Plant pathogenic pseudomonads such as Pseudomonas glumae, Ps. gladioli pv. gladioli, Ps . cepacia and Ps. avenae formed growth inhibition zone around their colonies on the lawn of other plant pathogenic bacteria, Agrobaclerium tumefaciens, Corynebacterium michiganense pv. michiganense, Erwinia carotovora subsp. carotovora, Ps. solanacearum , Ps. syringae pv. syringae, Xanthomonas campestris pv. citri and X. campestris pv. oryzae, used as indicators.The activity spectra shown on the indicator bacteria were much varied depending upon the species and isolates of pseudomonads, suggesting that various antibiotic substances participated in the formation of inhibition zones.

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Pseudomonas glumae strains showed different antibiotic activities against P. solanacearum depending upon kind of media used. When triphenyl tetrazolium chloride medium (TTC medium) was used, all strains of P. glumae formed growth inhibition zones around their colonies on the lawn of P. solanacearum used as indicator.Pre-treatment of the roots of tomato seedlings with the suspension of antibiotic productive strains of P. glumae suppressed the severity of wilt incited by challenge inoculation with P. solanacearum.The disease suppression was positively correlated with length of dipping time and concentration of the bacterial suspension used for pre-treatment. Dipping of the roots of tomato seedlings into the bacterial suspension of ca. 1010cfu/ml for 24hr showed highest suppressiveness.The pre-treatment of tomato roots with non-antibiotic-producing strain or heat-killed cells of P. glumae also showed protection, suggesting that some mechanisms other than antibiotic productivity were involved in the suppression of the disease.

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Foot rot disease caused by Diaporthe destruens (formerly Plenodomus destruens) has become a major concern for the production of sweet potato [Ipomoea batatas (L.) Lam.] in Japan. A related fungus Diaporthe batatas, which causes dry rot disease of sweet potato, is native and is widespread in fields in Japan. The similar characteristics of these two pathogens pose a challenge for conventional disease diagnosis. Currently, there are no effective molecular measures for identifying and distinguishing D. destruens and D. batatas. Here, we demonstrate a real-time PCR assay that distinguishes and quantifies D. batatas and D. destruens from co-infected sweet potato. The assay was performed with various simulated DNA combinations of D. batatas and D. destruens ranging from 1:1 to 1:100000. The assay was also used with the ratios of D. batatas: D. destruens: sweet potato DNA ranging from 1:1:1 to 1:1:100000. These assays produced a specific amplification product for each of the pathogens, and quantified the fungal biomass over the entire range tested without detecting false positives. The assay was validated by using infected sweet potato collected from various fields; it showed sufficient sensitivity and specificity to quantify and distinguish D. batatas and D. destruens from these field samples. Thus, our real-time PCR assay would be a useful tool for diagnosis of D. batatas and D. destruens and is expected to provide the foundation for the design of integrated disease management strategies for foot rot disease in sweet potato.