Effects of arbuscular mycorrhizal fungi in the rhizosphere of two olive (Olea europaea) varieties Arbequina and Barnea under water deficit conditions.

One strategy to improve olive (Olea europaea ) tree drought tolerance is through the symbiosis of arbuscular mycorrhizal fungi (AMF), which helps alleviate water deficit through a combination of morphophysiological effects. Cuttings of olive varieties Arbequina (A) and Barnea (B) were grown with (+AMF) or without (-AMF) inoculum in the olive grove rhizosphere soil. One year after establishment, pots were exposed to four different water regimes: (1) control (100% of crop evapotranspiration); (2) short-period drought (20days); (3) long-period drought (25days); and (4) rewatering (R). To evaluate the influence of AMF on tolerance to water stress, stem water potential, stomatal conductance and the biomarkers for water deficit malondialdehyde, proline, soluble sugars, phenols, and flavonoids were evaluated at the end of the irrigation regimes. Stem water potential showed higher values in A(+) and B(+) in all water conditions, and the opposite was true for stomatal conductance. For proline and soluble sugars, the stem water potential trend is repeated with some exceptions. AMF inoculum spore communities from A(+ and -) and B(+ and -) were characterised at the morphospecies level in terms of richness and abundance. Certain morphospecies were identified as potential drought indicators. These results highlight that the benefits of symbiotic relationships between olive and native AMF can help to mitigate the effects of abiotic stress in soils affected by drought.

Agave Wilt Susceptibility by Reduction of Free Hexoses in Root Tissue of Agave tequilana Weber var. azul Commercial Plants in the Fructan Accumulation Process.

Agave tequilana stems store fructan polymers, the main carbon source for tequila production. This crop takes six or more years for industrial maturity. In conducive conditions, agave wilt disease increases the incidence of dead plants after the fourth year. Plant susceptibility induced for limited photosynthates for defense is recognized in many crops and is known as "sink-induced loss of resistance". To establish whether A. tequilana is more prone to agave wilt as it ages, because the reduction of water-soluble carbohydrates in roots, as a consequence of greater assembly of highly polymerized fructans, were quantified roots sucrose, fructose, and glucose, as well as fructans in stems of agave plants of different ages. The damage induced by inoculation with Fusarium solani or F. oxysporum in the roots or xylem bundles, respectively, was recorded. As the agave plant accumulated fructans in the stem as the main sink, the amount of these hexoses diminished in the roots of older plants, and root rot severity increased when plants were inoculated with F. solani, as evidence of more susceptibility. This knowledge could help to structure disease management that reduces the dispersion of agave wilt, dead plants, and economic losses at the end of agave's long crop cycle.

Cordyceps cateniannulata: An endophyte of coffee, a parasite of coffee leaf rust and a pathogen of coffee pests.

Here, we report on a Cordyceps species entering into a multi-trophic, multi-kingdom association. Cordyceps cateniannulata, isolated from the stem of wild Coffea arabica in Ethiopia, is shown to function as an endophyte, a mycoparasite and an entomopathogen. A detailed polyphasic taxonomic study, including a multilocus phylogenetic analysis, confirmed its identity. An emended description of C. cateniannulata is provided herein. Previously, this species was known as a pathogen of various insect hosts in both the Old and New World. The endophytic status of C. cateniannulata was confirmed by re-isolating it from inoculated coffee plants. Inoculation studies have further shown that C. cateniannulata is a mycoparasite of Hemileia vastatrix, as well as an entomopathogen of major coffee pests; infecting and killing Hypothenemus hampei and Leucoptera coffeella. This is the first record of C. cateniannulata from Africa, as well as an endophyte and a mycoparasite. The implications for its use as a biocontrol agent are discussed.

Antimicrobial activity of endophytic fungi from the medicinal plants Mammea americana (Calophyllaceae) and Moringa oleifera (Moringaceae) / [Actividad antimicrobiana de hongos endófitos de las plantas medicinales Mammea americana (Calophyllaceae) y Moringa oleifera (Moringaceae)].

