The effects of ploidy and a phenotype conferring a high water-soluble carbohydrate concentration on carbohydrate accumulation, nutritive value and morphology of perennial ryegrass (Lolium perenne L.)

Tetraploidy or the use of diploid genotypes with gents conferring high wate r-soluble carbohydrate concentrations are two mechanisms to increase the nu tritive value of perennial ryegrass. This experiment compared the morpholog y, nutritive value and diurnal variation in water-soluble carbohydrate (WSC ) concentrations of 56-day-old plants from six perennial ryegrass cultivars grown under controlled environment conditions. Three of these cultivars we re diploid (Melle, Aurora and Cariad) and three were tetraploids (Meltra, P rospero and AberOnyx) which had been derived from the respective diploid cu ltivars, Two of the diploid cultivars (Cariad and Aurora) had previously be en selected for high concentrations of water-soluble carbohydrates. The tet raploid cultivars had fewer (mean 59), larger tillers than the diploids (me an 83). However, with the exception of Melle and Meltra the dry matter yiel d of the diploid cultivars was not significantly different from their tetra ploid derivatives. The effect of tetraploidy on WSC concentrations was depe ndent on the genetic background of the cultivars. Melle, which had not been previously selected for increased WSC, had a significantly lower WSC conce ntration than its tetraploid derivative, Meltra. However, tetraploidy did n ot further increase the WSC concentration in those cultivars previously sel ected for high WSC concentrations. WSC concentrations in the leaf of both A urora and Melle rose by 65-70 g/kg throughout the photoperiod, suggesting t hat differences in the total WSC concentration of these cultivars were not due to any increase in the amount of carbon fixed by Aurora but rather due to differences in the allocation of carbon during growth and development. T his experiment demonstrated that tetraploidy was not beneficial in improvin g the WSC concentration of perennial ryegrass when imposed on two diploid c ultivars which had the genetic potential for increased WSC accumulation. Ho wever, tetraploidy significantly increased the WSC concentration and by imp lication the nutritive value of a cultivar derived from a perennial ryegras s cultivar with standard WSC concentrations.