Browsing by Author "Sreechithra, M S"

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    Management of collar rot of elephant foot yam (Amorphopallus paeoniifolius) using biocontrol agents and fungicides
    (Department of Plant Pathology, College of Agriculture , Vellayani, 2025-01-25) Sreechithra, M S; Sherin A Salam
    The research titled "Management of collar rot of elephant foot yam (Amorphophallus paeoniifolius (Dennst.)) using biocontrol agents and fungicides" was conducted in the Department of Plant Pathology, College of Agriculture, Vellayani, Thiruvananthapuram during 2022-2024 with the objectives of characterizing the pathogen causing collar rot and to manage it using biocontrol agents and fungicides. As part of the study, a survey was conducted at Thiruvananthapuram, Kollam, and Alappuzha districts, belonging to two agro-ecological units (AEU 8 and 9) of Kerala. Koch’s postulate of the ten isolates obtained during the survey was confirmed. Isolate I3 obtained from Venganoor area of Thiruvananthapuram district was found to be the most virulent and fast-growing. Cultural and morphological studies revealed that the isolates took only 3-5 days to complete its growth in Petri dish (9cm). The colony colour was white with no pigmentation. The colony texture of all isolates was fan-like except I6 and I10 which were fluffy and sparse towards the center respectively. The isolates took 6-12 days for sclerotial formation and the number of sclerotia ranged between 0 and 180. The isolate I3 produced the highest number of sclerotia (180) within 15 days, while I6 failed to produce any sclerotia. The hyphal width and septal distance ranged from 1.14 to 3.68 μm and 81.01 to 129.70 μm respectively. The size of sclerotia varied from 1.20 to 1.96 mm and isolate I3 recorded the largest sclerotial size of 1.96 mm. Based on cultural, morphological, and pathogenic characteristics, I3 was found to be the most virulent among the ten isolates. The identity of the pathogen was confirmed molecularly using ITS primers as Athelia rolfsii (Accession no. PQ268968) (teleomorph of Sclerotium rolfsii) with 100% homology. In order to isolate beneficial antagonistic bacteria against S. rolfsii, 82 collections were made from the soil with healthy elephant foot yam. Out of this, 15 were short listed based on the primary screening and from this two (B57 and B 43) showing the best antagonistic property was used for further studies. These antagonists were molecularly identified as Bacillus amyloliquefaciens (B57) (Accession no. PQ268963) (100% similarity) and B. velezensis (B43) (Accession no. PQ268964) (99.87% similarity). Both the isolates tested positive for cellulase and pectinase activity with B57 producing significantly higher quantities of NH3, IAA, siderophore and volatile compounds compared to isolate B43. Antagonistic property of B57 and B43 was compared with the widely used biocontrol agents in Kerala and it was found that B57 (64.16%) was on par with biocontrol check Trichoderma asperellum (KAU T6) (62.78 %), followed by B. velezensis (B43) (57.22 %). Among the fungicides assessed, mancozeb (75% WP) and trifloxystrobin (25%) + tebuconazole (50%) 75 WG inhibited the pathogen completely at all concentrations tested and performed better than other treatments even at a lower concentration of 0.005%. In the in vivo study, the treatments trifloxystrobin (25%) + tebuconazole (50%) 75 WG @ 0.05% and @0.1% gave 100% control followed by the treatments B57, Trichoderma enriched neem cake and FYM and mancozeb 75 WP (0.2%) which were found to be on par. Plants treated with B57 and Trichoderma enriched neem cake and FYM inhibited the pathogen without producing any symptoms for up to 160 days and produced smaller lesions compared to others. It also gave better yield compared to other treatments. The chemical fungicides failed to enhance any biometric parameters and yield. The findings of the study confirmed that the collar rot of EFY in Kerala is caused by Sclerotium rolfsii (T: Athelia rolfsii). During the course of the study, a promising rhizobacterial antagonist (B. amyloliquefaciens (B57) (PQ268963)) was obtained. In vivo studies confirmed that, corm treatment and soil application of B. amyloliquefaciens (B57) (PQ 268963)) @20g/l at the time of planting and 30 and 45 DAP could enhance plant growth and yield and inhibit collar rot disease. Among the fungicides tried, corm treatment and soil application of trifloxystrobin (25%) + tebuconazole (50%) 75 WG at the time of planting, 30 and 45 days after planting could effectively inhibit the collar rot pathogen even at a lower dose of 0.05%.