Introduction: Infectious diseases represent one of the leading causes of death worldwide. Considering the growing global challenge of antimicrobial resistance, research into new sources of potentially effective antimicrobial agents from natural origins is of great importance for world health. Objective: To evaluate the antimicrobial activity of endophytic fungi from Mammea americana and Moringa oleifera upon Staphylococcus aureus (ATCC 29213), S. aureus (resistant strain USb003), Escherichia coli (ATCC 25922), and E. coli (resistant strain USb007). Materials and methods: We isolated endophytic fungi from the leaves, seeds, and stems of the two plants under study. We evaluated their antimicrobial activity through the formation of sensitivity haloes in dual tests in vitro, as well as in trials using crude ethanolic extracts from the endophytes. The minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and cytotoxicity o the substances were analyzed. Results: Three ethanolic extracts of Penicillium sp., Cladosporium (001), and Cladosporium (002) exhibited the greatest inhibition halos in sensitive and resistant strains of E. coli and S. aureus. The MIC and CBM found were statistically significant (p≤0.05) compared with the gentamicin control. Furthermore, the cytotoxicity test results of CC50>1,000 demonstrated that the endophytic fungi studied exhibit bactericidal characteristics without causing unintended damage. Conclusion: The endophytic fungi M. oleifera and M. americana represent a source of active secondary metabolites with antimicrobial and non-toxic properties. In light of these findings, further research should proceed with chemical identification of the compounds and the study of their mechanisms of action, especially given the paucity of current scientific knowledge concerning the isolation of endophytes in these plants.

Introducción. Las enfermedades infecciosas son una causa importante de muertes en el mundo. La resistencia antimicrobiana es un problema global, por lo que es conveniente la investigación de nuevas fuentes de agentes antimicrobianos de origen natural potencialmente efectivos. Objetivo. Evaluar la actividad antimicrobiana de hongos endófitos de Mammea americana y Moringa oleifera en la cepa sensible (ATCC 29213) y en la cepa resistente (USb003) de Staphylococcus aureus, así como en la cepa sensible (ATCC 25922) y la cepa resistente (USb007) de Escherichia coli. Materiales y métodos. Se aislaron 14 hongos endófitos de las hojas, semillas y tallos de las dos plantas en estudio. Se evaluó su actividad antimicrobiana mediante la formación de halos de sensibilidad por ensayo dual in vitro y pruebas con extractos etanólicos crudos provenientes de los endófitos a los que se les evaluó la concentración mínima inhibitoria (CMI), la concentración bactericida mínima (CBM) y la citotoxicidad. Resultados. Tres extractos etanólicos de Penicillium sp., Cladosporium sp. (001) y Cladosporium sp. (002) presentaron mayores halos de inhibición en cepas sensibles y resistentes de E. coli y S. aureus. La CMI y la CBM halladas fueron estadísticamente significativas (p≤0,05), comparadas con el control de gentamicina. Las pruebas de citotoxicidad (concentración citotóxica, CC50>1.000) demostraron que los hongos endófitos poseen características bactericidas y no ocasionan daño alguno. Conclusión. Se halló una fuente de metabolitos secundarios activos con propiedades antimicrobianas y no tóxicas en los hongos endófitos de M. oleifera y M. americana; estos hallazgos son importantes para continuar con la identificación química de los compuestos y el estudio de sus mecanismos de acción en estas plantas en las que el aislamiento de endófitos ha sido escaso.

Rapid differentiation of graft Citrus sinensis with and without Xylella fastidiosa infection by mass spectrometry.

