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Abstract: Radiation for medical use is a well-established therapeutic method with an excellent prognosis rate for various cancer treatments. Unfortunately, a high dose of radiation therapy comes with its own share of side effects, causing radiation-induced non-specific cellular toxicity; consequently, a large percentage of treated patients suffer from chronic effects during the treatment and even after the post-treatment. Accumulating data evidenced that radiation exposure to the brain can alter the diverse cognitive-related signalings and cause progressive neurodegeneration in patients because of elevated oxidative stress, neuroinflammation, and loss of neurogenesis. Epidemiological studies suggested the beneficial effect of hormonal therapy using estrogen in slowing down the progression of various neuropathologies. Despite its primary function as a sex hormone, estrogen is also renowned for its neuroprotective activity and could manage radiation-induced side-effects as it regulates many hallmarks of neurodegenerations. Thus, treatment with estrogen and estrogen-like molecules or modulators, including phytoestrogens, might be a potential approach capable of neuroprotection in radiation-induced brain degeneration. This review summarized the molecular mechanisms of radiation effects and estrogen signaling in the manifestation of neurodegeneration and highlighted the current evidence on the phytoestrogen mediated protective effect against radiation-induced brain injury. This existing knowledge points towards a new area to expand to identify the possible alternative therapy that can be taken with radiation therapy as adjuvants to improve patients' quality of life with compromised cognitive function.

Enterococcus faecalis is associated with streptococcosis like infection in fish. A whole-genome sequence study was conducted to investigate the virulence factor and antibiotic-resistance genes in three fish pathogenic E. faecalis. Genomic DNA was extracted from three strains of E. faecalis isolated from streptococcosis infected Nile tilapia (strains BF1B1 and BFFF11) and Thai sarpunti (strain BFPS6). The whole genome sequences of these three strains were performed using a MiSeq sequencer (Illumina, Inc.). All three strains conserved 69 virulence factor such as genes associated with protection against oxidative stress, bacterial cell wall synthesis, gelatinase toxin, multiple biofilm-associated genes and capsule producing genes. Moreover, 39 antibiotic-resistance genes against sixteen major groups of antibiotics were identified in the genome sequences of all three strains. The most commonly used antibiotic Tetracycline resistance genes were found only in BFPS6 strain, whereas, Bacteriocin synthesis genes were identified in both BFFF11 and BFPS6 strain. Phylogenetic analysis revealed that strains BF1B1 and BFFF1 form a different cluster than BFPS6. This is one of the first whole-genome sequence study of fish pathogenic E. faecalis, unfold new information on the virulence factor and Antibiotic resistance genes linked to pathogenicity in fish.

Nile tilapia ( Oreochromis niloticus ) is one of the most economically important cultured fish species throughout the world. Streptococcosis is a significant threat to global Nile tilapia farming. Enterococcus faecalis has recently emerged as an important pathogen of streptococcosis in Asia and Africa.

Streptococcosis is one of the major threats to Nile tilapia (Oreochromis niloticus) in most regions of the world. Recently, Enterococcus faecalis has been widely reported to be involved in streptococcosis in O. niloticus in Asia and Africa. This study aimed to isolate beneficial marine bacteria to evaluate their effects on growth, hematological parameters, nonspecific immunity, the gut bacteriome, and streptococcosis prevention efficacy in

Sugar beet plants in the experimental plots of Bangladesh Agricultural University showed wilting symptom along with white cottony mycelia and brown sclerotia on crowns and surrounding areas on the soil surface. We estimated 9.74% of plants in 144 sugar beet plots were infected with Sclerotium rolfsii that showed root rot symptom. Isolation of the fungus from infected tissues, and obtaining pure culture was carried out following standard protocol on potato dextrose agar (PDA) medium. Pure culture on PDA produced fluppy cottony mycelia with clamp connections and brown sclerotia ranging from 0.5 to 1.5 mm, typical of S. rolfsii within 3 weeks of incubation at ambient laboratory temperature (22 ± 2 °C). We further confirmed the identity of two isolates BTSB2 and BTSB6 by performing phylogenetic analysis of the internal transcribed spacer sequences along with morphological features. We also proved Koch’s postulate to confirm that isolate of S. rolfsii is the causal agent of sugar beet root rot, not a secondary fungal contaminant. Isolate BTSB2 grew well on PDA and OMA with an average radial growth rate of 2.3 and 2.1 mm/day, respectively. We found mannitol and glucose as the best carbon sources to support radial growth, whereas sucrose and starch supported maximum sclerotia production on synthetic medium. Highest radial growth was favored by media pH 5.0–7.0 at temperature 25 °C. This study characterized S. rolfsii as a causal agent of root rot of sugar beet in Bangladesh by detailed morphological and molecular investigations. Optimization of factors that support quick growth of the pathogen on synthetic media will help in easy production of inocula required for large-scale future inoculation studies.

Soil-plant–microbes relations within the plant rhizosphere are the determinants of plant and soil health, which is important for soil ecological environment for plant-microbe interactions. Plant growth-promoting rhizobacteria (PGPR) are considered to encourage plant growth and development directly or indirectly in soil. PGPR can demonstrate a diversity of characteristics responsible .for influencing plant growth and development. During this study, Twenty four different bacterial isolates were isolated, and detailed morphological, biochemical, and physiological characterizations of those isolates were accomplished. This experiment was performed with the 24 bacterial isolates to see their gram stain test, KOH test, catalase activity, cellulose degradation capability, in dole acetic acid (IAA) production, and phosphate solubilization activities, and also tested for growth within the different arsenic and salt stress conditions and 37°C temperature. Results revealed that among the rhizobacterial isolates, fifteen bacterial isolates were negative and nine was positive in gram reaction, while some were showed high IAA production ability, phosphate solubility capability, and cellulose degradation capacity within the culture media. The isolates were isolated from paddy soils and a few were characterized by a yellow color, flat elevation, and gram-positive, while some were characterized because of the yellowish color with round colony shape, raised elevation, gram-negative, and every one the isolates were positive in catalase production capacity and phosphate solubilization activity which is able to increase the available phosphorus within the soil for plants and also produced indole acetic acid that may use as a hormone to be used in growth enhancement of plants. Hence, these isolates need to be tested further for their effect on arsenic dynamics at the plant rhizosphere, selection of suitable plant species for the bacterial association, bacterial effect on arsenic uptake by plants, and potentials for field applications for sustainable agriculture.

Molecular mapping and application of quantitative trait loci (QTL) associated with a higher level of grain Zinc is a viable option to enhance zinc content in rice through breeding. An F2 population derived from a cross between a high yielding variety, BRRI dhan28, and a locally adapted Zn enriched cultivar, Kalobokri was used to map QTLs associated with higher levels of Zn in rice grain. The F2:3 progenies varied significantly (P ＜ 0.0001) in Zinc contents with a mean value remarkably higher than those in the superior parent. Through marker by trait analysis using IciMapping, we detected a large-effect QTL, qGZn3 on chromosome 3 between RM5419 and RM1164 spanning 1.83 Mb interval at the 0.05 level of significance with a threshold LOD of 10.61. This QTL showed a21.1% (R2 value) contribution to the total phenotypic variation for zinc content in the unpolished rice grains with 4.68 μg/g additive effect of Kalobokri alleles. We also detected 11 metal homeostasis related genes within the interval of qGZn3. In-silico analysis showed that four expressed sequence tags of one candidate gene (LOC_Os03g22810) encoding Cu/Zn superoxide dismutase, a metal-binding protein, are highly active in the endosperm as well as in the embryonic tissue of rice grain. Taken together, our results suggest that qGZn3 is a major QTL associated with high grain Zn content in the F2 progenies of rice. Our findings offer valuable genetic resources to facilitate breeding for high yielding and Zinc-enriched rice variety.

