THE GENUS NACOBBUS THORNE & ALLEN, 1944 (NEMATODA: PRATYLENCHIDAE): SYSTEMATICS, DISTRIBUTION, BIOLOGY AND MANAGEMENT
Keywords:biology, diagnostics, distribution, false root-knot nematode, histopathology, host range, life cycle, management, morphology, nacobbus aberrans, nacobbus dorsalis, potato rosary nematode, quarantine, races, systematics, thermal requirements, yield losses
AbstractThe two known species of Nacobbus, N. aberrans and N. dorsalis, are sedentary root endoparasites that occur in the Americas. The parasitic habits of these two so-called "false root-knot nematode" species include similarities to both root lesion and root-knot nematodes. The migratory and vermiform juveniles and immature adults behave like lesion nematodes, causing cavities and lesions inside the root tissues, whereas the mature females are sedentary and obese and induce root galls and specialized feeding sites as do true root-knot nematodes. Limited information is available on the less wellknown species N. dorsalis, which is present only in California where it has negligible economic importance and parasitizes only a few non-cultivated plants without evidence of attack on agricultural crops. In contrast, many studies have examined the biology, economic impact, and management of the more economically important N. aberrans, which occurs in temperate and subtropical latitudes of North and South America. This false root-knot (or potato rosary) nematode has a wide host range, which includes at least 84 plant species. Many common weeds are good hosts. The results of host and field studies conducted in North and South America indicate that N. aberrans populations can be separated into bean, potato and sugarbeet groups. The populations of each group have distinct host preferences and do not reproduce on graminaceous species or on leguminous species of the genera Medicago and Lupinus. The yield losses reported on staple and industrial crops infected by N. aberrans average 65% for potato in the Andean region of Latin America, 55% and 36% for tomato and bean in Mexico, respectively, and 10-20% for sugarbeet in the United States (Nebraska). Different levels of resistance, varying according to the nematode population, have been found in bean, chilli pepper, potato, and tomato. Most research on crop rotation, mixed cropping, and chemical and non-chemical strategies for management of N. aberrans has been conducted on bean, chilli pepper, and tomato in Mexico, potato in Argentina, Bolivia and Peru, and sugarbeet in the United States.