Radopholus similis
Cobb, 1893
Burrowing nematode

Excerpt taken from “The Family Pratylenchidae—Thorne, 1949,” Loof, Pieter A. A., Manual of Agricultural Nematology, Marcel Dekker, Inc., New York, 1991, pp. 406-10.

Dimensions: Females: L=0.52-0.88 mm; a=22-30; b=4.7-7.4; b’=3.5-5.2; c=8-13; c’=2.9-4.0; V=55-61; stylet=17-20 um. Males: L=0.54-0.67 mm; a=31-44; b=6.1-6.6; b’=4.1-4.9; c=8-10; c’=5.1-6.7; stylet=12-17 um; spicules=18-22 um; gubernaculum=8-12 um.

Specific characters: Female: Head composed of three to four annules. Lateral field with four longitudinal lines. Spermathecae round, with small, rod-shaped sperm. Hyaline part of tail 9-17 um long; terminus striated. Phasmids in anterior third of tail. Male: Head four-lobed, lateral sectors strongly reduced. Gubernaculum with small titillae. Bursa extends over about two-thirds of tail.

Geographic distribution: Originally described from the Fiji Islands, but occurs also in Australia, Florida, Central and South America, several Caribbean islands, tropical Africa. In the 1960’s it was imported into several European countries (France, Belgium, the Netherlands, Germany) with ornamental plants.

Hosts: The most important hosts are banana (“toppling-over disease”) and pepper (“yellows”- during the years after World War II, pepper culture on the Islands of Banka, Indonesia, was almost completely destroyed). More than 250 other plant species are known to be hosts, among them many ornamentals such as Philodendron and Maranta. To what extent it is a major pest of these has not yet been completely determined.

It has long been suspected that there exist different pathotypes within this species. DuCharme and Birchfield (1956) found indications for the occurrence of three pathotypes in Florida: one parasitizing citrus only, one banana and citrus, and one banana but not citrus. The first was not examined further, but the existence of the two others was proven and these have since been known as the citrus race and the banana race, respectively. The citrus race is known from Florida only; the banana race is widely distributed. Later there came indications that there exists more than one “banana race” (Edwards and Wehunt, 1971).

During the 1980’s several differences between the citrus race and the banana race were discovered. Huettel and Dickson (1981b) found differences in oocyte maturation; Huettel et al. (1983a) in sex pheromones; Huettel et al. (1983b) in enzymes; Huettel et al. (1983c) in proteins. Huettel et al. (1984a) found the haploid chromosome number to be four in the banana race, five in the citrus race. Finally, Huettel et al. (1984b) concluded that the two races were distinct species; the name R. similis was restricted to the banana race; the citrus race was described as R. citrophilus. Huettel and Dickson (1981a) found that both R. similis and R. citrophilus are able to propagate by parthenogenesis, though the normal method is by amphimixis.