Root Rot Management in Common Bean (Phaseolus vulgaris L.) Through Integrated Biocontrol Strategies using Metabolites from Trichoderma harzianum, Serratia marcescens, and Vermicompost Tea.

Common bean (Phaseolus vulgaris L.) is an essential food staple and source of income for small-holder farmers across Africa. However, yields are greatly threatened by fungal diseases like root rot induced by Rhizoctonia solani. This study aimed to evaluate an integrated approach utilizing vermicompost tea (VCT) and antagonistic microbes for effective and sustainable management of R. solani root rot in common beans. Fourteen fungal strains were first isolated from infected common bean plants collected across three Egyptian governorates, with R. solani being the most virulent isolate with 50% dominance. Subsequently, the antagonistic potential of vermicompost tea (VCT), Serratia sp., and Trichoderma sp. was assessed against this destructive pathogen. Combinations of 10% VCT and the biocontrol agent isolates displayed potent inhibition of R. solani growth in vitro, prompting in planta testing. Under greenhouse conditions, integrated applications of 5 or 10% VCT with Serratia marcescens, Trichoderma harzianum, or effective microorganisms (EM1) afforded up to 95% protection against pre- and post-emergence damping-off induced by R. solani in common bean cv. Giza 6. Similarly, under field conditions, combining VCT with EM1 (VCT + EM1) or Trichoderma harzianum (VCT + Trichoderma harzianum) substantially suppressed disease severity by 65.6% and 64.34%, respectively, relative to untreated plants. These treatments also elicited defense enzyme activity and distinctly improved growth parameters including 136.68% and 132.49% increases in pod weight per plant over control plants. GC-MS profiling of Trichoderma harzianum, Serratia marcescens, and vermicompost tea (VCT) extracts revealed unique compounds dominated by cyclic pregnane, fatty acid methyl esters, linoleic acid derivatives, and free fatty acids like oleic, palmitic, and stearic acids with confirmed biocontrol and plant growth-promoting activities. The results verify VCT-mediated delivery of synergistic microbial consortia as a sustainable platform for integrated management of debilitating soil-borne diseases, enhancing productivity and incomes for smallholder bean farmers through regeneration of soil health. Further large-scale validation can pave the adoption of this climate-resilient approach for securing food and nutrition security.

Plant growth promotion and biocontrol properties of a synthetic community in the control of apple disease.

BACKGROUND: Apple Replant Disease (ARD) is common in major apple-growing regions worldwide, but the role of rhizosphere microbiota in conferring ARD resistance and promoting plant growth remains unclear. RESULTS: In this study, a synthetic microbial community (SynCom) was developed to enhance apple plant growth and combat apple pathogens. Eight unique bacteria selected via microbial culture were used to construct the antagonistic synthetic community, which was then inoculated into apple seedlings in greenhouse experiments. Changes in the rhizomicroflora and the growth of aboveground plants were monitored. The eight strains, belonging to the genera Bacillus and Streptomyces, have the ability to antagonize pathogens such as Fusarium oxysporum, Rhizoctonia solani, Botryosphaeria ribis, and Physalospora piricola. Additionally, these eight strains can stably colonize in apple rhizosphere and some of them can produce siderophores, ACC deaminase, and IAA. Greenhouse experiments with Malus hupehensis Rehd indicated that SynCom promotes plant growth (5.23%) and increases the nutrient content of the soil, including soil organic matter (9.25%) and available K (1.99%), P (7.89%), and N (0.19%), and increases bacterial richness and the relative abundance of potentially beneficial bacteria. SynCom also increased the stability of the rhizosphere microbial community, the assembly of which was dominated by deterministic processes (|ß NTI| > 2). CONCLUSIONS: Our results provide insights into the contribution of the microbiome to pathogen inhibition and host growth. The formulation and manipulation of similar SynComs may be a beneficial strategy for promoting plant growth and controlling soil-borne disease.

Identification and mechanism characterization of Streptomyces griseoaurantiacus XQ-29 with biocontrol ability against pepper southern blight caused by Sclerotium rolfsii.

