Mechanism of Resistance to Plant Nematodes

Abstract

The mechanisms of plant resistance to nematodes are as yet not fully understood, although much work has been done to elucidate them. This paper will not cover the aspects of plant breeding and nematode reproduc­ tion and genetics, both closely connected with the problem of plant resis­ tance to nematodes, but rather will review our knowledge of the host-plant biochemistry and the nature of plant resistance to some nematode species. I aim not only to present the facts themselves, but also to discuss and speculate about the still insufficiently known problem of the biochemical mechanism of plant resistance to nematodes. I will be satisfied if I can add even a bit to the wide field of knowledge already presented by other nematologists (9, 14, 22, 31, 110, 111, 131). I am fully aware that some aspects of the problem will be omitted here, partly due to space limitations. The development of each plant species is accompanied by a permanent process of selection induced by confrontation with the pathogen. On the other hand, the pathogens adapt themselves to their future hosts. From the viewpoint of evolution it seems that plant resistance to patho­ gens is initially nonspecific. Susceptibility is built up later on, and is specific, formed on the one hand during the process of host selection by the patho­ gen, and on the other hand by its adaptation to the host. This process is accelerated by breeding new plant varieties having good nutritional values and giving high yields. Here the feature of resistance to pests or diseases becomes less prominent, except when breeding programs are carried on just to develop resistance. The knowledge of plant defense mechanisms will allow the selection of desired features for the varietal breeding program. The new variety will fulfill the role of host for a definite species or for one or more pathogens,