Phytopythium chamaehyphon causing corm and root rot of uncultivated taro ( Colocasia esculenta )

Taro ( Colocasia esculenta ) is a food crop cultivated in tropical areas of the world. However, when uncultivated, taro is considered an invasive plant species due to its ability to colonize aquatic and semi-aquatic areas and replace native plants. Disease symptoms were observed on uncultivated taro growing in water-saturated soil at the Bluebonnet Swamp Nature Center, Baton Rouge, Louisiana, USA. Symptoms consisted of corm and root rot, dead leaves, and wilting petioles. Roots samples from affected plants were collected and plated on corn meal agar amended with antibiotics. Mycelium growing on the plates were transferred to plates containing V8 juice agar. Examinations of the mycelia revealed ovoid sporangia, and coenocytic hyphae which suggested an oomycete. To determine the identity of the putative oomycete, DNA was extracted and used in PCR reactions. PCR products were sequenced and compared with sequences in the GenBank database using BLASTn. Based on results of molecular and phylogenetic analyses, the isolated oomycete was identified as Phytopythium chamaehyphon. Pathogenicity tests were conducted, and Koch’s postulates completed. This investigation reports the oomycete P. chamaehyphon as the causal agent of the uncultivated taro disease in Louisiana.