|Lee, Ing Ming|
Submitted to: European Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/9/1998
Publication Date: N/A
Interpretive Summary: Uncultured phytoplasmas (formerly called mycoplasmalike organisms) are the evident cause of many destructive diseases in several hundred plant species including many fruit trees. Quick decline of macadamia trees has become a serious problem in Hawaii in recent years. Studies on the etiology of this quick decline disease in past years strongly suggested that fungal pathogens contributed to girdling of lower trunk of affected macadamia trees and to their rapid decline. Recently, phytoplasmas were reported by others to be associated with macadamia trees showing decline symptoms. That report has complicated the determination of primary causal agents of this serious disease. The present study was to reevaluate the cause of macadamia quick decline in Hawaii. Ultrasensitive polymerase chain reaction (PCR) assays failed to detect the presence of phytoplasmas in all samples tested. However, two fungal pathogens were consistently isolated from affected trunks or branches. These data confirm previous reports that these fungi are the primary causal agents of quick decline of macadamia trees in Hawaii. The technology will be of benefit benefit to scientists and disease diagnoticians for screening for putative pathogens present in macadamia and other plant root stocks.
Technical Abstract: The cause of quick decline of macadamia trees in Hawaii was reevaluated. Twenty samples were collected from symtomatic and symptomless trees of the two susceptible cultivars cv. 333, and cv. 344 grown at Keaau and Kaiwiki on the island of Hawaii. Ultrasensitive nested-PCR assays using two universal primer pairs failed to detect the presence of phytoplasmas in all samples tested, contradicting the recent report that phytoplasma may play a role n macadamia decline. In contrast, two fungal pathogens, Nectria rugulosa and Xylaria arbuscula were consistently isolated from affected trucks or branches, confirming the previous reports that these fungi are the primary causal agents of quick decline of macadamia trees in Hawaii.