Control of Fusarium Wilt Using Streptomyces griseus with Plant Growth-Promoting Effect on Tomato

The efficacy of antagonistic Streptomyces griseus was evaluated against tomato wilt disease incited by Fusarium oxysporum. Among the different formulations, Streptomyces griseus with chitin amended formulation showed effective increase in seed germination and seedling vigour. Further, talc-based formulations of S. griseus mixed with or without chitin was developed and tested under greenhouse conditions. Lowest disease severity of 19.1% was observed in plants treated with self fusant (SFSg 5) S. griseus suspension (root dipping – 9 x 108 cfu / mL) followed by 19.5% in treatment of chitin amended S. griseus (root dipping – 9 x 108 cfu/mL) was recorded over control. Plant growth of the treated traits were analyzed and compared with control. The shoot length, root length, leaf area was increased significantly over the controls by the treatment of self fusant (SFSg 5) S. griseus suspension followed by nearby values were reached in chitin amended S. griseus was recorded. The chemical treatments had less effect compared with these formulations. Histochemical studies showed that cambium layers, xylem vessels per bundle, and the vessel diameter decreased in the plants inoculated with F. oxysporum over control and changes in variables were observed in infected plants treated with S. griseus. In conclusion, S. griseus can be a potential biocontrol agent against F. oxysporum for better crop production practices.

Antimicrobial and genetic strategies to defend kiwifruit against the bacterial pathogen Pseudomonas syringae pathovar actinidiae (Psa)

<p>A highly virulent strain of the bacterium Pseudomonas syringae pv. actinidiae (Psa-V), the causative agent of bacterial canker of kiwifruit, is threatening the $1.5 billion New Zealand kiwifruit industry. A strain of Psa-V was first identified in Italy in 2008 and related strain with a similar level of virulence arrived in New Zealand in November 2010. Since then it has been spreading rapidly throughout the country with devastating effects. Currently there is no effective treatment for growers to control Psa-V in their orchards and the potential impact of Psa-V on the New Zealand kiwifruit industry and growers is catastrophic. As part of a collaboration between Seeka Kiwifruit Industries, EastPack NZ, and a group of scientists nationwide (Taskforce Green) this work designed and implemented laboratory tests to quantify the effect of candidate antimicrobial sprays. Novel formulations with strong antimicrobial properties, including silver nanoparticles were also tested. This work was complemented by an investigation into the antibiotic resistance potential of Psa-V. A spontaneous streptomycin resistant mutant of Psa-V was generated and the molecular mechanism of resistance was elucidated. Further, gene knockout strategies aimed at facilitating the study of Psa-V virulence genes and ultimately developing a potential biocontrol agent were tested. Overall, this work together with several recent advances in the field should help advise the kiwifruit industry on best practice around the use of anti-Psa-V agents, and may make it possible to facilitate the generation and testing of candidate biocontrol agents in the near future.</p>

Antimicrobial and genetic strategies to defend kiwifruit against the bacterial pathogen Pseudomonas syringae pathovar actinidiae (Psa)

<p>A highly virulent strain of the bacterium Pseudomonas syringae pv. actinidiae (Psa-V), the causative agent of bacterial canker of kiwifruit, is threatening the $1.5 billion New Zealand kiwifruit industry. A strain of Psa-V was first identified in Italy in 2008 and related strain with a similar level of virulence arrived in New Zealand in November 2010. Since then it has been spreading rapidly throughout the country with devastating effects. Currently there is no effective treatment for growers to control Psa-V in their orchards and the potential impact of Psa-V on the New Zealand kiwifruit industry and growers is catastrophic. As part of a collaboration between Seeka Kiwifruit Industries, EastPack NZ, and a group of scientists nationwide (Taskforce Green) this work designed and implemented laboratory tests to quantify the effect of candidate antimicrobial sprays. Novel formulations with strong antimicrobial properties, including silver nanoparticles were also tested. This work was complemented by an investigation into the antibiotic resistance potential of Psa-V. A spontaneous streptomycin resistant mutant of Psa-V was generated and the molecular mechanism of resistance was elucidated. Further, gene knockout strategies aimed at facilitating the study of Psa-V virulence genes and ultimately developing a potential biocontrol agent were tested. Overall, this work together with several recent advances in the field should help advise the kiwifruit industry on best practice around the use of anti-Psa-V agents, and may make it possible to facilitate the generation and testing of candidate biocontrol agents in the near future.</p>

