Taxonomy, Phylogeny and Pathogenicity of Pythium Species in Rice Paddy Fields of Fars Province

In order to investigate the Pythium species of the rice paddy fields of Fars Province, Iran during 2013 to 2015, infected roots and crowns together with soil around seedlings and irrigation water were sampled. According to the morphological, morphometrical and physiological studies along with phylogenetic analyses based on internal transcribed spacer (ITS) of ribosomal DNA, fourteen Pythium species including Py. aphanidermatum, Py. catenulatum, Py. coloratum, Py. debaryanum, Py. dissotocum, Py. hydnosporum, Py. inflatum, Py. kashmirense, Py. nunn, Py. oopapillum, Py. plurisporium, Py. porphyrae, Py. pyrilobum, and Py. rhizo-oryzae were identified. All species are reported for the first time in the world from rice rhizosphere except Py. dissotocum, Py. inflatum and Py. rhizo-oryzae. Pythium oopapillum, Py. plurisporium, Py. porphyrae and Py. rhizo-oryzae were new to Iran. Pythium aphanidermatum, Py. rhizo-oryzae and Py. catenulatum were the most abundant species. Pathogenicity of Py. debaryanum, Py. oopapillum, Py. porphyrae, Py. plurisporium and Py. rhizo-oryzae on rice plants were reported in this study for the first time, worldwide.