Pseudomonas fluorescens FPH9601 (referred to as FPH) is known to suppress an important soil-borne disease, tomato crown and root rot caused by Fusarium oxysporum f. sp. radicis-lycopersici. However, the effect of FPH on disease suppression is unstable. To evaluate the effect of FPH on tomato crown and root rot and to clarify the cause of the instability, appropriate conditions for disease suppression and the effect of the FPH treatment on the invasion of Fusarium into tomato roots were examined. The FPH treatment was effective against the pathogen at up to 10^7 cells per milliliter based on several disease parameters, i.e., prevalence, severity based on prevalence, extent of browning of vessels, and extent of root rot. The invaded sites in tomato roots were as few as 0.4/cm root after 30 days in the FPH-treated seedlings, while one or more invasion sites per centimeter were observed in untreated seedlings during the 10day period after inoculation. The number of infectious Fusarium microorgamisms in tomato roots tended to be lower in the FPH-treated seedlings than in the untreated seedlings at all time points studied. In the field test, the first occurrence of the disease in the untreated plots was recognized at about three weeks after transplantation. The number of infected plants subsequently increased. On the other hand, the initial occurrence in the plots treated with FPH9601 or biopesticide containing FPH9601 were at about seven weeks after transplantation. Furthermore, subsequent disease development was also slow in the plots with FPH9601, indicatetly that FPH has an effect to retard the disease occurrence in the field.

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In hydroponic culture, the effects of biocontrol agents (BCAs) and lysine on bacterial wilt of tomato were examined using a pumice medium artificially infested with Ralstonia solanacearum. In small - pot experiments, the addition of lysine or lysine together with BCAs resulted in a remarkable reduction in the disease index of bacterial wilt. In a greenhouse experiment, while Pseudomonas fluorescens Me1RC2Rif did not decrease the disease index, no disease symptoms were observed when MelRC2Rif and lysine (1 mg g^<-1>) were added to the pumice medium, although the tomato yield decreased significantly. In the second year the amount of lysine was reduced to 0.25 mg g^<-1> and every two weeks, 0.25 mg g^<-1> of lysine was added together with Ralstonia pickettii K20. The disease index was significantly lower and the tomato yield was significantly higher in the K20, K20 + lysine and lysine treatments than in the control inoculated with only the pathogen. The quality of tomato, estimated based on the contents of sugar, lycopene and vitamin C, was not markedly different in the K20, K20 + lysine and lysine treatments from that in the control not inoculated with the pathogen.

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Big-vein disease occurs on lettuce worldwide in temperate regions. The causal agent is transmitted from diseased to healthy plants by zoospores of the lettuce root-infecting fungus Olpidium brassicae. To enhance the suppressive effect of soil solarization on the occurrence of lettuce big-vein disease, various supplementary materials were applied to soils before solarization. All the supplementary materials tested, i.e., methionine (40 kg/10 a), urea polymer (200 kg/10 a), and calcium cyanamide (100 kg/10 a), enhanced the suppressive effect of solarization, especially, calcium cyanamide showed the highest prevention value.

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Field experiments conducted during the period of 2003 to 2005 to evaluate the effect of soil disinfection on the soil microbial function. Organic matter decomposition activity after soil disinfection with 1,3-dichloropropene (1,3-D), chloropicrin (CP) and solarization was evaluated by measuring the cellulose- and glucose-decomposing activities. In 2003, a Haplic Andosol field (HA-soil) was used. Glucose decomposition activity was inhibited immediately after disinfection, and recovered to the level observed in a non-disinfected control soil. In 2004, a Low Humic Andosol (LA-soil) and the HA - soil were used. Although the cellulose decomposition activity (CDA) was suppressed immediately after disinfection, the activity in the HA-soil recovered within 10-12 weeks and the microbial community structure (determined by 16S rDNA-PCR-DGGE) also recovered within 17 weeks after disinfection. Although CDA recovered earlier in the LA-soil than in the HA-soil, it was temporarily suppressed again. In 2005, the effect of soil disinfection on CDA was evaluated using the LA-soil amended and not amended with compost immediately after disinfection. The activity was suppressed by soil disinfection and recovered readily during the growth period, irrespective of compost amendment. The number of ammonia-oxidizing bacteria decreased after disinfection and recovered within 2 to 4weeks in all the treatments in 2003 and 2004. We concluded that the disturbance of organic matter decomposition and nitrification associated with soil disinfection may be temporary and that the soil microbial function recovered significantly during the cropping season.

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Two hundred and forty-five plant-associated bacteria isolated from soil by techniques including hypocotyl trapping were subjected to screening based on the promotion of resistance to bacterial wilt and growth in tomato. Three isolates, KSR01, KSB07 and KLT08, were selected. When tomato seeds were treated with KSR01, growth was promoted and the disease severity associated with bacterial wilt was significantly reduced compared to that in the untreated control. KSR01 was re-isolated from the stem tissues of tomato subjected to seed treatment with KSR01 at 35 days after treatment, suggesting that KSR01 was endophytic in tomato. KSR01 did not produce antibacterial substances against Ralstonia solanacearum, the pathogen of bacterial wilt. This suggested that the mode of action of KSR01 against bacterial wilt consisted of the induction of resistance. KSR01 was identified as Herbaspirillum huttiensis by fatty acid analysis, 16S rRNA sequence and physiological and biochemical characteristics.

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FCD1 in Fusarium oxypsorum f. sp. lycopersici (FOL) has been predicted to encode a cellobiose: quinone oxydoreductase (CBQ) (Kawabe et al. 2006). We compared the activity of cellobiose dehydrogenase (CDH) and CBQ in the cultural filtrate between a wild-type strain of FOL and an FCD1-disruptant by using 2, 6-dichloro-indophenol (DCIP)- and cytochrome c-assays. The results showed that DCIP-reducing activity (=CDH+CBQ activity) decreased in the FCD1-disruptant. On the other hand, cytochrome c-reducing activity (=CDH activity) was equivalent between the both strains. These confirmed that FCD1 encodes a CBQ. Moreover, FCD1 was found to distribute in various formae speciales of E oxysporum, suggesting that FCD1 is not responsible for determination of host-specificity in FOL.

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To analyze the effect of irrigation on the occurrence of common scab of potato, we examined the relationship between the water content and water-soluble aluminum concentration under low soil water content conditions in two types of Andosols. The content of water-soluble aluminum per dry soil in the Haplic Andosol, conducive to this disease at a soil of pH of around 5.2, was low, ranging from 0.043 mg kg^<-1> to 0.070 mg kg^<-1>, regardless of the soil water content. On the other hand, the content of water-soluble aluminum per dry soil in the Umbric Andosol, suppressive for this disease at a soil pH of around 5.2, was 0.298 mg kg^<-1> under 30% soil water conditions, and the concentration of water-soluble aluminum in the soil solution increased with the increase in the water content. These results indicated that the water-soluble aluminum concentrations under the field conditions were different between the two Andosol types. Moreover, this study suggested that the effect of irrigation on the control of common scab of potato in the Haplic Andosol did not involve a synergy between the water-soluble aluminum concentration and soil water content. On the other hand, the soil water content was one of the control factors for the occurrence of common scab of potato in the Umbric Andosol, as indicated by the increase in the water-soluble aluminum concentration in the soil solution along with the increase in the soil water content.

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