THE EFFECT OF NEW TILLER GROWTH ON CARBOHYDRATES, NITROGEN AND SEED YIELD PER EAR IN LOLIUM-PERENNE L

To clarify whether new vegetative tillers that develop around anthesis in a Lolium perenne seed crop can depress seed yields, the possible c ompetition for carbohydrates or nitrogen between the seeds and new til lers 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 int ensity treatments. Two genotypes with different tillering rates were u sed. Seed yield per ear was largely independent of the number of tille rs and regrowth of cut tillers after the onset of anthesis. It increas ed in one genotype, but only under low light and a reduced nutrient av ailability, and no new tillers were produced. The amount of water-solu ble carbohydrates in the reproductive tillers increased in both clones under these conditions. Under more favourable conditions the increase d tillering rate and regrowth of tillers after cutting did not adverse ly affect seed yield per ear in either clone, although carbohydrate re serves in the flowering tillers were sharply reduced. Tiller removal i ncreased the concentration and amount of nitrogen in the remaining flo wering tillers, irrespective of the amount of regrowth. It is conclude d that competition for carbohydrates or nitrogen between the seeds and new vegetative tillers that develop after the onset of anthesis, is n ot a major cause of the low and variable seed yields in L. perenne see d crops. Processes within the ear itself are probably limiting. (C) 19 96 Annals of Botany Company