Multi-omics analysis of Streptomyces djakartensis strain MEPS155 reveal a molecular response strategy combating Ceratocystis fimbriata causing sweet potato black rot.

To investigate the potential antifungal mechanisms of rhizosphere Actinobacteria against Ceratocystis fimbriata in sweet potato, a comprehensive approach combining biochemical analyses and multi-omics techniques was employed in this study. A total of 163 bacterial strains were isolated from the rhizosphere soil of sweet potato. Among them, strain MEPS155, identified as Streptomyces djakartensis, exhibited robust and consistent inhibition of C. fimbriata mycelial growth in in vitro dual culture assays, attributed to both cell-free supernatant and volatile organic compounds. Moreover, strain MEPS155 demonstrated diverse plant growth-promoting attributes, including the production of indole-3-acetic acid, 1-aminocyclopropane-1-carboxylate deaminase, phosphorus solubilization, nitrogen fixation, and enzymatic activities such as cellulase, chitinase, and protease. Notably, strain MEPS155 exhibited efficacy against various sweet potato pathogenic fungi. Following the inoculation of strain MEPS155, a significant reduction (P < 0.05) in malondialdehyde content was observed in sweet potato slices, indicating a potential protective effect. The whole genome of MEPS155 was characterized by a size of 8,030,375 bp, encompassing 7234 coding DNA sequences and 32 secondary metabolite biosynthetic gene clusters. Transcriptomic analysis revealed 1869 differentially expressed genes in the treated group that cultured with C. fimbriata, notably influencing pathways associated with porphyrin metabolism, fatty acid biosynthesis, and biosynthesis of type II polyketide products. These alterations in gene expression are hypothesized to be linked to the production of secondary metabolites contributing to the inhibition of C. fimbriata. Metabolomic analysis identified 1469 potential differently accumulated metabolites (PDAMs) when comparing MEPS155 and the control group. The up-regulated PDAMs were predominantly associated with the biosynthesis of various secondary metabolites, including vanillin, myristic acid, and protocatechuic acid, suggesting potential inhibitory effects on plant pathogenic fungi. Our study underscores the ability of strain S. djakartensis MEPS155 to inhibit C. fimbriata growth through the production of secretory enzymes or secondary metabolites. The findings contribute to a theoretical foundation for future investigations into the role of MEPS155 in postharvest black rot prevention in sweet potato.

Drosophila hydei as a Potential Vector of Ceratocystis fimbriata, the Causal Agent of Sweetpotato Black Rot, in Storage Facilities.

Ceratocystis fimbriata, the causal agent of sweetpotato black rot, is a pathogen capable of developing and spreading within postharvest settings. A survey of North Carolina sweetpotato storage facilities was conducted to determine the arthropods present and identify potential vectors of C. fimbriata. Sixteen taxonomic categories were recovered, and the genus Drosophila (Diptera: Drosophilidae) accounted for 79% of individuals sampled, with Drosophila hydei being the most abundant species. Behavioral assays were conducted to determine if D. hydei is attracted to C. fimbriata-inoculated roots and if the pathogen could be recovered from external or internal surfaces of the insect. Flies were released in insect-trapping pitchers containing either C. fimbriata-inoculated or noninoculated roots or Petri dishes. No significant differences in fly number were detected in sweetpotato-baited pitchers; however, significant differences were found in the pitcher baited with a mature C. fimbriata culture. Flies were subjected to washes to determine if viable C. fimbriata was present (internally or externally); washes were plated onto carrot agar plates and observed for the presence of C. fimbriata colonies. Both external and internal washes had viable C. fimbriata inocula with no significant differences, and inoculated sweetpotatoes had a significantly higher number of flies carrying C. fimbriata. This study suggests that D. hydei can carry C. fimbriata from infected sweetpotatoes and move viable C. fimbriata inocula both externally and internally, making this the first report of any Drosophila sp. serving as a potential vector for the Ceratocystis genus.

Novel Multiresistant Osmotin-like Protein from Sweetpotato as a Promising Biofungicide to Control Ceratocystis fimbriata by Destroying Spores through Accumulation of Reactive Oxygen Species.

