Flower initiation in relation to maturity in crop plants. III. The flowering response of early and late cereal varieties to Australian environments

Abstract

The difference between early- and late-flowering characters in wheat, rye, barley, and oats has been studied by growing some Australian and overseas varieties in several field environments with mean temperatures ranging from 10 to 22°C, and mean photoperiod of 10½ to nearly 16 hr, together with vernalization and prolonged photoperiod. Similar genotypes were found in each of the four cereals. Early varieties all flowered at a low leaf number, which showed that the genotypes for early flower initiation in these varieties are almost or entirely insensitive to temperature and photoperiod. In consequence, varieties with such genotypes can be expected to flower early, even in tropical Australia. In contrast, the genotypes for lateness caused initiation at a higher leaf number, and more sensitivity to temperature and photoperiod, both before and after flower initiation. Contrary to the common assumption that very late varieties need a period of cold followed by long photoperiod for flower initiation, they were found to initiate both in summer (i.e, high temperature) and in winter (low photoperiod) at Melbourne. High temperatures (above 15°C), however, delayed initiation, which resulted in flowering at a higher leaf number than when the same varieties were grown at low temperatures. In addition, the young reproductive shoot died after initiation in a combination of high temperature and a 14–12 hr photoperiod, as happens when such varieties are springsown in temperate latitudes. Such a response also prevents flowering in tropical environments, where high temperatures are combined with a moderate photoperiod all the year round.