GENETIC ANALYSIS FOR EARLY MATURITY, YIELD AND QUALITY ATTRIBUTES OF INDIAN MUSTARD (Brassica juncea L.)

Abstract

This investigation was set out to study the genetic control in early generations of key traits for production of early maturing, high quality and high yielding Brassica juncea L. genotypes in Pakistan. Eight genotypes of B. juncea were chosen for one or more of several interesting taits for genetic improvement of B. juncea in Pakistan – early maturity, yellow seed colour, large seed size, high seed quality (low erucic acid in oil and glucosinolate in meal), high seed yield and oil and protein content. All the eight selected genotypes were crossed in a complete diallel design and genetic analysis was conducted on subsequent early generations in field experiments. The genetic analysis for each trait included Hayman analysis of diallel F1 progeny for additive and dominant effects, combining ability analysis and generation mean analysis. Based on the outcome of these genetic analyses, suitable breeding methodology will be recommended for further breeding of B. juncea in Pakistan. The parental material was obtained from National Agricultural Research Centre (NARC), Islamabad, Barani Agricultural Research Institute (BARI), Chakwal and Nuclear Institute for Food and Agriculture (NIFA), Peshawar. Two early maturing genotypes included in the parental material were selected after evaluating twenty genotypes in winter 2005-06. F1 generation was obtained from the complete diallel in winter season 2006-07 at BARI, Chakwal. The 56 F1 hybrids along with their parents were sown in Randomized Complete Block Design with three replications during next crop season 2007-08. Data were recorded for days to first flowering and physiological maturity, plant height, primary branches per plant, siliquae per plant, siliqua length, seeds per siliqua,1000-seed weight, seed yield per plot, oil and protein contents, erucic acid and glucosinolate contents. Analysis of variance showed significant differences for all the traits and therefore, data were further analyzed using Hayman’s approach which showed existance of both additive and dominance gene effects governing all the traits. However, estimates for genetic components of variation revealed that additive effects were more important for days to first flowering, days to physiological maturity, seeds per siliqua, 1000-seed weight, erucic acid and glucosinolate contents while, dominance effects were more prominent for plant height, number of primary branches per plant, number of siliquae per plant, siliqua length, seed yield per plot, oil and protein contents. Asymmetrical distribution of dominant genes among the parents was identified for all the characters except days to first flowering in which both parents had nearly equal number of dominant genes. Some of the traits like siliqua length, oil and protein contents and glucosinolate contents showed presence of directional dominance. For plant height, number of primary branches, siliquae per plant, siliqua length, seed yield per plot, oil and protein contents, over dominance was observed. The results for combining ability analysis indicated significant general combining ability for most of the traits except for plant height, siliqua length, oil and protein contents indicating that selection would not bring about significant improvement in these traits due to absence of significant variations. Combining ability analysis showed that UCD-8/4, KJ-119 and BRS-2 were good general combiners for maturity and yield related traits. NIFA RAYA x UCD-8/4, CANOLA RAYA x UCD-6/23, KJ-119 x UCD-6/23, CANOLA RAYA x UCD-8/4, KJ-119 x UCD-8/4, CANOLA RAYA x UCD-8/4, KJ-119 x BRS-2 and KJ-119 x CANOLA RAYA involved at least one of the good general combiner parents and showed high desired specific combining ability for many traits. Heterosis estimates indicated that significant negative and positive values were shown by many crosses for all the traits except for protein content, for which only one cross showed positive significant heterosis. Many of the crosses with significant positive heterosis for oil content involved yellow-seeded parents while seven of the crosses showed significant positive heterosis simultaneously for both erucic acid and glucosinolate contents. High broad sense heritability was observed for all the traits except for days to first flowering and days to physiological maturity. The estimates for genetic advance were moderate to high for all the traits. High values for heterosis, heritability and genetic advance for various traits indicated good genetic potential for selection. During the same crop season, five of the F1 crosses were selected on the basis of their performance regarding different yield related traits. To generate F2 generation, five F1 plants from each cross were selfed. Back cross generations i.e, BC1 and BC2, were also developed by crossing two F1 hybrids with both of the parents for all the five crosses. The seeds of eight parents, F1, F2, BC1 and BC2 were sown during crop season 2008-09. Data were collected for maturity and yield attributes and subjected to analysis of variance and generation mean analysis to derive information on the relative importance of additive effects, dominance deviations and epistasis with the help of six parameter model presented by Hayman. Significance of scaling tests indicated presence of epistasis. Results for generation mean analysis showed that additive gene effects were effective in most of the crosses for many traits however some crosses showed presence of dominance effects for days to physiological maturity, plant height, number of primary branches, 1000-seed weight and seed yield. Dominance x dominance interaction was prominent for all the traits while for siliqua length and seed yield, additive x dominance interaction was also important. Additive x additive component was also detected in few crosses for various traits. Duplicate epistasis was detected for 1000-seed weight and seed yield while complementary epistasis was observed for days to physiological maturity, plant height and number of primary branches. Presence of dominance effects along with duplicate epistasis for 1000-seed weight and seed yield indicated that selection might be better carried out in late segregating generations. From the information regarding genetic control of all these traits it is suggested that for the traits showing prominent role of non-additive effects and presence of over-dominance, selection can be delayed up to late segregating generations while for the traits observing more effective role of additive effects, selection can be carried out in early segregating generations. Some combinations have been identified which will be useful to develop and release early maturing, good quality and high yielding varieties of B. juncea in Pakistan.