Pepper southern blight, caused by Sclerotium rolfsii, is a devastating soil-borne disease resulting in significant loss to pepper, Capsicum annuum L. production. Here, we isolated an antagonistic bacterial strain XQ-29 with antifungal activity against S. rolfsii from rhizospheric soil of pepper. Combining the morphological and biochemical characteristics with the 16S rDNA sequencing, XQ-29 was identified as Streptomyces griseoaurantiacus. It exhibited an inhibition of 96.83% against S. rolfsii and displayed significant inhibitory effects on Botrytis cinerea, Phytophthora capsica and Rhizoctonia solani. Furthermore, XQ-29 significantly reduced the pepper southern blight by 100% and 70.42% during seedling and growth stages, respectively. The antifungal mechanism involved altering the mycelial morphology, disrupting cell wall and membrane integrity, accompanied by accumulation of reactive oxygen species and lipid peroxidation in S. rolfsii mycelia. Furthermore, XQ-29 promoted growth and stimulated resistance of pepper plants by increasing defense-related enzyme activities and upregulating defense-related genes. Correspondingly, XQ-29 harbors numerous functional biosynthesis gene clusters in its genome, including those for siderophores and melanin production. The metabolic constituents present in the ethyl acetate extracts, which exhibited an EC50 value of 85.48 ± 1.62 µg/mL, were identified using LC-MS. Overall, XQ-29 demonstrates significant potential as a biocontrol agent against southern blight disease.

Antagonistic potential and biological control mechanisms of Pseudomonas strains against banded leaf and sheath blight disease of maize.

Rhizoctonia solani, the causal agent of banded leaf and sheath blight (BL&SB), poses a significant threat to maize and various crops globally. The increasing concerns surrounding the environmental and health impacts of chemical fungicides have encouraged intensified concern in the development of biological control agents (BCAs) as eco-friendly alternatives. In this study, we explored the potential of 22 rhizobacteria strains (AS1-AS22) isolates, recovered from the grasslands of the Pithoragarh region in the Central Himalayas, as effective BCAs against BL&SB disease. Among these strains, two Pseudomonas isolates, AS19 and AS21, exhibited pronounced inhibition of fungal mycelium growth in vitro, with respective inhibition rates of 57.04% and 54.15% in cell cultures and 66.56% and 65.60% in cell-free culture filtrates. Additionally, both strains demonstrated effective suppression of sclerotium growth. The strains AS19 and AS21 were identified as Pseudomonas sp. by 16S rDNA phylogeny and deposited under accession numbers NAIMCC-B-02303 and NAIMCC-B-02304, respectively. Further investigations revealed the mechanisms of action of AS19 and AS21, demonstrating their ability to induce systemic resistance (ISR) and exhibit broad-spectrum antifungal activity against Alternaria triticina, Bipolaris sorokiniana, Rhizoctonia maydis, and Fusarium oxysporum f. sp. lentis. Pot trials demonstrated significant reductions in BL&SB disease incidence (DI) following foliar applications of AS19 and AS21, with reductions ranging from 25 to 38.33% compared to control treatments. Scanning electron microscopy revealed substantial degradation of fungal mycelium by the strains, accompanied by the production of hydrolytic enzymes. These findings suggest the potential of Pseudomonas strains AS19 and AS21 as promising BCAs against BL&SB and other fungal pathogens. However, further field trials are warranted to validate their efficacy under natural conditions and elucidate the specific bacterial metabolites responsible for inducing systemic resistance. This study contributes to the advancement of sustainable disease management strategies and emphasizes the potential of Pseudomonas strains AS19 and AS21 in combating BL&SB and other fungal diseases affecting agricultural crops.

Combined control of plant diseases by Bacillus subtilis SL44 and Enterobacter hormaechei Wu15.

