Pathogenicity of the Columbia Root-knot Nematode (Meloidogyne chitwoodi) on Wheat, Corn, Oat, and Barley.

sues formed a necrotic pit sur rounded by healthy root tissue (Fig. 7). No evidence of damage to stelar tissue was detected, Scotto La Massese (7) repor ted that C. pestis females became at tached to the root surface by their stylets in a manner similar to Gracilacus peratica Raski, a species which also forms colonies on the root surface of its hosts. G. peratica females become swollen and remain permanent ly at tached on the root surface by inserting the spear into the epidermis and the outer cortex (5). However, in the case of C. pestis on walnut roots, the nematode remains concealed beneath the epidermis of the secondary roots and feeds on per iderm and outer cortex. T h e initial damage caused by C. pestis on walnut roots seems to be limited, bu t it predisposes the infested plants to dieback (10). T h e extent of the nematode infestation, with the resul tant necrosis of phellogen and phel loderm induced by the parasite feeding activity, reduces the protective function of the per iderm and favors invasion by other pathogens. L I T E R A T U R E C I T E D