Vibrio cholerae O1 El Tor, causative agent of the ongoing seventh cholera pandemic, is native to the aquatic environment of the Ganges Delta, Bay of Bengal (GDBB). Recent studies traced pandemic strains to the GDBB and proposed global spread of cholera had occurred via intercontinental transmission. In the research presented here, NotI-digested genomic DNA extracted from V. cholerae O1 clinical and environmental strains isolated in Bangladesh during 2004 – 2014 was analyzed by pulsed-field gel electrophoresis (PFGE). Results of cluster analysis showed 94.67% of the V. cholerae isolates belonged to clade A and included the majority of clinical isolates of spatio-temporal origin and representing different cholera endemic foci. The rest of the strains were estuarine, all environmental isolates from Mathbaria, Bangladesh, and occurred as singletons, clustered in clades B and C, or in the small clades D and E. Cluster analysis of the Bangladeshi strains and including 157 El Tor strains from thirteen countries in Asia, Africa, and the Americas revealed 85% of the total set of isolates belonged to clade A, indicating all were related, yet did not form an homogeneous cluster. Overall, 15% of the global strains comprised multiple small clades or segregated as singletons. Three sub-clades could be discerned within the major clade A, reflecting distinct lineages of V. cholerae El Tor associated with cholera in Asia, Africa, and the Americas. The presence in Asia and the Americas of non-pandemic V. cholerae El Tor populations differing by PFGE and from strains associated with cholera globally suggests different ecotypes are resident in distant geographies.Author SummaryCholera is a major health threat, especially in the Ganges Delta, Bay of Bengal (GDBB). Vibrio cholerae, causative agent of cholera, is native to the GDBB aquatic environment. Recent genomic studies suggest GDBB is the cholera hotspot where the disease spreads globally via human activity. Pulsed-field gel electrophoresis (PFGE) of NotI-digested genomic DNA from V. cholerae El Tor endemic cholera strains was done, including Bangladesh aquatic environment and clinical strains from distant geographical regions representing three cholera-prone continents. Results showed the majority of pandemic strains belonged to a major cluster, suggesting clonal relatedness. Ecotypes were detected, indicating geographically specific lineages. It is concluded that epidemic strains in Bangladesh and thirteen countries of Asia, Africa, and the Americas are geographically adapted, with independent evolution of the bacterium in respective geographical regions.

Wheat blast is a fungal disease of wheat which is caused by a host-specialized ascomycete Magnaporthe oryzae Triticum (MoT) pathotype (Anamorph Pyricularia oryzae Triticum). It was first discovered in Paraná state of Brazil in 1985 and then gradually spread in wheat growing areas in several countries in Brazil, Bolivia, Paraguay and Argentina. It is a fearsome disease of wheat which causes yield loss up to 100%. It is now a threat to wheat production in about 3 million hectares of wheat growing areas in South America. Application of fungicides to control this disease is unreliable and breeding resistant varieties is also not durable. At conducive environmental conditions (18-30°C and > 80% RH) during ear emergence or grain filling, this disease can become an epidemic and devastate wheat crop within a week. In 2016, MoT emerged as an epidemic in eight districts of Bangladesh and has so far destroyed more than 15,000 hectares of wheat. The wheat blast pathogen in Bangladesh is determined as a South American lineage of M. oryzae. Scientists fear that MoT may spread to neighbouring South Asian wheat-growing countries and thus pose a serious threat to food and nutritional security of South America.

Marine sponges harbor diversified bacterial symbionts many of which produce a wide array of bioactive compounds including antibiotics. The sponge-associated bacteria of Saint Martin's Island area of the Bay of Bengal, Bangladesh is largely unexplored. This study, therefore, aimed to isolate and identify the bacteria from sponges of the Saint Martin's Island area for assessing the diversity of these sponge-associated bacteria, to determine the in vitro inhibitory effects of their extracellular products (ECPs) against fish pathogens, and to assess the prophylactic efficacy of ECPs of sponge-associated bacteria against Motile Aeromonas Septicemia (MAS) in Labeo rohita. A total of 645 bacterial isolates were isolated from nine sponges collected from different locations of Saint Martin's Island. Among these, 15 bacterial genera were identified based on their colony, morphological, physiological, and biochemical characteristics. Sixty representative isolates were identified up to species level through 16S rRNA gene sequence analyses where 31 different bacterial species were explored. Among these, Vibrio spp. was the most dominant bacteria followed by Bacillus spp., Burkholderia spp., and Oceanobacillus spp. All the bacterial isolates were screened against eight different fish and shrimp pathogens through in vitro agar well diffusion assays to identify potential antibiotic-producing bacteria. Bacillus subtilis strains WS1A and YBS29 were found to inhibit the fish pathogenic Aeromonas veronii strains. Fingerlings of L. rohita were fed the ethyl acetate extracts of ECPs of WS1A and YBS29 incorporated commercial feeds for 30 days. Then, fish were artificially challenged with A. veronii strains B55 and Aero1. Control group fish were fed the basal diet. Interestingly, WS1A and YBS29 treated fish showed no disease symptoms and mortality whereas severe disease symptoms with 100% mortality were found in the challenged control. The whole-genome sequence of B. subtilis strain WS1A was analyzed that decoded a number of orthologs to intrinsic genes of antimicrobial peptides. Finally, these results indicate that Bacillus subtilis strains WS1A and YBS29 could be promising for controlling MAS in L. rohita.

Here we have been focusing on mesoporous silica (MPS) as inorganic filler material to improve the mechanical strength of silicone rubbers. The MPS particles are more effective in reducing the coefficient of thermal expansion (CTE) and hardening silicone rubber composites when compared to commercially available nonporous silica particles. In this study, we utilize ultraviolet curing type silicone rubbers and prepare MPS composites according to a simple single-step method. From an industrial viewpoint, simplifying the fabrication processes is critical. The thermal stability and mechanical strength are examined in detail in order to showcase the effectiveness of MPS particles as filler materials.

This work reports the fabrication of mesoporous silica films with controllable wall thicknesses by spin coating of precursor solutions consisting of polystyrene-block-polybutadiene-block-polystyrene based triblock copolymers (Hydrogenated methyl Styrene Ethylene Butadiene methyl Styrene, HmSEBmS) and tetraethyl orthosilicate (TEOS) followed by calcination in air at 600 °C, for optical anti-reflection films. By changing the relative weight of the triblock polymer to TEOS, the pore-to-pore distance in the mesoporous silica film can be controlled without significantly affecting the size of the mesopores, thus, enabling effective control of the refractive index and porosity of the films. In terms of optical properties, the transmittance of the fabricated mesoporous silica film is approximately 3.3% higher than that of the uncoated glass substrate in the wavelength range of 400 to 750 nm.

We describe a simple and versatile method to synthesize hollow carbon nanospheres (HCNs) loaded with well-distributed metal nanoparticles (i.e., Ir-HCNs, MoO-HCNs, and WO/WO-HCNs). This procedure uses the electrostatic interaction between negatively charged metal precursors and positively charged micelle templates made of poly(styrene-b-2-vinyl pyridine-b-ethylene oxide). The ion pairs are neutralized inside the micelles and then coated with a layer of phenolic resol. Pyrolysis transforms the nanoparticles into HCNs decorated with metal/metal oxide nanoparticles. HCNs are an excellent substrate for the in situ growth of metal nanoparticles, and this procedure can even provide reasonable control over the average size of the metal nanoparticles.

Mesostructured fullerene (C-60) film is synthesized using polymeric reverse micelles of poly(styrene-b-2-vinyl pyridine-b-ethylene oxide) (PS-b-PVP-b-PEO) triblock copolymer. Effective interaction between the electron donating pyridine units and electron accepting C-60 is the driving force to form composite micelles. Mesostructured C-60 with pore size of 20-25 nm shows highly crystallized walls in which the lattice fringes are coherently extended across several mesopores. (c) 2017 Elsevier B.V. All rights reserved.

