Etiology of Rhizoctonia solani Kühn causing web blight disease of urdbean and its management
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Date
2018-07
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G.B. Pant University of Agriculture and Technology, Pantnagar - 263145 (Uttarakhand)
Abstract
Blackgram or urdbean [Vigna mungo (L.) Hepper] is one of the most important pulse crops of the ‘vigna’ group and its grain contains not only protein but also phosphoric acid in high amount. The crop is infested by a number of fungal, bacterial and viral diseases. Among them, web blight disease caused by Rhizoctonia solani Kühn. [Thanatephorus cucumeris (Frank) Donk] is one of the major serious constraints in its growth and production. It is said to be one of the most devastating fungal diseases of urdbean leading to heavy yield losses. The present investigations were undertaken to study symptomatology and progressive development of disease, study the effect of different culture media, temperatures and pH on mycelial growth and sclerotia formation and evaluate different fungicides, botanicals and bioagents against the pathogen in vitro and in vivo to develop a suitable integrated management strategy. Web blight symptoms on urdbean plants appeared on roots, stems, petioles as well as pods but the disease was most devastating on foliage. On the infected leaves, mycelium appeared as spider web, the characteristic symptom thus suggesting the name of the disease as "web blight". In vitro, on the basis of morphological and cultural characteristics and pathogenicity test, the pathogen was proved as Rhizoctonia solani Kühn. Out of five different culture media studied, PDA was found best for mycelial growth and development as well as sclerotia formation of Rhizoctonia solani. Best temperature and pH for the growth and development of R.solani was found at 30°C and pH 7, with maximum mycelial growth and sclerotia production. Among the fungicides tested in vitro Fluxapyroxad 62.5/l + Epoxiconazole 62.5/l was most effective against Rsolani and showed 100.00 per cent inhibition of its mycelial growth at 20 ppm. Among the botanicals tested in vitro, Tulsi @ 35 per cent was most effective in mycelia growth inhibition of R.solani i.e. 74.81 per cent in dual culture experiment, biocontrol agent Trichoderma harzianum (Th-14) showed better performance over Pseudomonas fluorescens (Psf 173) in inhibiting mycelial growth of Rsolani i.e. 60.70 per cent Under field conditions,three foliar sprays of fungicide a combination of (Fluxapyroxad 62.5/l + Epoxiconazole 62.5/l) @ 0.2 per cent at 15 days interval and seed treatment with T. harzianum + Carbendazim(4 g+2 g/kg), showed highest control in disease severity i.e. 67.96%, over the cheak .with highest grain yield i.e. 1391.80 Kg/ha followed by seed treatment with T.harzianum + Thiram(4 g+ 3g/kg) i.e 67.26 % with 1355.76 Kg/ha grain yield.
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