An overview of plant-nematode-nutrient interactions as they relate to nematode management challenges and a framework for an integrated approach are discussed. Special attention is given to the possibility of manipulating soil nutrition to adversely affect nematodes and benefit plants. Specific hypotheses designed to test the effect of increasing soil nutrition on nematode embryogenesis, infective behavior, and reproductive potential are proposed. Understanding the influence of mineral nutrition on host-nematode interactions may lead to integrated molecular, genetic and physiological approaches to developing a plant as well as to practical applications. In order to achieve the basic and applied aspects of the theme, however, interdisciplinary research with soil scientists and plant nutritionists is necessary.

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Twenty-day-old japonica rice seedling (Oryza sativa cv. Reiho) maintained in a glass house condition at 25 ±5 °C and 80 ±10% relative humidity were inoculated with 0, 10, 100, 1, 000 and 2, 500 Ditylenchus angustus/plant. At 1 week intervals up to 42 days after inoculation, plant growth parameters, net photosynthetic rates, chlorophyll content, reducing sugar, nonreducing sugar and free amino acid contents were measured. The 2 higher initial inocula (1, 000 and 2, 500) significantly decreased plant height, main stem height and leaf area of main stem from 7 days; fresh and dry weight of plant, tiller height, leaf area of tiller from 14 days after inoculation. With the 2 higher initial inocula, net photosynthetic rates on leaf area basis and chlorophyll content on fresh weight basis of the main stem decreased significantly from 14 days. Ditylenchus angustus infection significantly increased in both reducing and nonreducing sugars and free amino acid concentrations of the leaves of main stem 3 days after inoculation with increasing inoculum level. The increament of both sugars continued up to 7 days and amino acids up to 14 days, thereafter reducing sugars and free amino acids were decreased to the level of control and nonreducing sugars declined to 50% of the control level. The main stems inoculated with 1, 000 and 2, 500 nematodes/ plant were wilted in 42 and 28 days after inoculation, respectively.

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The polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis of the two internal transcribed spacer regions (ITS 1 and ITS 2), including the 5.8S gene and small portions of the 18S and 28S genes of the ribosomal DNA, was performed to distinguish Globodera rostochiensis, Heterodera elachista, H. trifolii, H. glycines and Heterodera sp. The single second-stage juveniles of each species were ruptured individually in a drop of lysis buffer (DNA extraction buffer), heat-treated, and added directly to a PCR reaction mixture. The size of amplified product was about 1.0 kb in G. rostochiensis, and about 1.1 kb in H. elachista, and about 1.05 kb in H. trifolii, H. glycines and Heterodera sp. The two restriction patterns of the amplified products with Rsa I and with one of Alu I, Mse I and Tha I were suitable for discrimination of these five species. No intraspecific variation in the two restriction patterns with AluI and RsaI was found in 17 isolates of H. elachista and H. glycines from Kanto district of Japan.

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In order to test our hypothesis that the genuine pathogen of the pine wilt disease mediated by Bursaphelenchus xylophilus is some species of phenylacetic acidproducing bacteria accompanying nematodes, we inoculated aseptic pine seedlings with aseptic nematodes. It was found that 1) phenylacetic acid was not the product of the nematode but that of the accompanying bacteria, and 2) the aseptic pine seedling inoculated under aseptic conditions with the aseptic nematode did not wilt. This finding confirms our hypothesis.

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