Optimization of parameters for Agrobacterium mediated transformation of black gram (Vigna mungo L. Hepper) using cotyledon explants

Agrobacterium tumefaciens strain LBA4404 harbouring binary vector pCAMBIA 2301, which contains a neomycin phosphotransferase gene (nptII) and a β-glucuronidase (GUS) gene (uid A) was used for transformation of Vigna mungo cotyledon derived calli. Wounding of explants before infection, osmotic effects of infection and cocultivation media had an effect on the competence of the tissue as well as transforming ability of Agrobacterium cells. Transient GUS expression studies revealed that a cell density of 108 cells/ml, 100 μM acetosyringone and 330 μM cysteine were effective in increasing the transformation frequency and obtaining stable transformants with a 3.8% transformation efficiency. IBA pulse treatment was effective in root induction of kanamycin selected putative transformants. Molecular analysis using polymerase chain reaction (PCR) of nptII gene confirmed the transgenic nature of T0 transformants.Key words: Black gram, genetic transformation, Agrobacterium tumefaciens, cotyledon

Mapping of QTLs for morphophysiological and yield traits under water-deficit stress and well-watered conditions in maize

Maize productivity is significantly impacted by drought; therefore, improvement of drought tolerance is a critical goal in maize breeding. To achieve this, a better understanding of the genetic basis of drought tolerance is necessary. Our study aimed to identify genomic regions associated with drought tolerance-related traits by phenotyping a mapping population of recombinant inbred lines (RILs) for two seasons under well-watered (WW) and water-deficit (WD) conditions. We also used single nucleotide polymorphism (SNP) genotyping through genotyping-by-sequencing to map these regions and attempted to identify candidate genes responsible for the observed phenotypic variation. Phenotyping of the RILs population revealed significant variability in most of the traits, with normal frequency distributions, indicating their polygenic nature. We generated a linkage map using 1,241 polymorphic SNPs distributed over 10 chromosomes (chrs), covering a total genetic distance of 5,471.55 cM. We identified 27 quantitative trait loci (QTLs) associated with various morphophysiological and yield-related traits, with 13 QTLs identified under WW conditions and 12 under WD conditions. We found one common major QTL (qCW2–1) for cob weight and a minor QTL (qCH1–1) for cob height that were consistently identified under both water regimes. We also detected one major and one minor QTL for the Normalized Difference Vegetation Index (NDVI) trait under WD conditions on chr 2, bin 2.10. Furthermore, we identified one major QTL (qCH1–2) and one minor QTL (qCH1–1) on chr 1 that were located at different genomic positions to those identified in earlier studies. We found co-localized QTLs for stomatal conductance and grain yield on chr 6 (qgs6–2 and qGY6–1), while co-localized QTLs for stomatal conductance and transpiration rate were identified on chr 7 (qgs7–1 and qTR7–1). We also attempted to identify the candidate genes responsible for the observed phenotypic variation; our analysis revealed that the major candidate genes associated with QTLs detected under water deficit conditions were related to growth and development, senescence, abscisic acid (ABA) signaling, signal transduction, and transporter activity in stress tolerance. The QTL regions identified in this study may be useful in designing markers that can be utilized in marker-assisted selection breeding. In addition, the putative candidate genes can be isolated and functionally characterized so that their role in imparting drought tolerance can be more fully understood