Co-incubation of plant growth promoting rhizobacteria (PGPRs) have been proposed as a potential alternative to pesticides for controlling fungal pathogens in crops, but their synergism mechanisms are not yet fully understood. In this study, combined use of Bacillus subtilis SL44 and Enterobacter hormaechei Wu15 could decrease the density of Colletotrichum gloeosporioides and Rhizoctonia solani and enhance the growth of beneficial bacteria on the mycelial surface, thereby mitigating disease severity. Meanwhile, PGPR application led to a reorganization of the rhizosphere microbial community through modulating its metabolites, such as extracellular polymeric substances and chitinase. These metabolites demonstrated positive effects on attracting and enhancing conventional periphery bacteria, inhibiting fungal pathogens and promoting soil health effectively. The improvement in the microbial community structure altered the trophic mode of soil fungal communities, effectively decreasing the proportion of saprotrophic soil and reducing fungal plant diseases. Certain combinations of PGPR have the potential to serve as precise instruments for managing plant pathogens.

Induction of volatile organic compounds in chrysanthemum plants following infection by Rhizoctonia solani.

This study investigated the effects of Rhizoctonia solani J.G. Kühn infestation on the volatile organic compound (VOC) emissions and biochemical composition of ten cultivars of chrysanthemum (Chrysanthemum × morifolium /Ramat./ Hemsl.) to bring new insights for future disease management strategies and the development of resistant chrysanthemum cultivars. The chrysanthemum plants were propagated vegetatively and cultivated in a greenhouse under semi-controlled conditions. VOCs emitted by the plants were collected using a specialized system and analyzed by gas chromatography/mass spectrometry. Biochemical analyses of the leaves were performed, including the extraction and quantification of chlorophylls, carotenoids, and phenolic compounds. The emission of VOCs varied among the cultivars, with some cultivars producing a wider range of VOCs compared to others. The analysis of the VOC emissions from control plants revealed differences in both their quality and quantity among the tested cultivars. R. solani infection influenced the VOC emissions, with different cultivars exhibiting varying responses to the infection. Statistical analyses confirmed the significant effects of cultivar, collection time, and their interaction on the VOCs. Correlation analyses revealed positive relationships between certain pairs of VOCs. The results show significant differences in the biochemical composition among the cultivars, with variations in chlorophyll, carotenoids, and phenolic compounds content. Interestingly, R. solani soil and leaf infestation decreased the content of carotenoids in chrysanthemums. Plants subjected to soil infestation were characterized with the highest content of phenolics. This study unveils alterations in the volatile and biochemical responses of chrysanthemum plants to R. solani infestation, which can contribute to the development of strategies for disease management and the improvement of chrysanthemum cultivars with enhanced resistance to R. solani.

OsEIL2 balances rice immune responses against (hemi)biotrophic and necrotrophic pathogens via the salicylic acid and jasmonic acid synergism.

Plants typically activate distinct defense pathways against various pathogens. Heightened resistance to one pathogen often coincides with increased susceptibility to another pathogen. However, the underlying molecular basis of this antagonistic response remains unclear. Here, we demonstrate that mutants defective in the transcription factor ETHYLENE-INSENSITIVE 3-LIKE 2 (OsEIL2) exhibited enhanced resistance to the biotrophic bacterial pathogen Xanthomonas oryzae pv oryzae and to the hemibiotrophic fungal pathogen Magnaporthe oryzae, but enhanced susceptibility to the necrotrophic fungal pathogen Rhizoctonia solani. Furthermore, necrotroph-induced OsEIL2 binds to the promoter of OsWRKY67 with high affinity, leading to the upregulation of salicylic acid (SA)/jasmonic acid (JA) pathway genes and increased SA/JA levels, ultimately resulting in enhanced resistance. However, biotroph- and hemibiotroph-induced OsEIL2 targets OsERF083, resulting in the inhibition of SA/JA pathway genes and decreased SA/JA levels, ultimately leading to reduced resistance. Our findings unveil a previously uncharacterized defense mechanism wherein two distinct transcriptional regulatory modules differentially mediate immunity against pathogens with different lifestyles through the transcriptional reprogramming of phytohormone pathway genes.

Lipase domain effector AGLIP1 in Rhizoctonia solani triggers necrotic killing in plants.

