PHENOTYPIC, BIOCHEMICAL AND CYTOLOGICAL STUDIES OF GAMMA RAYS INDUCED RAPESEED MUTANT POPULATIONS

Abstract

In order to appraise use of induced mutations for rapeseed breeding (B. napus) study was carried out. The gamma irradiation doses of 0.8, 1.0, and 1.2 kgy showed overall depressive effects on rapeseed plants in M 1 generation. The highest gamma irradiation recorded the highest reduction effects in emergence and in survival percentage leading to greater lethality as compared to control plants of parental variety Abasin-95. The induced morphological and chlorophyll mutations were studied in M 2 segregating populations under two diversified agro-climatic environments of Kaghan (elevation of 2030 m) and Peshawar (elevation of 510 m). The gamma dose at 1.0and 1.2 kgy induced the highest mutation frequency at Kaghan and Peshawar respectively. The gamma dose 0.8 kgy showed higher mutagenic efficiency and effectiveness compared to rest of the treatments. Viable mutations of interest such as modification in seed size and variation in seed color were noticed in high frequency in all gamma treated populations at both environments. Induced variability for quantitative traits including flowering, plant height, branches, pod length, seeds pod -1 , seed weight, oil content, protein, linolenic acid, oleic acid, erucic acid and glucosinolate content in individual M 2 mutant plants was estimated using Principal Component Analysis (PCA). Higher induced variability for yield and yield components, and plant maturity was noticed at Peshawar while at Kaghan more variability was observed for oil content and oleic acid traits in mutant populations. Comparative molecular cytogenetic study of rapeseed mutant plants and parental variety Abasin-95 was carried out. The FISH experiments designed with double target approach and of 5S rDNA and 25S rDNA probes. Chromosomes of all mutant lines were morphologically similar but had variability in number. Some of the mutant lines were aneuploid had a range of 37 to 35 chromosomes. The gamma irradiation significantly increased the frequency of changed cells in mutant plants as compared to untreated parental plants. Ribosomal DNA sites were effectively stained and eight pairs of chromosomes with chromosomal base type I- VIII in cells of parental cultivar Abasin-95 was observed. In addition to the occurrence of base type I chromosomes, a new chromosome type I 2 with rDNA sites was observed in the cells of mutant line RMN-200. A comparative analysis of 5S, 25S and double targeted (5S+25S) rDNA distribution in successive generations disclosed high polymorphism in mutant plants in comparison to their respective control. All three types of rDNA markers confirmed significant increase in number of rDNA sites in mutant plants (21) as compared to control (17). Presence of two groups of rDNA in abundant loci in very different chromosomal locations in rapeseed was confirmed in present study. Simultaneously FISH with 5S and 25S rDNA probes also identified inter-genomic and inter-individual polymorphism and chromosomal variations in rapeseed mutant plants. Rapeseed mutant lines of M 5 generation with modified oilcontent of parental variety Abasin-95 was used to investigate genotype and environment interaction and performance stability. Combined analysis of variance for pooled data over three locations namely Peshawar, Faisalabad, and Tandojam for two years showed significant differences among the mean squares for locations, years and genotypes and genotype and environment interaction for seed yield, and oil content. The mutant lines RMN-34 and RMN-14 significantly out yielded the rest of the mutant lines for both traits. The contribution of locations to total variation was higher (73.77 for seed yield & 93.20% for oil yield) as compared to (11.12 & 4.33%) of genotypes and G x E interaction (7.81%). GGE biplot divided environments in major rapeseed growing regions in Pakistan into four subsets. The graphic biplots of mutant genotype seed yield means and their stability suggested four different genotype groups. Group one highly desirable which was high yielding with high stability such as mutant lines RMN-847 (2n=36-38) and RMN-14 (2n=38). The group with high yield but low stability is desirable for specific selection such as specialty rapeseed oil as in case of mutant genotypes, RMN-34 (2n=38), whereas low yield and low stability mutant lines RMN-2111, (2n=38) and RMN-1191 (2n=35-38) were possible candidates for special breeding purposes such as disease or drought resistance selection. The most undesirable mutant genotype was RMN-200 (2n=38) with low yield but high yield stability. Rapeseed mutant genotype RMN-200 performed poorly for yield in all the three test locations. The mutant lines RMN-847, RMN-14 and RMN-34 along with parental cultivar Abasin-95 expressed more adaptability over test locations.