A new and simple method was tested to control tomato bacterial wilt disease caused by Pseudomonas solanacearum. A sheet of compactly woven polyester cloth, which is permeable to water and into which roots cannot penetrate ("root-proof" sheet) is only required. The "root-proof" sheet was placed under the plow layer at a 25cm depth in a heavily contaminated field of a greenhouse. The test plots were sterilized by solar heating during midsummer prior to transplanting tomatoes. In the control plot, all the plants died of the disease within almost one month after planting. In contrast, the plants in the "root-proof" sheet plot were unaffected for almost 4 months throughout the growth period. The effect of solar heating sterilization lasted nearly 320 days up to the terminal stage of the 2nd growth. An improved method was also tested by placing a layer of porous material such as a gravel layer on the lower side of the "root-proof" sheet. No infection of plants was observed in 3 successive full growings of tomato. This observation indicates that the plow layer was protected from recontamination by the elimination of the capillary movement of the soil water from the subsoil.

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Thirteen isolates of Monosporascus cannonballus POLLACK and UECKER collected from melon plants with root rot symptoms in various districts of Japan were compared for their morphological characteristics and pathogenicity. The fungi were isolated from the roots of melon plants, basal stems 10cm of above the ground, but not from stems above 20cm, fruits and seeds. Melon plants planted in the infected field soils stored for 1〜5 years under laboratory conditions showed root rot symptoms, and fungi were isolated from the roots. Recent outbreaks of melon root rot caused by M. cannonballus were discussed.

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Tomatoes were cultivated in soil infected with Verticillium dahliae to which five kinds of microbial materials were applied during the three year period from 1986 to 1988. In all the materials, since the disease incidence and severity of Verticillium wilt were reduced, the yield increased. The microbial population in soil tended to be higher in the plot with application of all the materials than in the no-application plot. It is possible that the high population of microbes hindered the infection of the pathogen and reduced the severity of the disease. On the other hand, since the number of microsclerotia in soil decreased after the application of the materials, it was assumed that antagonistic microbes multiplied. Soil pH showed slight changes. Two materials which increased the content of NH_4-N, generally reduced severity of Verticillium wilt seven to fourteen days after application, but the effect of it could not be confirmed.

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Glutamate dehydrogenase (GDH) was partially purified from Nitrosomonas europaea ATCC 25978 by sequential chromatography on a column of DEAE-Sepharose CL-6B, hydroxyapatite and Cellulofine GCL-2000-m. The GDH was separated into three fractions, F40, F50, and F100 by chromatography on a hydroxyapatite column. The molecular weights of the enzymes were estimated to be about 122,000 (F40), 85,000 (F50) and 125,000 (F100) by gel filtration. Optimal activity of GDH was observed at approximately 45℃ and at a pH of 9.5 to 10.0 (F40), 9.0 and 11.0 (F100) and 8.7 (F50). The enzymes of the F50 and F100 fractions were stable over a pH range of 4 to 12 at 5℃ and 20℃, and that of the F40 fraction over a pH range of 6 to 10. These GDH subtypes were quite specific for L-glutamate as a substrate and NADP as an electron acceptor. None of the metallic salts tested promoted the activity of any of the subtypes, whereas Hg^<2+> completely inhibited these GDH fractions. Hydroxylamine caused a marked inactivation of the F100 fraction whereas ADP, ATP, and GTP did not affect the activities. Some inhibitors such as SDS (F50) and EDTA (F100) inactivated these enzymes to some extent, but had no effect on the F40 fraction.

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In most soils, living microorganisms (the soil microbial biomass) make up about 1-3% of total soil organic matter. We review some of the methods available to measure soil biomass. These are (1) direct microscopic examination, (2) the fumigation-incubation method, (3) the fumigation-extraction method, (4) the substrate-induced respiration method and (5) the measurement of soil ATP. In soils which do not contain actively decomposing substrates, most of the biomass is dormant or resting, having a very low respiration rate, long mean cell-division time and slow turnover rate. Yet, paradoxically, it maintains an ATP concentration and adenylate energy charge at the same level as organisms growing exponentially in vitro. Two independent pieces of new research are presented to illustrate how the new fumigation-extraction procedures can be used to measure changes in biomass following substrate addition to soils. These are the effects of straw incorporation on soil biomass and nitrogen dynamics, and the origins of "priming effects" following substrate incorporation (glucose and ryegrass) to soil.

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