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Identification of fungal pathogens associated with cassava root rot in Thailand

Natthiya Buensanteai: School of Crop Production Technology, Suranaree University of Technology

<div>Cassava root rot (CRR) is the most serious diseases of cassava in Thailand, especially Northeastern region. The aim of this study was to identify the CRR causal agent. The study was carried out by collecting samples with root rot symptoms from various cassava planting areas including 3 districts of Nakorn-Ratchasima provinces, Thailand. The fungal pathogens were isolated from CRR lesions, the typical symptoms were often accompanied by wet, soft or dry rot symptom, and black pycnidia were found on the stalk and propagative stakes. The 139 representative samples were obtained into 5 genera according to the colony and spore morphology using a standard morphological study protocol. <em>Lasiodiplodia</em> spp. was the most frequently found fungus, constituting approximately 54 % of the total, followed by <em>Fusarium </em>spp., <em>Neoscytalidium </em>sp., <em>Phytophthora </em>spp., <em>Sclerotium</em> sp. and other fungal genera which were found at 29, 7, 4, 1 and 5%, respectively. The pathogenicity test of representative 33 single-spore isolates showed that they could cause stem and root rot symptoms on the inoculated susceptible cassava cv. Rayong 72 under both moist-chamber and green house conditions, the isolate L11HSR2 was the most virulent. By using 3 primers including ITS1/ITS4, Ef1-688F/Ef1-1251R and Bt2a/Bt2b primers to amplify the DNAs from 8 representative isolates, only the primer of the EF1-α region was effective in differentiating the isolates at species level and had an agreeable result with that identified by the standard morphological technique. When these eight isolates was compared against GenBank’s database using the Mega BLAST program, and the alignment data using the NJ, UPGMA and ML methods, could be identified as <em>L. theobromae</em><em>, </em><em>L</em>. <em>euphorbicola</em><em></em> and <em>N. hyalinum. </em>This is, so far, the first report of fungal pathogens complex species associated with CCR disease in Thailand.</div>