assig n the lines to geographic areas of most probable adaptation. Simple sc reening methods to quantify the effects of these two factors and their interaction are needed to assist breeding progress. Twenty wheat line s were evaluated for response to photoperiod and vernalisation under t wo controlled environments and under high ambient air temperatures in field conditions. Vernalised and non vernalised seedlings were transpl anted into pots and placed in three photoperiod (8, 12 and 16 h light) cabinets, in the greenhouse or in growth chambers. Days to anthesis d ecreased with increasing length of photoperiod. Vernalised plants flow ered earlier than non vernalised plants. There was a significant corre lation between days to anthesis in the greenhouse and the growth chamb er (r = 0.88, P<0.001). Length of basal vegetative period, effects of vernalisation, and photoperiod from the two screening techniques were positively correlated with each other. Growth habit score, vernalisati on requirement and heading date in the field were highly correlated wi th the main effect of vernalisation in the two controlled environments . The results indicated that selection for vernalisation response in a large number of genotypes can be achieved under high ambient air temp eratures in the field. The selected material can subsequently be scree ned for photoperiod response under greenhouse conditions. Using these techniques, 49 local and improved cultivars from the Mediterranean reg ion in west Asia and north Africa (WANA), showing differences in respo nse to photoperiod, vernalisation, and earliness independent of vernal isation and photoperiod, affecting time to anthesis, were identified. Most old local cultivars were sensitive to both photoperiod and vernal isation. All the improved genotypes were insensitive to photoperiod. R esponses to vernalisation were generally small under short photoperiod s, but were more pronounced in long photoperiod, particularly in winte r and facultative types from northern latitudes. These results should help to explain the adaptability of cultivars based on photoperiod and vernalisation requirements and their interaction.