Biological control of anthracnose (Colletotrichum gloeosporioides) in yam by Streptomyces sp.MJM5763

Metagenomic insights into the response of soil microbial communities to pathogenic Ralstonia solanacearum

Understanding the response of soil microbial communities to pathogenic Ralstonia solanacearum is crucial for preventing bacterial wilt outbreaks. In this study, we investigated the soil physicochemical and microbial community to assess their impact on the pathogenic R.solanacearum through metagenomics. Our results revealed that certain archaeal taxa were the main contributors influencing the health of plants. Additionally, the presence of the pathogen showed a strong negative correlation with soil phosphorus levels, while soil phosphorus was significantly correlated with bacterial and archaeal communities. We found that the network of microbial interactions in healthy plant rhizosphere soils was more complex compared to diseased soils. The diseased soil network had more linkages, particularly related to the pathogen occurrence. Within the network, the family Comamonadaceae, specifically Ramlibacter_tataouinensis, was enriched in healthy samples and showed a significantly negative correlation with the pathogen. In terms of archaea, Halorubrum, Halorussus_halophilus (family: Halobacteriaceae), and Natronomonas_pharaonis (family: Haloarculaceae) were enriched in healthy plant rhizosphere soils and showed negative correlations with R.solanacearum. These findings suggested that the presence of these archaea may potentially reduce the occurrence of bacterial wilt disease. On the other hand, Halostagnicola_larseniia and Haloterrigena_sp._BND6 (family: Natrialbaceae) had higher relative abundance in diseased plants and exhibited significantly positive correlations with R.solanacearum, indicating their potential contribution to the pathogen's occurrence. Moreover, we explored the possibility of functional gene sharing among the correlating bacterial pairs within the Molecular Ecological Network. Our analysis revealed 468 entries of horizontal gene transfer (HGT) events, emphasizing the significance of HGT in shaping the adaptive traits of plant-associated bacteria, particularly in relation to host colonization and pathogenicity. Overall, this work revealed key factors, patterns and response mechanisms underlying the rhizosphere soil microbial populations. The findings offer valuable guidance for effectively controlling soil-borne bacterial diseases and developing sustainable agriculture practices.

Green Management of Postharvest Anthracnose Caused by Colletotrichum gloeosporioides

Fruits and vegetables are constantly affected by postharvest diseases, of which anthracnose is one of the most severe and is caused by diverse Colletotrichum species, mainly C. gloeosporioides. In the last few decades, chemical fungicides have been the primary approach to anthracnose control. However, recent trends and regulations have sought to limit the use of these substances. Greener management includes a group of sustainable alternatives that use natural substances and microorganisms to control postharvest fungi. This comprehensive review of contemporary research presents various sustainable alternatives to C. gloeosporioides postharvest control in vitro and in situ, ranging from the use of biopolymers, essential oils, and antagonistic microorganisms to cultivar resistance. Strategies such as encapsulation, biofilms, coatings, compounds secreted, antibiotics, and lytic enzyme production by microorganisms are revised. Finally, the potential effects of climate change on C. gloeosporioides and anthracnose disease are explored. Greener management can provide a possible replacement for the conventional approach of using chemical fungicides for anthracnose postharvest control. It presents diverse methodologies that are not mutually exclusive and can be in tune with the needs and interests of new consumers and the environment. Overall, developing or using these alternatives has strong potential for improving sustainability and addressing the challenges generated by climate change.

