Analysis on Variability of Sclerotium rolfsii Causing Cucurbit Collar Rot

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Date
2017-07
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Department of Plant Pathology, BAU, Sabour Year: 2017
Abstract
Cultivation of cucurbits is largely affected by several biotic factors. Among diseases, collar rot causes significant damage to cucurbits and ultimately responsible for yield loss. Despite being a dreaded pathogen having wide host range (infects over 270 families of plants); the collar rot dynamics in cucurbits is untouched. Therefore, this study envisaged with collecting the preliminary information regarding to this pathosystem. Collar rot of cucurbits is caused by Sclerotium rolfsii Sacc., a soil inhabitant and non-specific facultative parasite that found in almost all types of agro-ecological systems. At first, the collection of isolates from various hosts and locations of Bihar was made. These isolates were addressed to morphological and biochemical variations. Great variability of isolates from different localities was observed. Additionally, the collected isolates showed variation in melanin production. An isolate, producing highest number of sclerotia (117/plate), was selected for the tests of fungicidal sensitivity and temperature adaptability. The fungicide belonging to sterol biosynthesis inhibition exhibited great potential to reduce the fungal growth. Therefore, new fungicide involving hexaconazole along with the common fungicide used for Sclerotium rot management, carbendazim, should be synthesized. The isolate adapted to high temperature (35°C) after 8th sub-culturing indicating the adjustment capability of this pathogen towardselevated temperature. Therefore, the problem associated to this fungus may be increased in future, particularly under changing climate. Moreover, biochemical changes in the artificially inoculated plants were determined in different plant organs for the five isolates exhibiting high variability in the morphological observation. High content of total phenol and chitinase was detected at collar region; however, peroxidase estimation rendered non-significant (p≥0.01) variation amongst the plant organs. To address the varietal response and seasonal impact on collar rot epidemics the pot experiment has been conducted twice in a season (rainy and winter; 4 experiments in total) with cucumber and bitter gourd. Disease incidence (DI) calculated and area under lesion progress curve (AULPC) plotted in order to understand the collar rot dynamics in cucurbit. Additionally, measurement of lesion size was made. The varietal response has been found significant (p≤0.05) for the two crops. Overall, cucumber shown high susceptibility compared to bitter gourd in both of the seasons. The rainy season exhibited higher DI and AUDPC compared to winter season for both of the crops indicating high temperature is favourable to this pathosystem. Nearly similar trend was observed for lesion length for each condition. Wide variation among isolates and adaptability of the pathogen to high temperature suggesting to develop improved strategy for management. Development of fungicide with sterol biosynthesis inhibitors can be a reliable option to manage this pathogen. Delay sowing of cucurbits in rainy season would account for lower disease development; therefore, development of late sown varieties is suggested. If agroecosystem, and facility and economical status of the farmer allow the cultivation of cucurbit in summer season should be addressed particularly in areas with sporadic and epidemic history of collar rot.
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