A lot of variations in vegetable amaranth germplasm have been observed in Bangladesh. It has been used as a cheap source of antioxidants, nutrients, protein, and dietary fiber. But no efforts had not been taken to know the status of antioxidant content, polyphenol, flavonoid, antioxidant vitamins and minerals, dietary fiber, nutritional and agronomic traits. In this study, Forty-three vegetable amaranth genotypes were evaluated to determine the status of total antioxidant content, polyphenol, flavonoid, antioxidant vitamins and minerals, dietary fiber, nutritional and agronomic traits and the magnitude of genetic diversity based on the contribution of those traits for meaningful grouping and proper utilization in future breeding program. The experiment was carried out in an open experimental field at Bangabandhu Sheikh Mujibur Rahman Agricultural University, Bangladesh in a randomized complete block design with three replications. Multivariate (Principal component and cluster) analysis was done us...

The opportunistic fish pathogen, Enterococcus faecalis has been reported to cause mass mortality in several fish species in different countries. The objectives of this study were to (i) identify E. faecalis from the diseased fishes through molecular techniques; (ii) assess the antibiotic susceptibility profile of E. faecalis isolates; and (iii) control disease in tilapia fish by treatment with medicinal plant extracts. A total of 48 isolates were phenotypically identified as Enterococcus species from tilapia, stinging catfish and walking catfish cultivated in several fish farms in Gazipur. Ten randomly selected isolates were identified as E.faecalis by 16S rRNA gene sequencing. Artificial infection revealed that most of the isolates caused moderate to high mortality in fishes with characteristic disease symptoms. These isolates exhibited resistance to multiple antibiotics in vitro. Bioassay revealed that organic extracts of Tamarindus indica and Emblica officinalis leaves, Allium sativum bulb, and Syzygium aromaticum bud inhibited the growth of E. faecalis. Methanol extracts of A. sativum and methanol and acetone extracts of S. aromaticum significantly reduced the mortality of fish artificially infected with E. faecalis as both preventive and therapeutic agents. This is the first report on molecular identification, and herbal control of fish pathogenic E. faecalis in Bangladesh.

Mesoporous noble metals are an emerging class of cutting-edge nanostructured catalysts due to their abundant exposed active sites and highly accessible surfaces. Although various noble metal (e.g. Pt, Pd and Au) structures have been synthesized by hard- and soft-templating methods, mesoporous rhodium (Rh) nanoparticles have never been generated via chemical reduction, in part due to the relatively high surface energy of rhodium (Rh) metal. Here we describe a simple, scalable route to generate mesoporous Rh by chemical reduction on polymeric micelle templates [poly(ethylene oxide)-b-poly(methyl methacrylate) (PEO-b-PMMA)]. The mesoporous Rh nanoparticles exhibited a ∼2.6 times enhancement for the electrocatalytic oxidation of methanol compared to commercially available Rh catalyst. Surprisingly, the high surface area mesoporous structure of the Rh catalyst was thermally stable up to 400 °C. The combination of high surface area and thermal stability also enables superior catalytic activity for the remediation of nitric oxide (NO) in lean-burn exhaust containing high concentrations of O2., Mesoporous noble metal nanostructures offer great promise in catalytic applications. Here, Yamauchi and co-workers synthesize mesoporous rhodium nanoparticles using polymeric micelle templates, and report appreciable activities for methanol oxidation and NO remediation.

Herein, we report the fabrication of highly oxidized silver oxide/silver/tin(IV) oxide (HOSBTO or Ag3+-enriched AgO/Ag/SnO2) nanocomposite under a robust oxidative environment created with the use of concentrated nitric acid. Tin(IV) hydroxide nanofluid is added to the reaction mixture as a stabilizer for the Ag3+-enriched silver oxide in the nanocomposite. The formation of Ag nanoparticles in this nanocomposite originates from the decomposition of silver oxides during calcination at 600 °C. For comparison, poorly oxidized silver oxide/silver/tin(IV) oxide (POSBTO with formula AgO/Ag/SnO2) nanocomposite has also been prepared by following the same synthetic procedures, except for the use of concentrated nitric acid. Finally, we studied in detail the anti-pathogenic capabilities of both nanocomposites against four hazardous pathogens, including pathogenic fish bacterium (Stenotrophomonas maltophilia stain EP10), oomycete (Phytophthora cactorum strain P-25), and two different strains of pathogenic strawberry fungus, BRSP08 and BRSP09 (Collectotrichum siamense). The bioassays reveal that the as-prepared HOSBTO and POSBTO nanocomposites exhibit significant inhibitory activities against the tested pathogenic bacterium, oomycete, and fungus in a dose-dependent manner. However, the degree of dose-dependent effectiveness of the two nanocomposites against each pathogen largely varies.

Uniformly sized mesoporous palladium (Pd) nanoparticles tethered to reduced graphene oxide (rGO) surfaces can be prepared with solution phase synthesis. rGO was modified with a block copolymer and a cationic surfactant was employed to assist in the formation of mesoporous metal nanoparticle on the surface of the rGO. This procedure effectively tethers Pd to rGO and ensures good electronic contact for enhanced electrocatalysis. The mesoporous Pd nanoparticles tethered to rGO were employed in the electrooxidation of formic acid. These hybrid composite materials exhibited excellent stability, specific activity and mass activity over state-of-the-art Pd/C catalysts as well as other similar structures reported in the literature.

Ansary M.W.R., Haque E., West H.M., Rahman M.M., Akanda A.M., Wang Y., Islam M. T. (2016): Medicinal plant extracts and protein kinase C inhibitor suppress zoosporogenesis and impair motility of Phytophthora capsici zoospores. Plant Protect. Sci., 52: 113–122. The effects of water and acetone extracts from 100 medicinal plants growing in Bangladesh, along with a selective inhibitor of protein kinase C (PKC), chelerythrine chloride, were tested on zoosporogenesis (release of zoospores from the sporangia) and motility of Phytophthora capsici zoospores. Among 10 active crude acetone extracts, those from Psidium guajava and Nigella sativa (100 μg/ml) suppressed zoosporogenesis relative to the control (100% zoospore release) to 60 and 40% released, respectively and inhibited motility of 100% of the zoospores within 60 min of treat ment. Chelerythrine chloride also suppressed zoosporogenesis (30% released) at 0.1 μg/ml and inhibited motility of 100% zoospores at 0.2 μg/ml within 60 minutes. Among water extracts of 100 medicinal plants, 56 impaired motility of zoospores in a dose- and time-dependent manner. Diluted (20-fold) water extracts of 10 plants including Ocinum gratissimum, Terminalia bohera , and Duranta plumeri inhibited motility and subsequently caused lysis of zoospores.

