Articles written in Journal of Genetics

    • Identification and introgression of QTLs implicated in resistance to sorghum downy mildew (Peronosclerospora sorghi (Weston and Uppal) C. G. Shaw) in maize through marker-assisted selection

      H. C. Lohithaswa K. Jyothi K. R. Sunil Kumar Puttaramanaik Shailaja Hittalmani

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      Sorghum downy mildew caused by Peronosclerospora sorghi is a major disease of maize and resistance is under the control of polygenes which necessitated identification of quantitative-trait loci (QTLs) for initiating marker-assisted introgression of resistant QTLs in elite susceptible inbred lines. In the present study, QTLs for sorghum downy mildew (SDM) resistance in maize were identified based on cosegregation with linked simple sequence repeats in 185 F2 progeny from a cross between susceptible (CM500-19) and resistant (MAI105) parents. F3 families were screened in the National Sorghum Downy Mildew Screening Nursery during 2010 and 2011. High heritability was observed for the disease reaction. The final map generated using 87 SSR markers had 10 linkage groups, spanning a length of 1210.3 cM. Although, we used only 87 SSR markers for mapping, the per cent of genome within 20 cM to the nearest marker was 88.5. Three putative QTLs for SDM resistance were located on chromosomes 3 (bin 3.01), 6 (bin 6.01) and 2 (bin 2.02) using composite interval mapping. The locus on chromosome 3 had a major effect and explained up to 12.6% of the phenotypic variation. The other two QTLs on chromosomes 6 and 2 had minor effects with phenotypic variation of 7.1 and 2%. The three QTLs appeared to have additive effects on resistance. The QTLs on chromosomes 3 and 6 were successfully used in the marker-assisted selection programme for introgression of resistance to SDM in eight susceptible maize lines.

    • Development and application of genomic resources for comparative and translational genomics in legumes through leveraging genomic sequence of Medicago truncatula


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      The expressed sequence tags (ESTs) of common bean were BLAST aligned with barred medic genome sequence and developed 1196 conserved intron spanning primers (CISPs) to facilitate genetic studies in legumes. Randomly selected 288 CISPs, representing loci on barrel medic genome, were tested on 10 selected members of legume family. On the source taxa, the highest single copy amplification success rates of 61.8% (barrel medic) and 56.2% (common bean) was obtained. The success rate of markers was 54.5% in cowpea followed by 53.5% in pigeonpea and chickpea, signifying cross taxon amplification and their potential use in comparative genomics. However, relatively low percentages of primer set amplified (40–43%) in soybean, urdbean and peanut. Further, these primers were tested on different varieties of chickpea, pigeonpea and cowpea. The PCR products were sequenced and aligned which resulted in detection of 26 SNPs and eight INDeLs in cowpea, seven SNPs and two INDeLs in chickpea and 27 SNPs and 14 INDeLs in pigeonpea. These SNPs were successfully converted in to size variation for gel-based genotyping. The CISP markers developed in this study are expected to aid in map saturation of legumes and in marker-assisted selection for accelerated crop improvement.

    • Genetic characterization of maize doubled haploid lines for Fusarium stalk rot caused by Fusarium verticillioides


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      Fusarium stalk rot disease (FSR) of maize caused by Fusarium verticillioides (Sacc.) Nirenberg is becoming an importantbiotic production constraint in many of the major maize growing areas causing substantial yield losses. Inbreds are preferred as parents inhybrid development owing to homozygous nature and high heterotic ability. Double haploid (DH) technology has emerged as a significantmilestone. A total of 339 DH lines were generated from two inbred lines, VL1043 (susceptible) and CM212 (resistant), through in vivohaploid induction method. The 339 DH lines along with parents were phenotyped for their response to the FSR at the College ofAgriculture, V. C. Farm, Mandya, India during summer, kharif and rabi seasons of the 2019–2020. Best linear unbiased predictors (BLUPs)were estimated for the FSR disease scores over three seasons. Awide range of BLUP scores of three to nine indicated the presence of highervariation for response of DH lines to FSR disease. The higher estimates of standardized range (1.31) and phenotypic coefficient of variation(19.80) also displayed higher variability. Nine lines were moderately resistant and 188 exhibited moderately susceptible reaction. Thedistribution of DH lines was positively skewed (1.34) and platykurtic (2.31) which suggested complementary epistasis and involvement oflarge number of genes in the disease expression.

    • Discovery of SNPs in important legumes through comparative genome analysis and conversion of SNPs into PCR-based markers


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      Compared to cereal crops several legumes are less characterized at the genomic level and rightly referred as orphan crops. Transfer of knowledge between model and crop legumes allows development of orthologous pan-taxon genomic tools to benefit research on resource poor taxa. Here, we developed 278 intron flanking gene-specific markers by BLAST aligning pigeonpea (Cajanus cajan (L.) Millsp.) expressed sequence tags (ESTs) with complete genome sequence of barrel medic (Medicago truncatula). A random 192 PCRprimer pairs representing loci across the haploid genome (n = 8) of barrel medic were tested on a few important members of legume family. The single copy amplification rates of 31.8% (peanut, Arachis hypogaea) to 77.6% (barrel medic) signifies the success of cross taxon primers and suggested their potential use in comparative legume genomics. Genetic diversity was assessed in 48 pigeonpea genotypes using 143 intron flanking markers which revealed 71 polymorphic markers with PIC values ranging from 0.04 to 0.45 with an average of 0.23 permarker. The PCR products of different varieties of pigeonpea, cowpea and chickpea were sequenced and aligned to find putative SNPs. Integration of these newly developed markers into genetic maps in resource poor legumes will not only aid in the map saturation but also in designing successful marker-assisted selection programmes.

    • Consequence of cyclic pollen selection for heat tolerance on the performance of different generations in maize (Zea mays L.)


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      The reproductive stage in many crops, including maize, is very sensitive to heat stress and the genetic overlap between gametophytic and sporophytic phase gives an opportunity to select superior stress tolerant genotype at gametophytic stage. An attempt was made to evaluate the response of cyclic pollen selection in the F1 and F2 generations on the performance of F3 generation progenies for seed yield and yield contributing traits under natural heat stress conditions. In this direction three groups of F3 progenies, namely (i) pollen selection in F1 and F2 generations (GG), (ii) pollen selection only in F2 generation (CG), (iii) no pollen selection in F1 and F2 generations (CC) were screened for heat stress at Agricultural Research Station (ARS), Bheemarayanagudi. The GG progenies recorded significantly higher chlorophyll content, more number of pollen grains per anther and less pollen sterility compared to CG and CC group of progeniesunder heat stress. Further, the F4 progenies obtained through cyclic pollen selection (in F1, F2 and F3) were also tested for heat stress tolerance at seedling stage. The significant improvement for heat stress tolerance was recorded in F4 progenies derived through cyclic pollen selection as compared to control (no pollen selection for heat tolerance in any generation) F4 progenies. The results indicated that cyclic pollen selection in F1, F2 and F3 generations improved the heat stress tolerance of the progenies in the succeeding generations. To provide genetic evidence for the effect of pollen selection for heat tolerance, the control F2 (C) and selected F2 (G) populations were compared for the segregation of SSR markers. The selected F2 (G) population showed significant deviation from normal Mendelian ratio of 1:2:1 and showed skewness towards the alleles selected from male parent. The results provide strong evidence for an increase in the frequency of parental alleles in the progenies that impart heat stress tolerance.

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