Effects of Nematode Attack on the Growth and Yield of Crop Plants

Abstract

Although it has been obvious from the first investigations on nematodes reducing the yield of crop plants (notably beet cyst nematode) that the extent of the damage was related to the degree of infestation of the soil, the exact nature of this relation remained vague in the minds of most investigators. Even so efforts to advise farmers on crop rotation against cyst nematode attack had already started in the first half of this century, most probably because the possibility of counting cysts in soil samples prompted investigators to attach a meaning to the numbers found. Hellinga (1942) even tried to determine a relation between numbers of Heterodera schachtii Schmidt cysts in samples taken in farmers’ fields before sowing beets and the decrease in the quantity of sugar produced. A highly ambiguous approach to the problem prevailed. However, little research was done on quantitative relations and the uncertainty of these relations, due to emphasis on effects of varying external conditions but without proper demonstration. Nevertheless, an increasing number of plant parasitic nematode species were claimed, in part rightly, to be of economic importance; but again, often without convincing evidence that the nematodes reduced the yields of crop plants at the population densities occurring in the field, or even that they could reduce yields at all. Even for such extensively investigated species as potato and beet cyst nematodes and Meloidogyne species it remained obscure how much growth reduction could be expected at particular population densities, especially the smaller ones.