HETEROSIS AND SOME GENETIC PARAMETERS FOR SEED AND STRAW YIELD AND THEIR RELATED TRAITS OF FLAX (Linum usitatissimum, L.)

Six genotypes of flax representing different agronomic characters were crossed in a half-diallel model in 2009/2010 winter season. The six parents and their 15 F1 crosses were evaluated in 2010/2011 and 2011/2012 seasons to study the heterosis over mid and better parents, phenotypic and genotypic correlations, heritability and expected gain from direct and indirect selection for yield and its related traits of flax. The results indicated clearly that mean squares of genotypes were highly significant for all studied traits in both seasons and their combined data. Desirable (negative or positive direction) significant or highly significant heterosis in nine and five crosses for days to first flower; eleven and seven cross combinations for plant height; eleven and three crosses for technical length; seven and three hybrid combinations for No. of basal branches plant-1; ten and eight crosses for No. of capsules plant-1; ten and eight cross combinations for 1000-seed weight; all studied cross combinations for seed yield plant-1 and all studied cross combinations and twelve cross combinations for straw yield plant-1 over mid parents and better parent were manifested, respectively. Highest positive estimates of heterosis for seed yield plant-1 were recorded by cross no. 6 (P2xP3), which was 117.16% and 107.38% over mid parents and better parent, respectively. While, highest positive estimates of heterosis for straw yield plant-1 were recorded by cross no. 13 (P4xP5), which were 134.20% and 122.21% over mid parents and better parent, respectively. The presence of high levels of mid and better parents heterosis indicates a considerable potential to embark on breeding of hybrid cultivars in flax. Significant and positive phenotypic and genotypic correlation coefficients were found between seed yield plant-1 and each of basal branches number plant-1, capsules number plant-1, 1000-seed weight and straw yield plant-1. While, significant and negative correlation coefficient was found between seed yield plant-1 and days number to first flower. Straw yield plant-1 was significantly and positively associated with each of plant height, technical length, basal branches number plant-1 and capsules number plant-1. Indicating that, in general, to increase seed yield plant-1, selection should be carried out for No. of basal branches plant-1, No. of capsules plant-1 and 1000-seed weight, and to improve straw yield plant-1, selection should be carried out for plant height, technical length, No. of basal branches plant-1 and No. of capsules plant-1, and to improve both seed and straw yields in the same time (dual purpose), selection should be practiced for No. of basal branches plant-1 and No. of capsules plant-1. Genetic variance (σ2G) of flax genotypes was higher than environmental (σ2e) variance in all studied traits; therefore broad-sense heritability estimates were high percentages for all studied traits in the combined data over both seasons. The expected gain from direct selection for seed and straw yield would improve these traits under consideration in a way better than the indirect selection for the other studied traits.