Contributions of shoot categories to growth and yield of winter wheat

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Abstract
Summary: Measurements were made at intervals during 1983–4 on the main stem and on tillers having defined morphological positions on plants of winter wheat cv. Avalon growing in a multifactorial experiment testing combinations of the following five factors: rotation, sowing date, amount of autumn N, amount of spring N, and timing of spring N. Some observations from similar experiments in the two previous seasons are also reported.The tillers in the axils of the first three leaves (Tp, T2and T3) appeared on most plants. An average of 1·8 other tillers were produced on each plant, including 0·14 at the coleoptile node. When number of shoots was maximal, main stems (M), T1and T2together accounted for 64% of the total number of shoots, 76% of the total green area and 87% of the total above-ground dry weight. More than half of the T1s died before maturity, two thirds of the T2s and almost all of the other tillers. The final population of 566 ears/m2was made up as follows: M 56%, T126%, T216%. The differences between categories in dry weight per shoot at maturity were relatively less than earlier. Contributions to the mean grain yield of 9·9 t/ha were: M 60%, T1, 22%, T214%. M had more grains per ear than T1, or T2which had similar numbers. Dry weight per grain was similar in all three categories.Most of the effects of treatments on dry weight/m2, which have been described previously by Prewet al.(1986), were due to effects on all shoot categories. Several treatments increased the number of shoots/m2by increasing the average number per plant of tiller categories that were produced later. This was always the result of an increase in the proportion of plants having many tillers. Neither the maximum number of tillers found on a plant, nor the duration of tiller production, was affected.Both within and between tiller categories, shoots that were produced last died first. Plants which started tillering late produced fewer, smaller, tillers than average and relatively few of these survived. The standard hierarchical order of tiller production and survival was disrupted when plants were damaged by stem-boring insects and when the period shortly before a tiller category was due to emerge was unusually dull and warm.

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