Molecular identification and genetic variation of Puccinia psidii, a rust fungus attacking ohia (Metrosideros polymorpha) and other Myrtaceae in Hawaii

PD: Shaobin Zhong

The Hawaiian ohia (Metrosideros polymorpha) is a major component of the native forest on all major islands of the Hawaiian Archipelago (Friday and Herbert 2005). Over 80% of Hawaii forest consists of ohia trees, which provide niches for many endemic and endangered plants and animals. However, a new rust disease was recently (2005) found on native ohia trees and other related species, including the endangered species Eugenia koolauensis, in the Oahu island. The rust causes serious damages on leaves, stems and shoots of ohia plants. Based on host family associations and rDNA sequence analysis, the rust fungus was identified to be Puccinia psidii. This rust species has caused serious damage on Eucalyptus and other genera in the family Myrtaceae in Brazil, other areas of South America, Central America, the Caribbean, and Florida. Its recent occurrence in Oahu and other Islands poses a potential threat to Hawaiian ohia forests. However, questions remain to be addressed, including: 1) Are the rust strains found on Hawaiian ohia the same as those reported in other areas (Brazil and Florida) and hosts? 2) Can a reliable and rapid technique be developed to detect the ohia rust strains? Therefore, the specific objectives of this project are to 1) Develop a DNA based system for rapid detection of ohia rust isolates found on ohia and other related host species in Hawaii, 2) Investigate the genetic variation of Puccinia psidii using DNA markers. The DNA-based detection system will facilitate appropriate control measures and/or eradication procedures more quickly and effectively than traditional methods used for pathogen detection. This highly sensitive diagnostic procedure can be further adapted for routine screening of plant materials in the Myrtaceae family in support of quarantine and biosecurity measures against possible incursions of this rust pathogen in non-infected areas. The optimized detection and monitoring protocols can be adapted to detect other invasive plant pathogens that potentially damage crops and forests in Hawaii. Information about genetic variation in the rust population in Hawaii would lead to a conclusion on how many races of the pathogen were introduced into Hawaii.

Supported by Hawaii Department of Agriculture