RATIONALE: Xylella fastidiosa causes citrus variegated chlorosis (CVC) in sweet orange trees. A diagnostic method for detecting CVC before the symptoms appear, which would inform citrus producers in advance about when the plant should be removed from the orchard, is essential for reducing pesticide application costs. METHODS: Chemometrics was applied to high-performance liquid chromatography diode array detector (HPLC-DAD) data to evaluate the similarities and differences between the chromatographic profiles. A liquid chromatography/atmospheric pressure chemical ionization mass spectrometry selected reaction monitoring (LC/APCI-MS-SRM) method was developed to identify the major compounds and to determine their amounts in all samples. RESULTS: We evaluated the effect of this bacterium on the variation in the chemical profile in citrus plants. The organs of C. sinensis grafted on C. limonia were analyzed. Chemometrics was applied to the obtained data, and two major groups were differentiated. Flavonoids were observed in one group (leaves) and coumarins in the second (roots), both at higher concentrations in the plants with CVC symptoms than in those without the symptoms and those in the negative control. The rootstocks also interfered in the metabolism of the scion. CONCLUSIONS: The developed LC/APCI-MS-SRM method for detecting CVC before the symptoms appear is simple and accurate. It is inexpensive, and many samples can be screened per hour using 1 mg of leaves. Knowledge of the influence of the rootstock on the chemical profile of the graft is limited. This study demonstrates the effect of the rootstock in synthesizing flavonoids and increasing its content in all parts of the graft.

Lignocellulolytic characterization and comparative secretome analysis of a Trichoderma erinaceum strain isolated from decaying sugarcane straw.

The fungus Trichoderma reesei is employed in the production of most enzyme cocktails used by the lignocellulosic biofuels industry today. Despite significant improvements, the cost of the required enzyme preparations remains high, representing a major obstacle for the industrial production of these alternative fuels. In this study, a new Trichoderma erinaceum strain was isolated from decaying sugarcane straw. The enzyme cocktail secreted by the new isolate during growth in pretreated sugarcane straw-containing medium presented higher specific activities of ß-glucosidase, endoxylanase, ß-xylosidase and α-galactosidase than the cocktail of a wild T. reesei strain and yielded more glucose in the hydrolysis of pretreated sugarcane straw. A proteomic analysis of the two strains' secretomes identified a total of 86 proteins, of which 48 were exclusive to T. erinaceum, 35 were exclusive to T. reesei and only 3 were common to both strains. The secretome of T. erinaceum also displayed a higher number of carbohydrate-active enzymes than that of T. reesei (37 and 27 enzymes, respectively). Altogether, these results reveal the significant potential of the T. erinaceum species for the production of lignocellulases, both as a possible source of enzymes for the supplementation of industrial cocktails and as a candidate chassis for enzyme production.

Ability of endophytic fungi associated with Withania somnifera L. to control Fusarium Crown and Root Rot and to promote growth in tomato.

Fusarium crown and root rot (FCRR), caused by Fusarium oxysporum f. sp. radicis-lycopersici (FORL), is a soilborne tomato disease of increased importance worldwide. In this study, Withania somnifera was used as a potential source of biological control and growth-promoting agents. Seven fungal isolates naturally associated with W. somnifera were able to colonize tomato seedlings. They were applied as conidial suspensions or a cell-free culture filtrate. All isolates enhanced treated tomato growth parameters by 21.5-90.3% over FORL-free control and by 27.6-93.5% over pathogen-inoculated control. All tested isolates significantly decreased by 28.5-86.4% disease severity over FORL-inoculated control. The highest disease suppression, by 86.4-92.8% over control and by 81.3-88.8% over hymexazol-treated control, was achieved by the I6 isolate. FORL radial growth was suppressed by 58.5-82.3% versus control when dual cultured with tested isolates and by 61.8-83.2% using their cell-free culture filtrates. The most active agent was identified as Fusarium sp. I6 (MG835371), which displayed chitinolytic, proteolytic, and amylase activities. This has been the first report on the potential use of fungi naturally associated with W. somnifera for FCRR suppression and for tomato growth promotion. Further investigations are required in regard to mechanisms of action involved in disease suppression and plant growth promotion.

Motility and Survival of Salmonella Enterica Subspecies Enterica Serovar Enteritidis in Tomato Plants (Solanum lycopersicum L).

