Rice Pathogen Research Articles

Antibacterial activity and rice-induced resistance, mediated by C15surfactin A, in controlling rice disease caused by Xanthomonas oryzae pv. oryzae

Xanthomonas oryzae pv. oryzae (Xoo) is an important pathogen in rice. C15surfactin A, produced by Bacillus velezensis HN-2, displayed antibacterial activity against Xoo and effectively inhibited its infection of rice. The median inhibitory concentration of C15surfactin A was 9.27 μg/mL. Scanning electron and transmission electron microscopy examination showed that C15surfactin A caused significant damage to the cell wall structure of Xoo cells. On the other hand, dramatic increases in the activity of phenylalanine ammonia-lyase (Pal) and H2O2 content were observed in rice leaves inoculated with Xoo from 0 h to 72 h. Quantitative PCR assays indicated that C15surfactin A exposure upregulated the expression of the genes Pr1a, CatA, and Pal. The results showed that C15surfactin A could inhibit the growth of Xoo and effectively induce rice resistance to Xoo by triggering a hypersensitive reaction (HR) via mediation of the activities of antioxidant-related enzymes. Taken together, C15surfactin A has strong antibiotic activity against Xoo and effectively induces rice resistance to Xoo. These results highlight the potential of C15surfactin A as a biocontrol agent against Xoo in rice.

Three Proteins (Hpa2, HrpF and XopN) Are Concomitant Type III Translocators in Bacterial Blight Pathogen of Rice.

Type III (T3) proteic effectors occupy most of the virulence determinants in eukaryote-pathogenic Gram-negative bacteria. During infection, bacteria may deploy a nanomachinery called translocon to deliver T3 effectors into host cells, wherein the effectors fulfill their pathological functions. T3 translocon is hypothetically assembled by bacterial translocators, which have been identified as one hydrophilic and two hydrophobic proteins in animal-pathogenic bacteria but remain unclear in plant pathogens. Now we characterize Hpa2, HrpF, and XopN proteins as concomitant T3 translocators in rice bacterial blight pathogen by analyzing pathological consequences of single, double, and triple gene knockout or genetic complementation. Based on these genetic analyses, Hpa2, HrpF, and XopN accordingly contribute to 46.9, 60.3, and 69.8% proportions of bacterial virulence on a susceptible rice variety. Virulence performances of Hpa2, HrpF, and XopN were attributed to their functions in essentially mediating from-bacteria-into-rice-cell translocation of PthXo1, the bacterial T3 effector characteristic of transcription factors targeting plant genes. On average, 61, 62, and 71% of PthXo1 translocation are provided correspondingly by Hpa2, HrpF, and XopN, while they cooperate to support PthXo1 translocation at a greater-than-95% extent. As a result, rice disease-susceptibility gene SWEET11, which is the regulatory target of PthXo1, is activated to confer bacterial virulence and induce the leaf blight disease in rice. Furthermore, the three translocators also undergo translocation, but only XopN is highly translocated to suppress rice defense responses, suggesting that different components of a T3 translocon deploy distinct virulence mechanisms in addition to the common function in mediating bacterial effector translocation.

Ribavirin targets sugar transporter 6 to suppress acquisition and transmission of rice stripe tenuivirus by its vector Laodelphax striatellus.

