Present status, Heterosis and combining ability studies of inbred lines for the development of hybrid genotypes in Brassica juncea L.    

By: Shehzad Ahmad Kang and Dr. Farooq Ahmad Khan, Department of Plant Breeding and Genetics, University of Agriculture, Faisalabad, Pakistan.

Pakistan imports huge quantity of edible oil by spending a big amount of foreign exchange due to which the importance of oilseed crops in our country is continuously increasing with every passing day. During the year 2010-11, 1.7 million tons of edible oil which amounted to 2.69 billion US dollars has been imported while the local production in 2010-11 is provisionally estimated at 696 thousand tons (Anonymous, 2010-11). The major oilseed crops comprise cottonseed, canola, rapeseed/mustard and sunflower that are helpful to some extent to fulfill the requirements of edible oil in the country. In our country, the share of oil extracted from species belonging to Cruciferae family is the third highest after cotton seed.

The genus Brassica belongs to Cruciferae family that includes a number of important species. These species produce roots, stems, leaves, buds and seeds condiment which are edible. Some species are used as oilseed crops and some are used as forage. Brassica juncea, an important species of this genus, is an important oilseed crop of the world. The oil content of Brassica juncea varies between 28.6 to 45.7% (Turi et al. 2006). Its oil, in Indian subcontinent, is mainly used for edible purposes, hair oil and lubricants. Its seed residue is used in fertilizers and as feed for cattle.

Brassica juncea has many advantages over other members of its family (B. napus and B. compestris) as it has great potential of seed yield, more resistant to shattering and has more drought tolerance (Turi et al. 2006). Its young tender leaves are used in salad and older leaves with stem are eaten fresh and also grown as vegetable in many parts of the world. It matures earlier than B. napus and therefore escapes the attack of aphid and hairy caterpillar (Noshin et al. 2003).

Brassica juncea is largely grown as an oilseed crop in Pakistan, China, India and also widely cultivated in Europe, Canada, Australia and Russia. In Pakistan, the rapeseed and mustard yield is generally low compared to that of other countries. In Pakistan, during 2010-11, rapeseed and mustard was cultivated on an area of 439 thousand acres and its seed production was 157 thousand tons contributing 50 thousand tons in total edible oil production of 696 thousand tons (Anonymous, 2010-11).

There are a number of factors that are responsible in low production of rapeseed and mustard in Pakistan. One important factor is the lack of improved and high yielding cultivars that can be helpful to some extent in reducing the of production and consumption gap of edible oil. In our country, the direct competition of Brassica with wheat and other Rabi fodders has squeezed its area and inputs.

Keeping in view the above facts, Government of Pakistan is trying to increase production of various oilseed crops to decrease the import. Different research institutes are working on rapeseed and mustard to enhance the production of this valuable crop through the development of superior varieties and hybrids. Farmers are getting advanced production technologies, guidance and awareness about the use of such valuable crops through various seminars, workshops and farmer days arranged by these institutes.

An important phenomenon in biology is hybrids show better growth and fertility over their parents (Darwin, 1876). Such hybrid vigor, or heterosis, was rediscovered nearly a century ago as an amazing agricultural fact that has been found to occur in many crop species (Shull, 1908). The importance of heterosis in agriculture is clear from the impressive increases in yield calculated over the past 50 years, following the entry of hybrids to crop production (Duvick, 1999). Heterosis enhances crop production by at least 15 percent which in combination with modern, high yielding inbreds and better agronomic techniques, has resulted in a constant increase in performance (Duvick, 2001)

Sprague and Tatum (1942) described the concepts of general combining ability (GCA) and specific combining ability (SCA). General combining ability and Specific combining ability are associated to additive and non additive genetic effects respectively (Rojas and Sprague, 1952). The information on combining ability and type of gene action that control the expression of different traits might be helpful in proper planning of a successful breeding programme. Griffing’s diallel analysis (Griffing, 1956) provides an efficient estimation of combining ability and nature of gene action involved.

The present research work was planned with the objectives to estimate heterosis and combining ability of Brassica juncea accessions for seed yield and other morphological traits. This will help to sort out the breeding material for exploitation in hybridization programme to evolve new varieties of B. juncea.