The presence of enteropathogens such as Salmonella affects the quality and safety of vegetables that are consumed in a minimally processed state. Worldwide, tomatoes are one of the main vegetables whose raw consumption has caused health alerts. As such, the aim of this study was to determine the motility and survival of Salmonella enterica subspecies enterica serovar Enteritidis on greenhouse-grown tomato plants. A completely randomized experimental design was used, and bacteria were inoculated into the substrate at the time of transplanting as well as by puncturing the plant stem, petiole, and peduncle during the vegetative, flowering, and fruiting stages. Survival was monitored throughout the production cycle; motility was evaluated separately in plant organs separated from the point of inoculation. Salmonella enteritidis survived the 120 days of the experiment both at the point of inoculation and in other organs of the tomato plant. For all treatments, there was a significant difference (P < 0.05) between bacterial counts in the root (12.45 ± 2.52 to 160 ± 4.01 CFU/g), stem (16.10 ± 2.31 to 90.55 ± 3.62 CFU/g), flower (7.0 ± 2.15 to 51.10 ± 3.80 CFU/g), and fruit (8.75 ± 2.38 to 28.2 ± 3.29 CFU/g). The results of the study indicate that Salmonella enteritidis in contact with tomato plants is a latent danger because its ability to enter, survive, and move within tomato plants until reaching the fruit, limits the effectiveness of commonly used disinfection methods, it would potentiate the risk to human health.

Multi-enzyme complex of white rot fungi in saccharification of lignocellulosic material

ABSTRACT The multi-enzyme complex (crude extract) of white rot fungi Pleurotus ostreatus, Pleurotus eryngii, Trametes versicolor, Pycnosporus sanguineus and Phanerochaete chrysosporium were characterized, evaluated in the hydrolysis of pretreated pulps of sorghum straw and compared efficiency with commercial enzyme. Most fungi complexes had better hydrolysis rates compared with purified commercial enzyme.

Pleurotus spp. cultivation on Brachiaria sp. straw treatment with alkaline water: Oyster mushroom and substrate treatment.

The aim of this research was to evaluate the efficiency of aqueous alkali-treated Brachiaria straw for the cultivation of appropriate species of oyster mushroom. The substrate used in the cultivation of various Pleurotus spp. was soaked for 20min by using two different procedures: (i) 0.5-2.0% Ca(OH)2 in 100L water, and (ii) 50-250L water. As a result, 1% Ca(OH)2 dissolved in 100L water and 3.5kg of Brachiaria straw presented the best production. The most suitable species for the application of the present method were P. pulmonarius and P. sapidus. The success of this technique is directly related to the concentration of Ca(OH)2 and water, the species, and the origin and quality of raw material used as the substrate in the production of oyster mushroom.

Multi-enzyme complex of white rot fungi in saccharification of lignocellulosic material.

The multi-enzyme complex (crude extract) of white rot fungi Pleurotus ostreatus, Pleurotus eryngii, Trametes versicolor, Pycnosporus sanguineus and Phanerochaete chrysosporium were characterized, evaluated in the hydrolysis of pretreated pulps of sorghum straw and compared efficiency with commercial enzyme. Most fungi complexes had better hydrolysis rates compared with purified commercial enzyme.

Bioavailability of Compounds Susceptible to Enzymatic Oxidation Enhances Growth of Shiitake Medicinal Mushroom (Lentinus edodes) in Solid-State Fermentation with Vineyard Prunings.