Osmotin-like proteins (OLPs) play an important role in host-plant defense. In this study, a novel multiresistant OLP (IbOLP1) was screened from sweetpotato (Ipomoea batatas) with a molecular weight of 26.3 kDa. The expression level of IbOLP1 was significantly higher in resistant cultivars than susceptible ones after inoculation with Ceratocystis fimbriata, which causes black rot disease in sweetpotato. The expression of IbOLP1 in Pichia pastoris led to the lysis of yeast cells themselves. The recombinant IbOLP1 displayed antifungal, antibacterial, and antinematode activity and stability. IbOLP1 could restrain the mycelial growth and lyse spores of C. fimbriata, distinctly reducing the incidence of black rot in sweetpotato. The IbOLP1 can trigger the apoptosis of black rot spores by elevating the intracellular levels of reactive oxygen species. Collectively, these findings suggest that IbOLP1 can be used to develop natural antimicrobial resources instead of chemical agents and generate new, disease-resistant germplasm.

Long-Read Sequencing Genome Assembly of Ceratocystis fimbriata Enables Development of Molecular Diagnostics for Sweetpotato Black Rot.

Ceratocystis fimbriata is a destructive fungal pathogen of sweetpotato (Ipomoea batatas) that leads to losses at all stages of sweetpotato production. Accurate detection of C. fimbriata would allow for more efficient deployment of management tactics in sweetpotato production. To develop a diagnostic assay, a hybrid genome assembly of C. fimbriata isolate AS236 was generated. The resulting 31.7-MB assembly was near-chromosome level, with 18 contigs, 6,481 predicted genes, and a BUSCO completion score of 98.4% when compared with the fungus-specific lineage database. Additional Illumina DNA reads from C. manginecans, C. platani, and a second C. fimbriata isolate (C1421) were then mapped to the assembled genome using BOWTIE2 and counted using HTSeq, which identified 148 genes present only within C. fimbriata as molecular diagnostic candidates; 6 single-copy and 35 highly multi-copy (>40 BLAST hits), as determined through a self-BLAST-P alignment. Primers for PCR were designed in the 200-bp flanking region of the first exon for each candidate, and the candidates were validated against a diverse DNA panel containing Ceratocystis species, sweetpotato pathogens, and plants. After validation, two diagnostic candidates amplified only C. fimbriata DNA and were considered to be highly specific to the species. These genetic markers will serve as valuable diagnostic tools with multiple applications including the detection of C. fimbriata in seed, soil, and wash water in sweetpotato production.

Inhibitory effect of cinnamaldehyde on Fusarium solani and its application in postharvest preservation of sweet potato.

Root rot caused by Fusarium solani is one of major postharvest diseases limiting sweet potato production. Antifungal effect and possible mode of action of cinnamaldehyde (CA) against F. solani were investigated. CA concentration of 0.075 g/L inhibited conidial viability of F. solani. CA vapor of 0.3 g/L in air completely controlled the F. solani development in sweet potatoes during storage for 10 days at 28 °C, and protected soluble sugar and starch in the flesh from depletion by the fungus. Further results demonstrated that CA induced reduction in mitochondrial membrane potential (Δψm), ROS accumulation, and cell apoptosis characterized by DNA fragmentation in F. solani. Moreover, CA facilitated decomposition of mitochondria-specific cardiolipin (CL) into its catabolites by the catalytic action of phospholipases. Altogether, the results revealed a specific antifungal mechanism of CA against F. solani, and suggest that CA holds promise as a preservative for postharvest preservation of sweet potato.

Antifungal Volatile Organic Compounds from Streptomyces setonii WY228 Control Black Spot Disease of Sweet Potato.

