Phytoplasmas are not associated with quick decline of macadamia trees in Hawaii

Association of phytoplasma with quick decline of macadamia trees in Hawaii was reevaluated. Twenty samples were collected from symptomatic 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 phytoplasmas in all samples tested, contradicting the recent reports that phytoplasma may play a role in macadamia decline or quick decline. In contrast, infection of trunks by two fungal pathogens, Nectria rugulosa and Xylaria arbuscula were consistently associated with declining but not healthy macadamia trees, supporting the previous suggestion that sudden death of macadamia trees is primarily caused by girdling of trunks resulting from infection by fungal pathogens.