Meloidogyne root knot nematodes are one of the most commercially important types of plantparasitic nematodes. They are a sedentary, obligatory root endoparasite that infects over 3000 plant species (Abad et al. 2003). They are high on the list of living pathogens affecting world food production and related sectors due to their economic importance on a global scale (Sasser 1977). They are found in a wide range of geographical situations around the world, but are more common in tropical and sub-tropical climate zones, and cause significant economic losses in a variety of agriculture and horticulture crops, including vegetables (Sikora and Fernandez 2005).
Corresponding Author Email: firstname.lastname@example.orgMeloidogyne incognita Kofoid and White, Meloidogyne javanica Treub, Meloidogyne arenaria Neal and Meloidogyne hapla Chitwood are the four principal species found to cause massive economic harm in vegetable crops. The first three species, which are prevalent in tropical and subtropical regions, are also found in temperate places, particularly if they are protected. M. hapla, the later species, is found in temperate zones and at greater altitudes in the tropics (Hunt and Handoo 2009). Meloidogyne incognita is the most common species in vegetable agriculture in India, followed by Meloidogyne javanica and Meloidogyne arenaria. M. hapla has also been found to infest vegetables growing in temperate hilly locations. Furthermore, they not only decrease crop yields but also have an impact on vegetable quality.
Globally, an average of 10 percent annual yield loss is recorded in vegetables due to root knot nematodes.However, depending on the nematode type, location, and crop species, significantly higher % losses have been reported and the people of the soil.Aside from the direct harm, root knot nematodes operate as a predisposing agent for the entry of soil-borne fungal and bacterial pathogens, exacerbating the situation by creating disease complexes and substantial yield losses ranging from 40 to 70% in vegetable crops grown across the country.In addition, root knot nematode species (M. incognita, M. javanica, and reniform nematode (Rotylenchulus reniformis) infest crops such as tomato, chilli, gherkins, okra, muskmelon, watermelon, and flower crops such as carnations, roses, gerbera and anthuriums that are grown under protected cultivation and cause massive crop (Rao et al. 2015a)
Races of root knot nematodes and their distribution
Races of root knot nematodes have been found in four well-known species of root knot nematodes, including M. incognita and M. javanica, M. arenaria and M. hapla. The host range differences in four major Meloidogyne species were first reported by Sasser (1952).
Parasitism and symptom expression:
Second stage (J2) infective juveniles wander freely in soil in search of a suitable host, then inject hydrolytic enzymes released by oesophageal glands into plant cells through their stylet and migrate intracellularly until they reach the developing vascular cylinder. This migration continues for a short distance before J2 becomes sessile in the differentiation zone (cortical tissue).J2 begins feeding on xylem and phloem cells and induces specialised multinucleate feeding cells or giant cells in the phloem or nearby parenchyma by embedding its head in vascular tissue and the rest of its body in the cortex, which is parallel to the longitudinal axis of the roots.Multinucleated giant cells are feeding sites that form as a result of repeated end mitosis without cytokinesis. Adjacent cells multiply through hyperplasia, resulting in multiple knots or galls on the root system.These cells are highly specialised cellular modifications that provide nematode development and reproduction with a constant feeding source.Second stage juveniles feed optimally for 2-3 weeks and, under ideal conditions, moult into third and fourth juvenile stages in a short period of time (usually 4-6 days).
Under intensive vegetable cultivation, root knot nematodes’ high reproductive potential, polyphagous nature, and unique survival strategy made management more complex.It is nearly tough to eradicate root knot nematodes once they have established themselves in the field.Unless there is a regulatory requirement for total nematode control, eradicating nematodes is neither economically nor environmentally friendly.Root knot nematode management in vegetable crops through cultural, physical, biological, chemical, and genetics-based methods.