The Pathological Effect of Representative Xiphinema and Longidorus Species On Selected Host Plants1)

The effect of representative Longidorus and Xiphinema species on plant growth under controlled conditions, and their histopathology, were investigated. L. africallus, X. brevicolle and X. index reduced growth of their respective host plants to varying degrees, related to their inoculum levels and the root productivity potential of the hosts. The formation of swollen root tips as a result of feeding of L. africanus was due to a retardation of meristematic activity, hyperplasia of the cortical parenchyma, and a maturation of the root tip region including initial lateral root formation. In an herbaceous host, bur marigold, the infected root tips were irreversibly nonfunctional, whereas in grape, apical growth of infected tips was still possible though greatly reduced. Typically darkened grape roots infected by X. index bore lesions composed of groups of suberized cells in the outer cortex and epidermis, and an underlying layer of phellogen tissue in the cortex.