There are many plant-parasitic species in the

root-knot nematode Root-knot nematodes are plant-parasitic nematodes from the genus ''Meloidogyne''. They exist in soil in areas with hot climates or short winters. About 2000 plants worldwide are susceptible to infection by root-knot nematodes and they cause appr ...

genus (''Meloidogyne'') that attack coffee such as '' M. incognita'', '' M. arenaria'', '' M. exigua'', '' M. javanica'' and '' M. coffeicola''. Study has already shown interspecific variability coffee, in which show how this species can be adapting to new hosts and environments.

Morphology and anatomy

''Meloidogyne exigua'' females are small with medium stylet (12–14 µm) and strong basal knobs.Carneiro, M.D. G. & Cofcewicz, T. E. 2008. Taxonomy of Coffee-Parasitic root-knot nematodes, Meloidogyne spp. In: Souza, R. M (Ed). Plant-Parasitic nematodes of coffee. Campos dos Goytacazes, BR, springer, PP. 87–122. This genus has sexual dimorphism; females are swollen and males keep vermiform as adults. The female has a pear shape when swollen. It is not possible differentiate one species from other on coffee in the field due to coffee being a host of several species of ''Meloidogyne''. ''M. exigua'' can be found in Brazil, Guatemala, Colombia and Costa Rica. ''M. coffeicola'' has a long neck and brownish body color. Its stylet is 15–17.6 µm long with no prominent knobs. Females also swell, less than ''M. exigua'', however. This species is found in Brazil, exclusively. Another way to distinguish ''Meloidogyne'' species is by the perineal patterns. The perineal pattern involves anus, vagina and surrounding area. Each species has a unique pattern that can distinguish them, but only a trained nematologist is able to verify those small differences. ''Meloidogyne exigua''s perineal pattern has a hexagonal shape, with a dorsal arch above the anus and lateral lines not very pronounced on the perineal pattern, while ''M. coffeicola'' pattern have a more simple conformation with striations between vulva and anus forming a target.Castro, J. M. C., Campos, V. P. &Dutra M. R. 2004. Ocorrência de Meloidogyne coffeicola em Cafeeiros do Município de Coromandel, Região do Alto Paranaíba em Minas Gerais. Fitop. bras. 29: 227. Due to difficulties to identify ''Meloidogyne'' species just by perineal pattern, other reliable techniques were developed, such as Isoenzyme characterizations. OliveiraOliveira, D. S., Oliveira, R. D. L., Freitas, L. G., & Silva, R. V. 2005. Variability of Meloidogyne exigua on Coffee in the Zona da Mata of minas Gerais State, Brazil. Journal of Nematology 37 (3): 323–327. reported difficulties to use perineal pattern and

isoenzyme In biochemistry, isozymes (also known as isoenzymes or more generally as multiple forms of enzymes) are enzymes that differ in amino acid sequence but catalyze the same chemical reaction. Isozymes usually have different kinetic parameters (e.g. dif ...

s helped to confirm species without mistakes. ''M. exigua'' is distinguished by its

esterase An esterase is a hydrolase enzyme that splits esters into an acid and an alcohol in a chemical reaction with water called hydrolysis. A wide range of different esterases exist that differ in their substrate specificity, their protein structure, ...

phenotypes E1 and E2, while ''M. coffeicola'' by Est C2.

Life cycle

Attracted by exudates released by the coffee roots, J2

nematode The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant-Parasitism, parasitic nematodes also known as eelworms. They are a diverse animal phylum inhab ...

