PhD.

Brinjal or Eggplant [Solanum melongena L. (2n = 24), family: Solanaceae] is an important vegetable grown worldwide in tropical and subtropical regions. It is attacked by several diseases and insect pests which led to lower yield potential and it is varies from location and season. Among the various biotic stresses, bacterial wilt disease and shoot and fruit borer are most devastating stresses and they are widely dispersed throughout brinjal growing areas of the world. The management of these two biotic stresses by cultural, biological and chemical methods is difficult due to the soil-inhabitant nature of the wilt pathogen and internal feeding nature of insect pest. Developing host plant resistance using germplasm in gene banks is an effective method to mitigate these stresses. In this context, the present investigation entitled “Introgression of resistance to bacterial wilt and shoot and fruit borer in brinjal (Solanum melongena L.)” was done following three-way cross mating design during July 2022 to November 2024. One hundred and one genotypes belonging to four Solanum species were screened against bacterial wilt in the sick plot at NBPGR, Vellanikkara, in randomized block design (RBD) from June to December of 2022. Out of these , 19 were highly resistant (0% plants wilted), 12 were resistant (1-20% plants wilted), 26 were moderately resistant (21-40% plants wilted), 19 were moderately susceptible (41-60% plants wilted), 19 were susceptible (61-80% plants wilted), and 6 were highly susceptible (>80% plants wilted) based on per cent disease incidence (PDI). The highly resistant genotypes were used for confirmatory screening in the next experiment. The second experiment involved pot culture for bacterial wilt resistance screening, yield and quality to select suitable resistant genotypes for hybridization. The bacterial wilt pathogen was isolated, cultured, and confirmed through morphological and molecular characterization. Seedlings were transplanted in grow bags in a completely randomized design (CRD) from December 2022 to June 2023. Artificial screening was conducted one month after transplanting, by drenching virulent bacterial suspension at the injured portion and wilting symptoms recorded periodically. One accession, IC624213 (S. violaceum) was identified as highly resistant followed by thirteen as resistant and four as moderately resistant to bacterial wilt. The genotypes showed significant variation for yield and related traits. Organoleptic evaluation of fruits was conducted with 21 descriptors. It showed significant variation in odour, appearance, texture, flavor, taste, and overall quality attributes. A selection index was constructed by giving equal weightage to bacterial wilt resistance, yield, and overall quality of the fruits. The top two ranked genotypes, IC636521 and IC624240, were selected for a three-way cross hybrid breeding program. The five selected parents viz., Ponni, Vengeri, IC618016, IC636521 and IC624240 were crossed in half-diallel fashion and produced ten single cross hybrids.
These hybrids were evaluated for brinjal shoot and fruit borer resistance (BSFB) and yield from January to June 2024. The mean per cent of shoot infestation (PSI) and per cent of fruit infestation (PFI) were ranging between 3.95% (Vengeri x IC636521) - 24.19% (Surya, BSFB susceptible check) and 3.46% (IC618016 x IC636521) - 40.19% (Surya), respectively. The PFI was significant and positively correlated with total sugars, PSI, protein and negatively correlated with trichomes on the leaf, polyphenol oxidase, and phenol. Yield and its attributing traits showed significant variation between the parents, hybrids and checks. The ANOVA for combining ability revealed the presence of significant general combining ability (GCA) for parents and specific combing ability (SCA) for hybrids for all the traits. It also suggested predominance of non-additive gene action for days to 50 per cent flowering, plant height, average fruit weight, fruit yield per plant and additive gene action for number of branches per plant, number of fruits per plant, fruit length, and fruit breadth. Significant heterosis was observed for most of the hybrids for quantitative traits. The organoleptic evaluation revealed that out of 21 organoleptic descriptors, only seven descriptors showed significant differences among genotypes with the least variation which validated the accurate selection of parents.
The ten single cross hybrids were crossed with five parents in three-way fashion to produce thirty three-way cross (TWC) hybrids. These hybrids were evaluated for resistance to bacterial wilt, BSFB and yield from July to November, 2024. The screening for bacterial wilt resistance was performed by artificial inoculation of pathogen at seedling stage by root injury method and transplanted to sick plot at NBPGR, Vellanikkara. The BSFB screening was performed by random xl planting of BSFB susceptible check, Surya (not inoculated). The parents, TWC hybrids and checks showed significant variation for bacterial wilt resistance under severe bacterial wilt stress condition (artificial inoculation + sick plot planting and favourable weather of rainy season). Similarly, the genotypes exhibited significant variation for BSFB resistance and yield traits. Since, the three-way cross hybrids developed due to one round of crossing which allowed for further segregation and recombination which lead to accumulation of favourable alleles/genes and makes them heterogeneous and broad genetic bases. Hence, a selection index was constructed to identify the transgressive segregants in terms of combined resistance with better marketable fruit traits by giving first preference to individual plants that are completely free from bacterial wilt symptoms till harvesting period followed by PFI and marketable yield of the plant. A total of 77 individual plants were immune to bacterial wilt and other insect pests and among these thirty were free from fruit borer infestation. The ranks were assigned to individual lines to forward them in future breeding programme. Seven DNA markers reported for bacterial wilt resistance were validated using resistant and susceptible parents and randomly selected wilt resistant TWC hybrids. Out of seven primers, one primer (SSR-46) exhibited polymorphism with expected sizes of 240 bp (resistant) and 220 bp (susceptible check). Thus, SSR–46 indicated the presence of tight linkage with bacterial wilt resistant gene/loci of S. melongena. The in silico The 5kb flanking region of the amplicon was matched with a gene, UDP-Glucuronate:Xylanalpha-Glucuronosyltransferase. This gene enables the activity of xylan glucuronosyltransferase (GUX), which is involved in hemicellulose xylan (cell wall polysaccharide) biosynthetic process. The literature or recent researches suggested that GUX is vital for proper cell wall and vascular tissue development and involved in diverse physiological processes in plant growth, development and defence response to pathogens. Thus, this key finding suggests the possibility of establishment of association between the GUX with bacterial wilt resistance in future. The top thirty promising lines (which include 21 transgressive segregants lines) obtained with combined resistance and better marketable yield can be forwarded to next generations. The validated molecular marker can be used for early selection of bacterial wilt resistant lines.