VALIDATION OF MOLECULAR MARKERS LINKED TO YMD RESISTANCE AND GENETIC ANALYSIS OF YIELD COMPONENTS IN BLACK GRAM [VIGNA MUNGO (L.) HEPPER]
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Date
2023-12-03
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Acharya N G Ranga Agricultural University
Abstract
The present investigation was carried out with the chief objectives of assessing the role of different non-allelic interactions in the inheritance of various traits of black gram and to validate the reported molecular markers linked to YMD. Other parameters like mean, variability, heritability, expected genetic advance, correlation analysis, path coefficient analysis and divergence studies were also carried out for the 40 black gram germplasm lines. The required field experiments to achieve the targeted objectives were conducted at RARS, Lam, Guntur during 2019-20 and 2020-21 and the molecular biology experiments were carried out at Agricultural College, Bapatla during 2020-21.
The analysis of variance indicated significant differences among the 40 genotypes for all the traits under study. High PCV and GCV were recorded for plant height, clusters per plant, pods per plant and grain yield per plant. The estimates of heritability and genetic advance as per cent of mean were high for the characters viz., plant height, clusters per plant, pods per plant, seed per pod and grain yield per plant indicating the probable operation of additive gene action in inheritance of these traits and simple selection is sufficient to improve these traits. Considering the nature and magnitude of character associations and their direct and indirect effects, it can be inferred that clusters per plant, pods per plant, seed per pod, pod length, test weight and days to maturity could serve as important traits in any selection programme for selecting high yielding genotypes in black gram.
The D2 analysis grouped the 40 black gram genotypes into ten clusters. It revealed maximum divergence between clusters IV and IX, followed by clusters VIII and IX, clusters VII and IX and clusters II and IX suggesting that there is wide genetic diversity between these clusters. The genotypes from these clusters which are having better per se performance may result in superior transgressive segregants depending on the gene action. The PCA analysis identified that the maximum contributing traits towards the existing variability are days to 50% flowering, days to maturity, plant height, pod length, clusters per plant, grain yield per plant, branches per plant and seed per pod. It also revealed that the first three principal components contributed 79.592 per cent towards the total variability. Further, the diverse
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genotypes PU 31, LBG 623, IPU 94-1, TU 94-2, GAVT 7, UAHS BG 1 and Vamban 8 which are far apart from each other in the two dimension and three dimension diagrams may result in good hybrid combinations to produce transgressive segregants in their respective F2 and subsequent segregating generations.
The 40 germplasm lines phenotyped for YMD, exhibited high range of variation with respect to the disease reaction. Fifteen genotypes recorded no visible symptoms or even small yellow specks with restricted spread on foliage, indicating that they are resistant to yellow mosaic disease. These genotypes could be utilized as donors for transfer of disease resistance into agronomically superior genotypes which are lacking disease resistance.
The results of generation mean analysis indicate that additive-dominant model is adequate only for one trait i.e. test weight. All other ten traits viz., days to 50% flowering, plant height, branches per plant, clusters per plant, pods per plant, pod length, seed per pod, days to maturity, grain yield per plant and reaction to YMD had significance for one or more scaling tests and also had significant Chi-square values of joint scaling tests. This clearly indicate the inadequacy of additive-dominant model to explain inheritance in these traits. Hence, the estimates of inter-allelic or non-allelic gene effects were obtained using six parameter model of generation mean analysis. In spite of having significant additive [d] and dominance [h] components, the non-allelic interactions overpowered them due to their higher estimates hence, had a great role in the inheritance of these ten traits. Inadequacy of additive-dominant model for explaining the inheritance of the ten out of eleven traits emphasizes the complex nature of gene effects suggesting that simple selection procedures may not be sufficient to improve the yield and its contributing traits.
From the results of the studies pertaining to validation of molecular markers reported to be linked to YMD resistance, it was found that four reported markers viz., CYR 1, YR 4, DMB-SSR 158 and MYMVR-583 could only produce monomorphic bands and could not differentiate the resistant and susceptible genotypes. With regards to the remaining three molecular markers, it was found that they could only differentiate few lines as resistant or susceptible. And in considerable number of genotypes these markers did not co-segregated with the phenotype. There are many deviations from the expected amplification of the target fragment in both resistant and susceptible genotypes. This clearly suggest that these markers failed in differentiating resistant and susceptible genotypes.
The claim made by the researchers that the reported markers (at least the three markers which are producing polymorphic bands) were linked to resistance, need not be differed as they have used mapping populations in developing these markers. However, there might be few more genes that are responsible for complete resistance against YMD and are need to be identified using mapping populations produced from parental lines having varying degree of genetic background. Further, the amplification of amplicons linked to resistant genes in phenotypically susceptible genotypes indicate that the marker is not tightly linked to the gene of interest and might be segregated and separated due to crossing over between the marker and the gene in question. Hence, to identify YMD resistant line, tightly linked markers for all the genes responsible for resistance need to be identified.