SUMMARYStudies on genetic variability, character association and path co-efficient analysis were conducted on 40 rice genotypes. Analysis of variance revealed considerable variability among the genotypes for all the characters. A high genotypic and phenotypic co-efficient of variation was observed for grain yield per plant, straw yield per plant, productive tillers per plant, spikelets per panicle, harvest index, 1000 grain weight, number of panicles per running meter, spikelet fertility, plant height, days to 50 per cent flowering and panicle length. Spikelets per panicle showed the highest broad sense heritability (95.81%). Grain yield per plant showed high value of heritability coupled with low genetic advance. The genotypic correlations among the yield traits and their path co-efficient were estimated. The grain yield per plant showed significant positive correlation with harvest index, 1000 grain weight, straw yield per plant, plant height and productive tillers per plant. The traits days to maturity, plant height, straw yield per plant and harvest index had moderate to high positive direct effect on grain yield per plant. The study revealed that genetic improvement of grain yield in rice is admissible by selecting characters having high positive correlation and positive direct effect.

Genetic diversity was assessed in 40 genotypes of rice for 12 quantitative characters including grain yield using Mahalanobis D 2 statistics. The D 2 values between all possible pairs of 40 genotypes ranged from 26.32 to 404.814. The results revealed that 40 genotypes were grouped into 8 clusters with substantial divergence between them. Cluster I was very large comprising 24 genotypes followed by cluster II with 10 genotypes, while clusters III to VIII were solitary clusters. The maximum inter-cluster distance was obtained between cluster VI and VII (D = 20.12) followed by those between cluster VII and VIII (D = 18.56) which may serve as potential parents for hybridization, whereas, minimum between cluster III and IV (D = 5.13). The highest intra cluster distance was recorded for cluster II (D = 7.96) and lowest for cluster I (D = 6.62). The genotypes in the cluster VI had lowest mean value (89.67) for days to 50 per cent flowering indicating their use in breeding program for development of early maturing varieties. Cluster VIII recorded high grain yield per plant showing its potential for yield improvement. The characters number of spikelets per panicle and days to 50 per cent flowering contributed maximum in the manifestation of genetic divergence. RDN-20, RDN-11, Phule Radha, RDN-18 and RDN-5 may serve as potential donors for future hybridization programmes.

SUMMARYThe present investigation including nine generations of four crosses was undertaken to study the genetics of yield and yield components through generation mean analysis. Additive, dominance and epistasis interactions were found operating in control of almost all characters. Dominance gene action was found predominant in inheritance of yield and yield contributing characters like number of primary branches, clusters per plant and 100 seed weight indicating conventional selection procedure may not be effective enough for improvement of these characters, therefore, selections should be postponed in later generations or intermating among the selected segregants followed by one or two generations of selfing could be useful to break the undesirable linkage and allow to accumulate favourable alleles. Both additive and non-additive gene effects were involved in the expression of plant height, number of pods, oil per cent, protein per cent, and days for maturity. Reciprocal recurrent selection or bi-parental mating design should be used to improve these characters. Key

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