Meloidogyne arenaria

Meloidogyne arenaria is a species of plant pathogenic nematodes. This nematode is also known as the peanut root knot nematode. The word 'Meloidogyne' is derived from two Greek words that mean 'apple-shaped' and 'female'. The peanut root knot nematode, M. arenaria is one of the 'major' Meloidogyne species because of its worldwide economic importance. M. arenaria is a predominant nematode species in the United States attacking peanut in Alabama, Florida, Georgia, and Texas. The most damaging nematode species for peanut in the USA is M. arenaria race 1 and losses can exceed 50% in severely infested fields. Among the several Meloidogyne species that have been characterized, M. arenaria is the most variable both morphologically and cytologically. In 1949, two races of this nematode had been identified, race 1 which reproduces on peanut and race 2 which cannot do so. However, in a recent study, three races were described (races 1, 2, and 3). López-Pérez et al (2011) had also studied populations of M. arenaria race 2, which reproduces on tomato plants carrying the Mi gene and race 3, which reproduces on both resistant pepper and tomato. M. arenaria has the same history as the other root knot nematodes. Meloidogyne spp were originally grouped together with the cyst nematodes (Heterodera spp) but they were later separated after they were confirmed to be significantly different from each other. The changes that were made when discovering Meloidogyne spp of nematodes are described below; Crop damage by this nematode is mostly faced in warmer regions and it is rarely found in areas where the average monthly temperatures approach freezing. The peanut root knot nematode, race 1 is found in all areas where peanuts are grown. The peanut root-knot nematode is the most serious nematode pest of the crop and questionably the most serious soil-borne disease problem. For example, the nematode is present in almost all fields where the crop is grown in Florida and economic damage is estimated to occur in greater than 50% of these fields. Individual peanut fields heavily infested with the root-knot nematode have sustained yield losses greater than 75%. In addition to causing considerable damage alone, it also increases the severity and incidence of other soil-borne diseases such as southern stem rot and Cylindrocladium blackrot. M. arenaria is C-rated pest in California. Different development stages of this nematode have unique features that are used to describe them. Among the characters commonly used to define nematode species and populations, morphometric characters have a marked significance. Females are swollen, pear-shaped pearly white and sedentary. They deposit their eggs in a gelatinous mass, which usually protrudes from galled root tissue. Females of this nematode are completely endoparasitic. Mature females of M. arenaria are identified by the cuticular markings in the perineal area, stylet length, punctations on the cuticle. When describing the morphology of M. arenaria race1, Eisenback et al., (1981) reported that in females, the dorsal arch is flattened and rounded. The striae in the arch are slightly indented at the lateral lines and generally form a shoulder on the arch. The stylet is very robust and the cone and shaft are broad. The labial disc and lips are dumb bell shaped and it has large lateral lips that are separated from the medial lips and the head region. In a study in Argentina, perineal patterns of 100 females from a population of M. arenaria, race 2 growing on tomato plants were analyzed and moderate morphological variations observed. The overall shape was rounded in most cases, but it was oval-shaped in a small proportion (4%). Forty-six percent of females showed low dorsal arch while 38% depicted a high dorsal arc, while the rest were intermediate. Lines in the post-anal region were smooth or wavy, continuous or broken, occasionally forming shoulders (18% of females). Wings were generally not observed. Phasmids were visible in 25% of the patterns and the mean distance between them was 24.33 ± 1.61 mm. Only seven out of one hundred females presented perineal patterns with lateral lines weakly demarcated by forked striae. Adult females were pyriform and lacking a terminal protuberance in the posterior area of the body. The female body lengths ranged between 465 mm and 1,129 mm. The excretory pore of the females was located closer to the base of the stylet than to the median bulb, at approximately 2-stylet lengths, in agreement with a typical M. arenaria specimen. The stylet was dorsally curved. Second stage juveniles of this nematode are short (400–600 micrometers) with very short stylets (10-15micrometers). The stylet is lightly sclerotized with indistinct Knobs. The cephalic framework is also weakly sclerotized. The esophageal gland overlaps the intestine ventrally and the tail tapers to a pointed tip with a clear terminus In a study, second stage juveniles (J2s) averaged 458.51 ± 20.48 mm in length and 15.35 ± 0.76 mm in width. The rectum was undilated. Tail length (from anus to posterior end) was 56.21 ± 2.78 mm and the tail tip was rounded. Males of M. arenaria are long (1.0 to 2.0 mm). The stylet is short and has distinct knobs. The esophageal gland overlaps the intestine ventrally. The tail is short and rounded and has no bursa. Spicules open a short distance from the tail tip. The males also have a head cap that is low and slopes posteriorly with 2 or 3 incomplete annulations around the head region. The stylet is pointed and the lumen opening has a small protuberance on the ventral side. From their study, Garcı´a and Sa´nchez-Puerta, (2012) also reported that the mean length of the male body was 1.6 ± 0.31 mm. The head of the males was flat to concave and showed a moderately elevated labial disc. The males also had four lateral lines, which were easily observed.