CONSTRUCTION OF LINKAGE MAPPING AND IDENTIFICATION OF QUANTITATIVE TRAIT LOCI (QTL) FOR EARLINESS, GRAIN SIZE AND LEAF RUST RESISTANCE IN BREAD WHEAT (Triticum aestivum L.) 2538
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Date
2018-06
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JAU,JUNAGADH
Abstract
Present experiment was carried out at the Biotechnology Laboratory of the Department of Genetics and Plant Breeding, J.A.U., Junagadh during the year 2014 to 2017. The experimental material comprised of P1, P2, F1, F2 and F2:3 generations of two wheat crosses viz., GW-11 X GW-322 and DL-788-2 X GW-322 especially for grain size related traits and earliness related traits, respectively to fulfill the objective of linkage and QTL mapping as well as to estimate gene effects using means of the five generations for grain yield and its components in bread wheat.
Out of 200 SSR markers screened for parental polymorphism for grain size and related traits, about 23% of SSR markers showed good polymorphism between two parental lines. Out of 46 tests for calculated chi-square, 42 test markers do not deviate significantly from expected ratios revealing that observed data are in agreement with expected ratio of 1:2:1. The linkage map was constructed using software IciMapping v.4.1. Recombination frequencies were converted into map distance using Kosambi’s mapping function. The markers were grouped with minimum logarithm of the odds (LOD) of 3.0 with walking speed was set at 1.0 cM. Seven linkage groups with a total map length of 77.31 cM were constructed using data from 46 SSR marker loci for 74 F2 plants which ranged from minimum of 2.74 cM (LG2) to maximum of 26.89 cM (LG3).
In case of earliness and related traits, out of 200 markers screened, only 11% of SSR markers showed good polymorphism between two parental lines. Out of 22 tests, all the test markers showed non-significant chi-square which revealed that observed data are agreement with expected ratio of 1:2:1 segregation ratio. Four linkage groups with a total map length of 267.12 cM were constructed using data from 22 marker loci for 74 F2 plants that ranged from minimum of 8.62 cM (LG4) to maximum of 126.56 cM (LG1).
Genotypic data of F2 and phenotypic data of on 74 F2:3 lines were analyzed for identification of the main effect QTLs using the software ICIM-ADD mapping in QTL IciMappingV4.1. A linkage map of grain size related traits output data file was used for the construction of QTL mapping. A total six QTL had been identified for grain size and related traits, one each for 100-grain weight (LG3 at 13 cM, LOD 6.68, 42.20 PVE%); number of grain per main spike (NGPMS) (LG4 at 4 cM, LOD 3.28, 19.48 PVE%); grain
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yield per plant (GYPP) (LG5 at 14 cM, LOD 7.17, 36.25 PVE%); number of effective tillers per plant (NETPP) (LG7 at 3 cM, LOD 14.34, 59.17 PVE%); and two QTLs for grain weight per the main spike (GWPMS) (LG3 at 20 cM, LOD 4.64, 15.29 PVE% and LG6 at 11 cM, LOD 12.29, 58.03 PVE%). Similarly, earliness and related traits output data file of linkage map was used for the construction of QTL mapping. One QTL was identified for days to 50% flowering (LG1 at 58.0 cM, LOD 3.06, 18 PVE %) and two QTLs for days to maturity (LG1 at 21 cM, LOD 8.89, 31.51 PVE% and LG3 at 38 cM, LOD 12.83, 45.16 PVE%).
Scaling tests C and D and joint scaling test showed non-significant chi-square and hence additive-dominance model was found adequate for grain yield per plant and 100-grain weight in the cross GW-11 x GW 322 and length of main spike in the cross DL 788-2 x GW 322. In three-parameter model, only mean (m) effect was found significant in above three cases besides significance of additive (d) and dominance (h) effects for length of main spike in cross DL 788-2 x GW 322.
Significant chi-square in joint scaling test confirmed the results obtained in individual scaling test C and D in both the crosses (except above three cases) indicating the presence of epistasis. The five-parameter model revealed that in addition to the significance of m, (d) and (h) effects, both (i) and (l) were significant for number of grains per main spike and biological yield per plant in cross GW 11 x GW 322 and days to 50% flowering, plant height, number of spiklets per main spike, peduncle length of main spike days to maturity, number of grains per main spike, grain yield per plant and biological yield per plant in the cross DL 788-2 x GW 322. The hybrids showing epistasis had significant and positive dominance (h) effect for days to maturity and number of grains per main spike in both the two crosses and plant height and peduncle length of main spike in the cross DL 788-2 x GW 322.
Wider phenotypic range and higher co-efficient of range was observed in F2 generation as compared to F2:3 generation for days to 50% flowering, plant height, number of grain per main spike, grain weight per main spike and biological yield per plant GW-11 X GW-322 as well as for plant height, number of grain per main spike, grain weight per main spike and harvest index in DL 788-2 x GW 322. High estimates of heritability (above 60%) coupled with high genetic advance as per cent of mean (above 20%) was observed in both F2 and F2:3 generations for plant height, number of effective tillers per plant and grain yield per plant in GW-11 X GW-322 as well as for plant height, number of effective tiller per plant, peduncle length of main spike, grain yield per plant, biological yield per plant, harvest index in DL 788-2 x GW 322.
Key words: Linkage mapping, QTL mapping, SSR marker, Gene effects, Bread wheat
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BIOTECHNOLOGY