Identification and genomic analyses of a novel endophytic actinobacterium Streptomyces endophytica sp. nov. with potential for biocontrol of yam anthracnose

Anthracnose disease caused by Colletotrichum gloeosporioides is one of the devastating diseases of yams (Dioscorea sp.) worldwide. In this study, we aimed to isolate endophytic actinobacteria from yam plants and to evaluate their potential for the control of yam anthracnose based on bioassays and genomic analyses. A total of 116 endophytic actinomycete strains were isolated from the surface-sterilized yam tissues from a yam orchard in Hainan Province, China. In total, 23 isolates showed antagonistic activity against C. gloeosporioides. An endophytic actinomycete, designated HNM0140^T, which exhibited strong antifungal activities, multiple biocontrol, and plant growth-promoting (PGP) traits was subsequently selected to colonize in the tissue-cultured seedlings of yam and was tested for its in vivo biocontrol potential on yam anthracnose. The results showed that treatment with strain HNM0140^T markedly reduced the severity and incidence of yam anthracnose under greenhouse conditions. Morphological and chemotaxonomic analyses showed that strain HNM0140^T was assigned to the genus Streptomyces. Phylogenetic analysis based on the 16S rRNA gene sequences indicated that strain HNM0140^T formed a separate cluster together with Streptomyces lydicus ATCC 25470^T (99.45%), Streptomyces chattanoogensis NRRL ISP-5002^T (99.45%), and Streptomyces kronopolitis NEAU-ML8^T (98.97%). The phylogenomic tree also showed that strain HNM0140^T stably clustered with Streptomyces lydicus ATCC 25470^T. The ANI and dDDH between strain HNM0140^T and its closest related-type species were well below the recommended thresholds for species demarcation. Hence, based on the phylogenetic, genomic, and phenotypic analyses, strain HNM0140^T should represent a new streptomycete species named Streptomyces endophytica sp. nov. Genomic analysis revealed that strain HNM0140^T harbored 18 putative BGCs for secondary metabolites, some PGP-related genes, and several genes coding for antifungal enzymes. The presented results indicated that strain HNM0140^T was a promising biocontrol agent for yam anthracnose.

J, Nadig SM, Manjunathagowda DC, Gurav VS, Singh M. Anthracnose of Onion (Allium cepa L.): A Twister Disease

The onion (Allium cepa L.) is a lucrative and high-value vegetable–spice crop in India, but it is sensitive to several of diseases caused by fungi, bacteria, viruses, and nematodes, of which a fungal disease, anthracnose, caused by Colletotrichum spp., is a major issue for both onion producers and researchers since it severely affects the bulb production. Twister disease is currently one of the most common problems in onion production, particularly in humid regions, and it reduces productivity while also lowering the value and profitability. Twister disease is visualised by white or pale-yellow water-soaked oval depressed lesions on leaf blades, which are the first symptoms. Lesions expand as the disease advances, and numerous black-coloured, slightly elevated structures/fruiting bodies appear in the middle area, arranged in concentric rings. Curling, twisting, chlorosis of the leaves, and aberrant extension of the neck or pseudo-stem occurs, followed by rotting of the bulb. In an unmanaged crop, an excess gibberellin production by Colletotrichum gloeosporioides and Gibberella moniliformis is suspected to induce twisting and aberrant neck elongation, which will ruin onion productivity. It is difficult and environmentally unfriendly to control these infections. Since, to the best of our knowledge, this is the first review on onion anthracnose, we tried to consolidate information. This review updates our knowledge of the pathogen, including the disease cycle, infection pathways, and disease management techniques. As a result, growers will be benefit from the application of cultural, biological, and chemical measures and the use of resistant varieties.

Antifungal Potential of Bacillus velezensis CE 100 for the Control of Different Colletotrichum Species through Isolation of Active Dipeptide, Cyclo-(D-phenylalanyl-D-prolyl)

