Pak. J. Bot., 46(5): 1871-1875, 2014. COMBINING ABILITY FOR MATURITY AND PLANT HEIGHT IN BRASSICA RAPA (L.) SSP. DICHOTOMA (ROXB.) HANELT ADNAN NASIM 1 , FARHATULLAH 1* , NAQIB ULLAH KHAN 1 , SYED MUHAMMAD AZAM 1 , ZEESHAN NASIM 2 AND M. AFZAL 1 1 The University of Agriculture, Peshawar, Pakistan 2 Institute of Biotechnology and Genetic Engineering, Peshawar, Pakistan * Corresponding author’s e-mail: drfarhat@aup.edu.pk Abstract A 5 × 5 F 1 diallel cross hybrids of Brassica rapa (L.) ssp. dichotoma (Roxb.) Hanelt along with parents were evaluated through combining ability for days to flowering (initiation and completion), days to maturity and plant height. Highly significant differences were recorded for all the traits. Mean squares due to general, specific and reciprocal combining ability were significant for all the traits except plant height for which the latter two components were non-significant. Prevalence of additive (plant height), non-additive (days to flowering completion; days to maturity) and reciprocal effects (days to flowering initiation) were detected. Parental line G-403 was best general combiner for all the traits. The F 1 hybrids G-902 × G-265 (days to flowering initiation), G-902 × G-403 (days to flowering completion), G-265 × G-1500 (days to maturity) and G-909 × G-265 (plant height) were superior and may be exploited for future breeding programs. Key words: Brassica rapa, Diallel, Combining ability, Maturity, Plant height. Introduction Brassica occupies a prominent place in world's agrarian economy as vegetables, oilseed, feed, fodder, green manure and condiment (Malode et al., 2010). In Pakistan rapeseed and mustard is a major oil seed crop along with others. Brassica napus (canola) is generally has lower levels of glucosinolates and erucic acid, better in oil content and quality than rapeseed cultivars, but late maturing and susceptible to insects, particularly aphids (Ahmad et al., 2012).The domestic production cannot meet the national requirements and a considerable proportion is imported (Fayyaz et al., 2014). There is a huge production consumption gape which can be reduced by breeding improved cultivars (Azam et al., 2013) .The success in breeding programs of a crop species largely relies on the presence of genetic diversity in the germplasm and knowledge about the inheritance of various characteristics of the genotypes (Moghaddam et al., 2009). Early maturity and short stature variables are desirable from breeding perspective. Early harvest of Brassica is desirable to escape the crop from disease and aphid attack that normally coincides with the flowering stage (Kaur et al., 2009). Plant height is critical with respect to yield and agronomic parameters. Generally the dwarf varieties being resistant to lodging and more responsive to fertilizer were found high yielder than the tall ones (Rahman et al., 2009). Combining ability is a principal scheme to test the knack of the different inbred lines for substantiating their inclusion in future breeding programs on the basis of their GCA, SCA and RCA. Combining ability is the relative ability of an inbred to transmit desirable characteristics to its hybrids. GCA is “the average performance of a line in a series of hybrid combinations” whereas in SCA “certain combinations do relatively better or worse than would be expected on the basis of the average performance of the lines involved” (Sprague & Tatum, 1942). Breeding strategies may not result in appreciable improvement in the dearth of genetic variability and the knowledge of gene action operating in trait expression (Cheema & Sadaqat, 2004). In addition to identification of promising cross combinations, the combining ability is used to get information on inheritance of various traits of interest (Suchindra & Singh, 2006; Parmar et al., 2011). GCA component is largely a function of additive x additive genetic variance and that of SCA is prevalently due to non-additive genetic variance (dominance variance) but either would include various type(s) of epistatic interactions if it exists. The present study was therefore aimed to identify the superior general and specific combiners and to determine the mode of gene actions operative in expression of various traits. Materials and Methods The experiment was conducted during crop season 2011-12 at The University of Agriculture, Peshawar, Pakistan. Twenty five Brassica rapa (L.) ssp. dichotoma (Roxb.) Hanelt (syn. B. campestris var. brown sarson) genotypes (20 F 1 hybrids + 5 parental lines) were planted in a randomized complete block design with two replications. Each genotype was planted in two rows with row length of 4 meters each. Rows and plants spacing were kept 50 and 30 cm, respectively. Recommended cultural practices were followed from sowing till harvesting. Data were recorded and analyzed through Steel and Torrie (1980) and combining ability analysis was carried out according to Griffing (1956) Method-I, based on Eisenhart's Model-II. Results According to analysis of variance, highly significant differences were recorded for all the traits (Table 1), and then the data were subjected to combining ability analysis. The GCA, SCA and RCA mean squares were significant for all the traits except plant height for which the latter two components were non-significant (Table 2). The various effects, operative and prevalent mode of gene action are detailed below: