Tiller population dynamics in wheat

In field-sown wheat grown in Canterbury, variation in the density of ears accounts for most of the differences between grain yields (Dougherty 1973; Scott 1978; Scott et al. 1977). Ear number is a component of yield which is determined during August and September during which the crop produces a number of shoots or tillers at different times. Since few tillers survive to produce an ear, information on population changes in tillers was needed, especially as tiller mortalities of 40% are common in the Canterbury environment (Dougherty & Langer 1974). There is little information existing in the literature on the components of yield of ear-bearing tillers, although earlier work showed that the first-formed main stem ear contributed a major proportion to grain yield (Clements et al. 1973). The aim of the experiments reported in this thesis was twofold. First, to characterise the various groups of tillers and to monitor changes in tiller populations, and secondly to analyse the components of yield on those tillers which survived to produce an ear. In the first season (1976-1977), Karamu, a short-strawed awned wheat, and Kopara, a tall wheat were analysed together. As there were a number of interactions, indicating that the cultivars were responding differently to treatment, it was decided to monitor the tiller populations of the two cultivars separately in 2 trials for the 1977-1978 season. The thesis begins with a review of previous work on tillering in the temperate cereals. The remaining chapters with the exception of the Discussion in Chapter 9 discuss results of autumn-sown wheat over two seasons. Each of these chapters (2 to 8) is a complete unit where the methodology is outlined and the results are presented and discussed.