Colletotrichum species are important fungal pathogens causing anthracnose of tropical and subtropical fruit and vegetable crops. Dual culture assay indicated that Bacillus velezensis CE 100 was a strong antagonist against C. acutatum, C. coccodes, C. dematium, and C. gloeosporioides. The volatile organic compounds produced by B. velezensis CE 100 affected mycelial growth of Colletotrichum species tested in our study and caused twisted hyphal structures of all these fungal species. Chloroform crude compounds of B. velezensis CE 100 inhibited four Colletotrichum species in a concentration-dependent manner and induced severe damage in hyphal morphology of these fungal pathogens, including swelling, bulging, and multiple branching. Moreover, the active cyclic dipeptide, cyclo-(D-phenylalanyl-D-prolyl), was isolated from chloroform crude extract and identified by nuclear magnetic resonance (NMR) and mass spectrometry. The inhibitory effect of cyclo-(D-phenylalanyl-D-prolyl) on conidial germination of C. gloeosporioides occurred in a concentration-dependent manner. The conidial germination rate was completely inhibited by a concentration of 3 mg/mL of cyclo-(D-phenylalanyl-D-prolyl). Scanning electron micrographs revealed that the exposure to cyclic dipeptide resulted in seriously deformed hyphae and conidia with shriveled surfaces in dipeptide-treated C. gloeosporioides. Therefore, active dipeptide-producing B. velezensis CE 100 is a promising biocontrol agent for Colletotrichum species causing anthracnose.

Identification of QTLs Controlling Resistance to Anthracnose Disease in Water Yam (Dioscorea alata)

Anthracnose disease caused by a fungus Colletotrichum gloeosporioides is the primary cause of yield loss in water yam (Dioscorea alata), the widely cultivated species of yam. Resistance to yam anthracnose disease (YAD) is a prime target in breeding initiatives to develop durable-resistant cultivars for sustainable management of the disease in water yam cultivation. This study aimed at tagging quantitative trait loci (QTL) for anthracnose disease resistance in a bi-parental mapping population of D. alata. Parent genotypes and their recombinant progenies were genotyped using the Genotyping by Sequencing (GBS) platform and phenotyped in two crop cycles for two years. A high-density genetic linkage map was built with 3184 polymorphic Single Nucleotide Polymorphism (NSP) markers well distributed across the genome, covering 1460.94 cM total length. On average, 163 SNP markers were mapped per chromosome with 0.58 genetic distances between SNPs. Four QTL regions related to yam anthracnose disease resistance were identified on three chromosomes. The proportion of phenotypic variance explained by these QTLs ranged from 29.54 to 39.40%. The QTL regions identified showed genes that code for known plant defense responses such as GDSL-like Lipase/Acylhydrolase, Protein kinase domain, and F-box protein. The results from the present study provide valuable insight into the genetic architecture of anthracnose resistance in water yam. The candidate markers identified herewith form a relevant resource to apply marker-assisted selection as an alternative to a conventional labor-intensive screening for anthracnose resistance in water yam.

Structure and Function of Rhizosphere Soil and Root Endophytic Microbial Communities Associated With Root Rot of Panax notoginseng

Panax notoginseng (Burk.) F. H. Chen is a Chinese medicinal plant of the Araliaceae family used for the treatment of cardiovascular and cerebrovascular diseases in Asia. P. notoginseng is vulnerable to root rot disease, which reduces the yield of P. notoginseng. In this study, we analyzed the rhizosphere soil and root endophyte microbial communities of P. notoginseng from different geographical locations using high-throughput sequencing. Our results revealed that the P. notoginseng rhizosphere soil microbial community was more diverse than the root endophyte community. Rhodopseudomonas, Actinoplanes, Burkholderia, and Variovorax paradoxus can help P. notoginseng resist the invasion of root rot disease. Ilyonectria mors-panacis, Pseudomonas fluorescens, and Pseudopyrenochaeta lycopersici are pathogenic bacteria of P. notoginseng. The upregulation of amino acid transport and metabolism in the soil would help to resist pathogens and improve the resistance of P. notoginseng. The ABC transporter and gene modulating resistance genes can improve the disease resistance of P. notoginseng, and the increase in the number of GTs (glycosyltransferases) and GHs (glycoside hydrolases) families may be a molecular manifestation of P. notoginseng root rot. In addition, the complete genomes of two Flavobacteriaceae species and one Bacteroides species were obtained. This study demonstrated the microbial and functional diversity in the rhizosphere and root microbial community of P. notoginseng and provided useful information for a better understanding of the microbial community in P. notoginseng root rot. Our results provide insights into the molecular mechanism underlying P. notoginseng root rot and other plant rhizosphere microbial communities.

