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.
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.
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.