ROOT LESION NEMATODES

LESION (PRATYLENCHUS ) SPECIES FOUND IN CALIFORNIA:

This listing of species of lesion nematode found in California illustrates the importance of requesting a species identification for this genus when perennial crops are of concern. Only two species, P. vulnus and P. penetrans are likely to cause problems on perennial crops in California.

Other species, though, such as P. neglectus, and P. thornei are fairly common in perennial situations where they are thought to be feeding on weeds.

Root lesion nematodes remain vermiform throughout their juvenile and adult stages. They are migratory root endoparasites that inhabit both soil and roots. There is no distinct infective stage because all juvenile and adult stages can enter into and come out of roots. These nematodes generally prefer entering roots in the zone of elongation behind the root tips and at the junctions of lateral roots. Several may enter a root through the same site. Feeding and movement are confined chiefly to the cortical region within the root.

Females lay eggs singly as they move, mostly in the root cortex but also in the soil. Males are rare or absent in P. brachyurus, P. minyus, P. scribneri, P. thornei, and P. zeae. Each female lays one to two eggs a day for many days, although the total number of eggs laid by one female has not been properly assessed. Generation time is somewhat slow compared with many nematode genera and may vary from 30 to 60 days, depending on species and temperature. Root lesion nematodes may overwinter in old plant root material that remains in the soil after harvest. For example, P. brachyurus may overwinter in cotton roots remaining in the soil from the previous crop. P. penetrans and P. vulnus may survive in the larger root fragments of orchard trees. These roots can provide some protection during adverse dry, hot, or cold soil conditions and from nematicidal agents, including soil fumigants.

Pratylenchus vulnus on walnut
Pratylenchus penetrans on Easter lily
Pratylenchus vulnus on prune
Pratylenchus vulnus on prune
Pratylenchus penetrans on Begonia, before fumigation
Pratylenchus penetrans on Begonia, after fumigation
Pratylenchus vulnus on walnut
Pratylenchus vulnus on prune
From: McKenry, M.V. and P. A. Roberts. 1985. Phytonematology Study Guide. University of California, Division of Agriculture and Natural Resources.

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