PG Thesis

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Subject: search.filters.subject.Ralstonia solanacearum

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    Evaluation of brinjal (Solanum melongena L.) genotypes for resistance to bacterial wilt (Ralstonia solanacearum)
    (Department of Plant Breeding and Genetics , College of Agriculture, Padannakkad, 2023-12-11) Muslepally Niharika; Namboodiri Raji Vasudevan
    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, College of 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 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. solanacearum in brinjal. However, the role of sugar content in plant defense is still unclear and requires further studies for 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 among all 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 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 calyx prickles) 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.
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    Rootstock evaluation and grafting studies in brinjal (Solanum melongena L.)
    (Department of Vegetable Science, College of Horticulture, Vellanikkara, 2019) Sadanand Kumabar; Narayanankutty, C
    The present investigation was conducted at Agricultural Research Station, Mannuthy and Centre for Hi-Tech Horticulture and Precision Farming, Vellanikkara, Thrissur during the year 2018-2019 with the objective to evaluate ten available rootstocks comprising of Surya, Haritha, SMI, SM2, SM3, SM116, SM398, Solanum sisymbrifolium, Sokmum torvum KAUl, Solanum torvum TNAUl for resistance to bacterial wilt in both field evaluation and artificial Inoculation and to study the field performance of grafted brinjal plants on bacterial wilt resistant rootstocks. In the field trials Solanum sisymbrifolium was highly susceptible to bacterial will with 96.6% wilt incidence whereas SM398 (40% PDI), SM2 (40% PDl), SMI (23.3% PDI), Solanum torvum KAUl (16.6% PDI) and Solanum torvum TNAUl (20% PDI) were found moderately resistant to bacterial wilt. Genotypes such as Surya, Haritha, SM3 and SM1I6 found highly resistant to bacterial wilt even when spot planted with susceptible check genotype Pusa Ruby which showed 100 percent wilt incidence. The PDI in check genotype Pusa Ruby ranged from 86.67 per cent to 100 per cent. Solanum sisymbrifolium spot planted with Pusa Ruby took minimum number of days to wilt incidence (23.40 days) whereas SM398 took maximum days to will (32.3 days). Under artificial inoculation the genotype Solanum sisymbrifolium exhibited 73.33 per cent will incidence along with the susceptible check Pusa Ruby which exhibited 86.6 per cent wilt incidence and both the genotypes were classified as susceptible to bacterial wilt. All other genotypes viz,, Surya, Haritha, SM 1, SM2, SM3, SM 116, SM398, Solanum torvum KAU1 and Solanum fon'um TNAUl did not show any wilt incidence under artificial inoculation and were resistant to bacterial wilt. Solanum sisymbrifolium took more number of days to wilt (16.81 days) when compared to the susceptible check Pusa Ruby (9.77 days). The root dip method recorded highest PDI in both susceptible genotype Solanum sisymbrifolium (86.67%) and the susceptible check Pusa Ruby (100%) when compared to media drenching and stem injection methods and the number of days to wilt incidence was also the lowest in root dip method (11.70 days) followed by stem inoculation (12.25 days) and media drenching (26.50 days). Significant differences were observed with respect to plant height, plant spread, stem girth, number of primary branches, fruits per plant, fruit length, fruit girth, average fruit weight, yield per plant, total phenolic, dry matter, number of wilted plants, root length and root spread among ail the rootstocks used when compared to non-grafted control and all the grafted plants produced significantly better performance for all the above parameters irrespective of the rootstocks used. Maximum yield per plant (6.69 kg), number of fruits per plant (94.80), plant spread, stem girth, number of primary branches, fruit lengtli (22.22 cm), root length (63.65 cm) and root spread (87.05 cm) were recorded when cullivar Haritha was used as a rootstock. The highest plant height, fruit girth (10.97 cm) and average fruit weight (78.00 g) were recorded on SMI 16 rootstock. Highest dry matter content was found in fruits of grafted plants of SM398 (11.12%) and the total phenolic content was the highest when SM3 (113.30 mg/l OOg) was used as rootstock. Maximum numbers of wilted plants were observed in non-grafted control. The perfonnance of non-grafted control plants was poor for all the above characters studied. Grafting did not significantly influence earliness, duration of the crop or number of harvests or total soluble solids content of fruits in brinjal. It had no significant effect on incidence of other pests on the crop except for bacterial wilt. From above studies it could be summarised that spot planting could be used as an effective tool for screening brinjal genotypes against bacterial wilt. Grafting technology could be successfully utilised in brinjal not only for bacterial wilt resistance but also for obtaining higher productivity. Haritha was found to be best rootstock for grafting in brinjal as it recorded significantly higher yield per plant, number of fruits per plant, plant spread, stem girth, number of primary branches, fruit length, root length and root spread followed by SMI 16 rootstock which recorded the highest plant height, fruit girth and average fruit weight.