KEY MESSAGE: We highlight the emerging role of the R. solani novel lipase domain effector AGLIP1 in suppressing pattern-triggered immunity and inducing plant cell death. The dynamic interplay between plants and Rhizoctonia solani constitutes a multifaceted struggle for survival and dominance. Within this complex dynamic, R. solani has evolved virulence mechanisms by secreting effectors that disrupt plants' first line of defense. A newly discovered effector, AGLIP1 in R. solani, plays a pivotal role in inducing plant cell death and subverting immune responses. AGLIP1, a protein containing a signal peptide and a lipase domain, involves complex formation in the intercellular space, followed by translocation to the plant cytoplasm, where it induces cell death (CD) and suppresses defense gene regulation. This study provides valuable insights into the intricate molecular interactions between plants and necrotrophic fungi, underscoring the imperative for further exploration in this field.

The efficacy of chemical inducers and fungicides in controlling tomato root rot disease caused by Rhizoctoniasolani.

Chitosan is an environmentally friendly natural substance that is used in crop disease management as an alternative to chemical pesticides. A significant issue restricting output in Egypt is root rot, which is a disease, caused by Rhizoctonia solani. Therefore, a greenhouse experiment was conducted to assess the effects of R. solani on 60-day-old tomato plants under fungal infection and to determine the antifungal activity of chitosan and Rizolax T fungicide against the pathogenic fungus. The findings demonstrated that 4 g/L of chitosan seed application completely obstructed the radial mycelial growth of R. solani and decreased the disease severity. Pathogenic infection significantly decreased morphological characteristics and total chlorophyll but significantly increased carotenoid, total thiol, non-protein thiol, protein thiol, antioxidant enzymes, oxidative stress, total phenolic, total flavonoid, and isoflavone compared to healthy plants. Tomato plants treated with chitosan exhibited lower rates of oxidative stress, but higher levels of all previously mentioned parameters compared to untreated infected plants. The number and molecular mass of protein banding patterns varied in all treated tomato plants as compared to the healthy control. There are 42 bands in the treatments, and their polymorphism rate is 69.55%. Moreover, the number and density of α- and ß-esterase, and peroxidase isozymes in treated tomato plants exhibited varied responses. Moreover, in treated and control plants, chitosan treatment raised the expression levels of phenylalanine ammonia-lyase, pathogenesis-related protein-1, ß-1,3-glucanases and chitinase. In conclusions, chitosan reduces R. solani infection by controlling the biochemical and molecular mechanisms in tomato plants during infection.

Development of a Greenhouse Assay to Screen Soybean Varieties for Resistance to Aerial Blight Caused by Rhizoctonia solani Anastomosis Group 1-IA.

Aerial blight, caused by the fungus Rhizoctonia solani anastomosis group (AG) 1-IA, is an economically important soybean disease in the mid-Southern United States. Management has relied on fungicide applications during the season, but there is an increasing prevalence of resistance to commonly used strobilurin fungicides and an urgent need to identify soybean varieties resistant to aerial blight. Because the patchy distribution of the pathogen complicates field variety screening, the present study aimed to develop a greenhouse screening protocol to identify soybean varieties resistant to aerial blight. For this, 88 pathogen isolates were collected from commercial fields and research farms across five Louisiana parishes, and 77% were confirmed to be R. solani AG1-IA. Three polymorphic codominant microsatellite markers were used to explore the genetic diversity of 43 R. solani AG1-IA isolates, which showed high genetic diversity, with 35 haplotypes in total and only two haplotypes common to two other locations. Six genetically diverse isolates were chosen and characterized for their virulence and fungicide sensitivity. The isolate AC2 was identified as the most virulent and was resistant to both active ingredients, azoxystrobin and pyraclostrobin, tested. The six isolates were used in greenhouse variety screening trials using a millet inoculation protocol. Of the 31 varieties screened, only Armor 48-D25 was classified as moderately resistant, and plant height to the first node influenced final disease severity. The study provides short-term solutions for growers to choose less susceptible varieties for planting and lays the foundation to characterize host resistance against this important soybean pathogen.

Anaerobic Soil Disinfestation and Vermicompost to Manage Bottom Rot in Organic Lettuce.