Rice stripe tenuivirus (RSV) is one of the most destructive pathogens of rice and other cereal crops. The virus is transmitted by the small brown planthopper (SBPH, Laodelphax striatellus) in a circulative-propagative manner. Thus, blocking transmission by the insect vector would provide an effective strategy to prevent epidemic outbreaks of the disease. In this study, we explored the effect of ribavirin on acquisition and transmission of the virus by specifically inhibiting the expression of sugar transporter 6 (LsSt-6), which was recently reported as a key vector component for RSV transmission. Ribavirin at the highest concentration tested (250 μmol L-1 ) significantly reduced RSV acquisition and transmission efficiency by SBPHs through inhibiting LsSt-6 messenger RNA (mRNA) level. Survival of the model insect Spodoptera frugiperda cell line (Sf9) was 95.0 ± 2.2 and 85.6 ± 2.1% after exposure to 250 μmol L-1 ribavirin or 8-azaguanine, respectively. Further study confirmed that 250 μmol L-1 ribavirin also significantly reduced LsSt-6 mRNA and protein levels in Sf9 cells. However, 8-azaguanine did not significantly inhibit viral infectivity and LsSt-6 mRNA levels in SBPH or the Sf9 cell line. This result provides evidence that ribavirin has the potential to disrupt LsSt-6 expression but not others like viral RNAs to prevent acquiring RSV, which leads to less viral accumulation in SBPH tissues and thereby lower transmission efficiency. © 2020 Society of Chemical Industry.

EndophyticBbacteria origin of healthy rice plants produce antifungal volatile compound inhibited the growth of Pyricularia oryzae Cav., the causal agent of rice blast disease

Endophytic bacteria have been known as producers for bioactive compound in which widely used in the field of crop protection. Several isolates of endophytic bacteria have demonstrated their potential ability as biocontrol agents by inhibiting the development of major rice pathogens. However, their ability to produce bioactive compounds has not been explored. The study reported the ability of the endophytic bacteria isolates in producing antifungal volatile compounds to inhibit the growth of Pyricularia oryzae Cav., the causal agent of rice blast disease. The experiment was conducted by dual culture method using bipartite compartments in which the bacterial isolates and P. oryzae were grown separately and placed by facing to each other. The bacterial isolates were grown on ISP2 agar media, whereas P. oryzae was grown on PDA media. Nine isolates were tested for their ability in producing antifungal volatile compound. The potential of antifungal volatile compound was observed by the P. oryzae growth compared to control. Furthermore, its effect on the P. oryzae mycelia was observed under microscope. The result demonstrated that all of the tested isolates were able to produce volatile compound which were able to inhibit the growth of P. oryzae . In addition, the compounds were also causing mycelial alteration.

Un nuevo agente de biocontrol de Drechslera oryzae


 El hongo patógeno del arroz Drechslera oryzae se inoculó en un mismo sustrato junto a Trichoderma harzianum en distintas condiciones medioambientales. Los mecanismos ejercidos por T. harzianum para antagonizar a D. oryzae y que en algunos casos actuaron sinérgicamente fueron: competencia por el espacio y los nutrientes, micoparasitismo y posible antibiosis. La capacidad antagonista de T. harzianum aumentó con los valores de temperatura y actividad del agua.

The biocontrol potential of acid-resistant Rhodopseudomonas palustris KTSSR54 and its exopolymeric substances against rice fungal pathogens to enhance rice growth and yield

Some of the most economically damaging diseases of cultivated rice are caused by pathogenic fungi. They cause major losses of crop and crop yield. To identify an alternative method of combating these fungi that avoids the use of fungicides, this study investigated the antagonistic activity of the acid-resistant, plant growth promoting bacterium, Rhodopseudomonas palustris KTSSR54 and its bioactive compounds. Exopolymeric substances (EPS), lipopeptides and photo-pigments extracted from strain KTSSR54 showed antifungal activity against three rice fungal pathogens (Bipolaris oryzae NPT0508, Curvularia lunata SPB0627 and Magnaporthe oryzae PTRC63). Among the antifungal extracts, EPS most effectively controlled all tested fungal pathogens. Its minimum inhibitory concentration (MIC) values ranged from 3.75 to 30 mg/ml. Living cells of KTSSR54 and its EPS altered abnormal mycelia of all tested rice fungal pathogens, in the form of wilting and swelling, respectively. They displayed significant activity against all tested fungi to increase rice seed germination percentage. However, EPS at the minimum fungicidal concentration (MFC) showed phytotoxicity toward rice seeds and damaged seedling vigor. Otherwise, infected rice leaf showed no sign of disease symptoms after most treatments involving with live KTSSR54 cells or EPS. Soil pot experiments demonstrated that inoculation with strain KTSSR54 (roughly 108 cells/ml), followed by treatment with EPS at ½ MIC or MIC could protect infected rice from fungal pathogens. The yield loss from 100-grain weight was roughly 2.5 times less than the loss from all uninoculated KTSSR54 sets. Acid-resistant strain KTSSR54 and its EPS have great potential as biocontrol agents for controlling rice fungal pathogens and could be applied in paddy fields, particularly on acidic soil.