Volatile organic compounds (VOCs) produced by microorganisms are considered promising environmental-safety fumigants for controlling postharvest diseases. Ceratocystis fimbriata, the pathogen of black spot disease, seriously affects the quality and yield of sweet potato in the field and postharvest. This study tested the effects of VOCs produced by Streptomyces setonii WY228 on the control of C. fimbriata in vitro and in vivo. The VOCs exhibited strong antifungal activity and significantly inhibited the growth of C. fimbriata. During the 20-day storage, VOC fumigation significantly controlled the occurrence of the pathogen, increased the content of antioxidants and defense-related enzymes and flavonoids, and boosted the starch content so as to maintain the quality of the sweet potatoes. Headspace analysis showed that the volatiles 2-ethyl-5-methylpyrazine and dimethyl disulfide significantly inhibited the mycelial growth and spore germination of C. fimbriata in a dose-dependent manner. Fumigation with 100 µL/L 2-ethyl-5-methylpyrazine completely controlled the pathogen in vivo after 10 days of storage. Transcriptome analysis showed that volatiles mainly downregulated the ribosomal synthesis genes and activated the proteasome system of the pathogen in response to VOC stress, while the genes related to spore development, cell membrane synthesis, mitochondrial function, and hydrolase and toxin synthesis were also downregulated, indicating that WY228-produced VOCs have diverse modes of action for pathogen control. Our study demonstrates that fumigation of sweet potato tuberous roots with S. setonii WY228 or use of formulations based on the VOCs is a promising new strategy to control sweet potato and other food and fruit pathogens during storage and shipment. IMPORTANCE Black spot disease caused by Ceratocystis fimbriata has caused huge economic losses to worldwide sweet potato production. At present, the control of C. fimbriata mainly depends on toxic fungicides, and there is a lack of effective alternative strategies. The research on biological control of sweet potato black spot disease is also very limited. An efficient biocontrol technique against pathogens using microbial volatile organic compounds could be an alternative method to control this disease. Our study revealed the significant biological control effect of volatile organic compounds of Streptomyces setonii WY228 on black spot disease of postharvest sweet potato and the complex antifungal mechanism against C. fimbriata. Our data demonstrated that Streptomyces setonii WY228 and its volatile 2-ethyl-5-methylpyrazine could be a candidate strain and compound for the creation of fumigants and showed the important potential of biotechnology applications in the field of food and agriculture.

Characterization, identification and virulence of Metarhizium species from Cuba to control the sweet potato weevil, Cylas formicarius Fabricius (Coleoptera: Brentidae).

AIMS: Entomopathogenic Metarhizium fungi are widely recognized for their biological control potential. In Cuba, several fungus-based bio-insecticides have been developed and are produced as part of integrated pest management (IPM) programmes for economically relevant agricultural pests. Screening of fungal isolates from the INISAV strain collection was used for the development of bio-insecticides against important pest insects as, for example the sweet potato weevil, Cylas formicarius. METHODS AND RESULTS: Six fungal isolates from Cuba were microscopically, morphologically and molecular-taxonomically characterized using marker sequences ef1a, rpb1 and rpb2, and the 5TEF region of the ef1a gene. Five isolates were assigned to the species Metarhizium anisopliae sensu stricto and one isolate to Metarhizium robertsii. The pathogenic potential was evaluated against adults of C. formicarius, and growth and conidial production on different nutritional media were determined. Metarhizium anisopliae strain LBM-267 displayed pronounced virulence against the sweet potato weevil and abundant conidia production on several culture media. CONCLUSIONS: Entomopathogenic fungal isolates from Cuba were assigned to the taxonomic species M. anisopliae sensu stricto and M. robertsii. Virulence assessment with respect to C. formicarius led to the identification of two M. anisopliae isolates holding biocontrol potential. Isolate LBM-11 has previously been developed into the bio-insecticide METASAVE-11 that is widely used to control several species of plant pathogenic weevils, Lepidoptera and thrips in Cuba. Isolate LBM-267 has not been employed previously but is as virulent against C. formicarius as LBM-11; its growth and conidial production capacities on different nutritional media will likely facilitate economically feasible bio-insecticide development. SIGNIFICANCE AND IMPACT OF THE STUDY: Metarhizium anisopliae isolate LBM-267 has been selected as a promising candidate for biocontrol of the sweet potato weevil, an economically important agricultural pest in Cuba, and for further R&D activities within the framework of the Biological Control Program of Cuba.

Effect of tebuconazole and trifloxystrobin on Ceratocystis fimbriata to control black rot of sweet potato: processes of reactive oxygen species generation and antioxidant defense responses.