Rhizoctonia solani Kühn (teleomorph: Thanatephorus cucumeris [Frank] Donk) is an aggressive soilborne pathogen with a wide host range that survives saprophytically between crops, presenting a challenge for organic vegetable farmers who lack effective management tools. A 2-year field experiment was conducted at two organic farms to compare anaerobic soil disinfestation (ASD) and worm-cured compost (vermicompost) to manage bottom rot caused by R. solani subspecies AG1-IB in field-grown organic lettuce (Lactuca sativa). At each farm, four replicate plots of seven treatments were arranged in a randomized complete block design. Randomization was restricted by grouping treatments to evaluate ASD, and treatments to evaluate vermicompost in starter plugs. ASD experiment treatments were three different ASD carbon sources that are commonly used and widely available to local farmers in Vermont: compost, cover crop residues, and poultry manure fertilizer, as well as a tarped control. Vermicompost experimental treatments were vermicompost compared with two types of controls: a commercial biocontrol product (RootShield PLUS + G), and unamended (untarped control). This study demonstrated that the ASD method is achievable in a field setting on Vermont farms. However, neither ASD nor vermicompost produced significant disease suppression or resulted in higher marketable yields than standard growing practices. Given the laborious nature of ASD, it is likely more appropriate in a greenhouse setting with high-value crops that could especially benefit from being grown in plastic tarped beds (e.g., tomatoes and strawberries). This study is the first known attempt of field-implemented ASD for soil pathogen control in the northeastern United States.

Eliciting transcriptomic and antioxidant defensive responses against Rhizoctonia root rot of sorghum using the endophyte Aspergillus oryzae YRA3.

Environmental pollution due to the improper use of the chemical fungicides represents a vital ecological problem, which affects human and animal health, as well as the microbial biodiversity and abundance in the soil. In this study, an endophytic fungus Aspergillus oryzae YRA3, isolated from the wild plant Atractylis carduus (Forssk.) C.Chr, was tested for its biocontrol activity against Rhizoctonia root rot of sorghum. The antagonistic potential of A. oryzae YRA3 was tested against Rhizoctonia solani in vitro. A full inhibition in the growth of R. solani was recorded indicating a strong antagonistic potential for this endophyte. To investigate the chemical composition of its metabolites, GC/MS analysis was used and thirty-two compounds in its culture filtrate were identified. Among these metabolites, some compounds with an antifungal background were detected including palmitic acid, 2-heptanone, and 2,3-butanediol. To these antifungal metabolites the antagonistic activity of A. oryzae YRA3 can be attributed. In the greenhouse experiment, treating of the infected sorghum plants with A. oryzae YRA3 significantly reduced severity of the Rhizoctonia root rot by 73.4%. An upregulation of the defensive genes (JERF3), (POD) and (CHI II) was recorded in sorghum roots when were inoculated with A. oryzae YRA3. In addition, an increment in the activity of peroxidase and polyphenol oxidase, as well as the total phenolic content in the sorghum roots was also recorded. Furthermore, the results obtained from the greenhouse experiment revealed a growth-promoting effect for inoculating the sorghum plants with A. oryzae YRA3. It can be concluded that A. oryzae YRA3 can be a probable biological agent to control this disease in sorghum. However, its evaluation under field conditions is highly needed in the future studies.

Knockout of transcription factor OsERF65 enhances ROS scavenging ability and confers resistance to rice sheath blight.

Rice sheath blight (ShB) is a devastating disease that severely threatens rice production worldwide. Induction of cell death represents a key step during infection by the ShB pathogen Rhizoctonia solani. Nonetheless, the underlying mechanisms remain largely unclear. In the present study, we identified a rice transcription factor, OsERF65, that negatively regulates resistance to ShB by suppressing cell death. OsERF65 was significantly upregulated by R. solani infection in susceptible cultivar Lemont and was highly expressed in the leaf sheath. Overexpression of OsERF65 (OsERF65OE) decreased rice resistance, while the knockout mutant (oserf65) exhibited significantly increased resistance against ShB. The transcriptome assay revealed that OsERF65 repressed the expression of peroxidase genes after R. solani infection. The antioxidative enzyme activity was significantly increased in oserf65 plants but reduced in OsERF65OE plants. Consistently, hydrogen peroxide content was apparently reduced in oserf65 plants but accumulated in OsERF65OE plants. OsERF65 directly bound to the GCC box in the promoter regions of four peroxidase genes and suppressed their transcription, reducing the ability to scavenge reactive oxygen species (ROS). The oserf65 mutant exhibited a slight decrease in plant height but increased grain yield. Overall, our results revealed an undocumented role of OsERF65 that acts as a crucial regulator of rice resistance to R. solani and a potential target for improving both ShB resistance and rice yield.

