Isolation Of Pythiaceae From Para Rubber Hevea Brasiliensis In Eastern Thailand For Identification Of Pythiaceae Virus

Abstract

Mycoviruses are viruses infecting fungi of which dsRNA genome is the most common. Mycovirus infection may confer the hyper and hypo-virulence phenotypes of fungi. This study focused on isolation of virus in Pythiaceae, a family of fungus-like organism. The members of this family are plant pathogens including Phytophthora, Pythium and Phytopythium. Species in Phytophthora cause abnormal leaf fall disease (ALF) in para rubber tree (Hevea brasiliensis). Pythiaceae were isolated from rubber leaves showing ALF symptoms collected from plantations in Chanthaburi and Rayong province, Thailand. All 79 Pythiaceae isolates were screened for extrachromosomal DNA and dsRNA elements. One isolate, R84 was found harboring 3 dsRNA element approximately 8.0, 3.7 and 2.3 kb. However, upon consecutive subcultures the only largest segment remained. Two-step reverse transcription using Pythiaceae virus specific primers revealed that the dsRNA was not one of reported Pythiaceae viruses. A partial cDNA clone of 233 nt out of the largest 8.0 kb dsRNA element contained a fragment of a gene encoding ALG2 mannosyltransferase-like protein but the genus of the dsRNA could not be specified. The dsRNA host was identified as Pythium cucurbitacearum, which has never been reported associated with rubber diseases. Isolate R84 showed hyper-resistance to hymexazol fungicide. The dsRNA found in this study might be responsible for resistant to fungicide of Py. cucurbitacearum isolate R84.