Helicotylenchus multicinctus (Cobb, 1893) Golden, 1956

California Plant Pest Rating for

Helicotylenchus multicinctus (Cobb, 1893) Golden, 1956

Pest Rating: B

PEST RATING PROFILE

Initiating Event:

None. An evaluation of the risk involved with the possible introduction and spread of H. multicinctus in California is documented herein and a permanent rating is proposed for the species.

History & Status:

Biology and symptoms: The banana spiral nematode, Helicotylenchus multicinctus, is considered an endoparasite of host plant roots as it is able to complete its life cycle within the roots where all eggs, juvenile stages, and adult males and females may be found. Unlike other species of the genus, the banana spiral nematode invades outer layers of host cortical tissue producing characteristic small necrotic lesions which are initially yellow and then turn reddish brown to black in color. Apparently, the nematode does not invade deeper cortical tissue. In rare situations when infestation are high, root lesions can coalesce so that the necrosis becomes extensive resulting in root distortion and decay, stunting and toppling of top growth (McSorley & Parrado, 1986). The nematode species attacks rhizomes, corms, primary and secondary roots. Additionally, it is found in soil around plant roots. Because of its feeding and development biology the nematodes are easily introduced and spread to non-infested regions through infested soil, plant root and other root “seed stock”.

Hosts: The nematode is an important pest of banana and has also been recorded globally on several plant hosts of primary interest to California agriculture and environment. Hosts include mango, citrus, maize, rice, grapevine, fig, carrots, avocado, onions, peas, melon, common bean, cabbage, sugarbeet, garlic, grasses, and ornamentals (CABI, 2014; Vovlas, 1983). Ornamental banana plants are commonly propagated in regions of California.

Damage Potential: Knowledge of the extent of plant damage and loss has been gained through reports of laboratory and natural field studies conducted mainly on banana. After the burrowing nematode, Radopholus similis, the banana spiral nematode, Helicotylenchus multicinctus is considered as the most damaging plant pathogenic nematode species on bananas under conducive environmental conditions of temperature greater than 15.6 C and minimum precipitation 127 cm (Gowen & Quénéhervé, 1990). Both nematode species often occur together on bananas and plantains, however, in regions where the burrowing nematode is rare or absent, damage caused by H. multicinctus is more readily manifested (Gowen & Quénéhervé, 1990). Economic damage to banana has been reported from almost every region where banana and plantain are grown all which have similar climates and environments to California. Estimates of crop losses caused by H. multicinctus are not available and compounded as often other plant parasitic nematode species may be associated with the host and interact with environmental factors.

Disease Cycle: In experimental studies of H. multicinctus on banana roots, Blake (1966) reported that within 3 days of inoculation of adult nematodes, the latter fed on parenchymatous cells with their bodies partly embedded in the root. After 4 days, they were completely within the cortical tissue to a depth of 4-6 cells. Migration through the cortical tissue did not occur. Tissue surrounding infected cells was damaged with discoloration and necroses occurring near the infection points.

Transmission: Infected planting material: plant roots, bulbs, tubers, corms, rhizomes (suckers), seedlings, infested soil and growing medium with accompanying plants.

Worldwide Distribution: Banana spiral nematode is distributed wherever banana is cultivated globally. It has been recorded in several countries Europe, Asia, Pacific Islands, Africa, South America and North America (USA). In the USA, it has been reported in Alabama, Arkansas, California, Delaware, Florida, Georgia, Hawaii, Louisiana, Maryland, and Massachusetts (Birchfield, et al., 1978; CABI, 2014; Schenck & Schmitt, 1992).

Official Control: Helicotylenchus multicinctus is Chile’s Harmful Organism list (USDA PCIT, 2014). It is currently a Q-rated species in California.

California Distribution: There are early reports of Helicotylenchus multicinctus detected in Riverside, Los Angeles and San Diego Counties (Sher, 1966; Siddiqui et al., 1974).

California Interceptions: From 1989 to February 2015, there have been nine detections of Helicotylenchus multicinctus associated with Musa spp. and Ficus spp. imported to California nurseries (CDFA Nematode Detection Records).

The risk Helicotylenchus multicinctus would pose to California is evaluated below.

Consequences of Introduction:

1) Climate/Host Interaction: Evaluate if the pest would have suitable hosts and climate to establish in California. Score:

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.
– Medium (2) may be able to establish in a larger but limited part of California.
– High (3) likely to establish a widespread distribution in California.

Risk is Medium (2) – Helicotylenchus multicinctus is likely to spread within California wherever host plants are grown in favorable climate.

2) Known Pest Host Range: Evaluate the host range of the pest. Score:

– Low (1) has a very limited host range.
– Medium (2) has a moderate host range.
– High (3) has a wide host range.

Risk is Medium (2) – Banana is the main host, and ornamental banana plants are commonly grown in regions of California. There are several other plant species that are also hosts.

3) Pest Dispersal Potential: Evaluate the natural and artificial dispersal potential of the pest. Score:

– Low (1) does not have high reproductive or dispersal potential.
– Medium (2) has either high reproductive or dispersal potential.
– High (3) has both high reproduction and dispersal potential.

