First report of downy mildew on buffalo gourd (Cucurbita foetidissima) caused by Pseudoperonospora cubensis in North Carolina.
C. foetidissima (buffalo gourd) is a viny perennial crop native to the USA. This plant, characterized by long, triangular, gray-green leaves and fruits that are 5 to 10 cm in diameter and yellow at maturity, is feral and considered a weed to many. However, C. foetidissima serves several purposes in Native American cultures and its oil-rich seeds have potential economic profitability. C. foetidissima grows well in dry arid regions, but is widely distributed throughout the USA, growing in 22 states and Mexico. In August through October of 2014, P. cubensis was observed on C. foetidissima plants in Lenoir, Rowan, and Haywood counties in North Carolina. These plants were grown in sentinel plots as part of the CDM-IPM PIPE, the cucurbit downy mildew disease-forecasting system. The disease was characterized by irregular brown lesions with chlorotic halos and sporulation on the abaxial leaf surface. The oomycete was collected from infected leaves and observed with a microscope, revealing characteristic P. cubensis structures. Based on morphological characteristics, DNA sequence analysis and pathogenicity test, the pathogen was confirmed as P. cubensis. The perennial nature of C. foetidissima makes this host of particular importance, as it is believed P. cubensis may overwinter on wild cucurbits. This is thought to be the first report of P. cubensis infecting C. foetidissima in field settings in the USA.