Morphological and molecular diversity of Radopholus on coffee in Vietnam and description of R. daklakensis sp. n. from Robusta coffee

Abstract

Four isolates of Radopholus arabocoffeae and one isolate of R. duriophilus were collected during a survey of plant-parasitic nematodes on coffee in Vietnam. Radopholus species only occurred in the Western Highland region. Information on the degree of variability in morphometrics, and morphological and molecular characters amongst and within these species are reported. The survey also yielded a Radopholus isolate collected from Robusta coffee roots and soil in Dak Lak, which is herein described as a new species, R. daklakensis sp. n. Within the genus, R. daklakensis sp. n. is most similar to R. arabocoffeae and R. duriophilus in morphology and morphometrics. It differs from R. arabocoffeae by the stylet knobs always directed posteriorly and the conical tail shape with rounded terminus in females. Radopholus daklakensis sp. n. differs from R. duriophilus by the stylet knobs, which are always directed posteriorly vs rounded, and dorsal knob sometimes projected anteriorly, and sperm rod-shaped vs oval and kidney-shaped. Radopholus daklakensis sp. n. differs from R. similis by the absence of a postrectal intestinal sac, four incisures of the lateral fields terminating far posterior to the position of the phasmid, the bursa in male reaching one-third of tail to half, never reaching tail terminus and smaller stylet length in females. The canonical discriminant analysis separated the Radopholus species by characters such as lip height, stylet length, b, b′, c, V and ratio tail length/stylet length. Phylogenetic analysis of Radopholus species using ITS-rDNA sequences or sequences from the D2-D3 expansion region of the 28S rRNA gene also confirm R. daklakensis sp. n. to be distinct.