Genetic diversity of Magnaporthe oryzae, the blast pathogen of rice in different districts of Karnataka, India determined by simple sequence repeat (SSR) markers

Blast disease caused by a filamentous heterothallic ascomycetous fungus Magnaporthe oryzae is one of the most devastating diseases of rice crop in different parts of the world. A variety of DNA markers are used for understanding the diversity and virulence spectrum of this fungus. In our current investigation, 21 simple sequence repeat markers are taken to analyse genetic diversity among 72 M. oryzae isolates obtained from different geographical locations of Karnataka, India. Results showed that there is significant variation among the isolates of M. oryzae with 92 polymorphic bands with an average of 4.38 bands for each marker. Average locus heterozygosity and polymorphic information content (PIC) of total markers were 0.73 and 0.60 respectively; Cluster analysis interestingly indicated a correlation of grouping with the geographical boundaries. We have also plotted virulence spectrum for each group and found out mixed types of reaction pattern in each group. SSR based genetic diversity of the pathogen is evolved as per the geographical boundaries and the extent of diversity might help the pathogen significantly in adapting to the changed environment. Hence during breeding program locus heterozygosity, PIC and virulence spectrum have to be considered for obtaining stable resistance cultivars.

Allele mining unlocks the identification of RYMV resistance genes and alleles in African cultivated rice

BackgroundRice yellow mottle virus (RYMV) is a major rice pathogen in Africa. Three resistance genes, i.e. RYMV1, RYMV2 and RYMV3, have been previously described. RYMV1 encodes the translation initiation factor eIF(iso)4G1 and the best candidate genes for RYMV2 and RYMV3 encode a homolog of an Arabidopsis nucleoporin (CPR5) and a nucleotide-binding domain and leucine-rich repeat containing domain (NLR) protein, respectively. High resistance is very uncommon in Asian cultivated rice (Oryza sativa), with only two highly resistant accessions identified so far, but it is more frequent in African cultivated rice (Oryza glaberrima).ResultsHere we report the findings of a resistance survey in a reference collection of 268 O. glaberrima accessions. A total of 40 resistant accessions were found, thus confirming the high frequency of resistance to RYMV in this species. We analysed the variability of resistance genes or candidate genes in this collection based on high-depth Illumina data or Sanger sequencing. Alleles previously shown to be associated with resistance were observed in 31 resistant accessions but not in any susceptible ones. Five original alleles with a frameshift or untimely stop codon in the candidate gene for RYMV2 were also identified in resistant accessions. A genetic analysis revealed that these alleles, as well as T-DNA insertions in the candidate gene, were responsible of RYMV resistance. All 40 resistant accessions were ultimately linked to a validated or candidate resistance allele at one of the three resistance genes to RYMV.ConclusionThis study demonstrated that the RYMV2 resistance gene is homologous to the Arabidopsis CPR5 gene and revealed five new resistance alleles at this locus. It also confirmed the close association between resistance and an amino-acid substitution in the leucine-rich repeat of the NLR candidate for RYMV3. We also provide an extensive overview of the genetic diversity of resistance to RYMV in the O. glaberrima species, while underlining the contrasted pattern of diversity between O. glaberrima and O. sativa for this trait. The different resistance genes and alleles will be instrumental in breeding varieties with sustainable field resistance to RYMV.

