Banana Pest and Disease Management in the Tropical Pacific: A guidebook for banana growers
Chapter II: Key Pests and pathogens of banana in the Pacific
II-2. Plant Parasitic Nematodes
Plant-parasitic nematodes are microscopic roundworms that feed on plants. Most species feed on roots, but some feed on plant foliage. Among those nematodes infecting plant roots, some are ectoparasitic and others are endoparasitic. Ectoparasitic nematodes feed on plant tissues from outside of the plant, whereas endoparasitic nematodes feed from within the plant. Nematodes can be further categorized as migratory and sedentary. If the adult female moves freely through the soil or plant tissues, the nematode is referred to as migratory. An adult female that is immobile and remains in one area of the root is termed sedentary. Three migratory endoparasitic nematodes that feed on the root cortex of banana plants are the burrowing (Radopholus similis), spiral (Helicotylenchus multicinctus), and lesion (Pratylenchus spp.) nematodes. Their feeding results in dead root cells, or lesions (Fig.2-6A). Sedentary endoparasitic nematodes that feed on banana include the root-knot (Meloidogyne spp.) and reniform (Rotylenchulus reniformis) nematodes (Fig. 2-7). They penetrate banana roots, migrate and settle at a feeding site, and cause the surrounding cells to enlarge. Although root galls are not commonly seen on banana roots, heavily root-knot nematode-infected banana roots become swollen (Fig. II-6B). A nematode survey conducted between 2007 and 2008 throughout Hawai‘i revealed five major genera of nematodes that are commonly associated with banana roots: spiral, burrowing, root-knot, reniform, and lesion nematodes (Figs. 2-7 A -F).
Damage caused by plant-parasitic nematodes on banana
Although plant-parasitic nematodes behave like hidden pests and are often ignored, damage caused by nematodes on banana is well documented, resulting in significant yield loss in banana production worldwide (Davide & Marsigan 1985, Speijer et al. 1999). Burrowing and spiral nematodes are reportedly responsible for yield losses of 30–50% in Costa Rica and Panama, 40% in Africa, 30–60% in India (Davide 1995) and more than 50% in East Africa (Speijer & Kajumba 1996, Kashaija et al. 2004). Banana nematodes attack root and corm tissue, causing damage that can reduce bunch size, shorten production life, prolong the vegetative cycle, and cause banana plants to topple (Fig. 2-8) (McSorley and Parado 1986, Bridge 1988, Chabrier and Quénéhervé 2003). Although limited studies are available on nematode damage on banana in the Pacific Islands, recent publications from American Samoa, Mariana Islands, and Hawai‘i showed that mixed populations of nematode species dominated by spiral nematode (H. multicinctus) commonly occur in banana fields (Brooks 2004, Quintanilla unpublished, Wang & Hooks 2009).
To estimate banana growth reduction caused by a combination of plant-parasitic nematodes commonly found in Hawai‘i, field soil was collected from an established banana field (> 5-years old) in Wai‘anae, HI. A greenhouse experiment was conducted to compare plant growth of tissue-cultured apple banana in 5.6-L pots containing autoclaved or non-autoclaved soil. Autoclave-sterilizing soil was used to render soil free of plant-parasitic nematodes. The non-autoclaved soil contained 18,368 spiral, 15,232 root-knot, 672 burrowing, and 6,720 reniform nematodes per one 5.6 L-size pot. At 7.5 months after planting, all the banana plant growth measurements (Fig. 2-9) were higher in the autoclaved soil than in the non-autoclaved soil (P < 0.10). One measurement, plant height, was approximately 20% reduced in the banana plants grown in the non-autoclaved soil. By the end of the experiment, root-knot nematodes had become the most dominant nematodes, followed by spiral and burrowing nematodes. A few plant-parasitic nematodes were also recovered from the autoclaved pots.
When subjected to regression analysis between plant growth parameters (root weight, leaf weight, stem weight, pseudostem diameter, and plant height) and nematode numbers (root-knot, spiral, and burrowing nematodes), significant regression relationships were found between many of these parameters (Table 2-1). Among the three most dominant nematode species, only spiral nematodes’ numbers correlated significantly to with plant height (R = - 0.25, P < 0.05), indicating that spiral nematode infection significantly reduced plant height. The combination of spiral and burrowing nematodes also regressed negatively to plant height to a greater extent than a combination of all three nematode species (R = - 0.26, P < 0.05). This indicated that infection with root-knot nematode did not reduce plant height. Similar regression analysis was observed between stem, leaf, and root weights with all three nematodes, alone and in combination, except there was no regression between root-knot nematodes and leaf weight. The combination of burrowing and spiral nematodes in a model often improves the R-value when regressed with all plant growth parameters. This indicates that burrowing and spiral nematodes were the main contributors to the decline in growth of banana in this nematode-infested soil.