Isolation and Evaluation of Rhizosphere Actinomycetes With Potential Application for Biocontrolling Fusarium Wilt of Banana Caused by Fusarium oxysporum f. sp. cubense Tropical Race 4

Fusarium wilt of banana caused by Fusarium oxysporum f. sp. cubense tropical race 4 (TR4) is globally one of the most destructive soil-borne fungal diseases. Biological control using environmental microorganisms is considered as an alternative and sustainable strategy. Actinomycetes have the potential to explore biocontrol agents due to their production of diverse metabolites. The isolation and identification of high-efficiency and broad-spectrum antagonistic actinomycetes are the key for the application of biocontrol agents. In the present study, 60 actinomycetes were obtained from the rhizosphere soil of Machilus pingii in the primitive ecological natural reserve of Hainan province, China. Seventeen isolates and their extracts exhibited significant antifungal activity against F. oxysporum TR4. Particularly, strain BITDG-11 with the strongest inhibition ability had a broad-spectrum antifungal activity. The assay of its physiological and biochemical profiles showed that strain BITDG-11 had the ability to produce IAA and siderophores and had a positive response to gelatin liquefaction and nitrate reduction. Enzyme activities of chitinase, β-1,3-glucanase, lipase, and urease were also detected. Average nucleotide identity calculated by comparison with the standard strain genome of Streptomyces albospinus JCM3399 was 86.55% below the novel species threshold, suggesting that the strain could be a novel species. In addition, Streptomyces BITDG-11 obviously reduced the disease index of banana plantlets and promoted plant growth at 45 days post inoculation. The higher and lasting expression levels of defense genes and activities of antioxidant enzymes were induced in the roots of banana. Genome sequencing revealed that the Streptomyces BITDG-11 chromosome contained large numbers of conserved biosynthesis gene clusters encoding terpenes, non-ribosomal peptides, polyketides, siderophores, and ectoines. Fifteen bioactive secondary metabolites were further identified from Streptomyces BITDG-11 extract by gas chromatography-mass spectrometry. Dibutyl phthalate demonstrating a strong antifungal activity was the major compound with the highest peak area. Hence, Streptomyces sp. BITDG-11 has a great potential to become an essential constituent of modern agricultural practice as biofertilizers and biocontrol agents.

Antagonismo de rizobacterias sobre hongos fitopatógenos, y su actividad microbiana con potencial biofertilizante, bioestimulante y biocontrolador

Las rizobacterias forman parte de la gran cantidad de microorganismos que actúan como agentes de biocontrol, produciendo metabolitos que inducen resistencia sistémica en las plantas que inhiben el crecimiento de patógenos. El objetivo de esta investigación fue evaluar la capacidad de diez rizobacterias de los géneros Rhizobium, Bradyrhizobium, Sinorhizobium, Ochrobactrum y Pseudomonas para producir ácido cianhídrico (HCN), sideróforos y ácido indol-acético (AIA), disolver fosfato, fijar nitrógeno e inhibir el crecimiento de fitopatógenos. Se realizaron todas las pruebas fisiológicas y bioquímicas correspondientes, así como la prueba de antagonismo in vitro contra los fitopatógenos Fusarium oxysporum, Colletotrichum gloeosporioides y Rhizoctonia solani.  Cinco cepas produjeron una mayor cantidad de AIA en relación a las otras en presencia de triptófano, la cepa ES1 (Ochrobactrum sp.) produjo HCN, el 50 % de las cepas evaluadas liberaron sideróforos, el 60 % disolvió fósforo, y todas resultaron positivas para la fijación de nitrógeno. Nueve cepas inhibieron el crecimiento de F. oxysporum entre 40 % y 65 %, la cepa Alf (Pseudomonas fluorescens) inhibió además el crecimiento de C. gloeosporioides en un 22 %, y ninguna inhibió el crecimiento de R. solani. Los rizobios evaluados y la cepa de Pseudomonas fluorescens podrían ejercer efectos beneficiosos sobre las plantas a través de mecanismos directos e indirectos, o una combinación de ambos, lo que las convierte en una opción sostenible para la producción de cultivos.

