First report of Pythium Arrhenomanes associated with root rot of maize (Zea Mays) in Oman

Maize is an important fodder crop in Oman. During November 2013, maize plants grown at the Sultan Qaboos University, Alkhoud (Oman), exhibited root rot symptoms, associated with weakened plants and the disease was observed as patches in the field. After isolating from symptomatic plants onto PDA, representative isolates were transferred to V8 agar where smooth, globose, light brown oogonia (31 to 33 µm in diameter) were produced. Identification of the pathogen was morphologically based on Plaats-Niterink (1981) and was confirmed by sequencing the ITS region (primers ITS1/ITS4) for two isolates. A BLAST search showed that the two isolates from Oman share 99% nucleotide identity with the ex-type of Pythium arrhenomanes (CBS 324.62, GenBank accession No. AY598628.1) (Levesque and DeCock, 2004). Pythium arrhenomanes was first described by Drechsler in 1928 causing root rot of corn in Wisconsin and Illinois (Elliott, 1942). Pathogenicity tests of P. arrhenomanes were conducted by inoculating maize seeds with suspensions of the pathogen in pots containing autoclaved soil. In order to fulfill Koch’s postulates, re-isolations were performed from the plants that had survived and identity of the pathogen was confirmed molecularly. P. arrhenomanes induced root rot symptoms on the inoculated seedlings as observed in the field and fresh weight was significantly reduced (P<0.05). The two P. arrhenomanes isolates were deposited at Sultan Qaboos University Culture Collection under the accession number (Msa.Pa01 and Msa.Pa02). To our knowledge, this is the first report of P. arrhenomanes in Oman and also as a root pathogen of maize in the country.