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    Management of bacterial wilt disease of tomato by the root endophytic fungus piriformospora indica, rhizobacteria and bacterial endophytes
    (Department of Agricultural Microbiology, College of Agriculture, Vellayani,Thiruvananthapuram, 2018) Athira, S; Anith, K N
    The study entitled “Management of bacterial wilt disease of tomato by the root endophytic fungus Piriformospora indica, rhizobacteria and bacterial endophytes” was conducted during 2016-2018 at Department of Agricultural Microbiology, College of Agriculture, Vellayani with the objective of assessing the potential of root endophytic fungus Piriformospora indica, plant growth-promoting rhizobacteria and bacterial endophytes in suppressing bacterial wilt incidence in tomato. The bacterial wilt pathogen, Ralstonia solanacearum was isolated from infected tomato plants on Semi selective medium from South Africa (SMSA). Koch’s postulates were proved by artificial inoculation of tomato seedlings. A functional relationship between population and optical density of the broth culture was worked out and was used for determining the inoculum density for challenge inoculation in the biocontrol experiment. In vitro antagonistic interaction between the bioagents and the pathogen was worked out both by direct and indirect assays. In all direct assays which involved cross streak plating, agar plug diffusion technique, disc diffusion and spot on lawn method, it was found that Bacillus amyloliquefaciens VLY24, Bacillus velezensis PCSE10 and Streptomyces leeuwenhoekii KBT004 exhibited antagonism against Ralstonia solanacearum. Indirect antagonism was checked by agar well diffusion and disc diffusion methods using culture filtrate. Out of the eight bacterial bioagents tested, only two i.e., Bacillus velezensis PCSE10 and Bacillus amyloliquefaciensVLY24 had inhibitory effect on the pathogen. Dual culture plate assay on PDA has shown that three bacterial bioagents, Rhizobium radiobacter PCRE10, Bacillus megaterium NAT001 and Streptomyces leeuwenhoekii KBT004 were compatible with Piriformospora indica. However, when the compatible bacteria were co-cultured in a single fermentor system along with Piriformospora indica it was observed that Bacillus megaterium NAT001 failed to grow along with the fungal endophyte. Suppression of bacterial wilt incidence by the individual and combined application of bacterial bioagents and fungal endophytes were tested with the wilt susceptible tomato variety Naveen (Indo-American hybrid seeds Pvt. Ltd, Bengaluru) and the moderately tolerant KAU variety Vellayani Vijay. Bioagents were applied during the nursery production of seedlings and the 21 days old seedlings were transplanted to pots filled with unsterile garden soil. Challenge inoculation with the pathogen was done five days after transplanting by drenching the pots with 10 ml each of the bacterial suspension (107cfu/ml). The disease incidence was scored at weekly intervals for 21 days. When the bioagents were tested individually for the suppression of bacterial wilt incidence in the hybrid variety Naveen, maximum disease suppression was observed in plants treated with Rhizobium radiobacter PCRE10 (15 percent) after 21 days. The disease suppressive ability of Bacillus velezensis PCSE10 (25 percent) was also significantly superior to all other treatments. Selection of bacterial bioagents for combined application with Piriformospora indica was done based on compatibility with the fungal endophyte and inhibitory action against Ralstonia solanacearum. Combined application of the fungal endophyte and Bacillus amyloliquefaciens VLY24 suppressed the wilt incidence to the highest extent (40 percent). When bacterial wilt suppression in Vellayani Vijay was tested by the individual application of bacterial bioagents, maximum disease suppression was recorded in plants treated with Streptomyces leeuwenhoekii KBT004 (30 percent), when observed 21 days after challenge inoculation. The combination of Piriformospora indica with Rhizobium radiobacter PCRE10 (50 percent) and Bacillus velezensis PCSE10 (50 percent) showed significantly lower disease incidence compared to the rest of the treatments. In the plant growth promotion experiment done with the variety Vellayani Vijay in the nursery stage, maximum plant height was observed in plants treated with Rhizobium radiobacter PCRE10 (14.49cm). However, those plants treated with Bacillus pumilus VLY17 had the highest number of leaves per plant (4.58). Combined inoculation of Piriformospora indica and Bacillus amyloliquefaciens VLY24 resulted in improved shoot fresh weight (2.08 g per plant) which was on a par with the plants treated with Bacillus velezensis PCSE10 (1.95 g plant-1). However, shoot weight on dry weight basis was the maximum for plants treated with Bacillus velezensis PCSE10 (122.55 mg plant-1) which was at par with those treated with combination of Piriformospora indica and Bacillus amyloliquefaciens VLY24 (104.78 mg plant-1). The present study revealed that biological management of bacterial wilt in tomato could be a feasible strategy under controlled conditions. The same has to be validated under field conditions before making any recommendations.
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    Evaluation of tomato (Solanum lycopersicum L.) hybrids for yield and bacterial wilt resistance
    (Department of Olericulture, College of Agriculture, Vellayani, 2017) Shashidhar M Sonnad; Sarada, S