Photoperiod and vernalisation response of Mediterranean wheats, and implications for adaptation

Abstract

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 photoperiod requirements. A better understanding of the genetic control of flowering in wheat, as expressed by vernalisation requirements and photoperiod response, will guide breeders in targeting crosses of different types and will also improve our understanding of regional adaptation requirements. Characterisation of large numbers of breeding lines for photoperiod and vernalisation response in wheat is needed to assign the lines to geographic areas of most probable adaptation. Simple screening methods to quantify the effects of these two factors and their interaction are needed to assist breeding progress. Twenty wheat lines were evaluated for response to photoperiod and vernalisation under two controlled environments and under high ambient air temperatures in field conditions. Vernalised and non vernalised seedlings were transplanted into pots and placed in three photoperiod (8, 12 and 16 h light) cabinets, in the greenhouse or in growth chambers. Days to anthesis decreased with increasing length of photoperiod. Vernalised plants flowered earlier than non vernalised plants. There was a significant correlation between days to anthesis in the greenhouse and the growth chamber (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, vernalisation requirement and heading date in the field were highly correlated with 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 temperatures in the field. The selected material can subsequently be screened for photoperiod response under greenhouse conditions. Using these techniques, 49 local and improved cultivars from the Mediterranean region in west Asia and north Africa (WANA), showing differences in response to photoperiod, vernalisation, and earliness independent of vernalisation and photoperiod, affecting time to anthesis, were identified. Most old local cultivars were sensitive to both photoperiod and vernalisation. All the improved genotypes were insensitive to photoperiod. Responses to vernalisation were generally small under short photoperiods, but were more pronounced in long photoperiod, particularly in winter 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.