Potato scab is a serious plant disease caused by several Streptomyces sp., and effective control methods remain unavailable. Although antagonistic bacteria and phages against potato scab pathogens have been reported, to the best of our knowledge, there is no information about fungi that are antagonistic to the pathogens. The aim of this study was to isolate fungal antagonists, characterize their phylogenetic positions, determine their antagonistic activities against potato scab pathogens, and highlight their potential use as control agents under lower pH conditions. Fifteen fungal stains isolated from potato field soils were found to have antagonistic activity against three well-known potato scab pathogens: Streptomyces scabiei, Streptomyces acidiscabiei, and Streptomyces turgidiscabiei. These 15 fungal strains were phylogenetically classified into at least six orders and nine genera based on 18S rRNA gene sequencing analysis. These fungal isolates were related to members of the genera Penicillium, Eupenicillium, Chaetomium, Fusarium, Cladosporium, Mortierella, Kionochaeta, Pseudogymnoascus, and Lecythophora. The antagonistic activities of most of the fungal isolates were highly strengthened under the lower pH conditions, suggesting the advantage of combining their use with a traditional method such as soil acidification. This is the first report to demonstrate that phylogenetically diverse fungi show antagonistic activity against major potato scab pathogens. These fungal strains could be used as potential agents to control potato scab disease.
Climatic change through global warming and drought is a major issue for agricultural production. Most researchers who discuss climate changes report the yield changes estimated by using crop process models; however, studies focusing on the impact of climatic change on agricultural product markets are very few. This paper examines the relationship between climatic change and world food markets, i.e., supply and demand of crops, by using a world food model and newly estimated yield functions. These yield functions include rainfall and temperature as climate variables, and the estimated parameters are used in the world food model. The stationarity of these yield data is tested and appropriate functional forms are selected. The results suggest that yields of major crops will decrease because of rising temperatures in many countries and regions, however, market price impacts of changes in production of these crops are not large because of trade. The countries which suffer severe damage because of higher temperature may need to consider changes in cropping patterns and practices.
Common scab of potato tubers caused by pathogenic Streptomyces spp. is a cause of serious economic loss worldwide. For the rapid and accurate quantification of pathogenic Streptomyces spp. residing in soil, a new competitive real-time PCR method using fluorescent quenching-based probes (quantitative competitive quenching probe PCR: QCQP-PCR) was developed. The virulence gene of pathogenic Streptomyces spp., nec1 , was selected as the target for QCQP-PCR. A specific primer set to amplify the nec1 gene, and a fluorescently labelled probe that specifically hybridizes with the nec1 amplicon were designed. For QCQP-PCR, an internal standard DNA (IS DNA) that is identical to the nec1 amplicon but has a 4-base mismatch in the probe-hybridizing region, and a fluorescently labelled probe IS, which specifically hybridizes with IS DNA at the mutagenized region, were PCR-synthesized. The target nec1 gene was co-amplified with the known copy number of IS DNA by PCR using the same primer set in the presence of the specific probes. The PCR products were monitored in real-time by measuring the fluorescence intensity (quenching) of each probe. The initial amount of the nec1 gene was quantified based on the ratio of the PCR products of the same PCR cycle. The results revealed that QCQP-PCR could be used to precisely quantify the nec1 gene, even in the presence of PCR inhibitors in the soil samples examined. The lower limit of quantification was 20 copies per tube, which corresponded to 1500 copies per g dry soil. The quantification achieved by this method was completed within 5 h, i.e. the duration of the entire analysis. These results demonstrate the usefulness of the present method for monitoring pathogenic Streptomyces species in soil.
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