Survival Pattern and Toxin Production of Pathogens in Spiced and Non Spiced Fried Rice

Aims: There is no data regarding the survival rate of pathogens in party foods held at different temperature and time interval in Nigeria. Hence, the need to study the survival rate of selected food borne pathogens in Fried rice (spiced and non – spiced) served at parties, monitor toxin production and the rate at which it is produced with respect to time and holding temperature as well as determine the effect of spices on the survival of food pathogens.
 Place and Duration of Study: Lagelu and Ibadan North Local Government Authority Area of Ibadan, Oyo State, Nigeria, between May 2017 and September 2017.
 Methodology: We obtained 10 fried rice samples (5 spiced and 5 non- spiced) from different parties inside sterile food warmers and transferred to the Food Microbiology Laboratory. Pathogens inoculated were obtained from the culture collection unit of the Food Microbiology laboratory and they were Bacillus cereus, Staphylococcus aureus, Salmonella typhi and Escherichia coli. Inoculum size of the pathogens was determined prior to inoculation. Initial temperature of the fried rice sample was taken and after inoculation, samples were taken at an interval of 2 hours to determine the survival rate of the pathogens. Brine Shrimp Lethality (BSL) assay was used to determine the level of toxin produced.
 Results: The microbial load of all pathogens inoculated increased from its initial size as the holding temperature reduces and holding time increases. For E. coli, there was an increase from 5.3 log10CFU/g to 9.3 log10CFU/g and 8.3 log10CFU/g in non–spiced fried rice and spiced fried rice, respectively, initial load for S. typhi also increase from 4.1 log10CFU/g to 9.1 and 8.4, for B. cereus and S. aureus there was an increase form 6.3 log10CFU/g to 9.0 and 8.4 for non-spiced and spiced rice respectively. Toxicity test shows that the lethal dose was high at 8 hours (LC50:1.5) which connotes that the toxicity was high at this holding time.
 Conclusion: Holding cooked foods at ambient temperature for 6 h or longer without appropriate reheating constitute a major critical control point for party food. Keeping foods at the right temperatures is an essential food safety practice. Adequate knowledge and application of this by caterers will reduce the rate of food borne illness in the country.

Efficacy of new fungicides against sheath blight disease management of rice caused by Rhizoctonia solani under field condition

Rice (Oryza sativa L.) is second most important cereal and the staple food for more than half of the world’s population. Sheath blight is one major biotic constraints that affects rice production in India and is considered economically important disease of rice in the world The disease is caused by Rhizoctonia solani Kuhn (Teleomorph: Thanetophorus cucumeris (Frank) Donk), a fungal pathogen of both rice and soyabeans. The yield loss due to this disease is reported to range from 5.2-50 per cent depending on the environmental conditions, crop stages at which the disease occurs, cultivation practices and cultivars used. The disease has been named as “sheath blight” because of primary infection on leaf sheath. The fungus attack the crop from tillering to heading stage and leaf blade symptoms also observed. Initial symptoms are noticed on leaf sheath near water level. As the spot enlarge, the centre become grayish with irregular brown blackish border. The fungus Rhizoctonia solani produced usually long cells of septate mycelium which are hyaline within young, yellowish brown. It produced large number of globose sclerotia which initially turn white, late turn brown to purplish brown. Sclerotia as a major source of primary inoculum.In the study an experiment was laid out in the field condition during 2017-18 at experimental field of IGKV, Raipur to control the sheath blight disease of rice by application of different doses of chemical fungicide, the treatment of Propiconazole 13% + Difenconazole 13.9% SC (Tespa), Propiconazole 25% EC (Tilt), Tebuconazole 50% +Trifloxystrobin 25% WG (Nativo), Azoxystrobin 23% EC (Amistar), Validamycin 5% L (Vamcin), Captan 70% + Hexaconazole, WB (Takat), Hexaconazole 5% EC (Contaf), Carbendazin 50 WP (Bavestin) where tested in field under artificial condition. The Hexaconaxoke 5% EC found highly effective in reducing the Sheath blight disease severity (11.11%) and increase the grain yield (5566 kg/ha). The maximum disease severity (20.77%) and lowest grain yield (2600 kg/ha) was recorded under control condition.