Dragon fruit (Hylocereus polyrhizus) is a high value newly introduced fruit crop in Bangladesh. It has drawn considerable public attention due to its appealing flesh color, sweet taste and fruit qualities. Recently, basal rot of dragon fruit plants was observed in several farmer's fields, nurseries and in the research field of Bangabandhu Sheikh Mujibur Rahman Agricultural University (BSMRAU) where about 10-15% of plants were infected in each location. Initially, the symptoms appeared in the basal part near the soil as brown lesions which gradually extended to the upper stem and finally becoming soft and watery (Figure 1a). Infected plants were collected from Kapasia of Gazipur district (Latitude 24.266 and Longitude 90.633) to isolate the causal organism. Isolations were carried out following the procedure reported by Briste et al. (2019). Briefly, infected plant parts were surface sterilized in 2% NaOCl for 1 min followed by 70% ethanol for 5 min and rinsed 3 times with sterile double distilled water. A large piece of a surface sterilized plant was cut into small pieces (2 mm × 2 mm) from the margin of the necrotic lesion and placed on half strength potato dextrose agar (PDA) and incubated for 7 days at 25 °C. The BTFD1 and BTFD4 isolates were purified from single spores resulting in white colonies with a growth rate of 1cm/day on PDA (Figure 1b). Colonies produced single celled microconidia from unbranched, short monophialidic conidiophores and septate macroconidia as well as chlamydospores in PDA which is consistent with Fusarium oxysporum (Figure 1c). To confirm the identity of the isolates, the internal transcribed spacer (ITS1, 5.8S rRNA and ITS2) and translation elongation factor-1alpha (EF-1α) were amplified using primers ITS-1/ ITS-4 and EF1-728F/ EF1-986R, respectively (Surovy et al. 2018). The ITS sequences of the isolates BTFD1 and BTFD4 (GenBank accession # MN727096 and MN727095, respectively) showed 100% similarity with the sequence from F. oxysporum strain JJF2 (MN626452). Sequence identity for EF-1α (GenBank accession # MN752123 and MN752124, respectively) was 100% with the sequence from F. oxysporum strain CAV041_EO (MK783088). The isolates (BTFD1 and BTFD4) were identified as F. oxysporum based on the aligned sequences of ITS and EF-1α, molecular phylogenetic analyses by maximum likelihood tree (Figure 2a) and maximum parsimony tree methods (Figure 2b). The isolates were stored at 4°C on dried filter paper as well as in an ultra-low temperature freezer (-80°C) at IBGE, BSMRAU, Bangladesh and are available on request. To ensure pathogenicity, isolate BTFD1 was grown on PDA, incubated at 25°C for 7 days and 250 ml conidial suspension (with 1 × 105 conidia/ml) was prepared. Twelve,three-month-old healthy dragon fruit plants were inoculated. Pathogenicity tests were carried out in two sets using three replications in each set. In one set, only the basal part of the plants was dipped into the conidial suspension and in another set the whole plant was dipped into the conidial suspension for two hours. Sterile distilled water was also used in another set of plants as a control. The inoculated plants were placed on wet tissue in a plastic box (31cm × 24cm × 8cm) covered and incubated at 25°C. After 10 days, all inoculated plants in both sets developed rot symptoms similar to those observed in the field, while the control plants remained healthy (Figure 1d). The pathogen was successfully re-isolated from the inoculated symptomatic parts on half strength PDA medium and had morphology as characterized before, thus fulfilling Koch's postulates. This disease has been reported in Argentina and Malaysia (Wright et al. 2007; Hafifi et al. 2019). To the bet of our knowledge, this is the first report of Fusarium basal rot of dragon fruit in Bangladesh caused by F. oxysporum.

Phytophthora capsici is the most destructive peronosporomycete pathogen that causes damping-off and blight on many vegetable crops including pepper and cucurbits worldwide resulting in serious economic losses. This study was conducted to isolate and characterize novel beneficial bacteria from cropping field soils and evaluate their effects on several asexual life stages of P. capsici in vitro, and if these bacteria could suppress damping-off disease in vivo. Out of 30 bacterial isolates from this study, B-1, B-10 and B-17 significantly inhibited hyphal growth through induction of excessive branching, swelling, and cellular disintegration of P. capsici. These isolates were identified as Pseudomonas spp. through 16S rRNA gene sequencing. Live cells or culture supernatants of these antagonists also significantly suppressed formation of sporangia, release of zoospores and mycelial growth in liquid culture as revealed by dry weight of the pathogen. Interestingly, zoospores of P. capsici became immotile within a very short period of time after exposure to the 10-fold diluted culture supernatants of B-1, B-10 and B-17. However, at higher concentration of culture supernatants (5-fold diluted), part of the immotile zoospores lysed within 30–60 min. Cucumber plants grown from Pseudomonas treated seeds showed enhanced resistance to the damping-off disease caused by P. capsici compared with plants grown from non-treated seeds. Results from this study demonstrated that Pseudomonas spp. from native agro-ecological niche have great potential for controlling cucumber damping-off disease and may be used in integrated disease control to reduce reliance on synthetic chemicals.

This investigation was aimed to evaluate 22 promising vegetable amaranth genotypes for antioxidant, leaf quality, and agronomic traits for two test seasons. The experiment was conducted to study the degree of genetic parameters, associations among different traits, and their contribution towards foliage yield. The analysis of variance for twelve traits was found highly significant. High mean, high range of variability, and high genotypic variance were observed for all the traits except content of Ca, protein, and carotenoid. Close differences between genotypic and phenotypic variances and genotypic and phenotypic coefficients of variation were observed for all the traits. High to moderate genotypic coefficients of variation and heritability coupled with high to moderate genetic advance in percent of mean was observed for all the traits. Considering all genetic parameters, selection based on Fe, Zn, Mn, ascorbic acid content, fiber content, plant height, leaves plant -1 , diameter of stem base, and foliage yield would be effective for the improvement of vegetable amaranth. Foliage yield had a significant positive genotypic correlation with three antioxidant traits (ascorbic acid, Fe, and Mn), two leaf quality traits (protein and fiber), and three agronomic traits (plant height, leaves plant -1 , and stem base diameter). Fiber content, leaves plant -1 , plant height, and stem base diameter had high positive direct effects and Fe, Mn, and carotenoid exhibited moderate positive direct effects on foliage yield. Based on genetic interrelationships and path coefficient values, direct selection for antioxidants (Fe and Mn), fiber content, leaves plant -1 , plant height, and stem base diameter would significantly improve the foliage yield of vegetable amaranth. Selection based on protein content concomitantly required considering the Fe and Ca contents of the genotypes.

The motility of zoospores is critical in the disease cycles of the peronosporomycetes that cause devastating diseases in plants, fishes, vertebrates, and microbes. In the course of screening for secondary metabolites regulating the motility of zoospores of Phytophthora capsici, we discovered two new inhibitors from the ethyl acetate extract of the fermentation broth of a marine-derived strain Bacillus sp. 109GGC020. The structures of these novel metabolites were elucidated as new cyclic lipopeptides and named gageopeptins A (1) and B (2) by spectroscopic analyses including high resolution MS and extensive 1D and 2D NMR. The stereoconfigurations of 1 and 2 were assigned based on the chemical derivatization studies and reviews of the literature data. Although compounds 1 and 2 impaired the motility of zoospores of P. capsici in dose- and time-dependent manners, compound 1 (IC50 = 1 μg/ml) was an approximately 400-fold stronger motility inhibitor than 2 (IC50 = 400 μg/ml). Interestingly, the zoospores halted by compound 1 were subsequently lysed at higher concentrations (IC50 = 50 μg/ml). Compounds 1 and 2 were also tested against some bacteria and fungi by broth dilution assay, and exhibited moderate antibacterial and good antifungal activities.

Impact of salinity stress were investigated in three selected Amaranthus tricolor accessions in terms of nutrients, dietary fiber, minerals, antioxidant phytochemicals and total antioxidant activity in leaves. Salinity stress enhanced biochemical contents and antioxidant activity in A. tricolor leaves. Protein, ash, energy, dietary fiber, minerals (Ca, Mg, Fe, Mn, Cu, Zn, and Na), β-carotene, ascorbic acid, total polyphenol content (TPC), total flavonoid content (TFC), total antioxidant capacity (TAC) (DPPH and ABTS+) in leaves were increased by 18%, 6%, 5%, 16%, 9%, 16%, 11%, 17%, 38%, 20%, 64%, 31%, 22%, 16%, 16%, 25% and 17%, respectively at 50 mM NaCl concentration and 31%, 12%, 6%, 30%, 57%, 35%, 95%, 96%, 82%, 87%, 27%, 63%, 82%, 39%, 30%, 58% and 47%, respectively at 100 mM NaCl concentration compared to control condition. Contents of vitamins, polyphenols and flavonoids showed a good antioxidant activity due to positive and significant interrelationships with total antioxidant capacity. It revealed that A. tricolor can tolerate a certain level of salinity stress without compromising the nutritional quality of the final product. This report for the first time demonstrated that salinity stress at certain level remarkably enhances nutritional quality of the leafy vegetable A. tricolor. Taken together, our results suggest that A. tricolor could be a promising alternative crop for farmers in salinity prone areas- in the tropical and sub-tropical regions with enriched nutritional contents and antioxidant activity.

