THE EFFECT OF HANDLING ON THE YIELD OF 2 POPULATIONS OF LOLIUM-PERENNE SELECTED FOR DIFFERENCES IN MATURE LEAF RESPIRATION RATE

Two populations of Lolium perenne L. S23 (perennial ryegrass), selecte d for differences in mature leaf dark respiration. were used in a non- destructive indexing system for individual plants, to determine growth parameters. Population GL66, selected for high respiratory rates and low yield, responded strongly to the indexing treatment, when grown at low plant density. Dry weights of all plant parts decreased strongly, as did dry matter percentages of the leaf blades. At high density thi s population demonstrated the same trend, but additionally allocation to the shoot increased. In contrast. GL72, selected for low respirator y rates and a high yield, responded only at a high plant density. It i s argued that there might be a relation between the dissimilar respons e of the two populations to mechanical influences and the presence of the genotypes of the low-yielding population in the parent variety. Th e results also emphasize that non-destructive growth analyses can only be used when their effects on the plants are known.