Isolation and characterization of Bacillus subtilis strain 1-L-29, an endophytic bacteria from Camellia oleifera with antimicrobial activity and efficient plant-root colonization

Endophytic bacteria, which are common in plant tissues, may help to control plant pathogens and enhance plant growth. Camellia oleifera, an oil-producing plant, is widely grown in warm, subtropical, hilly regions in China. However, C. oleifera is strongly negatively affected by C. oleifera anthracnose, which is caused by Colletetrichum fructicola. To find a suitable biocontrol agent for C. oleifera anthracnose, 41 endophytes were isolated from the stems, leaves, and roots of C. oleifera. Bacterial cultures were identified based on analyses of 16S rDNA sequences; most strains belonged to the genus Bacillus. The antagonistic effects of these strains on C. fructicola were tested in vitro. In total, 16 strains inhibited C. fructicola growth, with B. subtilis strain 1-L-29 being the most efficient. Strain 1-L-29 demonstrated antagonistic activity against C. siamense, C. asianum, Fusarium proliferatum, Agaricodochium camellia, and Pseudomonas syringae. In addition, this strain produced indole acetic acid, solubilized phosphate, grew on N-free media, and produced siderophores. To facilitate further microecological studies of this strain, a rifampicin-resistant, green fluorescent protein (GFP)-labeled strain, 1-L-29gfp^r, was created using protoplast transformation. This plasmid had good segregational stability. Strain 1-L-29gfp^r was re-introduced into C. oleifera and successfully colonized root, stem, and leaf tissues. This strain remained at a stable concentration in the root more than 20 d after inoculation. Fluorescence microscopic analysis showed that strain 1-L-29gfp^r thoroughly colonized the root surfaces of C. fructicola as well as the root vascular tissues of Arabidopsis thaliana.

A novel strain of endophytic Streptomyces for the biocontrol of strawberry anthracnose caused by Glomerella cingulata

Anthracnose caused by Glomerella cingulata is one of the most devastating diseases of strawberry in Japan, particularly during its nursery period in the summer. In this study, we aimed to isolate and screen endophytic actinobacteria, to identify potential biocontrol agents capable of suppressing strawberry anthracnose. A total of 226 actinobacteria were successfully isolated from surface-sterilized strawberry tissues. In the first screening, 217 out of 226 actinobacteria isolates were studied for their suppression effect on strawberry anthracnose using a detached leaflet assay. It was discovered that isolates MBFA-172 and MBFA-227 markedly suppressed the development of anthracnose lesions. The efficacy of both isolates was then tested on two-month-old strawberry plug seedlings in a controlled environmental chamber. It was found that isolate MBFA-172 provided consistent disease suppression and was thus selected as a final candidate for further evaluation in a glasshouse experiment. Results showed that the severity as well as incidence rate of strawberry anthracnose was significantly reduced by treatment with isolate MBFA-172 compared with that of untreated control. Accordingly, the disease control efficacy provided by MBFA-172 was statistically comparable to the chemical fungicide propineb. A re-isolation experiment using a spontaneous thiostrepton-resistant mutated strain of isolate MBFA-172 revealed that it efficiently colonized the above-ground tissues of strawberry plants for at least three weeks after spray treatment. Using cultural, morphological, and physiological tests combined with 16S rRNA-based molecular analysis, MBFA-172 was identified as a moderately thermophilic Streptomyces thermocarboxydus-related species. Upon review, our results strongly indicated that MBFA-172 is a promising biocontrol agent for strawberry anthracnose.

Plant growth promotion and chilli anthracnose disease suppression ability of rhizosphere soil actinobacteria

AIM

The aim of this study was to screen potential plant growth promoting rhizobacterial (PGPR) actinobacterial isolate with effective inhibition against anthracnose causing fungal pathogen Colletotrichum capsici.

