Characterization and development of synthetic variety or hybrid genotypes in Canola (Brassica napus L.)    

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

The genus Brassica belongs to Cruciferae family that contains 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 fodder. Brassica napus L. is an important oilseed crop of the world. Brassica napus is a natural amphidiploid between Brassica campestris and Brassica oleracea. The oil contents of Brassica napus L. varies between 28.6 to 45.7% (Turi et al., 2006). Brassica napus L. have genome AACC and chromosome level 2n=4x=38. Edible oil is an important constituent for daily diet. Brassica seed oil has been important source of edible oil in Indo-Pak subcontinent especially Pakistan. Brassica napus has good seed production and oil quality characters i.e., early maturing and shattering resistant, low erusic acid and glucosinolate percentage than other Brassicas. Therefore, it has superiority over other Brassicas; because of these dominant traits it is counted to be the best future oilseed crop in the world. Its oil, in Indian subcontinent, is mainly used for edible purposes, hair oil, pickle and lubricants. Its seed residue is used in fertilizers and as feed for cattle.

Although Pakistan has made progress in agriculture, still it suffers from acute shortage of edible oil. Rape seeds and mustard are the second largest contributor after sunflower to the local vegetable oil production, the main reasons for low production of edible oil are due to direct competition of canola with wheat and Rabi fodders area and inputs are usually squeezed for canola. Moreover, due to the less attention for oil seed and genetic improvement of oil seed crops. The demand for oil seed is increasing due to the alarming increase in population, changing food habit and increase in per capita consumption of edible oil due to changing food habits of people. The more alarming indication is the gap between production and consumption of edible oil is that increasing every year. It is dire need to take measures to improve the production potential of domestic sources. The development of high yielding Brassica genotypes needs serious attention for improvement to overcome the shortage of edible oil. The improvement through breeding can be made successful by knowing the exact contribution of seed yield and other yield contributing traits.

Pakistan imports huge quantity of edible oil by spending enormous amount of foreign exchange due to which the importance of oilseed crops in the country is continuously increasing with every passing day. Local production of oil meets our needs is 696 thousand tons out of which the share of Brassica oil is second highest after cotton seed. During 2010-11 (July-March) 1.7 million tons edible oil which amounted to 2.69 billions US dollars has been imported (Anonymous, 2010-11). The major oilseed crops comprise viz. 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 second highest after sunflower oil.

Brassica napus has many benefits over other family members (Brassica juncea and Brassica compestris) as it has good potential for seed yield, good quality traits i.e. less than 30 micromoles glucosinolate per gram of oil free seed meal and less than 5% erusic acid in seed oil, more resistant to shattering and 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 Brassica juncea and therefore escapes the attack of aphid and hairy caterpillar (Noshin et al., 2003).

The Brassica species specially Brassica napus L. is one of the most important world sources of vegetable oil and due to spring and winter types of these species it is possible to be tolerant in the different climatic conditions (Huang et al., 2009). Due to restricted genetic basis of spring type of rapeseed varieties, winter type of rapeseed varieties can be suitable candidate for increasing yield potential and genetic variation of spring type in Winter x Spring type’s or semi winter type combinations (Qian et al., 2007).In oil seed rape seed breeding for hybrid and open pollinated varieties, general and specific combining ability effects (GCA and SCA) are important indicators of the potential of inbred lines in hybrid combinations. The line × tester analysis is one of the efficient methods of evaluating large number of inbred lines as well as providing information on the relative importance of GCA effects of lines and testers and also SCA effects of pairs of parental genotypes for interpreting the genetic basis of important plant traits. Estimation of genetic parameters for seed yield components is an important criteria of indirect selection for seed yield.

Brassica napus is grown on large scale as an oilseed crop in Pakistan, China and India as well as widely cultivated in Europe, Canada, Australia and Russia. In Pakistan, the rapeseed and mustard seed yield is generally low as compared to that of other countries. In Pakistan, during 2010-11 the rapeseed and mustard were 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).

Keeping in view the above facts, Government of Pakistan is trying to enhance the production of various oilseed crops to decrease the import bill. There are many oilseed research institutes in Pakistan working on rapeseed and mustard to increase the production of this valuable crop by the development of elite cultivars and hybrids. On the other hand, these institutes introduce advanced production technologies, seminars and workshops every year for the awareness of farmers and developing knowledge about the importance of such valuable crops.

An important phenomenon in biology, the hybrids show better growth and fertility over their parents (Darwin, 1876). Such hybrid vigour 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 due to maximum heterozygosity between inbred lines as follow the entry of hybrids to crop production over past 50 years (Duvick, 1999). Heterosis enhances crop production by at least fifteen percent which in combination with modern, higher seed yielding inbred lines and better agronomic techniques have resulted in constant increase in performance (Duvick, 2001)

Brassica species have high productivity i.e. good yield, and good agronomic characteristics.

Sprague and Tatum (1942) discovered 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). GCA promotes to develop synthetic variety and SCA lead to the development of hybrid genotypes. The information on combining ability and type of gene action that control the expression of different traits would help in proper planning of a successful breeding programme. Line x tester analysis (Kempthorne, 1957) provides an efficient estimation of heterosis and combining ability for GCA and SCA in Brassica napus L.

