Field experiments were conducted to determine the effect of green manure as fallow on common scab of potato caused by Streptomyces turgidiscabies. Significantly fewer diseased tubers were harvested from soil incorporated with lopsided oat or woolly pod vetch compared with those from oat and continuous potato cultivation in a planter experiment. Each field experiment consisted of lopsided oat cultivated during the spring and summer prior to the potato planting. Comparisons were also made with several other treatments, including cultivation of woolly pod vetch, oat, soybean, sugar beet, and potato (‘Yukirasya’, which is resistant to potato common potato scab) and soil application of Ferosand (Fe, mainly FeSO4, to decrease the soil pH). In field experiments conducted during 1999–2000, treatment with lopsided oat followed by lopsided oat or woolly pod vetch was significantly more effective at suppressing the disease severity than oat and continuous potato cultivation (P < 0.001). An increase in the marketable tuber ratio was also more significant than for oat and continuous potato cultivation (P < 0.001). In field experiments conducted during 2000–01, lopsided oat cultivation alone and with the application of Ferosand (1.8 t/ha) or resistant potato cultivar treatment were significantly more effective at suppressing the disease severity and incidence than sugar beet cultivation (P < 0.001), even under high disease intensity in the field. However, potato yield had a tendency to reduce after lopsided oat treatment with an application of Ferosand (1.8 t/ha) compared with lopsided oat alone or the application of Ferosand at 600 kg/ha, due to low pH conditions. In field experiments conducted during 2001–02, the lowest severity and incidence of common scab of potato were observed in soil treated with lopsided oat than with other treatments (P < 0.05 and P < 0.001, respectively). These findings suggest that lopsided oat used as fallow green manure can reduce the severity of common scab and increase potato yield.

The distribution of two races (1 and 2) of Phialophora gregata f. sp. adzukicola, the causal agent of brown stem rot of adzuki bean, was examined using a total of 483 isolates obtained from 39 fields in 19 locations on Hokkaido, Japan between 1997 and 1999. Race 1 was predominant (416 isolates or 86.1%) in the commercial fields tested. Race 2 was found in 26 fields (64.1%), including two fields of cultivar Kita-no-otome (resistant to race 1, but susceptible to race 2), indicating that race 2 was widely distributed in most of the production areas in Hokkaido. Using amplified fragment length polymorphisms (AFLP), a total of 67 polymorphic AFLP markers was recorded among 72 representative isolates (37 and 36 isolates of races 1 and 2, respectively), and 67 distinct haplotypes were detected. Cluster analysis revealed no close correlation between races and AFLP groups. Thus, no difference was observed between values of gene diversity in each race (0.263 and 0.284 in races 1 and 2, respectively), and the coefficient of gene differentiation was very low ( GST = 0.016). Gene differentiation between both races by analysis of molecular variance was not significantly different from zero (@= -0.001; p =0.403). However, the results of gene differentiation among regional populations (GST = 0.290, @ = 0.292; p < 0.001) are not necessarily consistent with the result that isolates from the same district were generally not tightly clustered.

Plant endoparasitic nematodes spend most of their life cycle hidden within plant roots and worldwide cause major losses to agriculture every year. Root-knot nematodes ('RKNs', Meloidogyne spp.) are sedentary endoparasitic nematodes that establish permanent feeding sites within plant roots as 2nd-stage juveniles (J2), and then spend the rest of their life-cycle at this site. In contrast, root-lesion nematodes (Pratylenchus spp.) are migratory endoparasites that move in roots and feed on different root cells, causing typical symptoms of brown lesions.There is great interest in studying the initial infection stages of both sedentary and migratory endoparasitic nematodes. In the case of RKNs, it is known that host cells undergo key initial changes of cell-cycle activation, DNA synthesis and nuclear division during the first 48 hr of infection and host cell selection (de Almeida Engler et al., 1999;Jones, 1981;Jones and Payne, 1978;Niebel et al., 1996). In the case of root-lesion nematodes, tracking invasive movement and behavior in root tissues also has potential to reveal the nature of resistant responses limiting the completion of the life-cycle. A major challenge is that current methods to identify nematodes inside plant roots during early stages of infection are either destructive or do not provide sufficient temporal or spatial resolution.Fluorescent compounds have been used to track solute movement in host plant tissues during parasitic nematode infection (Böckenhoff et al., 1996;Hofmann et al., 2007;Hutangura, 1999). Expression of fluorescent proteins has also been used to study feeding cell biology (Hofmann and Grundler, 2006;Hoth et al., 2005;Hoth et al., 2008) and is a common approach to identify specific cell types in plant roots (Birnbaum et al., 2003;Brady et al., 2007;Lee et al., 2006). Research on initial stages of nematode infection would thus greatly benefit from a fluorescence-based approach that would also enable invading nematodes to be identified in plant roots with high spatial resolution. Live cyst nematodes have recently been marked fluorescently using fluorescein isothiocyanate (FITC) (Schroeder and MacGuidwin, 2007). FITC is a fluorescent fluorescein conjugate that has also been used to show uptake from solution by J2 RKNs (Rosso et al., 2005). An earlier study made use of a different fluorescein conjugate, fluorescein diacetate (FDA), to label RKN juveniles and to distinguish between living and dead nematodes (Bird, 1979). FDA is a non-fluorescent conjugate that becomes fluorescent after entering a cell and being hydrolyzed by endogenous esterases. In addition to facilitating identification of live nematodes, background fluorescent signals and requirement for extensive washing are kept to a minimum because FDA does not fluoresce, and free fluorescein remains in live cells. In this study, we tested whether FDA can be applied to label individual nematodes fluorescently for direct non-destructive observation of their movement inside plant roots. MATERIALS AND METHODS Nematode stocks and FDA t...

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Inoculation test was conducted to confirm the influence of Pratylenchus penetrans on the infection of adzuki bean by Phialophora gregata f. sp. adzukicola, causal agent of brown stem rot of adzuki bean, in the green house. It was considered that high densities of P. penetrans enhanced the invasion of P. gregata f. sp. adzukicola to adzuki bean and the ratio of the highest brownish node to total nodes of adzuki bean. From the result, P. penetrans was clarified as one factor which enhanced the invasion of P gregata f. sp. adzukicola to adzuki bean. Jpn. J. Nematol. 35(2), 71-77 (2005). Key words: brown stem rot of adzuki bean, fungus-nematode interaction, Phialophora gregata f.sp. adzukicola, Pratylenchus penetrans.