Impact of fungicides on Rhizoctonia solani Kuhn causing sheath blight disease of rice

Rhizoctonia solani Kuhn, is an important pathogen of rice causing sheath blight disease. The pathogen thrives in soil and is polyphagous in nature. Till date no resistant variety has been registered against the disease which is the main reason of dependence on chemical management of the disease. In the present study six chemicals with different concentrations viz. 50 ppm, 100 ppm and 200 ppm along with control were evaluated in vitro against the pathogen. The chemicals were also tested in vivo for management of sheath blight. The in vitro study was conducted using the ‘poisoned food technique’ and the in vivo study was done in the field condition during kharif season in two subsequent years (2018 and 2019). Spraying of the fungicides was advocated twice after the natural infection i.e. at 45 and 60 days after transplanting. The observations revealed that all the fungicides were capable for significant inhibition of the fungus in ‘in vitro’ and the disease in ‘in vivo’ conditions.

Bacilli consortia positively regulates agronomic and growth traits in rice

In our study, soil samples from the rhizosphere of various uncultivated weeds were collected from fifteen different locations of Gujarat. Heat treatment was given at 65°C for 20 minutes prior to initial screening for spore-forming Bacilli spp. Among them, 20 nitrogen-fixing (NFB), 27 phosphate solubilizing (PSB) and 15 potassium mobilizing (KMB) isolates were screened primarily. After molecular identification only Bacilli isolates were further selected and characterized. Three superior Bacillus isolates were selected from each category by secondary screening. All three isolates for nitrogen fixation were found nif positive, while Bacillus megaterium (NAUN2) showed maximum 2.04 µmol/ml ammonia production followed by Bacillus sp. (NAUN1) and Lysinibacillus macroides (NAUN3) with 0.64 and 0.99 µmol/ml, respectively. Bacillus sp. (NAUP1) gave maximum 401.94 µg/ml phosphate solubilization on Pikovaskya broth media after third day while Bacillus sp. (NAUP2) and Brevibacillus sp. (NAUP3) showed 376.74 and 308.16 µg/ml phosphate solubilization, correspondingly. Lysinibacillus macroides (NAUK2) showed maximum 228.14 µg/ml potassium mobilization on Aleksandrov after the twentieth day while Lysinibacillus macroides (NAUK1), Bacillus megaterium (NAUK3) and Bacillus sp. (NAUP1) had effective 196.91, 158.18, 59.33 µg/ml potassium mobilization, respectively. Interestingly, no selected Bacilli isolates from the consortia were found to have inhibitory effect on other isolates in compatibility test. Out of the nine Bacillus isolates NAUK1, NAUK2, NAUK3 were found to be effective against rice pathogen Magnaportha oryzae on PDA plates. All the nine isolates were checked for IAA and siderophore production. Isolate NAUN1, NAUP3, NAUK1, NAUK2 and NAUK3 showed 37.2%, 17.9%, 33.6%, 38.9%, 48.2% siderophore production on CAS medium after 72 hrs, respectively. Isolate NAUP3 showed maximum 146.68 µg/ml IAA production while NAUN1, NAUN3, NAUP1, NAUK2 and NAUP2 showed 99.37, 99.37, 114.57, 101.46, 93.48 µg/ml IAA production, respectively after the seventh day. Rice seeds were inoculated with individual isolate and different Bacilli consortia, which significantly improved growth parameters as compared to control in pot study after 60 days of sowing. 100% RDF + NPK consortia gave significantly increased root length (11.65%), shoot length (10.28%), no. of leaves (17.39%), leaf area (11.68%) and chlorophyll content in leaf (4.76%). Similar trends were observed when the data was compared with absolute control. The spore forming Bacilli consortia was able to survive a wide range of temperature and pH fluctuations and found effective N-fixers, P-solubilizers, K-mobilizers, siderophore producers, IAA producers with antagonistic activity against rice pathogen Magnaportha oryzae.

