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 aroundanthesis in aLolium perenne seed crop can depress seed yields,the possible competition for carbohydrates or nitrogen betweenthe seeds and new tillers that develop after the onset of anthesiswas investigated. In two greenhouse experiments the number oftillers per plant was varied by a combination of cutting, nitrogensupply, light quality and light intensity treatments. Two genotypeswith different tillering rates were used. Seed yield per earwas largely independent of the number of tillers and regrowthof cut tillers after the onset of anthesis. It increased inone genotype, but only under low light and a reduced nutrientavailability, and no new tillers were produced. The amount ofwater-soluble carbohydrates in the reproductive tillers increasedin both clones under these conditions. Under more favourableconditions the increased tillering rate and regrowth of tillersafter cutting did not adversely affect seed yield per ear ineither clone, although carbohydrate reserves in the floweringtillers were sharply reduced. Tiller removal increased the concentrationand amount of nitrogen in the remaining flowering tillers, irrespectiveof the amount of regrowth. It is concluded that competitionfor carbohydrates or nitrogen between the seeds and new vegetativetillers that develop after the onset of anthesis, is not a majorcause of the low and variable seed yields inL. perenne seedcrops. Processes within the ear itself are probably limiting. Lolium perenne L.; perennial ryegrass; seed yield; seed set; tillering; carbohydrates; nitrogen; competition.