Nanoporous carbon (NC) materials have attracted great research interest for supercapacitor applications, because of their excellent electrochemical and mechanical stability, good electrical conductivity, and high surface area. Although there are many reports on metal-organic framework (MOF)-derived carbon materials, previous synthetic studies have been hindered by imperfect control of particle sizes and shapes. Here, we show precise control of the particle sizes of MOF-525 from 100 nm to 750 nm. After conversion of MOF-525 to NC, the effects of variation of the particle size on the electrochemical performance have been carefully investigated. The results demonstrate that our NC is a potential candidate for practical supercapacitor applications.

A new chromene, ( S )-banchromene ( 1 ), together with seven known compounds, ergosterol, beauvericin ( 2 ), fusaproliferin ( 3 ), radicinin ( 4 ), poly(3-hydroxybutyric acid) (PHB, 5 ), N -methylpyrrolidone and an inseparable mixture of isochromene derivatives 6a , 6b , were isolated from a culture of Fusarium sp. strain CAMKT24b1, an endophytic fungus from the leaves and twigs of Piper guineense (Piperaceae). The structures of these metabolites were elucidated on the basis of their spectroscopic data; the absolute configuration of 1 was determined by ab initio -calculation of the optical rotation. In tests with the zoospores of the grapevine downy mildew pathogen Plasmopara viticola , compounds 1 – 4 showed moderate to high levels of motility-impairing activity at concentrations as low as 2.5 μg/mL. Compound 2 was the most active, exhibiting both motility-halting and lytic activities. Furthermore, compounds 2 and 3 displayed significant cytotoxic activity against brine shrimp larvae ( Artemia salina ) at 10 μg/mL. This is the first report on motility inhibitory and lytic activities of metabolites from an endophytic Fusarium species against the zoospores of the downy mildew pathogen P . viticola .

Antifungal resistance and toxicity problems of conventional fungicides highlighted the requirement of search for new safe antifungal agents. To comply with the requirement, we discovered four new non-cytotoxic lipopeptides, gageopeptides A-D, 1-4, from a marine-derived bacterium Bacillus subtilis. The structures and stereochemistry of gageopeptides were determined by NMR data analysis and chemical means. Gageopeptides exhibited significant antifungal activities against pathogenic fungi Rhizoctonia solani, Botrytis cinerea, and Colletotrichum acutatum with minimum inhibitory concentration (MIC) values of 0.02-0.06 μM. In addition, these lipopeptides showed significant motility inhibition and lytic activities against zoospores of the late blight pathogen Phytophthora capsici. These compounds also showed potent antimicrobial activity against Gram positive and Gram negative bacteria with MIC values of 0.04-0.08 μM. However, gageopeptides A-D did not exhibit any cytotoxicity (GI5025 μM) against cancer cell lines in sulforhodamine B (SRB), 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT), and WST-1 ((4-[3-4-iodophenyl]-2-(4-nitrophenyl)-2H-5-tetrazolio)-1,3-benzene disulfonate)) assays, demonstrating that these compounds could be promising candidates for the development of non-cytotoxic antifungal agents.

Phosphorus (P) fixation limits availability of P to plants in tropical soil, which is a major constraint for crop production. The aim of our research was to isolate, screen and characterize phosphate solubilizing bacteria (PSB) from wheat and evaluate their efficacy in P nutrition in wheat. Upon screening, 9 isolates showing varying level of phosphate solubilizing activity in both agar plate and broth assays using Pikovskaya’s medium were obtained. The pH of the culture media was decreased with increased bacterial growth suggesting that they might secrete organic acids to solubilize insoluble phosphorus. In vitro wheat seedling bioassay with two superior PSB isolates (PSB1 and PSB8) and varying sources of P revealed that both isolates significantly enhanced seedling growth (shoot and root length, shoot and root dry weight) and nutrient contents (%N, %P and %K) in plant tissue compared to control (no PSB). The performance of PSB8 was superior to PSB1 in respect of all the parameters studied. The PSB8 was tentatively identified as Pseudomonas sp. through 16S rRNA gene sequencing. Our results suggest that Pseudomonas sp. PSB8 isolated from wheat might be useful for improving P nutrition in wheat in soils with low available P.

Strawberry (Fragaria × ananassa) was introduced to Bangladesh in 1996 and has gained remarkable acceptance. However, with the expansion of acreage, anthracnose crown rot (ACR) is posing a challenge to strawberry growers. In March 2016, typical ACR symptoms were observed on cultivar Strawberry Festival in a farmer’s field in Rajshahi District. Symptoms were evident on approximately 10% of plants and included flagging of young leaves, mimicking lack of water, and wilting of the entire plant in daytime heat. A lengthwise cut through the crown of diseased plants showed characteristic shades of red and white marbling similar to that described by Weir et al. (2012). Crowns of seven symptomatic strawberry plants were obtained after excising foliage and roots and washed under running water for 1 h. Crowns were then surface disinfested with 70% ethanol followed by 1% NaClO for 2 and 3 min, respectively. Small pieces (2 × 2 mm) of the internal infected marbled red tissues were cut with a sterile scalpel, placed on corn meal agar, and incubated for 7 days at 25°C. Conidia grown on tissue pieces and hyphal mats from the tissues were streaked on PDA plates to obtain single conidial colonies. Two of the single-conidial isolates (BRSP08 and BRSP09) that had white margins with circular, dull orange centers were selected to prove Koch’s postulates. The average mycelial growth rate was 9.8 mm/day at 25°C on PDA with cottony aerial growth and pale yellowish to pinkish color. Conidia were hyaline, cylindrical, with round ends, and measuring 14.90 to 18.19 × 4.05 to 6.20 μm (average ± SD, 16.22 ± 1.20 × 5.90 ± 0.84 μm) (n = 30). Appressoria were brown, globose to cylindrical, lobbed, and measuring 7.50 to 12.70 × 6.08 to 8.4 μm (10.72 ± 1.30 × 7.20 ± 0.80 μm) (n = 20). The morphological characteristics of these isolates are consistent with some Colletotrichum species within the C. gloeosporioides complex including C. siamense (Afanador-Kafuri et al. 2003; Weir et al. 2012). BRSP09 was used for molecular identification. Internal transcribed spacer regions and intervening 5.8S nrRNA gene (ITS) and genes encoding chitin synthase (CHS-1), actin (ACT), β-tubulin (TUB2), calmodulin (CAL), and the Apn2–Mat1–2 intergenic spacer and partial mating type (Mat1–2) gene (ApMat) of the selected isolate were amplified using primers ITS1F/ITS4, Bt2a/Bt-2b, CHS-79F/CHS-354R, ACT512F/ACT783R, CL1C/CL2C, and AM-F/AM-R, respectively (Silva et al. 2012; Weir et al. 2012). Sequencing of the purified polymerase chain reaction products was performed by Macrogen (Korea), and sequences were deposited in GenBank (LC420017 to LC420022). Neighbor-joining and maximum likelihood phylogenetic trees were inferred using MEGA 6.0 (Tamura et al. 2013) based on the multilocus alignment (ITS, TUB2, ACT, CHS-1, CAL, and ApMat) of the present isolate and related Colletotrichum spp. sequences previously deposited in GenBank. BLAST search and phylogenetic analysis revealed that BRSP09 is C. siamense (Mills et al. 1992). To confirm the pathogenicity of the fungus, ten 3-month-old tissue-cultured Strawberry Festival plants were inoculated by dipping the roots and crowns into either 300 ml of conidial suspension (8 × 10⁶ conidia/ml) of the isolates BRSP08 and BRSP09 or sterile distilled water (control) for 30 min. The inoculated plants were transplanted into plastic pots with artificial peat-based soil mix and maintained in the greenhouse with 28/20°C day/night temperature. The experiment was conducted twice. After 4 weeks, all plants inoculated with BRSP08 or BRSP09 were stunted and developed typical wilt symptoms similar to those observed in the field, whereas the control plants remained healthy. C. siamense was reisolated from crown tissues with typical ACR symptoms and identified using morphological and molecular methods mentioned above, fulfilling Koch’s postulates. This is the first report of ACR of strawberry caused by C. siamense and the members of C. siamense complex in Rajshahi District.

