MSc

The current study entitled “Evaluation of brinjal genotypes for resistance to bacterial wilt (Ralstonia solanacearum)” was carried out in the Department of Plant Breeding and Genetics, Collegeof Agriculture, Padannakkad during 2020-2023. The main objectives of the study were to evaluate brinjal genotypes for resistance to Bacterial wilt (BW) and examination of the mechanism of resistance through anatomical and biochemical parameters as well as estimation of yield characters in resistant lines. The experimental material consisted of thirty-one accessions which included eleven accessions (SM-1, SM-2, SM-3, SM-4, SM-5, SM- 8, SM-9, SM10, SM-31, SM-32, SM-33) collected from North Kerala, seventeen accessions (SM-11 to SM-27) from NBPGR. It also included three released varieties and hybrid of KAU (Haritha, Surya, Ponny and Neelima) as resistant checks and two susceptible checks (SM-26[S.incanum] and SM-27[S.insanum]). In experiment I, three weeks old seedlings of all brinjal genotypes were screened for resistance to BW in a completely randomized design with three replications. Based on percentage disease incidence (PDI), two accessions SM-15 and SM-25 were rated as highly resistant (HR: 0 PDI) and accessions SM-1 was rated as resistant (R: 1-10 PDI). Accessions SM-1, SM-2, SM-5, SM-11, SM-17, SM-24 and KAU hybrid Neelima were rated as moderately resistant (MR: 11-20 PDI). Accessions SM-4, SM-8, SM-14 and SM-19 were rated as susceptible (S: 21-30 PDI). Moderately susceptible (MS: 31-40 PDI) accessions were SM-3, SM-32, SM-33, SM-13 and SM-16. Accessions SM-9, SM-10, SM-12, SM-
18, SM-20, SM-21, SM-22, SM-23, SM-26 and SM-27 were rated as highly susceptible (HS: >40 PDI).
Biochemical parameters viz., Polyphenol oxidase (PPO) enzyme activity, total phenols, and total sugars (both reducing and non-reducing) were assessed at 12 and 24 hours post inoculation (hpi).In this analysis using twenty two accessions consisting of eight genotypes from resistant categories (HR, MR, R) and eight from HS group along with four RC (Ponny, Haritha, Surya and Neelima) as well as two SC (SM-26, SM-27) were used. A control group with mock inoculation was also part of the analysis. Two factor ANOVA demonstrated significant differences in these

129



biochemical parameters among all tested brinjal genotypes. At 12 and 24 hpi, the most significant rise in PPO activity was observed in the RC followed by the R group, HR germplasm and MR group compared to their respective control samples. Moreover at 24 hpi the resistant (R) genotypes exhibited a significant 3.5-fold increase in PPO activity compared to the control group. Resistant checks exhibited the highest phenolic content followed by the HR, R and MR germplasm at 12 and 24 hpi. The highest amount of total sugars, which includes both reducing and non-reducing sugars, was observed in RC followed by HR germplasm, R germplasm, and MR germplasm after 24 hpi. Correlation analysis revealed a significant negative correlation between biochemical parameters viz., PPO enzyme activity, total phenol content, total sugars including non-reducing sugars (12 and 24 hpi) and disease incidence. A positive correlation was observed between disease incidence and reducing sugars at 12 hpi whereas, negative correlation was observed between the same at 24hpi. The biochemical analysis indicated that PPO and phenols played a positive role in the resistance against R. solanacearumin brinjal. However, the role of sugar content in plant defense is still unclear and requires further studiesfor a better understanding of sugar metabolism. In the current study different aspects of the stem vascular anatomy viz., number of small and large vessels, total number of vessels, ratio of large to small vessels and average vascular area in the eggplant germplasm and correlation of these characters with disease incidence were analysed. A significant variation for anatomical characters was observed amongall the genotypes. Among the germplasm HR accessions SM-15, SM-25 and R accession SM- 1 showed highest number of large vessels, higher ratio of large vessels to small vessels and higher average vascular area compared to all other accessions. These anatomical parameters are found to play a significant role in the temporal and spatial distribution of the pathogen within the vascular vessels.
After analyzing the response of various brinjal genotypes to disease incidence, as well as considering biochemical and anatomical parameters, it was observed that eight genotypes (SM-1, SM-2, SM-5, SM-11, SM-15, SM-17, SM-24, and SM-25)
exhibited resistance against BW. These genotypes along with four KAU released resistant checks were further evaluated in the field in experiment II. Field evaluation
130



was carried out in a randomized block design with three replications for sixteen quantitative and two qualitative characters. Per se performance of all genotypes revealed significant variation for all the quantitative characters indicating presence of high genetic variability. Association analysis revealed that leaf area,root dry weight and average fruit weight showed significant positive genotypic correlation and direct effect depicting true association of these characters with fruit yield. Selection based on these characters will help achieve efficient improvement in fruit yield. Among the local accessions, resistant accession SM-1 exhibited the maximum early fruit yield of 972.68 g followed by the Moderately resistant accession SM-11 (965.77 g). Accession SM-1 was also superior for plant height, earliness, average fruit weight and SM-11 for number of fruits per plant. Therefore, resistant accession SM-1 could be regarded as a promising genotype for potential release as a new variety. Highly resistant accessions SM-15 (oval green fruits with intermediate calyxprickles) and SM-25 (oval purple fruits and no prickles on the calyx), displayed excellent plant and flower characteristics like stem girth, branching, days to first and 50 per cent flowering but reported lower early yields. These can be used in hybridization programs either as parents to develop F1 hybrid or as recombinants in recombination breeding for resistance to bacterial wilt.