ABSTRACTGroundnut improvement, through conventional method of breeding may not be able to create desired variability on which a robust breeding programme could be built. Also, groundnut as a self- pollinating crop naturally would have less variability in its gene pool. Thus, the present study was conducted (i) To determine the sensitivity of two groundnut genotypes to different treatment doses of Sodium azide (ii) To determine the effective treatment dose of Sodium azide for induction of variability among the genotypes, and, (iii) To evaluate variability for some agronomic traits modified by Sodium azide treatment. Two groundnut genotypes SAMNUT 22 and SAMNUT 24, obtained from IAR were treated with 10 mM, 20 mM,30 mM,40 mM, and 50 mM of Sodium azide concentration at the groundnut improvement lab for 6 and 12 hours. Each of the treated seeds and the controls were sown directly to well-prepared seed bed in the field to obtain the M1 plants. During the off season, a set of 10 seed each were picked from each treatment for seed multiplication. A total of 24 M1 families were evaluated in a Randomized Complete Block Design(RCBD) with two replications in 2018, while a total of 72 M2 families were also evaluated in a 9 x 12 augmented design with 4 checks. Data were collected and significant differences (P<0.05) were observed for the effect of Sodium azide treatment on emergence count, and number of pods per plot (NPP) for all genotypes. Highly significant differences (P < 0.01) were observed for number of days to 50% flowering, number of branches, plant height and 100 seed weight for all the genotypes. Highly significant (P < 0.01) difference for genotype by dose interaction was observed for number of pods per plots (NPP). SAMNUT 24(t = 1.2) was more sensitive to Sodium azide treatment than SAMNUT 22(t=0.5). The mutagenic frequency recorded in the present investigation ranged from 29 % to 5 %. The mutagenic frequency varied across the different concentration, also a decreasing trend with increase in concentration of the mutagen was observed. The mutation frequency was found to be low possibly because of low physiological damage and the low response of groundnut at the maturity stage. The higher effectiveness and efficiency of Sodium azide treatment observed at 10 mM for 12hours of SAMNUT 24 indicates that lower doses were more effective in inducing variability in agronomic traits of groundnut. A decrease in mutagenic effectiveness with increase in concentration dose of the mutagen was also observed across the genotypes this is as a result of the failure in proportional increase of mutation frequency with the increase in concentrations/doses of the mutagen. The differences in the mutagenic effectiveness of the genotypes studied indicate that the genotypes responded differently to Sodium azide treatment. The Mutagenic efficiency did not follow any particular trend (increase or decrease), it varied across the mutagenic treatments. A high significant difference was observed among treatments, controls and interaction of emergence count and number of seeds per pod (NSP) in the M2. Analysis of variance for the different traits revealed highly significant difference among the 2 genotypes for all the agronomic traits studied. The existence of these differences indicates the presence of sufficient genetic variability among the genotypes for these traits. The phenotypic component of variation estimates, were generally higher than the Genotypic component of variation estimates for all the studied traits except for plant height which had higher genotypic component of variation, thus indicating a level of environmental influence on the expression of the traits. The M2 mutant, 10 mM6 SAMNUT 24 at 6hours recorded the highest 100-seed weight (123.0 g) among the other mutants while 50 mM2 SAMNUT 22 at 6hours recorded the highest shelling percentage (93.0). Mutant 50 mM1 SAMNUT 24 at 12 hours had the highest number of pods per plot (386.6), mutant 10 mM3 SAMNUT 24 at 6hours had the highest plant height (33.6), mutant 40 mM2 SAMNUT 22 at 6hours had the least days to 50% flowering (28), Mutant 20 mM4 SAMNUT 24 at 12 hours had the highest pod yield per plot. The mutants had higher and better value than their controls, thus the presence of variability induced by Sodium azide on the agronomic traits. For the improvement of cultivated groundnut, it is pertinent to use diverse collections with more variability and also employ the use of varying concentration, for the purpose of variety development and for use in future breeding program.
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