Strawberry (Fragaria × ananassa) is a newly introduced small fruit crop in Bangladesh, which has gained considerable interest from both growers and consumers. Increasing incidence of wilt and crown rot diseases is a challenge for strawberry growers. In March 2016, wilted foliage and dead strawberry plants of cv. Strawberry Festival were found in a strawberry nursery in Rajshahi district of Bangladesh affecting 10% of the plants. Symptoms included wilting of foliage, drying and withering of older leaves, stunted growth, and reduced fruit production, leading to eventual plant collapse. A lengthwise cut through the crown of diseased plants showed distinct brown to reddish discoloration similar to that described by Koike et al. (2009). The crowns were surface sterilized in 2% NaOCl for 1 min followed by 70% ethanol for 5 min. Small pieces (2 × 2 mm) of the internal discolored tissue were placed on half-strength potato dextrose agar (PDA) medium and incubated for 7 days at 25°C. Single-spore isolates (BRSP-02 and BRSP-12) were obtained and plated to PDA, cornmeal agar, and V8 juice agar. Isolates had a growth rate 0.8 cm/day on PDA medium and produced sporodochia with septate macroconidia. Colonies also produced single-celled microconidia from unbranched, short, monophialidic conidiophores on PDA consistent with Fusarium oxysporum (Nelson et al. 1983). The internal transcribed spacer (ITS1, 5.8S rRNA, and ITS2), actin (ACT), and translation elongation factor 1-alpha (EF-1α) of the isolates were amplified using primers ITS-1/ITS-4, ACT-512F/ACT-783R, and EF1-728F/EF1-986R, respectively (Carbone and Khon 1999; White et al. 1990). ITS sequences of the isolates BRSP-02 and BRSP-12 (GenBank accession nos. LC383470 and LC383471, respectively) showed 99% similarity with the sequence from F. oxysporum strain SHBV2 (KY090783). Sequence identity for EF-1α (GenBank accession nos. LC383472 and LC383473, respectively) was 98 to 99% with the sequence from F. oxysporum isolate BRIP59170 (KX434915). The ACT sequences (GenBank accession nos. LC383784 and LC383785, respectively) showed 97 to 98% similarity with the sequence from F. oxysporum isolate C-11 (KY798318). Based on the aligned sequences of ITS and EF-1α, molecular phylogenetic analysis by the maximum likelihood method and maximum parsimony method, the isolates (BRSP-02 and BRSP-12) were named as F. oxysporum. The isolates are archived in the Department of Biotechnology at Bangabandhu Sheikh Mujibur Rahman Agricultural University in Bangladesh on dried filter paper at 4°C and are available on request. To confirm the pathogenicity of the fungus, five 3-month-old tissue-cultured ‘Strawberry Festival’ plants were inoculated by dipping the roots into either 400 ml of conidial suspension (with 5 × 10⁶ conidia/ml) of the isolate BRSP-12 or into sterile distilled water (control) for 15 min. The inoculated plants were transplanted into plastic pots with artificial peat-based soil mix and maintained in the greenhouse with a high daytime temperature of 25°C and low nighttime temperature of 20°C. After 3 weeks, all plants inoculated with isolate BRSP-12 were stunted and developed wilt symptoms similar to those observed in the field, whereas the control plants remained healthy. Plants were then dug out, and crowns were cut longitudinally to check for internal discoloration. Light orange discoloration of crown tissues was observed in inoculated plants, but all the control plants remained symptomless. The fungus was successfully reisolated on half-strength PDA medium from 100% of crowns and had morphology as characterized before, fulfilling Koch’s postulates. To the best of our knowledge, this is the first report of Fusarium wilt of strawberry in Bangladesh. This disease has been reported from a number of other countries including Argentina, Australia, China, South Korea, Spain, the United States, and Japan (Koike et al. 2009; Williamson et al. 2012).

Plant growth promoting rhizobacteria (PGPR) are the rhizosphere bacteria that may be utilized to augment plant growth and suppress plant diseases. The objectives of this study were to identify and characterize PGPR indigenous to cucumber rhizosphere in Bangladesh, and to evaluate their ability to suppress Phytophthora crown rot in cucumber. A total of sixty six isolates were isolated, out of which ten (PPB1, PPB2, PPB3, PPB4, PPB5, PPB8, PPB9, PPB10, PPB11 and PPB12) were selected based on their in vitro plant growth promoting attributes and antagonism of phytopathogens. Phylogenetic analysis of 16S rRNA sequences identified these isolates as new strains of Pseudomonas stutzeri, Bacillus subtilis, Stenotrophomonas maltophilia and B. amyloliquefaciens. The selected isolates produced high levels (26.78 to 51.28 μg mL−1) of indole-3-acetic acid, while significant acetylene reduction activities (1.79 to 4.9 µmole C2H4 mg-1 protein h-1) were observed in eight isolates. Cucumber plants grown from seeds that were treated with these PGPR strains displayed significantly higher levels of germination, seedling vigor, growth, and N content in root and shoot tissue compared to non-treated control plants. All selected isolates were able to successfully colonize the cucumber roots. Moreover, treating cucumber seeds with these isolates significantly suppressed Phytophthora crown rot caused by Phytophthora capsici, and characteristic morphological alterations in Ph. capsici hyphae that grew towards PGPR colonies were observed. Since these PGPR inoculants exhibited multiple traits beneficial to the host plants, they may be applied in the development of new, safe, and effective seed treatments as an alternative to chemical fungicides.

In our search for secondary metabolites regulating the motility behavior of zoospores of the grapevine downy mildew pathogen Plasmopara viticola, we found that extracts from an endophytic fungus Phomopsis sp. CAFT69 and its host plant Endodesmia calophylloides remarkably impaired motility of zoospores followed by lysis. The active principles in the extracts were isolated and identified as two new compounds, namely excelsional (1a) and 9-hydroxyphomopsidin (2a), together with excelsione (1b), phomopsidin (2b), alternariol (3a), alternariol-5-O-methyl ether (3b), the hitherto undescribed 5′-hydroxyalternariol (3c), altenusin (4) from the fungus, xanthochymol (5) and 1,5-dihydroxy-3-methoxyxanthone (mesuaxanthone, 6) from the plant. Bioassays revealed that compounds 1a/b, 2a/b, and 3a–6 displayed motility inhibition and lytic activities against zoospores of the grapevine downy mildew pathogen P. viticola in a dose- and time-dependent manner from 1 to 10 μg/mL. Their structures were elucidated by extensive spectroscopic analyses including 2D NMR techniques. This is the first report of an endophyte and its natural products from E. calophylloides and the first isolation of compounds 5 and 6 from this plant.

