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Pathogen Biology

Genus Belonolaimus:

Steiner described the first sting nematode Belonolaimus gracilis, which was collected from the rhizosphere of a pine tree (Pinus sp.) in Marion County, FL. Later this nematode was reported to damage various agronomic and horticultural crops in the Atlantic coast states as far north as Virginia. Rau later described B. longicaudatus and identified it as the more common species of Belonolaimus in agricultural settings. Most of the crop damage that was originally attributed to B. gracilis is now recognized as having been caused by B. longicaudatus. Currently there are nine described species of Belonolaimus. Belonolaimus longicaudatus, B. gracilis, B. euthychilus, B. maritimus, and B. nortoni are found in the United States, whereas B. anama, B. jara, B. lineatus, and B. lolii are found elsewhere. Other populations of Belonolaimus that differ from described species by host-range, morphology, and molecular characterization are reported and may represent new species.

Habitat and Distribution:

Belonolaimus longicaudatus is endemic to the coastal plains of the southeastern United States. It has been found as far north along the Atlantic Coast as New Jersey and as far west along the Gulf Coast as Texas, but is most common in Florida. Soil texture is apparently a major factor influencing the distribution of B. longicaudatus both within the soil horizon, and geographically. Reproduction of B. longicaudatus is minimal in soils with < 80% sand content or > 10% clay content. Golf course putting greens are typically constructed with high sand content, providing an ideal habitat for B. longicaudatus. Therefore, it is not surprising that B. longicaudatus has become established outside of its natural geographic range in golf course putting greens in Australia, the Bahamas, Bermuda, and California through introduction on infested planting material.

Morphology and Identification:

Sting nematodes are among the largest plant-parasitic nematodes, up to 3 mm long. The stylet of B. longicaudatus is long and thin, and the anterior region of the head is offset by a constriction (Figure 17). The median bulb of the esophagus is very pronounced, and the esophageal glands overlap the intestine. Female B. longicaudatus have the vulva located near the middle of the body (Figure 18) and have a rounded tail (Figure 19). Males have a long tail that narrows dorsally to a point, well developed spicules, and a small bursa (Figure 20). Juvenile stages look very similar to adults (Figure 21).

Figure 17	Figure 18
Figure 19	Figure 20
Figure 21

Feeding and host range:

Sting nematodes are ectoparasites, meaning that they typically feed with their bodies outside of plant tissue. To feed, sting nematodes insert their long stylet into tissue near the root tip and then ingest the contents of the root cells through it. After feeding on a root tip, a sting nematode can withdraw its stylet and move to another feeding site. Feeding by multiple sting nematodes on the same root tip (Figure 22) can cause root growth to cease and lead to a proliferation of lateral roots. The nematodes then feed on and damage these developing lateral roots, giving rise to a bunchy or stubby appearance.

Figure 22

The host range of B. longicaudatus is extensive and includes vegetables (e.g., beans, carrot, corn, crucifers, potato), fruits (e.g., citrus, strawberry), agronomic crops (e.g., cotton, peanut, sorghum, soybean), turfgrasses (e.g., bermudagrass, St. Augustinegrass, zoysiagrass) and forest crops (pine trees). Several studies suggest the existence of physiological races of B. longicaudatus. Physiological races are populations of a given species that show different host preferences than other populations of the same species.

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