Black rot, caused by Ceratocystis fimbriata, is one of the most destructive disease of sweet potato worldwide, resulting in significant yield losses. However, a proper management system can increase resistance to this disease. Therefore, this study investigated the potential of using tebuconazole (TEB) and trifloxystrobin (TRI) to improve the antioxidant defense systems in sweet potato as well as the inhibitory effects on the growth of and antioxidant activity in C. fimbriata. Four days after inoculating cut surfaces of sweet potato disks with C. fimbriata, disease development was reduced by different concentrations of TEB + TRI. Infection by C. fimbriata increased the levels of hydrogen peroxide (H2O2), malondialdehyde (MDA), and electrolyte leakage (EL), and the activity of lipoxygenase (LOX) by 138, 152, 73, and 282%, respectively, in sweet potato disks, relative to control. In the sweet potato disks, C. fimbriata reduced the antioxidant enzyme activities as well as the contents of ascorbate (AsA) and reduced glutathione (GSH) by 82 and 91%, respectively, compared with control. However, TEB + TRI reduced the oxidative damage in the C. fimbriata-inoculated sweet potato disks by enhancing the antioxidant defense systems. On the other hand, applying TEB + TRI increased the levels of H2O2, MDA, and EL, and increased the activity of LOX in C. fimbriata, in which the contents of AsA and GSH decreased, and therefore, inhibited the growth of C. fimbriata. These results suggest that TEB + TRI can significantly control black rot disease in sweet potato by inhibiting the growth of C. fimbriata.

Effects of continuous cropping of sweet potatoes on the bacterial community structure in rhizospheric soil.

BACKGROUND: Continuous cropping obstacles from sweet potatoes are widespread, which seriously reduce the yield and quality, causing certain economic losses. Bacteria of rhizospheric soil are the richest and are associated with obstacles to continuous cropping. However, few studies have examined how continuous sweet potato cropping affects the rhizospheric soil bacterial community structure. RESULTS: In the study, the Illumina MiSeq method was used to explore the variations in rhizospheric soil bacterial community structure of different sweet potato varieties after continuous cropping, as well as the correlation between soil characteristics and the bacterial community. The results showed that (1) the dominant bacterial phyla in rhizospheric soils from both Xushu 18 and Yizi 138 were Proteobacteria, Acidobacteria, and Actinobacteria. The most dominant genus was Subgroup 6_norank. The relative abundance of rhizospheric soil bacteria varied significantly between the two sweet potato varieties. (2) The richness and diversity indexes of bacteria were higher in Xushu 18 rhizospheric soil than in Yizi 138 soil after continuous cropping. Moreover, beneficial Lysobacter and Bacillus were more prevalent in Xushu 18, while Yizi 138 contained more harmful Gemmatimonadetes. (3) Soil pH decreased after continuous cropping, and redundancy analysis indicated that soil pH was significantly correlated with the bacterial community. Spearman's rank correlation coefficient analysis demonstrated that pH was positively associated with Planctomycetes and Acidobacteria, but negatively associated with Actinobacteria and Firmicutes. CONCLUSIONS: After continuous cropping, the bacterial community structure and physicochemical properties of sweet potato rhizospheric soil were changed, and the changes from different sweet potato varieties were different. The contents of Lysobacter and Bacillus were higher in the sweet potato variety resistant to continuous cropping. It provides a basis for developing new microbial fertilizers for sweet potatoes to alleviate the continuous cropping obstacle.

High-Quality Genome Resource of Diaporthe destruens Causing Foot Rot Disease of Sweet Potato.

Foot rot of sweet potato caused by Diaporthe destruens severely affects yield and quality worldwide. Research on this pathogen is limited due to nonavailability of genome resources. Here, we report a high-quality genome sequence of D. destruens isolate CRI 305-2, which was originally isolated from infected stem of sweet potato in Taizhou City, Zhejiang Province, China. The genome comprised a total length of 56,108,228 bp, consisted of 47 scaffolds with an overall G+C content of 48.7% and an N50 of 2,479,481 bp. This resource can be used as a reference for evolution mechanisms and comparative genomic research.

Contribution of ultrasound and slightly acid electrolytic water combination on inactivating Rhizopus stolonifer in sweet potato.

Effects of ultrasound (US, 300, 400, and 500 W) and slightly acidic electrolyzed water (SAEW, 10, 30, and 50 mg/L) combination on inactivating Rhizopus stolonifer in sweet potato tuberous roots (TRs) were investigated. US at 300, 400, and 500 W simultaneous SAEW with available chlorine concentration of 50 mg/L at 40 and 55 °C for 10 min significantly inhibited colony diameters (from 90.00 to 6.00-71.62 mm) and spores germination (p < 0.05). US + SAEW treatment could destroy cell membrane integrity and lead to the leakage of nucleic acids and proteins (p < 0.05). Scanning and transmission electron microscopy results showed that US + SAEW treatment could damage ultrastructure of R. stolonifer, resulted in severe cell-wall pitting, completely disrupted into debris, apparent separation of plasma wall, massive vacuoles space, and indistinct intracellular organelles. US500 + SAEW50 treatment at 40 and 55 °C increased cell membrane permeability, and decreased mitochondrial membrane potential of R. stolonifer. In addition, US500 + SAEW50 at 40 °C and US300 + SAEW50 at 55 °C controlled R. stolonifer growth in sweet potato TRs during 20 days of storage, suggesting effective inhibition on the infection of R. stolonifer. Therefore, US + SAEW treatment could be a new efficient alternative method for storing and preserving sweet potato TRs.