ß-Glucanase Family Genes Promote Resistance to Sheath Blight in Rice by Inhibiting the Permeability of Plasmodesmata.

Rice sheath blight (ShB) caused by Rhizoctonia solani is one of the most serious diseases that threatens rice (Oryza sativa) production. However, the mechanisms of defense against ShB in rice remain largely unknown. In this study, we identified that the expression levels of ß-glucanase (OsBGL) family genes sensitively respond to infection by R. solani, and OsBGLs positively regulate rice resistance to ShB. In addition, OsBGL2 colocalized with AtPDCB1 at the plasmodesmata (PD) and limited the PD permeability. The level of callose accumulation in osbgls mutants and overexpressors was examined, and OsBGLs were found contribute to callose accumulation. Taken together, these data suggest that OsBGLs can regulate the deposition of callose at the PD to reduce its permeability to defend itself against ShB. Through the identification of these genes and the elucidation of their functions, this research fills the gap in the mechanism of PD permeability in rice ShB resistance.

Taxonomical, functional, and cytopathological characterization of Bacillus spp. from Lake Magadi, Kenya, against Rhizoctonia solani Kühn in Phaseolus vulgaris L.

A decline in common bean production and the ineffectiveness of synthetic chemical products in managing plant pathogens has led to exploiting Kenyan soda lakes as an alternative search for biocontrol agents. This study aimed to identify phylogenetically Bacillus spp. from Lake Magadi and their antagonistic activity against Rhizoctonia solani under in vitro and in vivo conditions. The 16 S ribosomal RNA (rRNA) subunit sequences of six bacterial strains isolated from Lake Magadi showed diversity similar to the Bacillus genus; Bacillus velezensis, Bacillus subtilis, and Bacillus pumilus. In vitro, antagonism showed varied mycelium inhibition rates of fungi in the coculture method. Enzymatic assays showed the varied ability of isolates to produce phosphatase, pectinase, chitinase, protease, indole-3-acetic acid (IAA), and hydrogen cyanide (HCD). The in vivo assay showed M09 (B. velezensis) with the lowest root mortality and incidence of postemergence wilt. Pre-emergence wilt incidence was recorded as lowest in M10 (B. subtilis). Isolate M10 had the highest phenylalanine ammonia-lyase (PAL) for defense enzymes, while polyphenol oxidase (PPO) and peroxidase were recorded as highest in M09. For the phenolic content, M10 recorded the highest phenolic content. In conclusion, Lake Magadi harbors Bacillus spp, which can be used as a potential biocontrol of R. solani.

Suppression of Rice Osa-miR444.2 Improves the Resistance to Sheath Blight in Rice Mediating through the Phytohormone Pathway.

MicroRNAs (miRNAs) are a class of conserved small RNA with a length of 21-24 nucleotides in eukaryotes, which are involved in development and defense responses against biotic and abiotic stresses. By RNA-seq, Osa-miR444b.2 was identified to be induced after Rhizoctonia solani (R. solani) infection. In order to clarify the function of Osa-miR444b.2 responding to R. solani infection in rice, transgenic lines over-expressing and knocking out Osa-miR444b.2 were generated in the background of susceptible cultivar Xu3 and resistant cultivar YSBR1, respectively. Over-expressing Osa-miR444b.2 resulted in compromised resistance to R. solani. In contrast, the knocking out Osa-miR444b.2 lines exhibited improved resistance to R. solani. Furthermore, knocking out Osa-miR444b.2 resulted in increased height, tillers, smaller panicle, and decreased 1000-grain weight and primary branches. However, the transgenic lines over-expressing Osa-miR444b.2 showed decreased primary branches and tillers, but increased panicle length. These results indicated that Osa-miR444b.2 was also involved in regulating the agronomic traits in rice. The RNA-seq assay revealed that Osa-miR444b.2 mainly regulated the resistance to rice sheath blight disease by affecting the expression of plant hormone signaling pathways-related genes such as ET and IAA, and transcription factors such as WRKYs and F-boxes. Together, our results suggest that Osa-miR444b.2 negatively mediated the resistance to R. solani in rice, which will contribute to the cultivation of sheath blight resistant varieties.

