Rotylenchulus species: Identification, distribution, host ranges, and crop plant resistance

A review is given of the 10 known species of Rotylenchulus that occur largely in tropical and subtropical latitudes. They can be distinguished with a simple dichotomous key. Hundreds of studies have examined the biology, economic impact, and management of the type species, R. reniformis. Information also is available regarding the geographical distribution, host range, and histopathology induced by R. borealis, R. macrodoratus, R. macrosoma and R. parvus. Relatively little is known regarding R. anamictus, R. brevitubulus, R. clavicaudatus, R. leptus, and R. sacchari. R. reniformis and R. parvus both appear to have a cosmopolitan distribution in warm latitudes; R. borealis, so far, has been reported primarily from Europe and Africa; R. macrodoratus and R. macrosoma have been found primarily in the Mediterranean region. There are clear anatomical differences in the trophic site induced by R. macrodoratus (uninucleate giant cell) compared to those induced by R. borealis, R. macrosoma, R. parvus, and R. reniformis (syncytia). There are also differences in the abilities of these species to parasitize various hosts. R. reniformis appears to have the widest host range and has been reported to reproduce on 86% of 364 plant species examined. Many common weeds are good hosts. However, more than 50 crop or ornamental plants support little or no reproduction by most populations of R. reniformis. Examples include barley, maize, onion, rice, several Crotalaria species and resistant cultivars of soyabean. Varying levels of resistance also have been found in cotton, olive, papaya, potato, sweet potato, tobacco, tomato, and various legumes. Most research on crop rotation and mixed cropping for management of R. reniformis has been done on cotton and soyabean in the USA, and on legumes in India.