K. Madhavi Reddy

Isolation, characterization and evolution of NBS-LRR encoding disease-resistance gene analogs in eggplant against bacterial wilt

Bacterial wilt (causal organism-Ralstonia solanacearum) is one of the most important soil-borne diseases of eggplant (Solanum melongena) worldwide. The best way to control it economically is to develop cultivars resistant to this soil-borne pathogen. Resistance gene (R-gene) cloning and sequencing to obtain resistance gene analogs (RGAs) is one of the most recent approaches for obtaining disease resistant cultivars. Three different types of degenerative PCR based primers were used for isolating RGAs from resistant cultivated/wild species through amplification of the target region of nucleotide binding site-leucine rich repeat (NBS-LRR). Genetic diversity was observed in the sequences isolated, and six sequences showing specific conserved motifs were shortlisted as Solanum melongena RGAs (Sm7RGA1, Sm7RGA2, Sm7RGA4, Sm7RGA8 and Sm7RGA10) and Solanum viarum RGA (SvRGA2). The RGAs isolated in this study belong to both toll interleukin-1 receptors (TIR)-NBS-LRR and non-TIR-NBS-LRR type R-genes and show similarity with other plant resistance genes. This study also confirmed the hypothesis that dicots have both TIR and non-TIR resistance genes. The present study on eggplant RGAs will help develop RGA based markers linked to bacterial wilt in eggplant and other plant species. Further, it will provide information and pave the way for elucidation at the molecular level of wild and cultivated species’ mechanism of resistance to bacterial wilt. This is the first report of NBS-LRR class resistance genes/RGA in resistant eggplant and its wild relatives against bacterial wilt (BW).

RETRACTED ARTICLE: Genetic inheritance and identification of a resistance gene analogue polymorphic (RGAP) marker linked to Chilli veinal mottle virus resistance in chilli (Capsicum annuum L.)

ABSTRACTChilli veinal mottle virus (ChiVMV) is a most destructive virus, which causes severe yield losses in pepper. Host plant resistance is the only option to tackle this problem. Eleven ChiVMV-resistant lines were selected from an initial screening of chilli pepper germplasm and their resistance was reconfirmed by artificial inoculation. To understand the genetic basis of inheritance and to identify a resistance gene analogue polymorphic (RGAP) marker associated with resistance, the ChiVMV-resistant chilli pepper line ‘IHR 2451’ (Parent 1) was crossed with the ChiVMV-susceptible line ‘IHR 3476’ (Parent 2) to develop six generations. Individual plants from all six generations (35 P1, 50 P1, 30 F1, 200 F2, 44 B1, and 41 B2) were artificially inoculated with ChiVMV (Bengaluru isolate) and the pattern of segregation of susceptibility or resistance was investigated using the chi-square (χ2) test. All F1 progeny plants were susceptible to ChiVMV. The pattern of segregation of resistant and susceptible plants...

Inheritance of Root Traits in an Interspecific Cross of Capsicum annuum × C. chinense in the Presence of Low Moisture

ABSTRACT Productivity of hot pepper (Capsicum annuum L.) is constrained when available moisture is not adequate. Capsicum genotypes with deep, strong roots enable plants to take up a higher volume of water when moisture is lacking, resulting in a more favorable plant water status. Little information is available on the genetic inheritance of root traits in peppers. The genetic components governing expression of root traits under low moisture were studied through six-generation mean analysis in an interspecific cross of IHR 3453 (Capsicum annuum) × IHR 4502 (C. chinense) of contrast root traits. The six generations (30 P1, 30 P2, 30 F1, 247 F2, 43 B1, and 47 B2) were developed and evaluated for root traits under low available moisture. Overall, root traits and shoot dry weight are complex in inheritance; additive and nonadditive components were important, indicating that reciprocal recurrent selection is the most effective breeding method for improving these traits. The dominance component (h) was highly significant and predominant in controlling most traits, except for root length. High heritability and high genetic advance over the mean indicate that selection is effective; however, it needs to be postponed to later generations. Recurrent selection, bulk pedigree, and single-seed descent methods were the most efficient strategies for improving root traits in Capsicum.

Isolation, characterization and genetic diversity of NBS-LRR class disease-resistant gene analogs in multiple virus resistant line of chilli (Capsicum annuum L.)

Viruses are serious threat to chilli crop production worldwide. Resistance screening against several viruses resulted in identifying a multiple virus resistant genotype ‘IHR 2451’. Degenerate primers based on the conserved regions between P-Loop and GLPL of Resistance genes (R-genes) were used to amplify nucleotide binding sites (NBS)—encoding regions from genotype ‘IHR 2451’. Alignment of deduced amino acid sequences and phylogenetic analyses of isolated sequences distinguished into two groups representing toll interleukin-1 receptor (TIR) and non-TIR, and different families within the group confirming the hypotheses that dicots have both the types of NBS-LRR genes. The alignment of deduced amino acid sequences revealed conservation of subdomains P-loop, RNBS-A, kinase2, RNBS-B, and GLPL. The distinctive five RGAs showing specific conserved motifs were subjected to BLASTp and indicated high homology at deduced amino acid level with R genes identified such as Pvr9 gene for potyvirus resistance, putative late blight resistance protein homolog R1B-23 and other disease resistance genes suggesting high correlation with resistance to different pathogens. These pepper RGAs could be regarded as candidate sequences of resistant genes for marker development.

Capsicum (Hot Pepper and Bell Pepper)

Capsicum is one of the most widely consumed vegetables and is also used as a spice for its pungency. Many species of Capsicum are being cultivated worldwide. Capsicums are considered as a commercial crop for their economical value. However, the yield of the crop suffers severely due to abiotic and biotic factors. Among the various abiotic stresses, low moisture and high temperature are the major constraints for productivity. Flowering and fruit-set stages were most sensitive for the abiotic stresses. Wide genotypic variability for abiotic stress tolerance is present in Capsicum species. Significant differences in fruit-set, yield, photosynthetic rates, stomatal conductance, total chlorophyll content, proline, and root characteristics have been reported. Pollen germination and fertilization were better in the tolerant capsicum varieties. Higher activities of hexokinase, phosphofructokinase and invertase in the pollen were responsible for the better pollen germination in the tolerant genotypes. Lesser oxidative stress and better antioxidative enzymes were observed as one of the tolerance mechanisms in the capsicum genotypes. Breeding for abiotic stress tolerance has also been attempted and a few cultivars have also been developed in hot pepper using root characteristics and yield as selection parameters under stress. Transgenic plants have also been developed using osmotin gene overexpression and also by overexpressing certain transcription factors. Enriching the soil microbia with mycorrhiza, Arthrobacter and Bacillus species has given encouraging results in giving abiotic stress tolerance. The use of chemicals like brassinolides, sitosterols, and nitric oxide has been found to improve the tolerance in capsicums. In spite of these management practices, crop improvement, transgenic approaches to overcome the abiotic stresses and emphasis for rootstock breeding is lacking. Therefore, future studies should focus on root and flower traits and also on rootstocks to overcome the abiotic stress in addition to the stress management practices.