Genetic variation and correlation among yield and quality traits in cocksfoot (Dactylis glomerata L.)

The objective of the present research was to study the genetic variability for total dry matter (DM) yield, tiller number, heading date and three quality traits, namely content of digestible dry matter (DDM), water-soluble carbohydrate (WSC) and crude protein (CP), in cocksfoot (Dactylis glomerata L.). Twenty-five parents were randomly chosen from a genetically broad-based population, and their respective half-sib (HS) families were generated. Clonally-propagated parents and their HS family seeds were grown as individual plants using a randomized complete block design with two replications in Alborz Research Center, Karaj, Iran, during 2002-04. The results of combined analyses over 2 years showed significant variances between clonal parents for all traits except CP. In the HS generation, between-family variances were only significant for tiller number, heading date and WSC. Clone x year (S2(GY)) and family x year (S2(FY)) interactions were significant for all traits except for WSC in HS families. The estimates of broad-sense heritability (h2(b)) were moderate to high for all traits (h2(b)=0·37-0·69), except CP. Narrow-sense heritability (h2(n)) estimates from analyses of progenies and from regression of HS progenies on parents (h2(op)) were moderate, relatively the same values as h2(b) for heading date, tiller number and WSC, which suggested that additive genetic variance was the main component controlling these traits. For DM yield and DDM, h2(n) and h2(op) estimates were low, whereas h2(b) estimates were moderate, which suggested that both additive and non-additive gene effects played an important role in the genetic regulation of these traits. Genetic correlations among CP with both WSC and DDM were generally negative, whereas WSC was positively correlated with DDM and tiller number. The genetic correlation among DM yield with DDM was weak and inconsistent and, in general, negative. DM yield had negative and positive correlation with heading date and tiller number, respectively. It was concluded that there was significant variation and moderate heritability for most traits in the cocksfoot populations evaluated to improve yield and quality traits. Selection for high WSC is a means to improve quality in general. The data also indicate that response to combined selection for both DDM and DM yield should be possible. Selection for DDM alone could result in reduction in yield.