METHODS AND RESULTS

In this study, actinobacterias were isolated from rhizosphere soil using dilution plate method and tested for antagonistic potential against pathogenic fungi C. capsici. In primary and secondary screening tests, the actinobacterial isolate BS-26 displayed high antagonistic activity against the fungal pathogen. Isolate BS-26 was identified as Streptomyces violaceoruber based on 16S rDNA sequencing. Furthermore, indole acetic acid production, phosphate solubilization and ammonia production have been confirmed in the S. violaceoruber that suggest their potential to be used as PGPR bacteria. A green house experiment showed that application of S. violaceoruber fermentation broth reduced the incidence of the chilli anthracnose and promoted the growth of chilli seedlings with a significant increase in germination %, total plant height, fresh weight and chlorophyll content when compared to controls.

CONCLUSION

Streptomyces violaceoruber can be applied as a biofertilizer and biocontrol agent for growing chillies against the attack of fungal pathogen C. capsici.

SIGNIFICANCE OF IMPACT OF THE STUDY

The damage caused by anthracnose disease is an issue of concern, affecting negatively the economy involved in chilli cultivation. As chemical methods of control have serious disadvantages, biocontrol approach using beneficial (PGPR) micro-organisms shall be a better alternative to control crop diseases.

Plenty Is No Plague: Streptomyces Symbiosis with Crops

Streptomyces spp. constitute a major clade of the phylum Actinobacteria. These Gram-positive, filamentous prokaryotes are ubiquitous in soils and marine sediments, and are commonly found in the rhizosphere or inside plant roots. Plant-interacting Streptomyces have received limited attention, in contrast to Streptomyces spp. extensively investigated for decades in medicine given their rich potential for secondary metabolite biosynthesis. Recent genomic, metabolomic, and biotechnological advances have produced key insights into Streptomyces spp., paving the way to the use of their metabolites in agriculture. In this Opinion article we propose how Streptomyces spp. could dominate future aspects of crop nutrition and protection. Risks and benefits of the use of these microorganisms in agriculture are also discussed.

Comparative Reliability of Screening Parameters for Anthracnose Resistance in Water Yam (Dioscorea alata)

Anthracnose, caused by Colletotrichum gloeosporioides, is one of the major constraints limiting water yam (Dioscorea alata) production in the tropics. In this region, yam anthracnose control is mostly achieved by the deployment of moderately resistant yam genotypes. Therefore, screening for new sources of anthracnose resistance is an important aspect of yam research in the tropics. The reliability and applicability of different yam anthracnose rating parameters has not been fully examined. Disease severity on detached leaves in the laboratory and leaf severity, lesion size, and spore production on whole plants in the greenhouse were used to screen an F1 yam population and correlate screening results with field evaluations. Anthracnose lesion size had the smallest predicted residual means but whole-plant severity and detached-leaf severity had the best variance homogeneity and relatively small predicted residual means. The concordance correlation coefficient (r_c) and κ statistic were used to determine the agreement between anthracnose rating parameters and field evaluations. Detached-leaf (r_c = 0.95, κ = 0.81) and whole-plant (r_c = 0.96, κ = 0.86) evaluations had high positive agreement with field evaluation but spore production (κ = 0.69) and lesion size (κ = 0.57) had moderate positive agreement. These results suggest that all the evaluated rating parameters can be used to successfully screen yam germplasm for anthracnose resistance but lesion size and spore production data may need to be transformed.

