Genetic and Molecular analysis with respect to Yellow Vein Mosaic Virus Resistance in Mungbean (Vigna radiata)
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Date
2015
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Rajendra Agricultural University, Pusa (Samastipur)
Abstract
Mungbean, [Vigna radiata (L.) Wilczek], is one of the most important legume crop of Asiatic region. The production of mungbean is severely hampered by mungbean yellow mosaic virus (MYMV) caused by begmoviruses transmitted by white fly, Bemesia tabaci. Use of disease resistant crop varieties is regarded as an economical and durable method of controlling viral diseases. The advancements in the field of biotechnology and molecular biology such as marker assisted selection can be utilized in developing MYMV resistance mungbean genotypes. Taking into consideration the above aspects, the present study was aimed to evaluate mungbean genotypes for resistance to MYMV disease, to characterize mungbean genotypes based on molecular markers and to identify useful molecular markers in relation to MYMV resistance. A total of 35 genotypes of mungbean were screened for resistance against MYMV disease under field conditions and forced inoculation methods. The genotypes were scored on the basis of the degree of incidence of MYMV disease by using 1-9 rating scale and percent disease incidence for their classification into different infection categories. Based on overall response across the seasons, the genotypes IPM 02-14 and PDM 139 were rated as resistant. Highly susceptible response was observed in only one entry, LGG 450. Rest of the genotypes showed moderately resistant to highly susceptible reactions against MYMV. In general, the disease was found to be more severe during kharif season in comparison to summer season. The reaction pattern of the mungbean genotypes based on forced inoculation method was similar to that deduced on the basis of screening of the genotypes against MYMV disease incidence under natural conditions.
Eighteen genotypes, namely, IPM 02-14, PDM 139, Pant Mung 4, HUM 12, HUM 1, TMB 37, Pusa 9531, Meha, HUM 16, IPM 99-1-6, Pusa 105, AKM 8803, AKM 9910, Pusa 031, TARM 2, LGG 407, T 44 and LGG 450, were included in the SSR markers based assessment of genetic differentiation and divergence as they showed extremities for MYMV reactions under natural field conditions. Seeds were grown and young seedlings were used for genomic DNA amplification. A panel of 24 microsatellite based primer pairs covering 12 chromosomes in the genome of mungbean were used for genomic DNA amplification. The statistical methods and parameters used for deriving inference were polymorphism information content, similarity coefficient and numerical taxonomic analysis of divergence. Altogether, 183 allelic variants including 112 shared and 71unique allelic variants were generated at 37 loci among the 18 mungbean entries with an average of 4.95 alleles per locus. The primer pairs CEDG 008, CEDG 068 and CEDG 154 among the total primer pairs used in the present study were found to be highly informative. The microsatellite loci with di-nucleotide repeat motifs, in general, tended to detect relatively greater number of alleles than the repeat loci with tri- nucleotide repeat motifs and complex repeat motifs. Appearance of more than one band in the same genotype was noticed revealing the existence of the duplicated region in the genome of mungbean. Presence of stutter bands in the primer pairs, namely, CEDGAG 001, CEDG 037, CEDG 066, CEDG 091, CEDG 092, CEDG 127, CEDG 154 and CEDG 172 indicated the presence of minor amplified products that had lower intensity than the main allele and normally lacked or had extra repeat units. The magnitude of similarity coefficient between LGG 407 and T 44 was found to be the maximum amongst pair-wise combinations of entries. The SSR primer based analysis revealed unique or genotype specific allele which could be useful as DNA fingerprints in the identification and preservation of mungbean genotypes. The use of 24 microsatellite markers in the analysis exhibited a remarkably higher level of genetic polymorphism, which allowed unique and unambiguous genotyping of 18 entries included in the analysis.
Cross combinations involving the highly susceptible genotype LGG 450 in combinations with the resistant genotypes IPM 02-14 and PDM 139 were made for the development of F2’s (IPM 02-14 x LGG 450 and PDM 139 x LGG 450) and BC1’s (IPM 02-14 x LGG 450 x IPM 02-14 and PDM 139 x LGG 450 x PDM 139) as the mapping populations. Amongst these three genotypes, LGG 450 was agronomically superior and high yielding but highly susceptible to MYMV, while IPM 02-14 and PDM 139 were low yielders but resistant to MYMV. Out of the seven disease response associated SSR primers used, only the primer pair CEDG 008 was validated and found to be suitable for discrimination of resistant and susceptible types. The present study led to identification and validation of MYMV response related marker, CEDG 008, which may be further utilized for generating superior genotypes with durable MYMV-resistance and hopefully aid in the development of resistant cultivars in relatively shorter time span, in addition to selection of MYMV resistant lines, genetic diagnostics of MYMV and isolation of the gene responsible for resistance to MYMV.
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