In the course of our screening for anti-peronosporomycetal agents, we isolated a new compound khatmiamycin (1), together with five known metabolites, GTRI-02 (3), 4-ethyl-5-methyl-heptanamide (4), aloesaponarin II (5), LL-C10037α (6) and LL-C10037β (7) from the culture broth of a terrestrial Streptomyces sp. ANK313. The structures of these metabolites were assigned on the basis of their spectroscopic data. Khatmiamycin (1) exhibited potent motility inhibitory (100%) and lytic (83±7%) activities against zoospores of the grapevine downy mildew pathogen Plasmopara viticola at 10 μg ml(-1), followed by compounds 5 (MIC 25 μg ml(-1)), 7, 6, 3 in the order of decreasing activity. Khatmiamycin (1) also showed potent antibacterial activity against Staphylococcus aureus and Streptomyces viridochromogenes (Tü57) by causing inhibition zones of 11 and 14 mm diameter, respectively, at the dose of 40 μg per disk. This is the first report on motility inhibitory and lytic activities of metabolites from a terrestrial Streptomyces species against the zoospores of downy mildew pathogen P. viticola.

The aim of this study was to investigate the effects of salinity on mineral nutrient distribution along roots and shoots of seven selected rice (Oryza sativa L.) genotypes, namely Pokkali, PVSB9, PVSB19, PNR381, PNR519, NS15 and Iratom24 differing in salt tolerance. The rice plants were grown in pots and subjected to varying levels of salinity stress (0, 3, 6, 9, 12 and 15 dS m−1). Mineral nutrients distribution in shoots and roots was measured after harvesting the plants at 95 days after transplanting. The responses of salt stress on mineral nutrient uptake and distribution along plant organs significantly differed among the rice genotypes. The contents of Na+ and Cl− in the roots and shoots of resistant genotypes (PVSB9, PNR381 and Pokkali) were significantly lower than the susceptible rice genotype (NS15). The concentrations of Na+ and Na+/K+ in shoots of sensitive rice genotype (NS15) sharply increased with increasing salinity above 6 dS m−1 than those of tolerant genotypes. The highest concentration ...

The biocontrol bacterium Lysobacter sp. SB-K88 suppresses damping-off disease in sugar beet and spinach caused by Aphanomyces cochlioides and Pythium sp. through characteristic plant colonization and antibiosis against the pathogens. This study aimed to unravel further details on mode of antagonism of SB-K88 against a damping-off pathogen A. cochlioides AC-5. The SB-K88 substantially inhibited growth and decomposed AC-5 mycelia and suppressed the release of zoospores from the hyphae. The excised root tips of sugar beet seedlings from seeds previously inoculated with SB-K88 were less attractive to AC-5 zoospores. Although aerial growth was not affected, however, root hairs of SB-K88 inoculated sugar beet seedlings were remarkably shorter and thicker than those of uninoculated control. When exposed to zoospores, the SB-K88 inhibited motility of zoospores and/or caused lysis, and then aggregated around the dead cystospores or lysed residues within 3–6 h likely to be micro-predatory behavior to a eukaryotic organism. Confocal laser scanning microscopic analysis revealed that number of lipid bodies and activities of mitochondria were markedly increased in the affected hyphae compared with control hyphae as visualized by established vital stains. Taken together, these results suggest that Lysobacter sp. SB-K88 suppresses damping-off diseases through exerting multifaceted antagonistic effects against the peronosporomycetes.

The rhizoplane bacterium Lysobacter sp. SB-K88 suppresses damping-off disease in sugar beet and spinach caused by Aphanomyces cochlioides through characteristic plant colonization and antibiosis. Interaction of the pathogen and SB-K88 on potato dextrose agar medium revealed remarkable curly growth, excessive branching, and inhibition of mycelial growth of the pathogen. This study elucidated the mode of antagonism of SB-K88 by detecting changes in ultrastructure and organization of cytoskeletal filamentous actin (F-actin) network in the affected hyphae and zoospores of A. cochlioides . Transmission electron microscopy aided in visualization of significant ultrastructural alterations including invagination of membrane, disintegration or necrosis of cell wall, accumulation of excessive lipid bodies, electron-dense enlarged vacuoles, and degradation of cytoplasm in the SB-K88-induced excessively branched and curled hyphae. Confocal laser scanning microscopy confirmed the role of SB-K88 or its metabolites in severe disruption of the organization of F-actin networks in both hyphae and zoospores of A. cochlioides . An inhibitor of actin polymerization, latrunculin B, also exhibited similar disruption of F-actin organization in the hyphae and zoospores of A. cochlioides . These results suggest that the inhibitory effect of Lysobacter sp. SB-K88 on A. cochlioides is likely due to a combination of F-actin disruption and ultrastructural alterations in the zoospore and hyphal cells.

The release of zoospores from sporangia and motility of the released zoospores are critical in the disease cycle of the Peronosporomycetes that cause devastating diseases in plants, fishes, animals and humans. Disruption of any of these asexual life stages eliminates the possibility of pathogenesis. In the course of screening novel bioactive secondary metabolites, we found that extracts of some strains of marine Streptomyces spp. rapidly impaired motility and caused subsequent lysis of zoospores of the grapevine downy mildew pathogen Plasmopara viticola at 10 μg/ml. We tested a number of secondary metabolites previously isolated from these strains and found that macrotetrolide antibiotics such as nonactin, monactin, dinactin and trinactin, and nactic acids such as (+)-nonactic acid, (+)-homonactic acid, nonactic acid methyl ester, homonactic acid methyl ester, bonactin and feigrisolide C impaired motility and caused subsequent lysis of P. viticola zoospores in a dose- and time-dependent manners with dinactin being the most active compound (MIC 0.3 μg/ml). A cation channel-forming compound, gramicidin, and a carrier of monovalent cations, nigericin also showed similar biological activities. Among all 12 compounds tested, gramicidin most potently arrested the motility of zoospores at concentrations starting from 0.1 μg/ml. All macrotetrolide antibiotics also displayed similar motility impairing activities against P. viticola, Phytophthora capsici, and Aphanomyces cochlioides zoospores indicating non-specific biological effects of these compounds toward peronosporomyctes. Furthermore, macrotetrolide antibiotics and gramicidin also markedly suppressed the release of zoospores from sporangia of P. viticola in a dose-dependent manner. As macrotetrolide antibiotics and gramicidin are known as enhancers of mitochondrial ATPase activity, inhibition of zoosporogenesis and motility of zoospores by these compounds are likely linked with hydrolysis of ATP through enhanced ATPase activity in mitochondria. This is the first report on motility inhibitory and lytic activities of macrotetrolide antibiotics and nactic acids against the zoospores of peronosporomycete phytopathogens. peerReviewed

A modified medium was used to culture mycelium and produce a large quantity of zoospores of Aphanomyces cochlioides, a principal pathogen of damping-off disease of sugar beet and root rot disease of spinach. The semisolid medium consisted of 17 g corn meal agar (CMA) added with 4 g of yeast extract (YE) per liter of 50 mM phosphate buffer (pH 6.8–7.0). This medium supported the production of ca. 106 zoospores ml−1 in 6-day-old cultures, approximately 11-fold higher than the commonly used CMA (17 g CMA per liter of water, pH 6.0 ± 0.2). Although morphological characters of the zoospores produced from the hyphae grown on CMA and CMA + YE were almost similar, they contrasted their developmental strategy after encystment induced by mechanical agitation. Cystospores originating from the zoospores on CMA regenerated zoospores (>80%), while those from CMA + YE germinated (ca. 80%) and produced hyphae. Furthermore, 4–10% of the germinated cystospores on CMA + YE had double germ tubes. The soluble protein profiles of zoospores produced on CMA and on CMA + YE demonstrated that several proteins were either different or expressed differently. Our results suggest that the culture medium directly influences zoosporogenesis in A. cochlioides hyphae and the developmental strategy of the produced zoospores.