Natural enemies of plant-parasitic nematodes in banana fields
During the 2007–2008 survey conducted in Hawai‘i, several commonly found natural enemies of plant-parasitic nematodes in the state included predatory nematodes, nematode-trapping fungi (Fig. 2-10), and a bacterial parasite of root-knot nematode, Pasteuria penetrans (Fig. 2-7 E). These naturally occurring predators or parasites of nematodes may not contribute significantly to the suppression of plant-parasitic nematodes below the economic threshold level, especially in intensively managed, long-established banana farms, but they could potentially keep the population of the nematode pests in check to a certain extent. A correlation analysis based on the survey results indicated that most farms that received high-input practices such as the application of synthetic fertilizers, glyphosate, and various types of fungicides generally had lower abundance of omnivorous and predatory nematodes (Wang and Hooks 2009).
Wang, K.-H., C.R.R. Hooks. 2009. Survey of nematodes on banana in Hawai‘i and methods used for their control. CTAHR Cooperative Extension Publication PD-69. http://www.ctahr.hawaii.edu/oc/freepubs/pdf/PD-69.pdf
Brooks, F.E. 2004. Banana nematodes. Pests and Diseases of American Samoa 9. 2 pp. https://www.ctahr.hawaii.edu/adap/ASCC_LandGrant/Dr_Brooks/BrochureNo9.pdf
Bridge, J. 1988. Plant-parasitic nematode problems in the Pacific islands. Journal of Nematology 20: 173–183.
Brooks, F.E. 2004. Plant-parasitic nematodes of banana in American Samoa. Nematropica 34: 65–72.
Chabrier, C., and P. Quénéhervé. 2003. Control of the burrowing nematode (Radopholus similis Cobb) on banana: Impact of the banana field destruction method on the efficiency of the following fallow. Crop Protection 22:121–127.
Davide, R.G. and L.Q. Marsigan. 1985. Yield loss assessment and evaluation of resistance of banana cultivars to the nematodes Radopholus similis Thorne and Meloidogyne incognita Chitwood. The Philippine Agriculturist 68:335–349.
Davide, R.G. 1995. Overview of nematodes as a limiting factor in Musa production. In: New Frontiers in Resistance Breeding for Nematode, Fusarium and Sigatoka. E.A. Frison, J.P. Horry, and D. de Waele (eds.). International Network for the Improvement of Banana and Plantain, Montpellier, France. p. 27–31.
Gowen, S.R., P. Quénéhervé, and R. Fogain. 2005. Nematode parasites of bananas and plantains. In: Plant Parasitic Nematodes in Subtropical and Tropical Agriculture. M. Luc, R.A. Sikora, and J. Bridge, 2nd edition. CAB International Edit, Wallingford, Oxon, UK. p. 611–643.
Kashaija, I.N., B.D. McIntyre, H. Ssali, and F. Kizito. 2004. Spatial distribution of roots, nematode populations and root necrosis in highland banana in Uganda. Nematology 6:7–12.
McSorley, R., and J.L. Parado. 1986. Helicotylenchus multicinctus on bananas: An international problem. Nematropica 16: 73–91.
Speijer, P.R., and C. Kajumba. 1996. Yield loss from plant parasitic nematodes in East African highland banana (Musa AAA). Musafrica 10:26.
Speijer, P.R., C. Kajumba, and F. Ssango. 1999. East African Highland banana production as influenced by nematodes and crop management in Uganda. International Journal of Pest Management 45:41–59.
Wang, K.-H., and C.R.R. Hooks. 2009. Plant-parasitic nematodes and their associated natural enemies within banana (Musa spp.) plantings in Hawaii. Nematropica 39: 57–73.
Home Gardener’s Corner
Banana suckers from an established banana mat will most likely carry endoparasitic nematodes such as burrowing, spiral, and lesion nematodes in the root system. Various precautions can be taken (see Chapter V) to mitigate the problem. Keep the banana root system in good health by periodically adding organic compost as mulch under the banana canopy. Reduce disturbance to the root system by minimizing the use of pesticides and tillage around the root system. Remove excess suckers; keep no more than 3–5 plants per banana mat. These steps can decrease the damage to banana from plant-parasitic nematodes. Refer to Chapter V for how to plant marigold as a living mulch to manage plant-parasitic nematodes after planting banana. If banana yields decline over time, it may be due to damage from plant-parasitic nematodes. Replanting with new, healthy banana plants may be worthwhile.