(migratory stage) moves toward to food source. The nematodes penetrate in the roots and search for a site to feed on. Several cells are selected to start uptaking food. Those cells are modified and grow bigger (hypertrophy) without cellular division. However, nuclei division start happening and many nuclei are produced inside generating giant cells. Surrounding cells will suffer hyperplasia and start cellular division wildly. For ''M. exigua'', these cells will become galls, but not for ''M. coffeicola''.Campos, V. P., Sivapalan, P. & Gnanapragasam, N. C. 1990. Nematode parasites of coffee, cocoa and tea. In: Luc, M., Sikora, R. A. & Bridge, J. (Eds). Plant Parasitic nematodes in subtropical and tropical agriculture. Wallingford, UK, CAB International, PP.387–430. The nematode starts to swell and get a swollen shape as it molts through the juvenile stages until the adult stage. Many eggs will be produced by the female nematode, and released in a gelatinous mass. ''M. exigua'' lays its eggs under the

epidermis The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and hypodermis. The epidermis layer provides a barrier to infection from environmental pathogens and regulates the amount of water rele ...

, unlike ''M.coffeicola'' that lays them outside of the roots. The juveniles that came out in the gelatinous mass will hatch and find a new feeding site and restart the cycle. Some juveniles may become males when the nematode population is high (competition), environmental condition are not favorable, or the plant is resistant. The life cycle of ''Meloidogyne exigua'' was reported to be around 35 days at 25–30 °C.

Pathology

''M. exigua'' causes galls on the

root system In mathematics, a root system is a configuration of vectors in a Euclidean space satisfying certain geometrical properties. The concept is fundamental in the theory of Lie groups and Lie algebras, especially the classification and representati ...

, which are visible with the naked eye. Although, ''M. coffeicola'' does not produce galls it causes peeling and cracking of roots instead. Reduction of root system is observed, mostly because nematodes feed closer to

xylem Xylem is one of the two types of transport tissue in vascular plants, the other being phloem. The basic function of xylem is to transport water from roots to stems and leaves, but it also transports nutrients. The word ''xylem'' is derived from ...

and

phloem Phloem (, ) is the living biological tissue, tissue in vascular plants that transports the soluble organic compounds made during photosynthesis and known as ''photosynthates'', in particular the sugar sucrose, to the rest of the plant. This tran ...

, where water and nutrients are transported into the plant. This blockage reduces root system development. Above ground symptoms include defoliation and leaf chlorosis leading to death of the plant.

Management

The first thing recommendation to control the gall nematodes is to plant healthy seeds in area not infested. Nematode-free seeds are important to avoid disseminating the pathogen to other areas. However, if areas are already contaminated, other measures will be needed. Some nematicides are still applied to stop J2 from infecting coffee plants. However, due

phytotoxicity Phytotoxicity describes any adverse effects on plant growth, physiology, or metabolism caused by a chemical substance, such as high levels of fertilizers, herbicides, heavy metals, or nanoparticles. General phytotoxic effects include altered plan ...

and high value their use became unpractical. Thus, new cultural methods started to be applied such as irrigation control, remove diseased plants, spacing rows and others not as common. ''M. exigua'' can survive for six months without the host, while ''M. coffeicola'' just survive for few days or weeks. Thus, not planting host plants for a period greater than six months can eradicate both plant feeders. Grafting is another method applied to control ''Meloidogyne'' species that attacks coffee. Resistant varieties are used as a support (stock) such Apoatã,Salgado, S. M. L., Resende, M. L. V. & Campos, V. P. 2005. Reprodução de Meloidogyne exigua em cultivares de cafeeiros resistentes e suscetiveis. Fitopatol. Bras. 30: 413–415. Nemaya, or other ''C. canephora'' varieties or hybrids. which will provide nutrients to the other variety on the top (scion) such Mundo Novo, that will be the one with flower and coffee fruit production. It is an easier method, that does not harm the environment. Other cultivar that is used to control ''M. exigua'' is IAPAR 59. It carries Mex-1 resistance gene, that causes hypersensitive response (HR) in the plant,Anthony, F., Topart, P., Martinez, A., Silva, M. & Nicole, M. 2005. Hypersensitive-like reaction conferred by the Mex-1 resistance gene against Meloidogyne exigua in coffee. Plant Pathology 54: 476–482. also having low reproductive factor to ''M. exigua''. This is a competitive variety with good agronomic factors.

References

{{Reflist Agricultural pest nematodes Coffee diseases Tylenchida Invertebrate common names