Risk is High (3) – Dispersal of the nematode pathogen is mainly through artificial means and infected planting materials, vegetative “seed” stock is the most common means of long distance spread. The nematode is also spread through infested soil and planting media, irrigation water, cultivation tools and equipments contaminated with infested soil.

4) Economic Impact: Evaluate the economic impact of the pest to California using the criteria below. Score:

A. The pest could lower crop yield.
B. The pest could lower crop value (includes increasing crop production costs).
C. The pest could trigger the loss of markets (includes quarantines).
D. The pest could negatively change normal cultural practices.
E. The pest can vector, or is vectored, by another pestiferous organism.
F. The organism is injurious or poisonous to agriculturally important animals.
G. The organism can interfere with the delivery or supply of water for agricultural uses.

– Low (1) causes 0 or 1 of these impacts.
– Medium (2) causes 2 of these impacts.
– High (3) causes 3 or more of these impacts.

Risk is Medium (2) – The extent of crop damage and loss is mainly known for banana. Helicotylenchus multicinctus could lower crop value in banana plants including those grown in nurseries as ornamentals for commercial and residential purposes. Phytosanitary measures and the use of nematode-free planting stock would need to be adopted to mitigate risk of spread of this nematode species. The extent of damage and loss to other host plants, including agricultural crops is not known. Infected nursery plants are at risk of introducing the nematode species to outdoor favorable sites.

5) Environmental Impact: Evaluate the environmental impact of the pest on California using the criteria below.

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.
B. The pest could directly affect threatened or endangered species.
C. The pest could impact threatened or endangered species by disrupting critical habitats.
D. The pest could trigger additional official or private treatment programs.
E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Score the pest for Environmental Impact. Score:

– Low (1) causes none of the above to occur.
– Medium (2) causes one of the above to occur.
– High (3) causes two or more of the above to occur.

Risk is Low (1) – Banana, the main host, is not commercially cultivated in California, and the affect of the nematode species on other host plants is not fully known. However, it is likely that Helicotylenchus multicinctus could impact home/urban gardening and ornamental plantings causing changes in cultivation practices in order to mitigate potential damage.

Consequences of Introduction to California for Helicotylenchus multicinctus

Add up the total score and include it here. (Score)

– Low = 5-8 points
– Medium = 9-12 points
– High = 13-15 points

Total points obtained on evaluation of consequences of introduction of Helicotylenchus multicinctus to California = (10).

6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included. (Score)

– Not established (0) Pest never detected in California, or known only from incursions.
– Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).
– Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.
– High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Evaluation is Low (-1). Early reports indicate that Helicotylenchus multicinctus has been detected in San Diego, Los Angeles and Riverside Counties. However, to date this species has never been detected in California’s agricultural production site monitored through statewide nematode surveys or CDFA’s various nematode detection regulatory programs.

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

Final Score: Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 9.

Uncertainty:

There may be some doubt associated with the true distribution of the banana spiral nematode in California partly due to the fact that for several years, members of the genus Helicotylenchus were given a general rating that required no State regulatory action against the pest. Subsequently, genus members were not always identified at the species level. On the other hand, it is quite unlikely that this was the case for H. multicinctus as its unique biology and morphology easily separates this species from all other species of the genus. Furthermore, H. multicinctus has not been detected in California’s commercial agricultural production sites monitored through various regulatory nematode detection programs. Future detections of H. multicinctus may indicate a wider distribution than presently known and result in a lower rating.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Helicotylenchus multicinctus is B.

References:

Birchfield W., J. P. Hollis and W. J. Martin. 1978. A list of nematodes associated with some Louisiana plants. Technical Bulletin, Louisiana State University, 101:22 p.

Blake, C. D. 1966. The histological changes in banana roots caused by Radopholus similis and Helicotylenchus multicinctus. Nematologica, 12:129-137.

CABI. 2014. Helicotylenchus multicinctus (banana spiral nematode) full datasheet. Crop Protection Compendium. www.cabi.org/cpc/

Gowen, S. & P. Quénéhervé. 1990. Nematode parasites of bananas, plantains and abaca. In: Luc, M., R. A. Sikora and J. Bridge, l (Eds). Plant parasitic nematodes in subtropical and tropical agriculture. Wallingford, UK, CAB International: 431- 460.

McSorley, R. and J. L. Parrado. 1986. Nematological reviews – Helicotylenchus multicinctus on bananas: An international problem. Nematropica, 16 : 73-91.

Schenck, S. and D. P. Schmitt. 1992. Survey of nematodes on coffee in Hawaii. Supplement to the Journal of Nematology 24:771-775.

Sher, S. A. 1966. Revision of the Hoplolaiminae (Nematoda) VI. Helicotylenchus Steiner, 1945. Nematologica 12:1-56.

Siddiqui, I. A., S. A. Sher and A. M. French. 1973. Distribution of plant parasitic nematodes in California. State of California Department of Food and Agriculture, Division of Plant Industry, 324 p.

USDA PCIT. 2014. USDA Phytosanitary Certificate Issuance and Tracking System. Phytosanitary Export Database. https://pcit.aphis.usda.gov/PExD/faces/ReportHarmOrgs.jsp

Vovlas, N. 1983. Morphology of a local population of Helicotylenchus multicinctus from southern Italy. Revue de Nématologie 6: 327-329.

Responsible Party:

Dr. John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110, plant.health[@]cdfa.ca.gov.