Calcineurin B-like interacting protein kinase 31 confers resistance to sheath blight via modulation of ROS homeostasis in rice.

Sheath blight (ShB) severely threatens rice cultivation and production; however, the molecular mechanism of rice defence against ShB remains unclear. Screening of transposon Ds insertion mutants identified that Calcineurin B-like protein-interacting protein kinase 31 (CIPK31) mutants were more susceptible to ShB, while CIPK31 overexpressors (OX) were less susceptible. Sequence analysis indicated two haplotypes of CIPK31: Hap_1, with significantly higher CIPK31 expression, was less sensitive to ShB than the Hap_2 lines. Further analyses showed that the NAF domain of CIPK31 interacted with the EF-hand motif of respiratory burst oxidase homologue (RBOHA) to inhibit RBOHA-induced H2 O2 production, and RBOHA RNAi plants were more susceptible to ShB. These data suggested that the CIPK31-mediated increase in resistance is not associated with RBOHA. Interestingly, the study also found that CIPK31 interacted with catalase C (CatC); cipk31 mutants accumulated less H2 O2 while CIPK31 OX accumulated more H2 O2 compared to the wild-type control. Further analysis showed the interaction of the catalase domain of CatC with the NAF domain of CIPK31 by which CIPK31 inhibits CatC activity to accumulate more H2 O2 .

Identification of a Novel Streptomyces sp. Strain HU2014 Showing Growth Promotion and Biocontrol Effect Against Rhizoctonia spp. in Wheat.

Wheat sharp eyespot is a serious disease caused by the phytopathogens Rhizoctonia cerealis and R. solani. Some species in the genus Streptomyces have been identified as potential biocontrol agents against phytopathogens. In this investigation, the physiological, biochemical, phylogenetic, and genomic characteristics of strain HU2014 indicate that it is a novel Streptomyces sp. most closely related to Streptomyces albireticuli. Strain HU2014 exhibited strong antifungal activity against R. cerealis G11 and R. solani YL-3. Ultraperformance liquid chromatography-mass spectrometry on the four extracts from the extracellular filtrate of strain HU2014 identified 10 chemical constituents in the Natural Products Atlas with high match levels (more than 90%). In an antifungal efficiency test on wheat sharp eyespot, two extracts significantly reduced the lesion areas on bean leaves infected by R. solani YL-3. The drenching of wheat in pots with spore suspension of strain HU2014 demonstrated a control efficiency of 65.1% against R. cerealis G11 (compared with 66.9% when treated by a 30% hymexazol aqueous solution). Additionally, in vitro and pot experiments demonstrated that strain HU2014 can produce indoleacetic acid, siderophores, extracellular enzymes, and solubilized phosphate, and it can promote plant growth. We conclude that strain HU2014 could be a valuable microbial resource for growth promotion of wheat and biological control of wheat sharp eyespot.

Biochemical defense mechanism associated with host-specific disease resistance pathways against Rhizoctonia solani AG3-PT potatoes canker disease.

