MSc

The study entitled "Management of snake gourd mosaic disease using endophytes" was conducted at Department of Plant Pathology, College ofAgriculture, Vellayani during 2023-2025 aimed at the utilisation ofbacterial endophyte viz., Bacillus velezensis PCSE 10 and fungal endophytes viz., Arbuscular Mycorrhizal Fungi (AMF) and Piriformospora indica for the management of snake gourd mosaic disease; and the elucidation of biochemical mechanisms involved in resistance or tolerance of snake gourd plants against viruses.
Mosaic, mosaic mottling, vein banding, puckering and blistering on leaves were the symptoms ofsnake gourd mosaic disease observed from fields at Instructional farm, College ofAgriculture, Vellayani, Thiruvananthapuram. Disease incidence and severity progressively increased over different months after transplanting, with the highest observed values at 3 MAT i.e., 100 per cent and 81.6 respectively. The virus inoculum was maintained in snake gourd variety Kaumudi through mechanical transmission and typical symptoms of mosaic disease appeared after 14 days of inoculation. The diseased samples reacted positively to primers specific to coat protein of PRSV (PRSV Fl and F2) and 2a protein of CMV (CMV 1 and 2); and amplicons of sizes 850 bp and 450 bp were obtained respectively.Successful root colonization of snake gourd plants with fungal endophytes viz., AMF (presence of arbuscules and vesicles) and P indica (chlamydospores) was observed at 30 days after inoculation with them. Pot culture studies with endophyte colonized snake gourd plants revealed that, those colonized with P indica took the highest number of days for symptom expression (22 days) followed by plants colonized with B. velezensis (21 days) and AMF (20 days). P. indica colonized plants recorded a reduced disease incidence (20.30 per cent, 33.48 per cent and 46.61 per cent) and severity (9.30, 14.60 and 48.00) followed by B. velezensis (33.47 per cent, 46.43 per cent and 66.33 per cent; 10.60, 18.67 and 64.00) and AMF colonized plants (40.74 per cent, 60.38 per cent and 73.59 per cent; 13.32,29.33 and 76.33) at 40, 50 and 60 DAS respectively. The combined application of endophytes did not give any significant difference in reducing the expression of disease symptoms.
Reaction of inoculated samples to polyclonal antibody of coat protein of CMV in DAC-ELISA and PRSV in DAS-ELISA was analysed. Among the endophyte colonized plants, P indica colonization resulted in the lowest virus load of CMV (0.0040, 0.0186 and 0.0202) and PRSV (0.0020, 0.0131 and 0.0149) followed by B. velezensis (0.0050, 0.0030;0.0200, 0.0143 and 0.0213, 0.0168) and AMF (0.0070,0.0048; 0.0236, 0.0161 and 0.0241, 0.0197) at 40, 50 and 60 DAS respectively. Based on the remission of symptoms and reduced virus titre values_,_ pre colonization with P. indica followed by individual pre colonizations with B. velezensis and AMF were identified as the three promising endophytes in alleviating symptoms of snake gourd mosaic disease.P. indica colonized plants gave the highest activities of peroxidase (30.46 g min' g' fw), polyphenol oxidase (20.32 g min'g' fw) and phenylalanine ammonia lyase (104.86 g min'g' fw) followed by colonization with B. velezensis (28.59, 14.41 and 99.28 g min'g' fw) and AMF (27.84, 4.64 and 96.51 g min'g' fw) at 50 DAS. Similarly, P indica colonization recorded the highest activities of catalase (292.31 mg g' fiw) and ascorbic acid oxidase (0.760 g min'g' fw) followed by B. velezensis (284.86 mg g' fw, 0.64 g min'g' fw) and AMF (278.73 mg g' fw,0.43 g min'g' fw) at 60 DAS. SDS PAGE analysis identified the induction of a novel protein (31.57 kDa) in plants in response to colonization with AMF. However, pre colonization with P. indica and B. velezensis PCSE 10 reduced the number of profiled proteins when compared to control plants.Field studies revealed that, P indica colonization increased the number of days taken for symptom development (36.8 days) followed by B. velezensis (31.4 days) and AMF (28.2 days). Similarly, reduced disease incidence was observed in P. indica colonized plants (88.36 per cent) followed by B. velezensis (92.95 per cent) and AMF (99.74 per cent) at 90 DAS. Also, P indica colonization resulted in the highest yield/snake gourd plant (7.037 kg).
The present study identified pre colonization of snake gourd plants with P. indica followed by colonization with B. velezensis and AMF as the three promising treatments in alleviating snake gourd mosaic disease owing to their ability in reducing virus titre and disease incidence/severity, induction of defense related enzymes and novel proteins. Similarly, the promising endophytic treatments reduced the expression of snake gourd mosaic disease symptoms with improved vegetative characters under field conditions.