Grapes are widely produced in northwestern Mexico, generating many wood trimmings (vineyard prunings) that have no further local use. This makes vineyard prunings a very attractive alternative for the cultivation of white-rot medicinal mushrooms such as Lentinus edodes. This type of wood can also offer a model for the evaluation of oxidative enzyme production during the fermentation process. We tested the effect of wood from vineyard prunings on the vegetative growth of and production of ligninolytic enzymes in L. edodes in solid-state fermentation and with wheat straw as the control substrate. The specific growth rate of the fungus was 2-fold higher on vineyard pruning culture (µM = 0.95 day-1) than on wheat straw culture (µM = 0.47 day-1). Laccase-specific production was 4 times higher in the vineyard prunings culture than on wheat straw (0.34 and 0.08 mU · mg protein-1 · ppm CO2-1, respectively), and manganese peroxidase production was 3.7 times higher on wheat straw culture than on vineyard prunings (2.21 and 0.60 mU · mg protein-1 · ppm CO2-1, respectively). To explain accurately these differences in growth and ligninolytic enzyme activity, methanol extracts were obtained from each substrate and characterized. Resveratrol and catechins were the main compounds identified in vineyard prunings, whereas epigallocatechin was the only one detected in wheat straw. Compounds susceptible to enzymatic oxidation are more bioavailable in vineyard prunings than in wheat straw, and thus the highest L. edodes growth rate is associated with the presence of these compounds.

Genomic characterization of Nitrospirillum amazonense strain CBAmC, a nitrogen-fixing bacterium isolated from surface-sterilized sugarcane stems.

Nitrospirillum amazonense is a nitrogen-fixing bacterium that shows potential to promote plant growth when inoculated into sugarcane and rice plants. This microorganism has been the subject of biochemical and genetic characterization to elucidate important functions related to host plant interaction and growth promotion, including the determination of draft genome sequences of two strains, Y2 and CBAmC, the second of which is the aim of the present study. CBAmC has been isolated from sugarcane (Saccharum spp.), and is currently used in a sugarcane consortium inoculant with four other nitrogen-fixing bacterial strains. The present paper describes a significant improvement in the genome sequence and assembly for the N. amazonense strain CBAmC, and determination for the first time of a complete genome sequence for this bacterial species, using PacBio technology. The analysis of the genomic data obtained allowed the discovery of genes coding for metabolic pathways and cellular structures that may be determinant for the success of the bacterial establishment and colonization into the host sugarcane plant, besides conferring important characteristics to the inoculant. These include genes for the use of sucrose and N-glycans, biosynthesis of autoinducer molecules, siderophore production and acquisition, auxin and polyamine biosynthesis, flagellum, σ-fimbriae, a variety of secretion systems, and a complete denitrification system. Concerning genes for nitrogenase and auxiliary proteins, it was possible to corroborate literature data that in N. amazonense these probably had originated from horizontal gene transfer, from bacteria of the Rhizobiales order. The complete genomic sequence of the CBAmC strain of N. amazonense revealed that the bacterium harbors four replicons, including three chromosomes and one chromid, a profile that coincides with that of other two strains, according to literature data, suggesting that as a replicon pattern for the species. Finally, results of phylogenomic analyses in this work support the recent reclassification of the species, separating it from the Azospirillum genus. More importantly, results of the present work shall guide subsequent studies on strain CBAmC as well as the development of a sugarcane inoculant.

False Bean Smut Caused by Slime Mold.

Identification of the "bean smut" reported in 1998 in abstracts from two conferences was later disseminated by a Plant Disease Note; citations in books, papers, and blogs; and in several official sites, including databases curated by the United States Department of Agriculture and Embrapa-Brazil. After seeing the illustration of the syndrome in 2002, the need became clear for a review of the so-called bean smut. Field collections indicated that it is common in no-till bean and soybean farming in Brazil. Our studies revealed that the "bean smut" attributed to Ustilago sp. or "Ustilago phaseoli" and, later, to "Microbotryum phaseoli" is not a real smut but is Physarum cinereum (Physaraceae, Physarales, Myxomycetes), sporulating superficially on leaves, stems, and pods of dry bean and soybean. To unravel this imbroglio, we produced detailed morphological documentation supported by molecular treatment. This will correct the spread and further incorporation of an error in the literature based upon mistaken taxonomical work related to a plant-associated nonpathogenic organism.