Piriformospora indica colonization increases the growth, development, and herbivory resistance of sweet potato (Ipomoea batatas L.).

KEY MESSAGE: Piriformospora indica symbiosis promoted the growth and photosynthesis, and simultaneously enhanced the resistance against insect herbivory by regulating sporamin-dependent defense in sweet potato. Piriformospora indica (P. indica), a versatile endophytic fungus, promotes the growth and confers resistance against multiple stresses by root colonization in plant hosts. In this study, the effects of P. indica colonization on the growth, physiological change, and herbivore resistance of leaf-vegetable sweet potato cultivar were investigated. P. indica symbiosis significantly improved the biomass in both above- and under-ground parts of sweet potato plants. In comparison with the non-colonized plants, the content of photosynthetic pigments and the efficiency of photosynthesis were increased in P. indica-colonized sweet potato plants. Further investigation showed that the activity of catalase was enhanced in both leaves and roots of sweet potato plants after colonization, but ascorbate peroxidase, peroxidase, and superoxide dismutase were not enhanced. Furthermore, the interaction between P. indica and sweet potato plants also showed the biological function in jasmonic acid (JA)-mediated defense. The plants colonized by P. indica had greatly increased JA accumulation and defense gene expressions, including IbNAC1, IbbHLH3, IbpreproHypSys, and sporamin, leading to elevated trypsin inhibitory activity, which was consistent with a reduced Spodoptera litura performance when larvae fed on the leaves of P. indica-colonized sweet potato plants. The root symbiosis of P. indica is helpful for the plant promoting growth and development and has a strong function as resistance inducers against herbivore attack in sweet potato cultivation by regulating sporamin-dependent defense.

Rapid diagnosis of Ralstonia solanacearum infection sweet potato in China by loop-mediated isothermal amplification.

Bacterial wilt of sweet potato is caused by Ralstonia solanacearum, which is distributed in southern China and causes significant economic losses each year. The pathogen is soil- and rhizome-borne, and thus its rapid detection may prevent the occurrence and spread of the disease. R. solanacearum has been listed as a quarantine disease in China. With the advent of molecular biology, many novel tools have been explored for the rapid identification of plant pathogens. In this study, a strain-specific detection method was developed for this specific pathogen that infects sweet potato using loop-mediated isothermal amplification (LAMP). A set of new LAMP-specific primers was designed from the orf428 gene, which can specifically detect the R. solanacearum bacterium that infect sweet potato. The LAMP reaction consisted of 8.0 mmol·L-1Mg2+, 1.4 mmol·L-1 dNTPs, and 0.32U µL-1 Bst 2.0 DNA polymerase and was performed at 65 °C for 1 h. The amplification products were detected by visualizing a mixture of color changes using SYBR Green I dye and assessing ladder-like bands by electrophoresis. Our method has specificity, i.e., it only detected R. solanacearum in sweet potato, and it has high sensitivity, with a detection limit of 100 fg·µL-1 genomic DNA and 103 CFU·mL-1 of bacterial fluid. In addition, R. solanacearum could be directly detected in infected sweet potato tissues without the need for DNA extraction. The LAMP method established in this study is a highly specific, sensitive, and rapid tool for the detection of bacterial wilt in sweet potato caused by R. solanacearum.

Comparative proteomic analysis of the sweetpotato provides insights into response mechanisms to Fusarium oxysporum f. sp. batatas.

