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Significance

Temperate climate nematology had its beginnings in 1743 with discovery of the wheat seed gall nematode, Anguina tritici, by John T. Needham. In contrast, one of the first plant-pathogenic nematodes discovered from the tropics, Radopholus similis, was not described until Nathan A. Cobb found it in bananas from Fiji almost 150 years later. Most tropical and subtropical nematology laboratories were not established nor local problems addressed until the latter half of the 20th Century. This late start accumulating basic information, including the presence of burrowing nematode and the need for quarantine regulations, furthered the worldwide spread of R. similis. The number of management strategies also lags behind those for temperate climate nematodes.

Bananas rank first among fruits produced worldwide and are annually worth about US$2.5 billion. However, only about 10% of the almost 86 million tons produced are traded commercially. The remaining 90% are grown and consumed by subsistence farmers and their families in developing tropical and subtropical regions. Burrowing nematode damage can cause yield losses of 30 to 60% on banana and a reduction in the productive life of the farm. Economic losses due to R. similis are sometimes difficult to assess as it often exists with other plant-pathogenic nematode species such as root-knot (Meloidogyne), lesion (Pratylenchus), or spiral (Helicotylenchus) nematode. Populations of root-knot and lesion nematodes, both of which feed inside plant roots, may increase if R. similis populations decrease.

The citrus race of R. similis has a limited distribution, including Florida, parts of the Caribbean, Cote d’Ivoire and Guyana; R. citri is restricted to Indonesia. Spreading decline in Florida was apparently responsible for yield losses of 40 to 70% in oranges and 50 to 80% in grapefruits in the mid-1900s. During a 10-year period, this accounted for a difference of 1338 versus 62 boxes/ha harvested from healthy versus infested groves, respectively. Exclusion management practices, pull and treat programs, and movement of the Florida citrus industry to new lands within the state have reduced the impact of burrowing nematode in Florida citrus. Economic loss from declining citrus trees in Indonesia has not been determined, but is thought to be substantial.

In black pepper plantations, diseased plants on trellis poles create a forest of yellow leaves and naked vines. Yellows disease was associated with the loss of 22 million pepper vines over a 20-year period in Indonesia and slow wilt was responsible for the death of 10% of vines in parts of India in the early 1900s.

Local, state and international quarantine regulations are a significant economic consequence of burrowing nematode disease. Preshipment certification is often needed for plant export from infested areas to noninfested areas. This includes shipping rooted citrus from Florida to California, for example, or potted anthuriums from Hawaii to California and Japan. Certified nurseries also need a phytosanitary inspection and certificate for each shipment. Costs associated with compliance to quarantine regulations seriously impact growers and consumers on both sides of the law. Preventing the spread of burrowing nematode to new growing areas, however, remains a critical part of its management.

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