Integrated management of fusarium wilt of yard long bean in homesteads

Abstract

The study entitled ‘Integrated management of Fusarium wilt of yard long bean in homesteads’ was undertaken at College of Agriculture, Vellayani and Integrated Farming System Research Station (IFSRS), Karamana during 2023-25 with an objective to develop an integrated management package for the vascular wilt of yard long bean incited by Fusarium oxysporum using bioagents and biofumigants in homesteads. The culture of F. oxysporum (accession no: MZ706472.1) maintained at IFSRS, Karamana was used for the study. The mycelia of the pathogen appeared as white and fluffy with a characteristic pale pink to purplish pigmentation. Microconidia were ovoid or elliptical with 0 - 1 septa, while macroconidia were fusiform with 3 – 4 septa. Chlamydospores were globose with a diameter of 6 -10 μm. The pathogen was mass multiplied in sorghum-sand medium (SSM) (2:1:1 ratio) and complete colonization of the fungus was recorded at 5 days after inoculation (DAI). Koch’s postulates were proved in 15-days-old yard long bean seedlings (var. Githika). The disease symptoms initiated as yellowing of older leaves at 7 days after transplanting, which further progressed as defoliation, withering, wilting and seedling death. In vitro studies on the evaluation of antifungal potential of bioagents, botanicals and biofumigants revealed that garlic bulbs (2 g plate-1) completely (100%) inhibited the pathogen. Rhizobium sp. (KAU) inhibited the mycelial growth by 67.77 per cent and tested positive for siderophore production, indicated by a colour change of Chrome Azurol S (CAS) agar from blue to orange. In vivo seed treatment studies revealed that sowing of seeds in soil applied with AMF @ 5 g seed-1 followed by transplanting was the promising treatment (no incidence of disease) for the management of Fusarium wilt, along with enhanced seed germination (100%), leaf number (11.00), leaf area (24.17 cm2), shoot length (16.17 cm), root length (19.83 cm) and root-shoot ratio (5.33) of the seedling. Seed treatment with Rhizobium sp. followed by transplanting was the next promising treatment with the highest leaf area (27 cm2). Scanning electron microscopy revealed intact cell structure and absence of clogging 128 in vascular tissues of the above plants where as the pathogen inoculated control recorded its hypha emerging out of xylem vessels, which were damaged and extensively clogged. A pot culture study was undertaken in yard long bean var. Githika to develop an integrated package for management of vascular wilt disease. The treatment viz., soil testbased lime application at 2 weeks before planting + soil application of Trichoderma sp. enriched in cow dung – neem cake mixture (9:1) @ 1 kg pot-1 at one week before sowing (WBS) + soil application of AMF @ 5 g seed⁻¹ at sowing followed by transplanting + soil application of PGPR mix II @ 20 g L-1 at 20, 40 and 60 DAS (T6), recorded the least disease incidence (55.50%) and disease severity (19.44%), with the highest yield (945 g plant-1with 54 pods), among the treatments. The highest AMF root colonization (49%) and number of nodules (47.00) were also recorded in this treatment. Significant reduction in the population of the pathogen in soil/ pot was also recorded in this treatment at 30 and 60 DAS. The next promising treatment was same as the best one, with soil application of PGPR mix II @ 20 g L-1 replaced by Trichoderma sp. enriched in cow dung – neem cake mixture (9:1) @ 1 kg pot-1 at 20, 40, and 60 DAS (T3) which recorded reduced disease incidence (66.66%) and severity (31.76%) with higher yield (908.33 g plant-1from 50.00 pods), AMF root colonization (45.00%) and nodules (40.67). Peak activity of peroxidase (12.07 μg g-1 min-1), polyphenol oxidase (1.587 μg g-1 min-1), and phenylalanine ammonia lyase (11.703 μg g-1 min-1) at 72 hours after inoculation was recorded in the promising treatment. Thus, the present study revealed the integrated disease management package viz., soil test-based lime application at 2 weeks before planting + soil application of Trichoderma sp. enriched in cow dung – neem cake mixture (9:1) @ 1 kg pot-1 at one WBS + soil application of AMF @ 5 g seed⁻¹ at sowing followed by transplanting + soil application of PGPR mix II @ 20 g L-1 at 20, 40 and 60 DAS can effectively manage vascular wilt of yard long bean incited by F. oxysporum in homesteads. Furthermore, the study confirms a beneficial quadripartite association among AMF, Trichoderma sp. and the plant growth promoting rhizobacteria in yard long bean plants, as observed from the 129 effective management of the disease and enhanced plant growth and yield attributes even in the presence of the soil borne pathogen.