Pleurotus spp. cultivation on Brachiaria sp. straw treatment with alkaline water

Abstract The aim of this research was to evaluate the efficiency of aqueous alkali-treated Brachiaria straw for the cultivation of appropriate species of oyster mushroom. The substrate used in the cultivation of various Pleurotus spp. was soaked for 20 min by using two different procedures: (i) 0.5-2.0% Ca(OH)2 in 100 L water, and (ii) 50-250 L water. As a result, 1% Ca(OH)2 dissolved in 100 L water and 3.5 kg of Brachiaria straw presented the best production. The most suitable species for the application of the present method were P. pulmonarius and P. sapidus. The success of this technique is directly related to the concentration of Ca(OH)2 and water, the species, and the origin and quality of raw material used as the substrate in the production of oyster mushroom.

Molecular mapping and candidate gene analysis for resistance to powdery mildew in Cucumis sativus stem.

Powdery mildew (PM) of cucumber (Cucumis sativus), caused by Podosphaera xanthii, is a major foliar disease worldwide and resistance is one of the main objectives in cucumber breeding programs. The resistance to PM in cucumber stem is important to the resistance for the whole plant. In this study, genetic analysis and gene mapping were implemented with cucumber inbred lines NCG-122 (with resistance to PM in the stem) and NCG-121 (with susceptibility in the stem). Genetic analysis showed that resistance to PM in the stem of NCG-122 was qualitative and controlled by a single-recessive nuclear gene (pm-s). Susceptibility was dominant to resistance. In the initial genetic mapping of the pm-s gene, 10 SSR markers were discovered to be linked to pm-s, which was mapped to chromosome 5 (Chr.5) of cucumber. The pm-s gene's closest flanking markers were SSR20486 and SSR06184/SSR13237 with genetic distances of 0.9 and 1.8 cM, respectively. One hundred and fifty-seven pairs of new SSR primers were exploited by the sequence information in the initial mapping region of pm-s. The analysis on the F2 mapping population using the new molecular markers showed that 17 SSR markers were confirmed to be linked to the pm-s gene. The two closest flanking markers, pmSSR27and pmSSR17, were 0.1 and 0.7 cM from pm-s, respectively, confirming the location of this gene on Chr.5. The physical length of the genomic region containing pm-s was 135.7 kb harboring 21 predicted genes. Among these genes, the gene Csa5G623470 annotated as encoding Mlo-related protein was defined as the most probable candidate gene for the pm-s. The results of this study will provide a basis for marker-assisted selection, and make the benefit for the cloning of the resistance gene.

New production process of the antifungal chaetoglobosin A using cornstalks

Abstract Chaetoglobosin A is an antibacterial compound produced by Chaetomium globosum, with potential application as a biopesticide and cancer treatment drug. The aim of this study was to evaluate the feasibility of utilizing cornstalks to produce chaetoglobosin A by C. globosum W7 in solid-batch fermentation and to determine an optimal method for purification of the products. The output of chaetoglobosin A from the cornstalks was 0.34 mg/g, and its content in the crude extract was 4.80%. Purification conditions were optimized to increase the content of chaetoglobosin A in the crude extract, including the extract solvent, temperature, and pH value. The optimum process conditions were found to be acetone as the extractant, under room temperature, and at a pH value of 13. Under these conditions, a production process of the antifungal chaetoglobosin A was established, and the content reached 19.17%. Through further verification, cornstalks could replace crops for the production of chaetoglobosin A using this new production process. Moreover, the purified products showed great inhibition against Rhizoctonia solani, with chaetoglobosin A confirmed as the main effective constituent (IC50 = 3.88 µg/mL). Collectively, these results demonstrate the feasibility of using cornstalks to synthesize chaetoglobosin A and that the production process established in this study was effective.

New production process of the antifungal chaetoglobosin A using cornstalks.

