Plants of Kalyansona, Condor and Janak semidwarf wheats, grown at a density of 130 plants m-2, were transferred every 4 days after floral initiation of the main shoot from temperature regimes of 27/22°C and 21/16°C to a regime of 15/10°C to determine if specific developmental stages of the ear are particularly important to the establishment of grain number. No stages between the appearance of double ridges and flag leaf emergence were significantly more sensitive to temperature changes than others, there being a progressive reduction in grain number per ear for every day that plants of Kalyansona and Condor remained at a higher temperature. Grain number of the main ear was closely correlated with the amount of dry matter in the stem, in the ear structure (chaff), and in the four uppermost leaves of the main shoot; the partial correlation coefficients demonstrated that leaf weight was best related to grain number. Thus large shoots with heavy ear structures had many grains and vice versa. It can be inferred from these results that the distribution of dry matter to the various plant organs before anthesis is in a strict proportionality irrespective of the availability of assimilates.
Experiments were designed to examine whether drought imposed on plants between sowing and flowering endows them with adaptations which enable them to cope more effectively with drought occurring during grain growth. Specifically, the character sought was adaptation persistence. In two experiments, one in a growth chamber, the other in a glasshouse, plants of two-rowed and six-rowed barleys, and of durum and aestivum wheats, were grown in canopies in 1-metre-deep pots filled with soil, so that the development of water stress might approximate that in the field. Various drying cycles were imposed during the vegetative phase, after which plants were rewatered and allowed to fill their grain during a further drying cycle. During the initial drying cycles there were morphological changes, including changes in area per leaf, leaf area per plant, specific leaf weight and in the numbers of plant organs; the plants to which water was applied sparingly had better water-use efficiency than those with a plentiful supply. On rewatering, however, the previously droughted plants became prodigal in their water use and in the final drying cycle there was little evidence that the earlier responses improved the efficiency of water use either per unit dry matter gain or per unit grain produced. Thus any adaptations were not persistent. Indeed, in general, plants which were heavier at anthesis (i.e. those which had lost more water by this stage), used water most efficiently in grain production. This result is discussed in relation to current photosynthesis and the remobilization of reserves during grain-filling. 14C data indicated that barley plants exposed to drought during grain growth did not retranslocate more stored materials than those which were frequently watered during this stage.
AbstvactThis study attempted to determine if and why there are differences among three cultivars of wheat in their responses to temperature. The three semidwarf cultivars examined, Kalyansona, Condor and Janak, are currently used commercially. Temperature regimes chosen matched the range to which plants in warm temperate climates with hot summers would be exposed at different stages of development. Plants were grown in a phytotron in sunlit cabinets.Responses to temperature were different among the cultivars. Kalyansona was relatively unresponsive to temperatures during the floret phase, being little affected in the sizes of upper leaves, in floret production and grain set, in overall plant growth or in grain yield. The sole character to respond to temperature in this cultivar was kernel weight, which declined with increasing grain phase temperature. In contrast, Condor demonstrated marked plasticity during the floret phase in all plant characters measured. Its plasticity was such that, at the lower temperatures, it outyielded Kalyansona by a substantial margin while at the higher temperatures its yield was relatively poor. On a plant basis, Janak performed similarly to Condor. Rates of photosynthesis were relatively unaffected by temperature in any cultivar.This wide range of response among three superficially similar cultivars has promising implications for the tailoring of cultivars for different temperature zones. The importance of different plant characters to temperature stability is considered in the discussion.
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