Radopholus arabocoffeae sp. n. (Nematoda: Pratylenchidae), a nematode pathogenic to Coffea arabica in Vietnam, and additional data on R. duriophilus

Abstract

AbstractRadopholus arabocoffeae sp. n., a new nematode pathogenic on Coffea arabica cv. Catimor, is described from Vietnam. Females of R. arabocoffeae sp. n. are characterised by the broad amphidial apertures with prominent margins. Males are characterised by the bursa extending to one third, rarely middle, of the tail. The new species belongs to the group of species with a long tail in the female. Radopholus arabocoffeae sp. n. is easily distinguished from R. similis by the bursa reaching to only one third of the tail vs extending to the tail terminus. Radopholus arabocoffeae sp. n. is differentiated from R. bridgei by the lateral field having three bands of equal width (vs middle one narrower than others), lateral field completely areolated over whole body vs not areolated except irregularly in neck and tail, hemizonid distinct vs indistinct, four lateral field incisures terminating far behind phasmid vs three incisures terminating at or just behind phasmid, lateral lines fusing at two thirds of tail vs fusing at one third of tail, longer spicule length (18-21 vs 15.5-18.0 μm), and male bursa usually extending to only one third of tail vs mid tail. Radopholus arabocoffeae sp. n. differs from R. colbrani by the rod-like vs round sperm, spicule length (18-21 vs 13-16 μm), tail length to stylet ratio (4.1-4.9 vs more than 5.1) and presence vs absence of a bursa. Radopholus arabocoffeae sp. n. differs from R. duriophilus by the rod-like vs kidney-shaped sperm. Males further differ from R. duriophilus by shorter stylet length (8.2-11.6 vs 11.5-15 μm), smaller distance between dorsal pharyngeal gland orifice and stylet base (1.7-3.4 vs 4-9.5 μm), shorter hyaline tail (2.6-3.4 vs 4-9.5 μm), and bursa extending to one third of tail vs mid-tail. Female R. arabocoffeae sp. n. differ from R. duriophilus by the broad amphidial aperture with prominent margin present vs absent. Males of R. arabocoffeae sp. n. differ from R. musicola by the rudimentary and amalgamated stylet base (vs with knobs), and inner lateral lines fusing at two thirds of the tail vs just posterior to the phasmid. The high level of ITS-rDNA sequence divergence of R. arabocoffeae sp. n. from other Radopholus spp. and the presence of nucleotide autapomorphies support a separate specific status of this new species. On carrot disks, the two species reproduced from 15-30°C; optimum reproduction occurring at 28°C. The reproductive capacity of R. duriophilus was higher than that of R. arabocoffeae sp. n. Radopholus duriophilus reproduced from single juveniles; R. arabocoffeae sp. n. did not. The correlation between initial densities of Pratylenchus coffeae, R. duriophilus and R. arabocoffeae sp. n. and the weight of C. arabica cv. Catimor fitted the Seinhorst model Y = ym for Pi ≥ T, and Y = ym ˙ m + ym(1–m)z(Pi–T). Coffea arabica cv. Catimor was very susceptible for to all three nematode species tested, but especially so to R. arabocoffeae sp. n. The reproductive capacity of R. arabocoffeae sp. n. on C. arabica cv. Catimor was higher than P. coffeae or R. duriophilus.