an evaluation of combining ability and gene effect in rice genotypes

five improved along with three local rice varieties were crossed in a line× tester method in 2001. fifteen f1 hybrids and eight parental genotypes were planted in a randomized complete block design with 3 replications at rice research institute of iran, rasht, in 2002. the main objective of the research was to estimate the general and specific combining ability and gene action for 10 agrnomic and qualitative traits. analysis of variance based on line×tester method showed that the mean squares of treatments, parents and crosses for all traits (except grain yield for crosses) were significant at 5% and 1% probability levels. general combining ability (gca) was positive and significant for grain yield in gharib and kadus varieties. there was also positively significant gca for grain length and shape in kadus, hassani, nemat and in line 830. therefore, these traits can be positively transferred to progenies. kadus and hassani varieties exhibited negative and significant gca for plant height and 50% of flowering. these genotypes can transfer early maturiy and dwarfism to progenies. the cross gharib/ir50 had positive and significant specific combining ability (sca) for grain yield. there were also the same sca for tiller number in crosses hashemi/ir28, gharib/kadus and hassani/line 830. estimation of genetic variance components indicated that the grain shape was controlled through additive gene effects. it showed that this trait can be transferred into progenies. the other such traits as tiller number, grain length, number of filled grain per panicle and plant height were controlled by dominance gene effects. therefore, these traits can be effecitively employed to produce hybrid varieties