Characterisation of populations of Longidorus orientalis Loof, 1982 (Nematoda: Dorylaimida) from date palm (Phoenix dactylifera L.) in the USA and other countries and incongruence of phylogenies inferred from ITS1 rRNA and coxI genes

Abstract

Needle nematode populations of Longidorus orientalis associated with date palm, Phoenix dactylifera, and detected during nematode surveys conducted in Arizona, California and Florida, USA, were characterised morphologically and molecularly. The nematode species most likely arrived in California a century ago with propagative date palms from the Middle East and eventually spread to Florida on ornamental date palms that were shipped from Arizona and California. This is the first validated continental record of this needle nematode species in the USA and the Americas. The USA populations of L. orientalis contained a small number of males that were not reported in the original description and are herein described. Longidorus orientalis was able to survive for at least 4 years at very low numbers in the warm and humid environment of Florida on date palms imported from California and Arizona. Association of L. orientalis with L. africanus was observed in all of the surveyed sites, indicating that date palm is a host of both nematodes. Phylogenetic relationships of L. orientalis with closely related Longidorus species, in addition to relationships between populations of L. orientalis from the USA, Greece, Iran and Spain, were inferred from the analyses of D2-D3 of 28S rRNA, ITS1 rRNA and partial coxI gene sequences. The PCR-D2-D3 expansion segments of 28S rDNA-RFLP diagnostic profile is provided. Longidorus orientalis populations display a high level of intraspecific variation (up to 15.5%) in coxI mtDNA sequences. Analysis of phylogenetic relationships of nematode populations revealed incongruence of the ITS1 rRNA and coxI mtDNA gene trees, which might be the result of selective introgression of mtDNA through gene flow between previously isolated populations introduced simultaneously into new geographical regions.