J. Expt. Biosci. 2(2):67-76, July 2011 ISSN 2223-9626 (Online), ISSN 2077-3358 (Print) GENE ACTION FOR SEED YIELD AND YIELD CONTRIBUTING CHARACTERS IN TURNIP RAPE (Brassica rapa L.) M.M. Rahman* 1 , M. A. Z. Chowdhury 2 , M.G. Hossain 3 , M. N. Amin 4 , M.A. Muktadir 5 and M.H. Rashid 6 *Corresponding author, E-mail: mosiur1979@yahoo.com Abstract A 7 x 7 diallel experiment (excluding reciprocal) on Brassica rapa (toria) was conducted to study the nature and magnitude of gene action analysis and inheritance of some selected genotypes for seed yield and other related characters such as days to 50% flowering, days to maturity, plant height, primary branches per plant, secondary branches per plant, length of siliqua, siliquae plant -1 , seeds siliqua -1 , 1000-seed weight, seed yield plant -1 , harvest index and oil content. The components of variation along with the derived genetic ratios for different traits, showed that the D and H components, which measure additive and dominance variation respectively, were significant for all the traits studied. The results indicated the importance of both additive and dominance components for the inheritance of all the traits in Brassica campestris. However, the magnitude of dominance was higher than the additive component for all the traits except days to maturity, siliqua per plant, which indicated that dominance component had a predominant role in the inheritance of these traits. The positive and negative estimation of h 2 indicated mean direction of dominance and respective genes towards positive and negative sides, respectively. The results showed that eight characters viz. plant height, primary branches plant -1 , 1000-seed weight, secondary branches plant -1 , siliquae plant -1 and seed yield plant -1 possessed positive effects, indicating the mean direction of dominance as well as importance of dominant genes in the expression of these traits. On the other hand days to flowering, days to maturity, seeds siliqua -1 , harvest index and oil content exhibited the values in negative direction, showing the excess of recessive genes for these traits. Key words: Brassica rapa (toria), Gene action, Additive and non-additive gene actions and Seed yield Introduction Toria (Brassica rapa) is an important oilseed crop considered as a catch crop in early rabi season of Bangladesh. The knowledge on the type of genetic variance present in the population is helpful in devising suitable breeding approach in the crop improvement programme. Varieties showing good in per se performance may not necessarily produce desirable progenies when used in breeding programs. About 20 to 107 percent standard heterosis in yield has been reported in F 1 hybrids of Brassica rapa (Rai, 1995). Considerable amount of heterosis for seed yield and its components in F 1 hybrids of rapeseed have also been reported (Patnaik and Murty, 1978; Verma et al., 1989). Again the genetic variation is the single most important issue that helps to choose a good parent. But very little work has, however, been done to understand the nature of gene action and the inheritance of yield and yield components in B. rapa under Bangladesh condition. The present investigation is an attempt in this direction and also to know the hybrid performance of the crosses involving the self incompatible lines. The nature and magnitude of gene action is an important factor in developing an effective breeding programme. Among the various mating designs developed for the determination of the genetic architecture of quantitative characters, the diallel cross method, out lined by Jinks (1954, 1955) and Hayman (1954 and 1958) has received considerable attention of the Geneticists and Plant Breeders. 1,3,4,5 Scientific officer, Plant Breeding Division, Bangladesh Agricultural Research Institute, Joydebpur, Gazipur-1701 2 Principle Scientific Officer (Crops), BARC, Farmgate, Dhaka 6 Lecturer, Genetics and Plant Breeding, SAU, Sher-e- Bangla nagar, Dhaka- 1207 67