Heterosis and Combining Ability Analysis for Oil Yield and Its Components in Rapeseed (Report‪)‬

Introduction Rapeseed (Brassica napus L.) oil ranks third behind soybean and oil palm showing the importance of this product. Apart from direct human and animal consumption, indutria1 uses include the manufacture of rapeseed oil and convert biomass to bioenergy have been developed in the recent years in world (Ofori and Becker 2008). Thus considering that the rapeseed oil, beside its use for food, feed and industrial purposes, is also used for metilester, which is important component for biodiesel production, it can be expected that the rapeseed production area will continue expanding in the next years. Rapeseed breeding strategies are mostly dealing with developing cultivars characterized by high and stable seed and oil yield, as well as by low content of glucosinolates and erucic acids for human consumption. Seed yield, oil yield and oil percent are quantitative traits, which expressions are the result of genotype, environmental effect and genotype-environment interaction (Huhn and Leon 1985). Complexity of these traits is a result of diverse processes that occur during plant development. Iran has been facing a chronic shortage of edible oil; a large quantity of edible oil is imported annually from other countries to fill the gap between local production and consumption (Dehghani et al. 2008). Iran has had an important rapeseed breeding program in recent years, supported by the Seed and Plant Improvement Institute (SPII). Increasing the genetic potential of yield, tolerance to biotic and abiotic stresses and early maturity are important objective of rapeseed breeding programs in Iran and other countries. The phenomenon of heterosis of [F.sub.1] hybrids can also reflect special combining ability (SCA) and general combining ability GCA of parental lines. Combining ability concepts are the basic tools for improved production of crops in the form of [F.sub.1] hybrids. Identifying parental combinations with strong heterosis for yield and obtain genetic parameters are the most important steps in the development of new cultivars (Diers et al. 1996; Becker et al. 1999; Melchinger 1999), and heterosis effects are generally more pronounced in crosses between genetically distinct materials. The ultimate goal would be the development of hybrid cultivars of rapeseed that can potentially utilize the total amount of heterosis available. Griffing's biometrical analysis (Griffing 1956) has been widely used to aid plant geneticists in the selection of parents for hybridization. In most instances, the analysis provides reliable information on the combining ability of parents, i.e., the potential of parents to produce superior progenies following hybridization, and the magnitude of additive and non-additive gene action (Shattuck et al. 1993). According to Singh and Chaudhary (1985), it is appropriate to use the square components of the effects to indicate the corresponding type of gene activity. The genetic ratio, proposed by Backer (1978), shows how much of the observed variance can be explained by additive and non-additive effects. Genetic ratio values near the unit indicate a preponderance of additive effects. The purpose of this paper was to study the main genetic components involved in the characters of oil yield, oil percent and some important yield component traits including number of lateral branches per plant (NBP), number of pods per plant (NPP), number of seeds per pod of plant (NSP), length pod of plant (LP), thousand seed weight (SW), oil percent (OP) and oil yield (OY) by means of a diallel cross among nine parents chosen international rapeseed cultivars.