The present study was carried out in the experimental area of the Department of Plant Breeding and Genetics, University of Agriculture Faisalabad. The research work was planned with the objectives to estimate heterosis and combining ability of Brassica juncea accessions for seed yield and other morphological traits. This will help to sort out the breeding material for exploitation in hybridization programme to evolve new varieties of B. juncea. Six genotypes of Brassica juncea (CR 5, DP 18-9, DP 7-91, RAS 3189, 0714-A, INDIA III) were crossed in a complete diallel fashion during 2009-10. Seed obtained by these crosses and their parents were sown in a randomized complete block design with three replications during 2010-11. Plant to Plant distance of 30 cm and row to row 60 cm was maintained. All the agronomic practices recommended for Brassica were followed throughout growing season. Data were recorded on days taken to 50% flowering, days taken to 50% maturity, plant height, number of primary branches per plant, number of secondary branches per plant, number of siliquae per plant, number of seeds per siliqua, 1000 seed weight and seed yield per plant.

Results of analysis of variance showed significant differences among genotypes for all the traits studied. These results revealed that genetic variability existed in the breeding material that allowed analyzing the data further for heterosis and combining ability analysis. Mean values for days taken to 50% flowering ranged from 74.1-92.0, for days taken to 50% maturity 103.5-125.6, for plant height 192.1-213.8 cm, for number of primary branches 2.80-5.71, for number of secondary branches 20.8-31.0, for number of siliquae per plant 607.4-746.4, for number of seeds per siliquae 10.50-14.67, for 1000 seed weight 2.76-3.70 g and for seed yield per plant 20.80-30.14 g. Ranges reported in literature were 44.4-172.05 for days taken to 50% flowering, 129.7-182.0 for days taken to 50% maturity, 100.42-233.3 cm for plant height, 3.1-15.0 for number of primary branches, 2.4-35.03 for number of secondary branches, 54.79-648.7 for number of siliquae per plant, 7.0-18.90 for number of seeds per siliquae, 2.50-5.79 g for 1000 seed weight and 3.9-31.33 g for seed yield per plant. Our material was better for days taken to 50% flowering, days taken to 50% maturity, plant height and number of siliquae per plant while further improvements are required for number of primary branches, number of secondary branches, number of seeds per siliquae, 1000 seed weight and seed yield per plant.

The cross combination CR-5 × RAS 3189 had significant and positive heterosis for number of primary branches, number of secondary branches, number of siliquae per plant, number of seeds per siliquae, seed yield per plant and showed significant and negative heterosis for plant height. The cross DP 7-91 × INDIA III exhibited significant and positive heterosis for number of primary branches, number of secondary branches, number of siliquae per plant, number of seeds per siliquae, seed yield per plant and showed significant and negative heterosis for days taken to 50% flowering. The cross combination RAS 3189 × DP 7-91 had significant and positive heterosis for number of primary branches, number of secondary branches and seed yield per plant while exhibited significant and negative heterosis for days taken to 50% flowering, days taken to 50% maturity and plant height. The cross combination RAS 3189 × 0714-A showed significant and positive heterosis for number of secondary branches, number of siliquae per plant, number of seeds per siliquae, 1000 seed weight, seed yield per plant and showed significant and negative heterosis for plant height. The cross combination RAS 3189 × INDIA III had significant and positive heterosis for number of primary branches, number of secondary branches, number of siliquae per plant, number of seeds per siliquae and showed significant and negative heterosis for days taken to 50% flowering and plant height.

The mean sum of squares due to general combining ability were significant for all the traits except 1000 seed weight and seed yield per plant while the mean sum of squares due to specific combining ability and reciprocal effects were significant for all the traits under study. The values of GCA variance were higher compared to that of SCA variance and the values of additive variance were higher than dominance variance for plant height, number of primary branches, number of siliquae per plant and number of seeds per siliquae, which indicated the additive genetic component of variation controlling the expression of these traits. The values of SCA variance were higher compared to that of GCA variance and the values of dominance variance were higher than additive variance for days taken to 50% flowering, days taken to 50% maturity, number of secondary branches, 1000 seed weight and seed yield per plant, which indicated the preponderance of non additive genetic component of variation controlling the expression of these traits.

The parent INDIA III exhibited significant and positive general combining ability effects for plant height, number of primary branches per plant, number of secondary branches per plant and number of siliquae per plant. The parent DP 18-9 had significant and positive GCA effects for plant height, primary branches per plant, and number of siliquae per plant. These accessions may be used in future breeding programme for the improvement of seed yield of Brassica. The cross combination DP 7-91 × INDIA III had significant and positive specific combining ability for plant height, number of siliquae per plant, number of seeds per siliquae and seed yield per plant while six cross combinations CR-5 × DP 18-9, CR-5 × 0714-A, DP 18-9 × INDIAIII, DP 7-91 × RAS 3189, RAS 3189 × 0714-A and RAS 3189 × INDIAIII had significant and positive specific combining ability for three characters. These cross combinations may be further evaluated for development of improved hybrids with higher yield potential.

Corresponding author’s email: shehzadpbg@gmail.com

Courtesy: PAKISSAN Team