MAIN CONCLUSION: Screening for resistance in 40 potato genotypes to Rhizoctonia solani AG-3PT-stem-canker, antioxidant enzymes activity as well as total phenol compounds were documented. Rhizoctonia solani AG-3PT-stem-canker is one of the most devastating diseases that leads to severe economic losses in potatoes, Solanum tuberosum globally. Crop management and eugenic practices, especially the use of resistance can be effective in reducing the disease incidence. However, the information about potato-R. Solani interaction is still limited. This study explored screening for resistance in forty potato genotypes to R. solani, analyzing biomass growth parameters (BGPs), as well as antioxidant enzymes activity of which peroxidase/peroxide-reductases (POXs), superoxide dismutase (SOD), polyphenol oxidase (PPO), catalase (CAT), phenylalanine ammonia-lyase (PAL), ß-1,3-glucanase (GLU) and total phenol compounds (TPCs) were taken into account. In addition, we analyzed up-regulation of two gene markers (PR-1 and Osmotin), using reverse transcription quantitative PCR (RT-qPCR). For which, the resistant 'Savalan', partially resistant 'Agria', partially susceptible 'Sagita' and susceptible 'Pashandi' were selected to explore the trails in their roots and leaves over the time courses of 1, 2 and 3-weeks post inoculation (wpi) following inoculation. Cluster analysis divided potatoes into four distinct groups, based on disease severity scales (0-100%) significance. The BGPs, shoot and root length, fresh and dry weight, and root volume were also significantly higher in infected potatoes compared to non-inoculated controls. Antioxidant enzymes activity also indicated the highest increased levels for POX (fourfold at 3wpi), CAT (1.5-fold at 3wpi), SOD (6.8-fold at 1wpi), and PAL (2.7-fold at 3wpi) in the resistant genotype, 'Savalan', whereas the highest activity was recorded in TPC (twofold at 1 wpi), PPO (threefold at 3wpi), and GLU (2.3-fold at 1wpi) in partially resistant genotypes. Although the defense-related enzymatic activities were sharply elevated in the resistant and partially resistant genotypes following inoculation, no significant correlations were between the activity trends of the related enzymes. The two related gene markers also showed comprehensive transcriptional responses up to 3.4-fold, predominantly in resistant genotypes. Surprisingly, the PR-1 gene marker, basically resistant to Wilting agent Verticillium dahlia was overexpressed in resistant 'Savalan' and 'Agria' against R. solani AG3-PT. Similar results were obtained on Osmotin gene marker resistant to late-blight P. infestans, and early-blight Alternaria solani that similarly modulates immunity against R. solani. Furthermore, there was a significant correlation between resistance, enzyme activity, and gene expression in the aforesaid cultivars. Studying the physiological metabolic pathways of antioxidant enzymes activity appears to be an important direction in research to elucidate resistance to R. solani in potatoes.

Whole-Genome Metalloproteases in the Wheat Sharp Eyespot Pathogen Rhizoctonia cerealis and a Role in Fungal Virulence.

Rhizoctonia cerealis is the causal agent of sharp eyespot, a devastating disease of cereal crops including wheat. Several metalloproteases have been implicated in pathogenic virulence, but little is known about whole-genome metalloproteases in R. cerealis. In this study, a total of 116 metalloproteases-encoding genes were identified and characterized from the R. cerealis Rc207 genome. The gene expression profiles and phylogenetic relationship of 11 MEP36/fungalysin metalloproteases were examined during the fungal infection to wheat, and function of an upregulated secretory MEP36 named RcFL1 was validated. Of 11 MEP36 family metalloproteases, ten, except RcFL5, were predicted to be secreted proteins and nine encoding genes, but not RcFL5 and RcFL2, were expressed during the R. cerealis infection process. Phylogenetic analysis suggested that MEP36 metalloproteases in R. cerealis were closely related to those of Rhizoctonia solani but were remote to those of Bipolaris sorokiniana, Fusarium graminearum, F. pseudograminearum, and Pyricularia oryzae. Expression of RcFL1 was significantly upregulated during the infection process and induced plant cell death in wheat to promote the virulence of the pathogen. The MEP36 domain was necessary for the activities of RcFL1. Furthermore, RcFL1 could repress the expression of wheat genes coding for the chitin elicitor receptor kinase TaCERK1 and chitinases. These results suggest that this MEP36 metalloprotease RcFL1 may function as a virulence factor of R. cerealis through inhibiting host chitin-triggered immunity and chitinases. This study provides insights on pathogenic mechanisms of R. cerealis. RcFL1 likely is an important gene resource for improving resistance of wheat to R. cerealis through host-induced gene silencing strategy.