The Fusarium wilt disease caused by Fusarium oxysporum f. sp. batatas (Fob) is one of the devastating diseases of sweetpotato. However, the molecular mechanisms of sweetpotato response to Fob is poorly understood. In the present study, comparative quantitative proteomic analysis was conducted to investigate the defense mechanisms involved. Two sweetpotato cultivars with differential Fob infection responses were inoculated with Fob spore suspensions and quantitatively analyzed by Tandem Mass Tags (TMT). 2267 proteins were identified and 1897 of them were quantified. There were 817 proteins with quantitative ratios of 1.2-fold change between Fob-inoculated and mock-treated samples. Further, nine differentially expressed proteins were validated by Parallel Reaction Monitoring (PRM). According to Gene Ontology (GO) annotation information, the proteins functioned in molecular metabolism, cellular component formation, and biological processes. Interestingly, the results showed that sweetpotato resistant response to Fob infection included many proteins associated with signaling transduction, plant resistance, chitinase and subtilisin-like protease. The functions and possible roles of those proteins were discussed. The results provides first insight into molecular mechanisms involved in sweetpotato defense responses to Fob.

Endophytic Bacillus amyloliquefaciens YTB1407 elicits resistance against two fungal pathogens in sweet potato (Ipomoea batatas (L.) Lam.).

The endophytic Bacillus amyloliquefaciens YTB1407 was previously reported to promote the growth of sweet potato (Ipomoea batatas cv. Yanshu 25). Here, we demonstrate in both in vitro and pot trial assays that pre-treatment with YTB1407 suspension could enhance resistance against root rot disease and black rot disease, caused by Fusarium solani Mart. Sacc. f. sp. batatas McClure and Ceratocystis fimbriata Ell. & Halst on sweet potato, respectively. When seedlings were infected with fungal pathogens at 10 days post irrigation, pre-treatment with YTB1407 suspension decreased these pathogens and YTB1407 bacterial biomass in sweet potato roots. The pre-treatment activated the expression of salicylic acid (SA)-responsive PR-1 gene, raised SA content, and reduced hydrogen peroxide (H2O2) in the host to resist F. solani, while it enhanced the expression levels of SA-responsive NPR1 and PR1 genes and increased SA content to resist C. fimbriata. The disease resistance control effect initiated by pre-treatment with YTB1407 for root rot pathogen (F. solani) was better than for black rot pathogen (C. fimbriata). The results indicated that Bacillus amyloliquefaciens YTB1407 played a pivotal role in enhancing resistance to two fungi pathogens in sweet potato, through production of some antifungal metabolites to decrease infection in the early stage as well as induction of SA-dependent systemic resistance.

Genome comparisons suggest an association between Ceratocystis host adaptations and effector clusters in unique transposable element families.

Ceratocystis fimbriata is a host specific fungal pathogen of sweet potato (Ipomoea batatas). The closely related species, C. manginecans, is an important pathogen of trees (e.g. Acacia mangium and Mangifera indica) but has never been isolated from tuber crops. The genetic factors that determine the host range and host specificity of these species have not been determined. The aim of this study was to compare the genomes of C. fimbriata and C. manginecans in order to identify species-specific genetic differences that could be associated with host specificity. This included whole-genome alignments as well as comparisons of gene content and transposable elements (TEs). The genomes of the two species were found to be very similar, sharing similar catalogues of CAZymes, peptidases and lipases. However, the genomes of the two species also varied, harbouring species-specific genes (e.g. small secreted effectors, nutrient processing proteins and stress response proteins). A portion of the TEs identified (17%) had a unique distribution in each species. Transposable elements appeared to have played a prominent role in the divergence of the two species because they were strongly associated with chromosomal translocations and inversions as well as with unique genomic regions containing species-specific genes. Two large effector clusters, with unique TEs in each species, were identified. These effectors displayed non-synonymous mutations and deletions, conserved within a species, and could serve as mutational hot-spots for the development of host specificity in the two species.

Novel antifungal mechanism of oligochitosan by triggering apoptosis through a metacaspase-dependent mitochondrial pathway in Ceratocystis fimbriata.

The antifungal effects of oligochitosan (OCS) against Ceratocystis fimbriata that causes black rot disease in sweet potato and its apoptosis mechanism were evaluated. OCS restrained the mycelial growth and spores germination of C. fimbriata, and decreased the ergosterol content of cell membrane. Transmission electron microscopy observation and flow cytometry analysis revealed that OCS induced morphology changes with smaller size and increased granularity of C. fimbriata, which was the typical feature of apoptosis. To clarify the apoptosis mechanism induced by OCS, a series of apoptosis-related parameters were analyzed. Results showed that OCS induced reactive oxygen species accumulation, Ca2+ homeostasis dysregulation, mitochondrial dysfunction and metacaspase activation, coupled with hallmarks of apoptosis including phosphatidylserine externalization, DNA fragmentation, and nuclear condensation. In summary, OCS triggered apoptosis through a metacaspase-dependent mitochondrial pathway in C. fimbriata. These findings have important implications for the application of OCS to control pathogens in food and agriculture.

