Phytoplasmas and their insect vectors: Implications for date palm

Authors: GURR,, G - Fujian Agricultural & Forestry University; BERTACCINI, A - University Of Bologna; GOPURENKO, D - New South Wales Agriculture; Krueger, Robert; ALHUDAIB, K - King Abdulaziz University; LIU, J - Fujian Agricultural & Forestry University; FLETCHER, M - Charles Stuart University

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 8/25/2015
Publication Date: 12/20/2015
Citation: Gurr,, G.M., Bertaccini, A., Gopurenko, D., Krueger, R., Alhudaib, K., Liu, J., Fletcher, M.J. 2015. Phytoplasmas and their insect vectors: Implications for date palm. In:Wakil, W., Faleiro, J.R., Miller, T.A, editors. Sustainable Pest Management in Date Palm: Current Status and Emerging Challenges. 1st edition. Cham, Switzerland:Springer International Publishing. p. 287-314. doi: 10.1007/978-319-24397-9_10.

Interpretive Summary: Date palm is affected by a variety of diseases and those associated with phytoplasmas are becoming more frequently reported. Phytoplasmas are bacteria characterised by a small genome size and the lack of a cell wall. Transmission is chiefly by insect vectors. Date palm declines associated with phytoplasmas have been reported from the Middle East, North Africa, and North America. The phytoplasmas associated with date palm declines in the Old World have been associated with phytoplasmas indistinguishable from Candidatus Phytoplasma asteris (16SrI group), whereas those reported from North America have been associated with phytoplasmas belonging to the lethal yellows phytoplasma (16SrIV). This chapter summarizes these pathosystems and reviews phytoplasma taxonomy, detection, and management in general terms.

Technical Abstract: Date palm is affected by a variety of plant diseases and those associated with phytoplasma presence are increasingly recognised as an emerging threat to the crop. Phytoplasmas are bacteria characterised by a small genome size and the lack of a cell wall. Unlike other bacteria, they are transmitted chiefly by insects in a manner similar to the more familiar transmission of plant viruses by aphids. In the case of phytoplasmas, planthoppers and leafhoppers are most commonly implicated as vectors. Study of the group, including proving that a given vector is responsible for vectoring the agent of a given disease, is challenging because the pathogen is not readily cultured in vitro, necessitating laborious transmission tests. Date palm is affected by Al-Wijam disease in Saudi Arabia and molecularly undistinguishable phytoplasmas (16SrI group - ‘Ca. P. asteris’) were recovered from affected palms and from the hemipteran insect most commonly found on the palms, Cicadulina bipunctata. A second insect, Assymetrasca decedens also contained phytoplasma DNA but this belonged to the 16SrXII-A group that was not found in date palms. Date palm is also infected by the phytoplasma that is associated with lethal yellowing of coconut palm (16SrIV-A) and in the Americas is likely to be transmitted by Haplaxius (=Myndus) crudus. Texas phoenix decline is reported from warm regions of the south eastern USA and may be transmitted by two species of Derbidae. Phytoplasmas belonging to the 16SrIV-F and 16SrIXIV groups have also been isolated from date palm. Preventing spread in infected vegetative planting material and of vectors is key to limiting the impact of phytoplasma diseases. Management in affected areas can use antibiotics on high values trees, but this is not economical for extensive crops. In these situations, vector control by insecticide use or habitat management (e.g. removal of alternative hosts and mulching) can be useful, but the long lifespan of individual palms means that even low vector pressure can lead to infection over successive years. The development of resistant varieties and replanting is the most effective long-term approach developed so far for phytoplasma disease management in this plant species.