Sudden death syndrome (SDS) of soybean is a complex root rot disease caused by the semi-biotrophic fungus Fusarium solani (F. solani) and a leaf scorch disease; caused by toxins produced by pathogen in the roots. However, the mechanism of soybean resistant to F. solani is still poorly understood. Eighteen soybean cultivars were screened for SDS resistance, with one cultivar showing susceptibility and one cultivar showing resistance to F. solani infection. Histochemical analysis with diaminobenzidine (DAB) and Trypan blue staining indicated an accumulation of reactive oxygen species (ROS) and cell death in surrounding area of SDS which was higher in susceptible cultivar than in resistant cultivar. Furthermore, exogenous salicylic acid (SA) application also induced some level of resistance to F. solani by the susceptible cultivar. A biochemical study revealed that the activities of superoxide dismutase (SOD), peroxidase (POD), and enzymes involved in scavenging ROS, increased in susceptible cultivar after SDS infection. In addition, hydrogen peroxide (H2O2) and malondialdehyde (MDA) content also increased in the susceptible cultivar than in resistant cultivar. High-performance liquid chromatography (HPLC) analysis indicated that free and total salicylic acid (SA) content increased in the susceptible cultivar than in resistant cultivar. In addition, a real-time quantitative PCR analysis showed an accumulation of pathogen related (PR) genes in the resistant cultivar than in susceptible cultivar. Our results show that (i). F. solani infection can increase endogenous SA levels, antioxidase activities, ROS and cell death in susceptible soybean cultivar to induce resistance against Fusarium solani. (ii). F. solani infection induced the expression of SA marker genes in resistant soybean cultivar to enhance resistance.
BackgroundThe dynamic of soil-borne disease is closely related to the rhizosphere microbial communities. Maize-soybean intercropping can suppress soybean root rot as compared to monoculture. However, it is still unknown whether rhizosphere microbial community participates in the regulation of intercropped soybean root rot.MethodsIn this study, the difference of rhizosphere Fusarium and Trichoderma community was compared between healthy or root-rotted soybean rhizosphere soil from soybean monoculture and maize-soybean intercropping, and the inhibitory effect of potential biocontrol Trichoderma against pathogenic Fusarium were examined.ResultsThe abundance of rhizosphere Fusarium was remarkably different between intercropping and monoculture, while Trichoderma was largely accumulated in healthy rhizosphere soil of intercropping rather than monoculture. Four rhizosphere Fusarium species identified were all pathogenic to soybean but displayed distinct composition and isolation proportion in the corresponding soil types. As the dominant and most aggressive species, F. oxysporum was more frequently isolated in diseased soil of monoculture. Furthermore, of three Trichoderma species identified, T. harzianum dramatically increased in the rhizosphere of intercropping rather than monoculture as compared to T. virens and T. afroharzianum. For in-vitro antagonism test, Trichoderma strains had antagonistic effects on F. oxysporum with the percentage of mycelial inhibition ranging of 50.59%-92.94%, and they displayed good mycoparasitic abilities against F. oxysporum through coiling around and entering into the hyphae, expanding along cell-cell lumen and even dissolving cell walls of target fungus.ConclusionThese results indicate maize-soybean intercropping significantly increase the density and composition proportion of beneficial Trichoderma to antagonist the pathogenic Fusarium species, thus contributing to the suppression of soybean root rot under intercropping.
Background: The Zoige alpine wetland is one of the most important wetlands in China because of its complex natural environment, abundant ecological resources, and unique climatic conditions. The ecology of soil fungi is poorly understood, and recent comprehensive reports on Trichoderma are not available for any region, including the Zoige alpine wetland ecological region in China. Our results may be used as a reference for a greater understanding of soil microorganism at various ecological regions, ecological rehabilitation and reconstruction and as microbial resources. Results: One hundred soil samples were collected from different soil types and soil layers in Zoige alpine wetland ecological regions in 2013. Using the traditional suspension plating method, a total of 80 Trichoderma strains were isolated. After a preliminary classification of morphological characteristics and the genes glyceraldehyde-3-phosphate dehydrogenase (gpd), 57 strains were representatively selected and eventually identified as seven species via phylogenetic analyses of multilocus sequences based on the genes transcription elongation factor 1 alpha (tef1), encoding RNA polymerase II subunit B (rpb2) and ATP citrate lyase (acl1). Among them, Trichoderma harzianum was the dominant species and had the highest isolation frequency (23%) in this zone, while Trichoderma polysporum and Trichoderma pyramidale were rare species, with isolation frequencies of less than 1%.Conclusions: Our detailed morphological observation and molecular phylogenetic analyses support the recognition of Trichoderma zoigense was described for the first time as a new species.
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