Actinomycetes from Eucalyptus and their biological activities for controlling Eucalyptus leaf and shoot blight

In Thailand, Eucalyptus plantations rapidly expand across the country. Leaf and shoot blight caused by Cryptosporiopsis eucalypti, Cylindrocladium sp. and Teratosphaeria destructans is a serious disease in Eucalyptus plantations. In this study, a total of 477 actinomycete strains were successfully isolated from roots and rhizosphere soil of Eucalyptus. Four hundred and thirty nine isolates were classified as streptomycetes and 38 isolates were non-streptomycetes. Among these isolates, 272 (57.0%), 118 (24.7%) and 241 (50.5%) isolates were antagonistic to Cryptosporiopsis eucalypti, Cylindrocladium sp. and Teratosphaeria destructans, respectively. All isolates were tested for their abilities to produce siderophores, indole acetic acid (IAA) and solubilise phosphate. Most isolates (464, 97.3%) produced siderophores. The majority of isolates (345, 72.3%) solubilised phosphate. In addition, almost half of these isolates (237, 49.7%) produced indole acetic acid. Strain EUSKR2S82 which showed the strongest inhibitory effect against all tested fungi with plant growth promoting ability was selected to test with Eucalyptus. This strain could colonize plant roots and increase Eucalyptus roots length. In a detached leaves bioassay, the disease severity of EUSKR2S82-inoculated Eucalyptus leaves was only 30% compared to 95% in the control treatment. The 16S rRNA gene sequence analysis revealed that the strain EUSKR2S82 was related to Streptomyces ramulosus NRRL-B 2714(T) (99.44% similarity). Identification of non-streptomycete isolates using 16S rRNA gene sequences classified them into 9 genera: Actinoallomurus, Actinomadura, Amycolatopsis, Cryptosporangium, Microbispora, Micromonospora, Nocardia, Nonomuraea and Pseudonocardia. It is evident that Eucalyptus tree harbored several genera of actinomycetes. The selected isolate, EUSKR2S82 showed potential as a candidate for biocontrol agent of leaf and shoot blight of Eucalyptus and to promote growth.

Suppressing activity of staurosporine from Streptomyces sp. MJM4426 against rice bacterial blight disease

AIM

To identify the active compounds from the Streptomyces sp. MJM4426 that can protect rice from bacterial blight disease (BB), and to evaluate the potential of this Streptomyces strains and the compound for biocontrol of rice bacterial blight disease.

METHODS AND RESULTS

The ethyl acetate extract of Streptomyces sp. MJM4426 can significantly protect rice leaf explants from the infection of Xanthomonas oryzae pv. oryzaeKACC 10331 (Xoo), the pathogen which cause BB. To identify the active compounds, the ethyl acetate extract of Streptomyces sp. MJM4426 was fractionated through a Sephadex LH-20 column chromatography, and further purified by preparative HPLC guided by the inhibitory activity against BB in rice leaf explants. UPLC-Q-TOF/MS analysis showed the active compound displayed its m/z values at [M+H](+) 467·2086 and [M+FA-H](-) 511·1963, and the molecular formula was estimated as C28 H26 N4 O3 which is identical to commercial standard staurosporine. In this study, the isolated staurosporine dramatically suppressed bacterial blight in rice leaf explants with the lowest concentration at 12·5 μmol l(-1) , however, it exhibited low inhibitory activity against Xoo with the MIC value at 256 μg ml(-1) . In addition, greenhouse study showed both crude extract and purified staurosporine can suppress the bacterial blight at the concentration of 5000 and 200 μg ml(-1) respectively.

CONCLUSION

Streptomyces sp. MJM4426 can protect rice leaf explants from the infection of Xoo by producing staurosporine, but not by direct inhibitory activity against Xoo.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first report that staurosporine can protect rice leaf against bacterial blight disease and showed the potential of Streptomyces sp. MJM4426 as an alternative to chemical bactericide for bacterial blight disease in rice.

Streptomyces sanglieri which colonised and enhanced the growth of Elaeis guineensis Jacq. seedlings was antagonistic to Ganoderma boninense in in vitro studies

Actinomycete strain AUM 00500 was 99.5 % similar to Streptomyces sanglieri NBRC 100784(T) and was evaluated for antagonistic activity towards Ganoderma boninense, the causative fungus of basal stem rot of oil palm. The strain showed strong antifungal activity towards G. boninense in in vitro and SEM analysis showed various modes of inhibition of the fungus. Ethyl acetate extracts of single culture and inhibition zone of cross-plug culture by HPLC indicated that strain AUM 00500 produced two different antibiotics of the glutarimide group namely cycloheximide and actiphenol. In greenhouse trials, oil palm seed treated with spores of S. sanglieri strain AUM 00500 at 10(9) cfu/ml showed significant (P < 0.05) increase in oil palm seedlings growth when compared to the control. Streptomyces sanglieri strain AUM 00500 successfully colonised the epidermal surface of the roots of treated oil palm seedlings and it was recovered from root fragments plated on starch casein agar.

