University of Hawaii System newsletter

New Species of Plant Pathogen Discovered

Posted on | February 26, 2010 | Comments Off on New Species of Plant Pathogen Discovered

plant rot

Symptoms of black flags—veinal necrosis, fruit rot, fruit mummification, leaf spot, leaf blight and stem blight.

Mānoa Associate Specialist Scot Nelson discovered a new species of plant pathogen named Phytophthora morindae after the medicinal plant host it that it infects, Morinda citrifolia (noni, Indian mulberry). This new pathogen causes a devastating foliar and fruit blight disease of noni known locally as black flag. This pathogen species is a member of one of the world’s most significant genera of plant pathogens, Phytophthora, meaning plant destroyer. The discovery was published in Mycologia.

Black flag disease is important because it can cause the complete defoliation of a noni field within a few weeks after infection. However, the disease has remained geographically isolated within the lower Puna District on the island of Hawaiʻi since 1999, and has not been reported elsewhere in the Pacific or worldwide. The rather mysterious and sudden appearance of this disease raises unanswered questions about the evolution of P. morindae and its close DNA relatedness to other Phytophthora species, which do not occur in Hawaiʻi.

Although Nelson discovered the pathogen and the disease in 1999, a decade passed before sufficient data on pathogenicity, pathogen morphology and DNA sequences were obtained to justify the establishment of a novel species. Key collaboration with USDA mycologist Z. Gloria Abad, the acting director of the Molecular Diagnostics Laboratory in Beltsville Maryland, provided the key pieces of information.