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Subject: Plant Pathology × Author: Agrawal, Manish × End date: 2012 × Start date: 2010 × Type: Thesis × Thesis Type: M.Sc ×
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    ThesisItemOpen Access
    Studies on variability in sheath blight fungus, rhizoctonia solani Kuhn AG-1 IA and its management in rice
    (CCSHAU, 2012) Agrawal, Manish; Shyam Sunder
    Considerable variations were observed among 37 isolates of Rhizoctonia solani AG-1 IA collected from different cultivars and locations in Haryana with respect of their cultural characters, virulence pattern and sensitivity to fungicides. The colony diameter of the isolates varied between 39 to 90 mm and based on colony growth, the isolates of R. solani were categorized in three groups viz., slow growing having colony diameter <60 mm, fast growing with colony diameter >85 mm and intermediate where colony diameter ranged between 60 to 85 mm. The colony color of the isolates varied between light brown to dark brown. The isolates differed greatly in number of sclerotia formed per plate (54-119) and sclerotial characters. The growth of the isolates had no correlation with colony color and number of sclerotia formed. The majority of the isolates (23) of the pathogen produced optimum growth at 30°C while nine isolates preferred a temperature of 25°C and the remaining isolates had non-significant differences in growth at 25°C and 30°C. Few of the isolates exhibited growth at 15°C but none at 40°C. The isolates of R. solani differed significantly in their pathogenic behavior on six paddy cultivars. Based on mean disease severity, the 37 isolates were categorized in three virulence group viz., VG-I, VG-II and VG-III. These isolates also varied in their sensitivity to hexaconazole and carbendazim. None of the isolates was found insensitive to any of the fungicides. Amongst 291 rice genotypes evaluated for their resistance against sheath blight, none proved highly resistant or resistant, only 12 genotypes viz. BC1F1-1094-128-549-01-0, BC2-46-12-1270-2-0, CB 05-754, CR 2612-1-2-2-1, HKR 05-128, KJT 3- 2-7-72, R 1570-2144-2-1547, RP Bio path-3, RPHR 25-104-1-2, SYE 35-4-16-63, TRC 05-2-6-4-39-3- 6 and UPR 2327-23 showed moderate resistance. In vitro, hexaconazole proved most toxic to the growth of R. solani with EC50 value of 0.18 ppm a.i followed by trifloxystrobin + tebuconazole (EC50:0.38 ppm a.i) and carbendazim (EC50:0.5 ppm a.i). Hexaconazole provided complete inhibition of sclerotial formation at 2.0 ppm a.i concentration closely followed by carbendazim (2.5 ppm a.i). In field testing, all the fungicides reduced disease severity and increased grain yield significantly. Azoxystrobin which proved most effective with 72.5 per cent reduction in disease severity closely followed by trifloxystrobin + tebuconazole and hexaconazole with 69.3 and 61.6 per cent disease control, respectively. All the non-conventional chemicals viz. 4-aminobenzoic acid, propionic acid, o-chlorobenzoic acid, 4-nitrobenzoic acid, thiourea, nicotinic acid, lithium sulphate, isobutyric acid and 4-aminobutyric acid reduced growth and sclerotia formation of R. solani on PDA, particularly at a concentration of 5 mM and more. These chemicals reduced sheath blight severity significantly in field.