Novel Genetic Dysregulations and Oxidative Damage in Fusarium graminearum Induced by Plant Defense Eliciting Psychrophilic Bacillus atrophaeus TS1

This study elaborates inter-kingdom signaling mechanisms, presenting a sustainable and eco-friendly approach to combat biotic as well as abiotic stress in wheat. Fusarium graminearum is a devastating pathogen causing head and seedling blight in wheat, leading to huge yield and economic losses. Psychrophilic Bacillus atrophaeus strain TS1 was found as a potential biocontrol agent for suppression of F. graminearum under low temperature by carrying out extensive biochemical and molecular studies in comparison with a temperate biocontrol model strain Bacillus amyloliquefaciens FZB42 at 15 and 25 °C. TS1 was able to produce hydrolytic extracellular enzymes as well as antimicrobial lipopeptides, i.e., surfactin, bacillomycin, and fengycin, efficiently at low temperatures. The Bacillus strain-induced oxidative cellular damage, ultrastructural deformities, and novel genetic dysregulations in the fungal pathogen as the bacterial treatment at low temperature were able to downregulate the expression of newly predicted novel fungal genes potentially belonging to necrosis inducing protein families (fgHCE and fgNPP1). The wheat pot experiments conducted at 15 and 25 °C revealed the potential of TS1 to elicit sudden induction of plant defense, namely, H2O2 and callose enhanced activity of plant defense-related enzymes and induced over-expression of defense-related genes which accumulatively lead to the suppression of F. graminearum and decreased diseased leaf area.

Detection of Pathogenic and Beneficial Microbes for Roselle Wilt Disease

Wilt disease of roselle (Hibiscus sabdariffa L.) is common in Taiwan; however, the causative agent remains unknown. The stems of wilted roselle are browned, slightly constricted, and covered by white aerial hyphae, suggesting that potential pathogens may originate from soil. To identify the potential pathogens, we conducted a rhizosphere microbiota survey in phenotypically healthy and diseased plants through fungal internal transcribed spacer (ITS) and bacterial 16S rRNA amplicon sequencing for uncovering the microbial compositions in the roselle rhizosphere. The fungal family Nectriaceae exhibited significantly higher abundance in diseased rhizospheres than in healthy rhizospheres, and this bacterial community was more specific to geography (i.e., plot-dependent) than to rhizosphere disease status. However, a few bacterial groups such as Bacilli were associated with the healthy rhizosphere. Fusarium species were the most dominant species of Nectriaceae in the survey and became the main target for potential pathogen isolation. We successfully isolated 119 strains from diseased plants in roselle fields. Koch’s postulates were used to evaluate the pathogenicity of these strains; our results indicated that Fusarium solani K1 (FsK1) can cause wilting and a rotted pith in roselles, which was consistent with observations in the fields. This is the first demonstration that F. solani can cause roselle wilt in Taiwan. Furthermore, these newly isolated strains are the most dominant operational taxonomic units detected in ITS amplicon sequencing in diseased rhizospheres, which serves as further evidence that F. solani is the main pathogen causing the roselle wilt disease. Administration of Bacillus velezensis SOI-3374, a strain isolated from a healthy roselle rhizosphere, caused considerable anti-FsK1 activity, and it can serve as a potential biocontrol agent against roselle wilt disease.

Characterization of the Mycovirome from the Plant-Pathogenic Fungus Cercospora beticola

Cercospora leaf spot (CLS) caused by Cercospora beticola is a devastating foliar disease of sugar beet (Beta vulgaris), resulting in high yield losses worldwide. Mycoviruses are widespread fungi viruses and can be used as a potential biocontrol agent for fugal disease management. To determine the presence of mycoviruses in C. beticola, high-throughput sequencing analysis was used to determine the diversity of mycoviruses in 139 C. beticola isolates collected from major sugar beet production areas in China. The high-throughput sequencing reads were assembled and searched against the NCBI database using BLASTn and BLASTx. The results showed that the obtained 93 contigs were derived from eight novel mycoviruses, which were grouped into 3 distinct lineages, belonging to the families Hypoviridae, Narnaviridae and Botourmiaviridae, as well as some unclassified (−)ssRNA viruses in the order Bunyavirales and Mononegavirales. To the best of our knowledge, this is the first identification of highly diverse mycoviruses in C. beticola. The novel mycoviruses explored in this study will provide new viral materials to biocontrol Cercospora diseases. Future studies of these mycoviruses will aim to assess the roles of each mycovirus in biological function of C. beticola in the future.