'Plant Breeding: Sustaining the Future' Abstracts of the XVIth EUCARPIA Congress, Edinburgh, Scotland, 10-14 September 2001 GENETIC VARIATION FOR YIELD AND QUALITY TRAITS IN HALF SIB FAMILIES OF PERENNIAL RYEGRASS (Lolium perenne) GROWN AS SPACED PLANTS AND SWARDS A.A. JAFARI, V. CONNOLLY Research Institute of Forest and Rangelands, PO Box 13185-116, Tehran, Iran

Breeding forage grasses for improved dry matter yield and quality traits is an important goal for improving animal performance.  In forage grass breeding evaluation id frequently done under spaced plant conditions, but for agriculture use is grown in dense swards in field conditions.  It would make breeding much easier, if performance under sward conditions could be predicted from spaced plants.  The objective of this study was to determine the extent and nature of genetic variability for three quality traits namely: digestible organic matter in dry matter (DOMD), water soluble carbohydrates (WSC), crude protein (CP) as well as dry matter (DM) yield in perennial ryegrass (Lolium perenne) under spaced plants and sward conditions.  One polycross containing 24 mid season genotypes were planted.  Prior to planting, each parent was vegetatively propagated to give 8 clones.  At harvest, seed from clonal replicates of each genotype was combined.  Both seed of half sib families and their clonally propagated parents were grown as spaced plants and sward over two years.  Near Infrared Spectroscopy (NIR) were used for estimation of the quantity parameters. Genetic analysis showed that, broad sense heritability was quality traits (h²_b = 0.48-0.80), but moderate for dry matter yield (h²_b = 0.25-0.49). Narrow sense heritability (h²_n, was low for dry matter yield (h²_n = 0.03-0.26) and high for DOMD and WSC (h²_n = 0.51-0.64). Genetic analysis indicated that non-additive genetic variance was the major component controlling DM yield, while additive genetic variance were more important for quality traits.  CP was negatively correlated with both yield and WSC, while WSC was positively correlated with DM yield and DOMD.  The genetic correlation of DOMD with both DM yield and CP was weak and inconsistent and in general it was negative.  In regard to breeding for improved quality and yield it was concluded that selection should focus on increased DM yield coupled with increased WSC/CP ratio especially in the vegetative leaf tissue. Because of no strong relationship between spaced plants and swards, selection should be based on performance under competitive sward conditions.