IbBBX24 Promotes the Jasmonic Acid Pathway and Enhances Fusarium Wilt Resistance in Sweet Potato.

Cultivated sweet potato (Ipomoea batatas) is an important source of food for both humans and domesticated animals. Here, we show that the B-box (BBX) family transcription factor IbBBX24 regulates the jasmonic acid (JA) pathway in sweet potato. When IbBBX24 was overexpressed in sweet potato, JA accumulation increased, whereas silencing this gene decreased JA levels. RNA sequencing analysis revealed that IbBBX24 modulates the expression of genes involved in the JA pathway. IbBBX24 regulates JA responses by antagonizing the JA signaling repressor IbJAZ10, which relieves IbJAZ10's repression of IbMYC2, a JA signaling activator. IbBBX24 binds to the IbJAZ10 promoter and activates its transcription, whereas it represses the transcription of IbMYC2 The interaction between IbBBX24 and IbJAZ10 interferes with IbJAZ10's repression of IbMYC2, thereby promoting the transcriptional activity of IbMYC2. Overexpressing IbBBX24 significantly increased Fusarium wilt disease resistance, suggesting that JA responses play a crucial role in regulating Fusarium wilt resistance in sweet potato. Finally, overexpressing IbBBX24 led to increased yields in sweet potato. Together, our findings indicate that IbBBX24 plays a pivotal role in regulating JA biosynthesis and signaling and increasing Fusarium wilt resistance and yield in sweet potato, thus providing a candidate gene for developing elite crop varieties with enhanced pathogen resistance but without yield penalty.

Metagenomic study of endophytic bacterial community of sweet potato (Ipomoea batatas) cultivated in different soil and climatic conditions.

The aim of this study was to clarify effects of soil and climatic conditions on community structure of sweet potato bacterial endophytes by applying locked nucleic acid oligonucleotide-PCR clamping technique and metagenomic analysis. For this purpose, the soil samples in three locations were transferred each other and sweet potato nursery plants from the same farm were cultivated for ca. 3 months. After removal of plastid, mitochondria and undefined sequences, the averaged numbers of retained sequences and operational taxonomic units per sample were 20,891 and 846, respectively. Proteobacteria (85.0%), Bacteroidetes (6.6%) and Actinobacteria (6.3%) were the three most dominant phyla, accounting for 97.9% of the reads, and γ-Proteobacteria (66.3%) being the most abundant. Top 10 genera represented 81.2% of the overall reads in which Pseudomonas (31.9-45.0%) being the most predominant. The overall endophytic bacterial communities were similar among the samples which indicated that the soil and the climatic conditions did not considerably affect the entire endophytic community. The original endophytic bacterial community might be kept during the cultivation period.

Potential of Pantoea dispersa as an effective biocontrol agent for black rot in sweet potato.

Biocontrol offers a promising alternative to synthetic fungicides for the control of a variety of pre- and post-harvest diseases of crops. Black rot, which is caused by the pathogenic fungus Ceratocytis fimbriata, is the most destructive post-harvest disease of sweet potato, but little is currently known about potential biocontrol agents for this fungus. Here, we isolated several microorganisms from the tuberous roots and shoots of field-grown sweet potato plants, and analyzed their ribosomal RNA gene sequences. The microorganisms belonging to the genus Pantoea made up a major portion of the microbes residing within the sweet potato plants, and fluorescence microscopy showed these microbes colonized the intercellular spaces of the vascular tissue in the sweet potato stems. Four P. dispersa strains strongly inhibited C. fimbriata mycelium growth and spore germination, and altered the morphology of the fungal hyphae. The detection of dead C. fimbriata cells using Evans blue staining suggested that these P. dispersa strains have fungicidal rather than fungistatic activity. Furthermore, P. dispersa strains significantly inhibited C. fimbriata growth on the leaves and tuberous roots of a susceptible sweet potato cultivar ("Yulmi"). These findings suggest that P. dispersa strains could inhibit black rot in sweet potato plants, highlighting their potential as biocontrol agents.