The present study was conducted in the experimental area of the Department of Plant Breeding and Genetics, University of Agriculture Faisalabad, Pakistan. Sixteen genotypes (120-R, B9527-1, MANROO, COMET, S-9, KN (20-35), UAF-1, N-RG, 20E, HYBRIPOL, V-22, STAR, 5-F, GOLARCHI, CRS-5, PO-9) were crossed in a Line×Tester 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 napus L. were followed throughout growing season. Data was 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.

Analysis of variance revealed significant difference in different genotypes for all characters studied. These results expressed that genetic variation found in breeding material that permitted data for further heterosis and combining ability analysis. The mean values for days taken to 50% flowering ranged from 76.0-99.0.The cross combination N-RG×KN(20-35) had maximum mean value (99.0) for days taken to 50% flowering. The mean values for days taken to 50% maturity ranged from 100.0 to 121.0. Among hybrids, the cross combination Among the hybrids CRS-5×120-R , S-9×B9527-1 showed minimum (102.0) mean value. The mean values ranged from 176.66-221.00 cm while the hybrid GOLARCHI×5-F showed maximum mean value 221.00 cm for plant height. For the trait of the number of primary branches per plant, the mean values ranged from 2.0-7.0 whereas the hybrid MANROO×5-F expressed maximum mean value (7.0). The mean value for the trait of number of secondary branches per plant ranged from 25.0-39.0 and the cross CRS-5×20E had highest mean value (39.0). The number of siliquae per plant ranged from 936.0-1256.0 while the hybrid CRS-5×KN(20-35) indicated maximum mean value (1256.0). The mean values ranged from (15.0-21.0) whereas the cross combination CRS-5×B9527-1 revealed highest mean value 20.0 for number of seeds per siliquae. The mean values ranged from 2.80-3.98 g and the hybrid S-9×5-F had highest mean value 3.98 g for 1000 seed weight. The mean values for seed yield per plant ranged from 21.20-44.50 g and the crossed material MANROO×B9527-1 expressed maximum mean value 44.50 g. Our material were better for all traits except 1000 seeds weight and seeds yield per plant while further improvements are required for both viz. 1000 seeds weight and seed yield per plant.

Out of 55 hybrids, fifty cross combinations showed significant negative heterosis over both mid and better parent whereas only three hybrids revealed significant results but positive heterosis over better parent for days taken to 50% flowering. For days taken to 50% maturity, only seventeen hybrids showed significant positive (nine) and negative (eight) heterosis over mid parent whereas fifteen crosses revealed significant positive (three) and negative (twelve) heterosis over better parent. For plant height, Out of 55 hybrids, Thirteen cross combinations show significant results for both mid better parent heterosis. Among these genotypes, nine hybrids showed significant positive (six) and significant negative (three) heterosis over mid parent while four genotypes showed significant results over better parent in both positive and negative direction respectively.

Eighteen hybrids showed significant and positive heterosis over better parent and twenty four hybrids expressed significant and negative heterosis over better parent Number of primary branches per plant. For the trait number of secondary branches per plant, thirty one genotypes revealed significant heterosis over mid parent while twenty one hybrids exhibited significant heterosis over better parent. Fourty four crosses indicated significant heterosis over mid parent whereas thirty genotypes expressed significant heterosis over better parent for the number of siliquae per plant. For number of seeds per siliquae fifteen hybrids showed significant heterosis over mid parent while only seven genotypes exhibited significant heterosis over better parent. Fourty eight hybrids indicated significant results heterosis over mid parent whereas thirteen cross combinations revealed significant heterosis over better parent for the trait of 1000 seeds weight. For seed yield per plant, Fourty nine genotypes exhibited significant heterosis results over mid parent while fourty seven hybrids indicated significant heterosis over better parent for seed yield per plant.

For combining ability analysis, The mean sum of squares due to lines were significant for all the traits except plant height and for testers while non significant results were found for traits of plant height and number of siliquae per plant. Highly significant results were found in line x tester interaction for all traits except the character days taken to 50% maturity. The estimates of SCA variance was noticed higher than GCA variance in all traits. But the variance ratio GCA/SCA estimated to be zero in character of 1000 seed weight. The contribution of lines x testers were revealed higher in case of days taken to 50% flowering, plant height, primary branches per plant, secondary branches per plant,1000 seed weight and seed yield per plant but the variance ratio showed very low in the traits of days taken to 50% maturity and number of seeds per siliqua. The parent N-RG showed highly significant result for positive GCA effect whereas the hybrid PO-9×5-F was best specific combiner followed by COMET×5-F hybrid for the trait days taken to 50% flowering. For days taken to 50% maturity, the genotype HYBRIPOL was best general combiner and the hybrid V-22×B9527-1 (7.90) was the best specific combiner. For plant height, the parent genotype S-9 was best general combiner whereas the hybrid MANROO×20E (-28.1) was best specific combiner. All parents and hybrids revealed non significant results for both GCA and SCA effects for number of primary branches per plant, number secondary branches per plant and number of seeds per siliqua. For Number of siliquae per plant, the STAR (line) and 20E (tester) were the best general combiner while the hybrid STAR×20E was the best specific combiner. The line PO-9 was best general combiner whereas the hybrid V-22×KN(20-35) was the best specific combiner for 1000 seeds weight. In the seed yield per plant the line N-RG revealed the best general combiner and The genotype V-22×KN(20-35) noticed the best specific combiner. The hybrids which have the best specific combining ability may be further evaluated for the development of improved hybrids with higher yield potential in Brassica napus L.

Corresponding author’s email: shehzadpbg@gmail.com

Courtesy: PAKISSAN Team