Developmental variation in relation to the accumulation and partitioning of dry matter in wheat (Trictum asetivum L.) in Western Australia

[Truncated abstract] All wheat cultivars recommended for commercial production in one or more agro-ecological regions in Western Australia represent a sub-set of the phasic development patterns characteristic of the wheat genus. That sub-set is locally described as being of “mid-season” maturity. All cultivars adapted to WA in that sub-set share the common characteristic of a short Basic Vegetative Period (=BVP) but differ considerably in their responses to vernalisation and photoperiod. That finding had not been expected. A short BVP, a zero response to vernalisation and high response to photoperiod have long been accepted (on anecdotal evidence) as the major factors determining adaptation to WA growing conditions. Under the circumstances the hypothesis tested, “that an association exists between particular combinations of factors determining developmental variation and specific agro-ecological areas of adaptation”, had to be rejected. These findings would benefit breeders in making decisions on the selection of unadapted cultivars, and the selection of the locally adapted parents to which they could be hybridized, but not for selection among early generation segregating populations. Not all cultivars of “mid-season” maturity are necessarily adapted and high yielding. Those that are, initiate floral primordia, and come to flower, within a few days of one another – irrespective of their different responses to vernalisation and photoperiod. They develop leaf canopies of similar size and at similar rates, and accumulate dry matter to similar extents and at similar rates. Over 80% of canopy size and dry matter accumulated are contributed by the main stem and 4 primary stems and in the rank order of MS > T1 = T2 > T3 >> T4. Few secondary and tertiary tillers, if any, survive. Spike bearing stems developed similar spikelet numbers / spike in the same rank order, and this applies to the number of grains formed / spikelet and the extent to which they enlarge. It was not possible to identify any consistent and inherent difference among the cultivars that could be exploited for improving crop performance. In explanation of the above it was noted that all adapted cultivars initiated more stems, spikes and spikelets than come to fruition. That suggests that competition for growth resources (water, nutrients and assimilates), which intensifies after stems commence elongation and spike formation occurs, is the major factor restricting all cultivars to similar numbers of stems, spike, spikelets and grains – hence the similarities observed in leaf area expansion, dry matter accumulation, grain yield and its components. It was ii also noted that the timing of the commencement of stem elongation was similar between cultivars in each experiment. Despite these generalised similarities there were numerous instances in which cultivars differed significantly from one another for some measured trait at some or other stage of their development, but such differences did not persist in measures taken at a later date...