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The developmental behaviour of 10 spring wheats and one winter wheat was studied under field conditions in terms of the responses of ear initiation and ear peep to photoperiod and temperature. Mean daily temperatures and photoperiods in the field varied within the ranges 5-25�_C and 11-15 hr respectively during the course of the experiment. Serial sowings between March and September, and the use of low intensity supplemental illumination provided additional variation in the field environment. There were no marked alterations in phenological patterns of development among spring wheats with later sowing. Rather there was a gradual alteration in the durations of pre-initiation and post-initiation phases, resulting in an overall reduction in the duration of development. Furthermore, the relative maturities of the cultivars generally remained the same over all sowing dates. The length of the ear initiation to ear peep phase was strongly dependent on the timing of ear initiation. The phenological data obtained for Australian wheat varieties showed that if marked alteration in the pattern of phasic development was to be effected in new cultivars, stronger control mechanisms over ear initiation and speed in completing post-initiation phases must be sought. The durations of pre-initiation and post-initiation phases were highly correlated with photoperiod and temperature. Coefficients of multiple determination for the duration of the pre-initiation phase varied between 80 and 90 % for vernalized plants of the spring cultivars and between 59 and 80% for unvernalized plants. Coefficients of determination for the ear initiation to ear peep phase ranged between 90.4 and 97.5 %. |
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