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The study entitled “Ecofriendly management of sheath blight disease of rice” was carried out at College of Agriculture (COA), Vellayani and Integrated Farming System Research Station (IFSRS), Karamana during 2017-19 with the objective to develop an effective eco-friendly strategy for the management of sheath blight disease.
The sheath blight fungus viz., Rhizoctonia solani (Accession No. KX674527) maintained at the Department of Plant Pathology, College of Agriculture, Vellayani was used for both in vitro and in vivo studies. Pathogenicity of the fungus was proved in the rice variety Uma. Characteristic sheath blight symptoms appeared on the inoculated sheath as water soaked, grey coloured lesions on the third day after inoculation (DAI) with a lesion length of 0.79 cm which increased to 3.86 cm on the seventh DAI. Development of white coloured sclerotia was observed on the fifth DAI on the inoculated leaf sheath which gradually turned to brown.
In vitro evaluation of organic preparations namely fermented egg lemon juice extract (10 %) and fermented Setaria barbata extract (10 %), botanicals namely garlic extract (10 %), non-hazardous chemicals namely potassium silicate (0.5 %) and their combinations in mycelial inhibition of the fungus was undertaken at IFSRS, Karamana in completely randomised design (CRD) with 14 treatments and three replications. The study revealed that all the treatments individually and in combinations resulted in complete mycelial inhibition of the fungus. Dipping sclerotia in fermented egg-lemon juice extract for 24, 48, 72 h resulted in maximum inhibition of mycelial regeneration from sclerotia (100, 100 and 96.60 % respectively) followed by fermented Setaria barbata extract (76.6, 83.3 and 83.66 % respectively).
The pot culture experiment in the rice variety Uma in CRD using eight treatments and four replications revealed that the maximum suppression of vertical spread of the disease was observed in plants sprayed at 35, 55 and 75 days after sowing (DAS) with potassium silicate (76.05 %) and was followed by the nursery application of AMF (200 g m-2), foliar spray of fermented Setaria barbata extract (75.06 %) and tebuconazole 50 % and trifloxystrobin 25 % WG (75.20 %). The minimum horizontal spread was observed in plants sprayed with potassium silicate (23.81 %) which was followed by plants treated with tebuconazole 50 % and trifloxystrobin 25 % WG (25.20 %).
The activity of peroxidase, polyphenol oxidase and phenylalanine ammonia lyase were recorded on 0, 24, 48 and 72 h after foliar spray. The study revealed that the maximum activity of peroxidase at 72 h after the third spray was observed in plants sprayed with potassium silicate and the plants where nursery application of AMF was undertaken. The highest activity of polyphenol oxidase was recorded in the plants sprayed with potassium silicate and tebuconazole 50 % and trifloxystrobin 25 % WG, which were on par. The foliar application of tebuconazole 50 % and trifloxystrobin 25 % WG revealed the maximum activity of phenylalanine ammonia lyase followed by AMF application at nursery stage.
Thus the present study revealed that rice sheath blight disease could be effectively managed by three foliar sprays of potassium silicate (0.5 %) or tebuconazole 50 % and trifloxystrobin 25 % WG (0.04 %) at 35, 55 and 75 DAS as evident from the maximum number of tillers per plant, the minimum vertical and horizontal spread of the disease as well as the highest activity of peroxidase and polyphenol oxidase in the inoculated plants.