Cochliophilin A (5-hydroxy-6,7-methylenedioxyflavone, 1), known as a host-specific attractant towards the zoospores of Aphanomyces cochlioides, a cause of root rot and damping-off diseases of Chenopodiaceae, was found in the Amaranthaceae plant, Celosia cristata, that is susceptible to the pathogen. The content of 1 in Celosia seedlings was quantified as 1.4 microg/g fresh weight. A new isoflavone, cristatein (5-hydroxy-6-hydroxymethyl-7,2'-dimethoxyisoflavone, 2), and five known flavonoids were also identified.

We observed that an antagonistic rhizoplane bacterium Pseudomonas sp. strain EC-S101 induces excessive lateral and apical branching in the hyphae of a root rot phytopathogen Aphanomyces cochlioides AC-5 resulting in radial growth inhibition of hyphae in a dual culture assay. Confocal laser scanning microscopic observations using fluorescent stains indicated an increased quantity of nuclei and lipid bodies in the affected hyphae during the early stage (less affected hyphae) at day 3 of interaction. At a more advanced stage (severely affected hyphae) at day 3, nuclei became smaller and round-shaped compared with the oval shape in AC-5 control hyphae. After 7 days, nuclei disintegrated, and the nuclear materials were released into the disorganized cytoplasm. With transmission electron microscopy at 5 days of interaction, we found that the cell walls of AC-5 hyphae were considerably thicker than those of the control. Enlarged vacuoles, lipid bodies sunk into vacuoles, and vacuoles filled with electron-dense material, followed by an invagination of the AC-5 hyphal cell wall, were commonly observed. Nonmembranous electron-transparent inclusion bodies irregular in size were often distributed in the affected hyphae. By integrating our observations, we conclude that antagonistic effects evoked by strain EC-S101 resulted in the death of AC-5 hyphae, which might contribute to the suppression of A. cochlioides AC-5-linked damping-off disease in its host plants.

A total of 150 bacteria were isolated from rhizoplanes of the host and non-host plants of a phytopathogenic Peronosporomycete Aphanomyces cochlioides. Upon screening, 5% of the isolates were evaluated as antagonists as they inhibited radial growth of A. cochlioides AC-5 hyphae in a dual culture assay. In addition, those antagonistic bacteria also induced characteristic morphological alterations in the A. cochlioides AC-5 hyphae that grew towards bacterial colonies. Hyphal morphological alterations observed in AC-5 and other tested strains of Peronosporomycetes included excessive branching, curly growth, unusually longer and pointed tip formation and swelling; all of these were comparable to the alterations induced by known antimicrobial compounds. Among the antagonistic bacteria, Pseudomonas sp. strain EC-S101 induced a unique branching pattern (tree-like) in AC-5 hyphae by continuous apical bifurcation of successive hyphae, where increases in number of branches and hyphal area were linearly correlated with time up to 10 h. Our observations suggested that the pathogen might have lost its ability of normal branch production; however maintained the capability of self-branching. Soluble extracts from the culture fluids of Pseudomonas sp. strain EC-S101 and Stenotrophomonas maltophilia EC-S105 induced similar excessive branching and curly growth in A. cochlioides hyphae as the respective bacterium. These results revealed that bacterial metabolites appeared to be responsible for induction of morphological alterations. Interestingly, the antagonistic bacteria that induced hyphal morphological alterations, also efficiently suppressed in vivo damping-off disease caused by AC-5. We suggest that antagonistic rhizoplane bacteria have the capability to induce diverse morphological alterations in Peronosporomycetes hyphae during in vitro interactions. Hyphal morphological alterations associated with growth inhibition and the induction of characteristic morphological changes indicate antagonistic activity against the Peronosporomycete.

We previously demonstrated that xanthobaccin A from the rhizoplane bacterium Lysobacter sp. strain SB-K88 suppresses damping-off disease caused by Pythium sp. in sugar beet. In this study we focused on modes of Lysobacter sp. strain SB-K88 root colonization and antibiosis of the bacterium against Aphanomyces cochlioides , a pathogen of damping-off disease. Scanning electron microscopic analysis of 2-week-old sugar beet seedlings from seeds previously inoculated with SB-K88 revealed dense colonization on the root surfaces and a characteristic perpendicular pattern of Lysobacter colonization possibly generated via development of polar, brush-like fimbriae. In colonized regions a semitransparent film apparently enveloping the root and microcolonies were observed on the root surface. This Lysobacter strain also efficiently colonized the roots of several plants, including spinach, tomato, Arabidopsis thaliana , and Amaranthus gangeticus . Plants grown from both sugar beet and spinach seeds that were previously treated with Lysobacter sp. strain SB-K88 displayed significant resistance to the damping-off disease triggered by A. cochlioides . Interestingly, zoospores of A. cochlioides became immotile within 1 min after exposure to a SB-K88 cell suspension, a cell-free supernatant of SB-K88, or pure xanthobaccin A (MIC, 0.01 μg/ml). In all cases, lysis followed within 30 min in the presence of the inhibiting factor(s). Our data indicate that Lysobacter sp. strain SB-K88 has a direct inhibitory effect on A. cochlioides , suppressing damping-off disease. Furthermore, this inhibitory effect of Lysobacter sp. strain SB-K88 is likely due to a combination of antibiosis and characteristic biofilm formation at the rhizoplane of the host plant.

Mg 2+ is one of the essential elements for bacterial cell growth. The presence of the magnesium cation (Mg 2+ ) in various concentrations often affects cell growth restoration in plant-associating bacteria. This study attempted to determine whether Mg 2+ levels in Sphingomonas yanoikuyae EC-S001 affected cell growth restoration in the host plant and what the threshold level is. S. yanoikuyae EC-S001, isolated from the rhizoplane of spinach seedlings grown from surface-sterilized seeds under aseptic conditions, displayed uniform dispersion and attachment throughout the rhizoplane and phylloplane of the host seedlings. S. yanoikuyae EC-S001 did not grow in potato-dextrose broth medium but grew well in an aqueous extract of spinach leaves. Chemical investigation of the growth factor in the spinach leaf extract led to identification of the active principle as the magnesium cation. A concentration of ca. 0.10 mM Mg 2+ or more allowed S. yanoikuyae EC-S001 to grow in potato-dextrose broth medium. Some saprophytic and/or diazotrophic bacteria used in our experiment were found to have diverse threshold levels for their Mg 2+ requirements. For example, Burkholderia cepacia EC-K014, originally isolated from the rhizoplane of a Melastoma sp., could grow even in Mg 2+ -free Hoagland's no. 2 medium with saccharose and glutamine (HSG medium) and requires a trace level of Mg 2+ for its growth. In contrast, S. yanoikuyae EC-S001, together with Bacillus subtilis IFO12113, showed the most drastic restoring responses to subsequent addition of 0.98 mM Mg 2+ to Mg 2+ -free HSG medium. Our studies concluded that Mg 2+ is more than just the essential trace element needed for cell growth restoration in S. yanoikuyae EC-S001 and that certain nonculturable bacteria may require a higher concentration of Mg 2+ or another specific essential element for their growth.

On the screening of 200 nonhost plants, an Amaranthus gangeticus extract was found to attract and subsequently inhibit the motility of Aphanomyces cochlioides zoospores. The attractant was identified as a rare N-trans-feruloyl-4-O-methyldopamine (1) and the motility inhibitor as nicotinamide (2) using bioassay-guided fractionation and spectroscopic methods. The attractant had no inhibitory effect on zoospore motility whereas 2 immediately halted the motility and caused encystment in a dose-dependent manner (MIC, 5 × 10 -8 M). Interestingly, the cystospores produced by 2 regenerated zoospores instead of germinating. Concomitant application of 1 and 2 produced cystospores that germinated to give hyphae. Preliminary TLC examinations revealed that Am. gangeticus seedling exuded sufficient amounts of nicotinamide from the roots. These results suggest that exudation of nicotinamide from Am. gangeticus might be involved in its resistance against the soilborne oomycete phytopathogen A. cochlioides.