GENETIC-VARIATION IN COCKSFOOT (DACTYLIS-GLOMERATA L) POPULATIONS FORMOTTLE VIRUS-RESISTANCE

Highly significant and continuous variation in the degree of injury du e to cocksfoot mottle virus (CfMV) infection was found among clones of 7 cocksfoot (Dactylis glomerata L.) populations, taken at random amon g surviving plants in 9 year old swards. Broad sense heritabilities fo r CfMV injury ranged from 0.52 to 0.91 within populations, and genotyp ic correlations between CfMV injury and total DM-yield ranged from -0. 46 to -0.88. The relationship between CfMV injury and DM-yield could b e described by a second degree curve. CfMV injury was to some extent g enotypically correlated in the positive direction with crude protein c ontent and digestibility, and negatively with crude fiber content, esp ecially in the first cut. Artificial infection of plants from the orig inal populations with CfMV in a simulated sward experiment, did not re veal any significant differences between populations in tolerance towa rds CfMV infection. Infection caused a 54.5% increase in the number of dead plants per plot, relative to uninfected plots, but only a 4.5% r eduction in dry matter yield. There is a clear tendency that synthetic populations selected for high yield are less tolerant towards CfMV in fection than unselected or low yielding populations. The resistance fo und in these cocksfoot populations is a sort of tolerance, and the res ults indicate that the level of tolerance can be increased by selectio n.