Abstract
An annual pulse crop cowpea (Vigna unguiculata (L.) Walp.), commonly named southern pea, is a nourishing constituent for the human diet and fodder. Gamma rays are a potent mutagenic agent to stimulate genetic variation with better characteristics, improving the yield relating traits in crops. Hence, the present study focused on exploring genetic variation between three generations in the mutant populations of cowpea through SCoT markers. The mutant populations of three successive generations, M1, M2 and M3, were induced by different doses [200, 400, 600, 800, 1000 and 1200 Gray (Gy)] gamma irradiation. The results depict that the quantitative characters were reduced by increasing the dosage of gamma irradiation in the M1 generation. In contrast, the second and third generation of plants showed a significant increase in yield and yield contributing traits than control and the maximum increase was noticed at 200 Gy and 400 Gy. Days to first flowering was delayed in irradiated plants than control of M1 generation. In contrast, in consecutive generations (M2 and M3), the early first flowering was noticed at 400 Gy and late flowering was observed at 800 Gy compared respectively to control and other doses. Seed yield per plant mean value was increased at 200 Gy in both generations (M2 and M3); it may produce new genotypes to desirable traits such as yield and quality. SCoT markers were used to explore genetic variation at the genomic level of mutant populations and screened with eight primers. Among them, seven primers showed amplification of 222 bands, in which 133 bands showed polymorphism. The polymorphic bands varied from 3.03–96.07%. The genetic variation, such as the number of different alleles (Na), effective number of alleles (Ne), Shannon’s information index (I), expected heterozygosity (He) and unbiased expected heterozygosity (uHe) showed an average value of 1.352 ± 0.092, 1.278 ± 0.027, 0.293 ± 0.023, 0.184 ± 0.016, and 0.194 ± 0.016, respectively. AMOVA depicted significant genetic variation between all generations and indicated a total of 95% within populations and 5% among population variation by the marker used. The present investigations prominently showed that the variations induced by gamma irradiation were inherited from successive generations of the improvement in cowpea quantitative traits. This investigation gives acceptable proof that the SCoT markers are a valuable tool to identify the genetic variation among the three generations of cowpea.
Highlights
Cowpea [Vigna unguiculata (L.) Walp.] is the most cultivated and consumed tropical grain legume, especially in Africa and Asian countries, which contain essential protein sources and rich in amino acids [1]
The present study focused on the effect of gamma irradiation in the yield and yielded contributing traits of three successive generations of cowpea and the genetic variability analysis using start codon targeted (SCoT) marker for M1, M2 and M3 generations of cowpea
Statistical analysis showed that day to first flowering depicts a significant negative correlation (p0.01) among yield characters; the yield was reduced at M1 generation (Table 6)
Summary
Cowpea [Vigna unguiculata (L.) Walp.] is the most cultivated and consumed tropical grain legume, especially in Africa and Asian countries, which contain essential protein sources and rich in amino acids [1]. Cowpea production was hindered by quality, low grain yields, and lack of improved cultivars [3]. Inducted mutation plays a vital role in creating variability for enhancing crop yield with desired traits. The physical and chemical mutagenesis creates genetic variation, produces new varieties with enhancing characteristics [4]. Mutation breeding can be a valuable technique to traditional breeding methods and have been successful in the improvement of qualitative and quantitative traits in many crops such as cowpea [5,6,7], soybean [8, 9], black gram [10,11,12]. Mutation breeding takes less time, easy to handle and is highly useful in producing crop cultivars than traditional breeding methods [13, 14].
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