Streptomyces sp. LK3 mediated synthesis of silver nanoparticles and its biomedical application

In the present study, the marine actinobacteria mediated biosynthesis of silver nanoparticles (AgNps) was achieved using Streptomyces sp LK3. The synthesized AgNps showed the characteristic absorption spectra in UV-vis at 420 nm, which confirmed the presence of nanoparticles. XRD analysis showed intense peaks at 2θ values of 27.51°, 31.87°, 45.57°, 56.56°, 66.26°, and 75.25° corresponding to (210), (113), (124), (240), (226), and (300) Bragg's reflection based on the fcc structure of AgNps. The FTIR spectra exhibited prominent peaks at 3,417 cm(-1) (OH stretching due to alcoholic group) and 1,578 cm(-1) (C=C ring stretching). TEM micrograph showed that the synthesized AgNps were spherical in shape with an average size of 5 nm. Surface morphology and topographical structure of the synthesized AgNps were dignified by AFM. The synthesized AgNps showed significant acaricidal activity against Rhipicephalus microplus and Haemaphysalis bispinosa with LC50 values of 16.10 and 16.45 mg/L, respectively. Our results clearly indicate that AgNps could provide a safer alternative to conventional acaricidal agents in the form of a topical antiparasitic formulation. The present study aimed to develop a novel, cost-effective, eco-friendly actinobacteria mediated synthesis of AgNps and its antiparasitic activity.

Genetic and functional characterization of culturable plant-beneficial actinobacteria associated with yam rhizosphere

Actinobacteria were isolated from the rhizosphere of yam plants from agricultural fields from Yeoju, South Korea and analyzed for their genetic and plant-beneficial functional diversity. A total of 29 highly occurring actinobacterial isolates from the yam rhizosphere were screened for various plant-beneficial traits such as antimicrobial activity on fungi and bacteria; biocontrol traits such as production of siderophore, protease, chitinase, endo-cellulase, and β-glucanase. The isolates were also screened for plant growth-promoting (PGP) traits such as auxin production, phosphate solubilization, 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase activity, and in vitro Arabidopsis growth promotion. 16S rDNA sequence-based phylogenetic analysis was carried out on the actinobacterial isolates to determine their genetic relatedness to known actinobacteria. BOX-PCR analysis revealed high genetic diversity among the isolates. Several isolates were identified to belong to the genus Streptomyces and a few to Kitasatospora. The actinobacterial strains exhibited high diversity in their functionality and were identified as novel and promising candidates for future development into biocontrol and PGP agents.

The potential of a fluorescent-based approach for bioassay of antifungal agents against chili anthracnose disease in Thailand

Severe chili anthracnose disease in Thailand is caused by Colletotrichum gloeosporioides and C. capsici. To discover anti-anthracnose substances we developed an efficient dual-fluorescent labeling bioassay based on a microdilution approach. Indicator strains used in the assay were constructed by integrating synthetic green fluorescent protein (sGFP) and Discosoma sp. red fluorescent protein (DsRedExp) genes into the genomes of C. gloeosporioides or C. capsici respectively. Survival of co-spore cultures in the presence of inhibitors was determined by the expression levels of these fluorescent proteins. This developed assay has high potential for utilization in the investigation of selective inhibition activity to either one of the pathogens as well as the broad-range inhibitory effect against both pathogens. The value of using the dual-fluorescent assay is rapid, reliable, and consistent identification of anti-anthracnose agents. Most of all, the assay enables the identification of specific inhibitors under the co-cultivation condition.