بررسي اثر محيط بر روي تركيب پذيري لاين هاي كلزا از نظر صفات زراعي و كيفيت روغن

Study of environmental effects on combining ability of rapeseed lines for agronomic characteristic and oil quality traits

Evaluation of inbred lines and their combining ability is one of the most important and expensive stages in hybrid seed production, by which superior parents and crosses can be identified. Diallel crosses is common and effective method to determine combining ability. In most of studies combining ability has been estimated in one environment. The present investigation carried out to study the effect of environments on combining ability estimation of different characteristics/ traits of rapeseed (Brassica napus L.). In this study 7 rapeseed inbred lines randomly selected and crossed in all combinations (including reciprocals) in 1999. Parents and crosses were evaluated in 2000 (environment no.1) and 2001 in two sowing dates (environments no.2 and 3) in RCBD with 2 replications. Twenty one agronomic and oil quality characteristics/ traits measured in parents and hybrids. Pooled combining ability analysis showed that general combinig ability (GCA) of parents was significant for all characteristics/ traits except Stearic acid. Specific combining ability (SCA) of hybrids was also significant for all characteristics/ traits. These results revealed that both additive and dominant (non-additive) gene action were important for these characteristics/ traits. The GCA x environment interaction was significant for all characteristics/ traits except Stearic acid. The SCA *environment inforaction was also significant for all characteristics/ traits. lt showed that combining ability of parents and hybrids were different from one environment to another. Estimation of combining ability effects also was not similar in different environments. Sometimes differences were high as they changed from positive to negative or vice versa. There were 11 cases in estimation of GCA effect and 44 cases in estimation of SCA effect that the sign of estimations were changed and the differences were significant. ln other hand estimation of combining ability effects by pooled data analysis showed better results. Mean performance of characteristics/ traits in parents and hybrids were not similar in different environments. Selection of superior parents and hybrids should be carried out according to mean performance and combining ability, hence selection by one year in one environment is risky and may led to undesirable results. Therefore, selection on the basis of multi-environment is recommended.