1983 Volume 29 Issue 1 Pages 9-16
To clarify the factors determining the number of heads per plant in relation to the degree of floral-induction in orchardgrass, the influence of floral-induction of main stem on heading behaviour of lateral tiller buds was investigated. Three clones of A-101 (early), L-102 (late) and EV72-7 (extremely early) were used. The details of growing procedure of materials had been described in the previous report of this series (III. Influence of fertilizer application on responsiveness to floral-induction treatment in aged plant. Bull. Natl Grassl. Inst. 17, 68-75.). Individual tillers separated from each clone were subjected to floral-induction treatment of 10℃ and 12-hour day-length for 7, 10, 14 and 21 days. After the treatment, they were grown under continuous light in a warm (25℃ day/15℃ night) glasshouse. Then the heading behaviour of the whole plants including lateral tillers, almost all of which left in the leaf sheaths of main stem during the treatment, was observed with special consideration to the position of nodes on main stem and the order of tillering (Figs.1 and 2). The periods of treatment required for the heading of main stem were 7 days in both of L-102 and EV72-7, and 14 days in A-101. When the period of treatment was not long enough to cause the heading of main stem, all the lateral tillers did not reach heading in all the clones tested. As the period of treatment became longer, the number of heads per plant became larger in each clone tested. But the tendency in the increase of the number of heads with lengthening the period of treatment was markedly different from clone to clone (Table 1). When the treatment was made for 21 days, only a part of the primary tillers reached heading and all the secondary tillers remained at vegetative stage in A-101 and L-102. In EV72-7, in contrast with the above two clones, all the primary tillers and about half of the secondary tillers reached heading and some of the tertiary tillers formed inflorescence primordia on their apices. As the position of nodes of main stem became lower, the lateral tillers of respective order reached heading earlier in each clone tested. The some uppermost primary tillers in A-101 and L-102, however, formed inflorescence primordia on their apices even though the immediately lower ones remained at vegetative stage. On the other hand, the heading was observed later in the lateral tillers of higher order than in those of lower order regardless of the clones tested (Table 2 to 5). From the above results, it was inferred that the differences among clones in the number of heads per plant at respective treatment-periods were attribuable to the following two factors ; (i) the degree of floral-induction of main stem, (ii) the dependence of lateral tillers on main stem in heading behaviour.
