The identification of cassava black stem and root rot agents in Thailand

Rungthip Sangpueak1, Suttisa Duchanee2, Chanon Saengchan1, Narendra Kumar Papathoti1, Nguyen Huy Hoang1, Toan Le Thanh3, Piyaporn Phansak4, and Natthiya Buensanteai1*
Cassava (Manihot esculenta Crantz) black stem and root rot (BSRR) caused by complex fungi is one of the most serious fungal disease of cassava in Thailand. The objective of this study was to identify the causal agent of BSRR disease of cassava in Nakhon Ratchasima province, Thailand. From June 2015 to May 2018, the outbreak areas in three districts of Nakhon Ratchasima province were surveyed for cassava plants with the characteristic symptoms. From 1800 diseased samples, 139 fungal pathogens were isolated and separated by morphological traits. Among them, 33 fungal isolates were subsequently tested for pathogenicity on detached stems and roots of CMR 43-08-89, a susceptible cassava cultivar, and proved to be pathogenic with different levels of aggressiveness. Next, PCR amplification of DNA of eight pathogenic isolates with high aggressiveness using two sets of universal primers ITS1/ITS4 and Ef1-688F/Ef1-1251R, revealed that the TEF1-α gene region could be used for the identification and classification at the species level. The analysis results fit well with that of the morphological studies on growth and colonial characteristics of the eight isolates. Based on the GenBank database, they were identified as Lasiodiplodia theobromae, L. euphorbiaceicola and Neoscytalidium dimidiatum.
Keywords: Cassava disease, Lasiodiplodia spp., Manihot esculenta, Neoscytalidium dimidiatum.
1Suranaree University of Technology, School of Crop Production Technology, Institute of Agricultural Technology, 30000, Nakhon Ratchasima, Thailand.
2National Science and Technology Development Agency (NSTDA), 12120, Pathum Thani, Thailand.
3Can Tho University, College of Agriculture, Department of Plant Protection, 900000, Can Tho, Viet Nam.
4Nakhon Phanom University, Faculty of Science, Division of Biology, 48000, Nakhon Phanom, Thailand.
*Corresponding author (natthiya@sut.ac.th).