Isolation of fungi-like pathogens associated with root rot in Colocasia esculenta

Background/Question/Methods

Taro (Colocasia esculenta) is a perennial, tropical plant that is grown worldwide due to its edible and ornamental uses. In the subtropical and warm temperate regions of the United States, however, taro is an aggressive invasive species forming dense stands within riparian and wetland ecosystems. Its ability to spread rapidly and displace native plant species has resulted in reduced biodiversity and clogged waterways. Since taro was introduced through plant trade, natural areas within and around cities are often susceptible to invasion. One such area is the Bluebonnet Swamp Nature Center, which lies in the city center of Baton Rouge, Louisiana. The invasion within the park has been problematic for many years, but intermittent die-backs have been linked to taro feathery mottled virus transmitted by a vector plant hopper (Tarophagus colocasiae). In October 2020, however, Louisiana State University researchers observed corm and root rot, yellowing leaves, and wilting petioles--symptoms different than those associated with the virus. Thus, the aim of this study was to isolate and identify other plant pathogens from diseased areas of taro plants. To accomplish this, diseased roots of infected plants were collected from the field and rinsed in water. Leaves of camelia plants were used for soil baiting techniques, and plated on CMA amended with PARP (pimaricin 5 mg/liter, ampicillin 250 mg/liter, rifampicin 10 mg/liter, and pentachloronitrobenzene 100 mg/liter), selective media to isolate oomycetes. All plates were incubated under dark conditions at 21 °C. Pythium-like isolates with white colonies were consistently obtained 3-4 days after incubation, and hyphal tips were cultured onto clarified V8 juice agar to have pure cultures. Mount microscope slides prepared for each isolate were and ovoid sporangia and coenocytic hyphae were observed under the microscope. DNA was extracted from each isolate and polymerase chain reaction (PCR) was conducted to amplify the mitochondrial cytochrome c oxidase subunit 2 (cox2) for molecular identification.

Results/Conclusions

Based on morphological and molecular approaches, isolated organisms were identified as Phytopythium sp. and Pythium sp.--two important oomycetes considered plant pathogens of taro plants in other areas. These results indicate the presence of Phytopythium sp. and Pythium sp. in the Bluebonnet Swamp Nature Center. Further experiments are required to determine if Phytopythium sp. and Pythium sp. are associated with the die-back of taro plants in Louisiana.