Nematodes are unsegmented roundworms belonging to the phylum Nematoda. Those considered to be pests of plants are active mainly in moist habitats and feed on roots. Some species are ectoparasites, feeding on root surfaces, while others are endoparasites, feeding internally on root tissues. Injection of saliva by nematodes induces distortion of roots, including galling, stubby roots, lesions, and stunting, leading to decreased translocation of water and nutri ents. Feeding by nematodes also predisposes trees to secondary infection by pathogens, and some species transmit viruses. The most common nematode pest in tree fruit is the root lesion nematode, Pratylenchus penetrans; this species damages roots by feeding and intracellular migration, leading to cortex damage and promotion of rot. Symptoms of nematode attack in tree fruit include stunting, chlorosis, wilting and curling of leaves and stems, heavy flowering leading to a large crop of small fruit, delayed or uneven maturation of fruit crops, and fruit drop.

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