Chaetoglobosin A is an antibacterial compound produced by Chaetomium globosum, with potential application as a biopesticide and cancer treatment drug. The aim of this study was to evaluate the feasibility of utilizing cornstalks to produce chaetoglobosin A by C. globosum W7 in solid-batch fermentation and to determine an optimal method for purification of the products. The output of chaetoglobosin A from the cornstalks was 0.34mg/g, and its content in the crude extract was 4.80%. Purification conditions were optimized to increase the content of chaetoglobosin A in the crude extract, including the extract solvent, temperature, and pH value. The optimum process conditions were found to be acetone as the extractant, under room temperature, and at a pH value of 13. Under these conditions, a production process of the antifungal chaetoglobosin A was established, and the content reached 19.17%. Through further verification, cornstalks could replace crops for the production of chaetoglobosin A using this new production process. Moreover, the purified products showed great inhibition against Rhizoctonia solani, with chaetoglobosin A confirmed as the main effective constituent (IC50=3.88µg/mL). Collectively, these results demonstrate the feasibility of using cornstalks to synthesize chaetoglobosin A and that the production process established in this study was effective.

A quorum sensing-defective mutant of Pectobacterium carotovorum ssp. brasiliense 1692 is attenuated in virulence and unable to occlude xylem tissue of susceptible potato plant stems.

Pectobacterium carotovorum ssp. brasiliense 1692 (Pcb1692) is an important emerging pathogen of potatoes causing blackleg in the field and soft rot during post-harvest storage. Blackleg diseases involve the bacterial colonization of vascular tissue and the formation of aggregates, also known as biofilms. To understand the role of quorum sensing in vascular colonization by Pcb1692, we generated a Pcb1692ΔexpI mutant strain. Inactivation of expI led to the reduced production of plant cell wall-degrading enzymes (PCWDEs), the inability to produce acyl homoserine lactone (AHL) and reduced virulence in potato tubers and stems. Complementation of the mutant strain with the wild-type expI gene in trans successfully restored AHL and PCWDE production as well as virulence. Transmission electron microscopy and in vitro motility assays demonstrated hyperpiliation and loss of flagella and swimming motility in the mutant strain compared with the wild-type Pcb1692. Furthermore, we noted that, in the early stages of infection, Pcb1692 wild-type cells had intact flagella which were shed at the later stages of infection. Confocal laser microscopy of PcbΔexpI-inoculated plants showed that the mutant strain tended to aggregate in intercellular spaces, but was unable to transit to xylem tissue. On the contrary, the wild-type strain was often observed forming aggregates within xylem tissue of potato stems. Gene expression analyses confirmed that flagella are part of the quorum sensing regulon, whereas fimbriae and pili appear to be negatively regulated by quorum sensing. The relative expression levels of other important putative virulence genes, such as those encoding different groups of PCWDEs, were down-regulated in the mutant compared with the wild-type strain.

Fermentation of Foc TR4-infected bananas and Trichoderma spp.

Fusarium wilt (also known as Panama disease) is one of the most destructive banana diseases, and greatly hampers the global production of bananas. Consequently, it has been very detrimental to the Chinese banana industry. An infected plant is one of the major causes of the spread of Fusarium wilt to nearby regions. It is essential to develop an efficient and environmentally sustainable disease control method to restrict the spread of Fusarium wilt. We isolated Trichoderma spp from the rhizosphere soil, roots, and pseudostems of banana plants that showed Fusarium wilt symptoms in the infected areas. Their cellulase activities were measured by endoglucanase activity, ß-glucosidase activity, and filter paper activity assays. Safety analyses of the Trichoderma isolates were conducted by inoculating them into banana plantlets. The antagonistic effects of the Trichoderma spp on the Fusarium pathogen Foc tropical Race 4 (Foc TR4) were tested by the dual culture technique. Four isolates that had high cellulase activity, no observable pathogenicity to banana plants, and high antagonistic capability were identified. The isolates were used to biodegrade diseased banana plants infected with GFP-tagged Foc TR4, and the compost was tested for biological control of the infectious agent; the results showed that the fermentation suppressed the incidence of wilt and killed the pathogen. This study indicates that Trichoderma isolates have the potential to eliminate the transmission of Foc TR4, and may be developed into an environmentally sustainable treatment for controlling Fusarium wilt in banana plants.