The effect of new tiller growth on carbohydrates, nitrogen and seed yield per ear in Lolium perenne L.

Abstract

To clarify whether new vegetative tillers that develop around anthesis in a Lolium perenne seed crop can depress seed yields, the possible competition for carbohydrates or nitrogen between the seeds and new tillers that develop after the onset of anthesis was investigated. In two greenhouse experiments the number of tillers per plant was varied by a combination of cutting, nitrogen supply, light quality and light intensity treatments. Two genotypes with different tillering rates were used. Seed yield per ear was largely independent of the number of tillers and regrowth of cut tillers after the onset of anthesis. It increased in one genotype, but only under low light and a reduced nutrient availability, and no new tillers were produced. The amount of water-soluble carbohydrates in the reproductive tillers increased in both clones under these conditions. Under more favourable conditions the increased tillering rate and regrowth of tillers after cutting did not adversely affect seed yield per car in either clone, although carbohydrate reserves in the flowering tillers were sharply reduced Tiller removal increased the concentration and amount of nitrogen in the remaining flowering tillers, irrespective of the amount of regrowth. It is concluded that competition for carbohydrates or nitrogen between the seeds and new vegetative tillers that develop after the onset of anthesis, is not a major cause of the low and variable seed yields in L. perenne seed crops. Processes within the ear itself are probably limiting.