Design of a new multiplex PCR assay for rice pathogenic bacteria detection and its application to infer disease incidence and detect co-infection in rice fields in Burkina Faso.

Crop diseases are responsible for considerable yield losses worldwide and particularly in sub-Saharan Africa. To implement efficient disease control measures, detection of the pathogens and understanding pathogen spatio-temporal dynamics is crucial and requires the use of molecular detection tools, especially to distinguish different pathogens causing more or less similar symptoms. We report here the design a new molecular diagnostic tool able to simultaneously detect five bacterial taxa causing important diseases on rice in Africa: (1) Pseudomonas fuscovaginae, (2) Xanthomonas oryzae, (3) Burkholderia glumae and Burkholderia gladioli, (4) Sphingomonas and (5) Pantoea species. This new detection tool consists of a multiplex PCR, which is cost effective and easily applicable. Validation of the method is presented through its application on a global collection of bacterial strains. Moreover, sensitivity assessment for the detection of all five bacteria is reported to be at 0.5 ng DNA by μl. As a proof of concept, we applied the new molecular detection method to a set of 256 rice leaves collected from 16 fields in two irrigated areas in western Burkina Faso. Our results show high levels of Sphingomonas spp. (up to 100% of tested samples in one field), with significant variation in the incidence between the two sampled sites. Xanthomonas oryzae incidence levels were mostly congruent with bacterial leaf streak (BLS) and bacterial leaf blight (BLB) symptom observations in the field. Low levels of Pantoea spp. were found while none of the 256 analysed samples was positive for Burkholderia or Pseudomonas fuscovaginae. Finally, many samples (up to 37.5% in one studied field) were positive for more than one bacterium (co-infection). Documenting co-infection levels are important because of their drastic consequences on epidemiology, evolution of pathogen populations and yield losses. The newly designed multiplex PCR for multiple bacterial pathogens of rice is a significant improvement for disease monitoring in the field, thus contributing to efficient disease control and food safety.

Blast resistance gene Pi54 over-expressed in rice to understand its cellular and sub-cellular localization and response to different pathogens

Rice blast resistance gene, Pi54 provides broad-spectrum resistance against different strains of Magnaporthe oryzae. Understanding the cellular localization of Pi54 protein is an essential step towards deciphering its place of interaction with the cognate Avr-gene. In this study, we investigated the sub-cellular localization of Pi54 with Green Fluorescent Protein (GFP) as a molecular tag through transient and stable expression in onion epidermal cells (Allium cepa) and susceptible japonica cultivar rice Taipei 309 (TP309), respectively. Confocal microscopy based observations of the onion epidermal cells revealed nucleus and cytoplasm specific GFP signals. In the stable transformed rice plants, GFP signal was recorded in the stomata, upper epidermal cells, mesophyll cells, vascular bundle, and walls of bundle sheath and bulliform cells of leaf tissues. These observations were further confirmed by Immunocytochemical studies. Using GFP specific antibodies, it was found that there was sufficient aggregation of GFP::Pi54protein in the cytoplasm of the leaf mesophyll cells and periphery of the epidermal cells. Interestingly, the transgenic lines developed in this study could show a moderate level of resistance to Xanthomonas oryzae and Rhizoctonia solani, the causal agents of the rice bacterial blight and sheath blight diseases, respectively. This study is a first detailed report, which emphasizes the cellular and subcellular distribution of the broad spectrum blast resistance gene Pi54 in rice and the impact of its constitutive expression towards resistance against other fungal and bacterial pathogens of rice.

Lysobacter gummosus OH17 induces systemic resistance in Oryza sativa ‘Nipponbare’

AbstractAlthough rice is one of the most cultivated, consumed, and essential crops worldwide, it is highly susceptible to a wide range of bacterial and fungal pathogens that significantly reduce the production and quality of rice. Recently, our research group reported that the plant growth‐promoting rhizobacterium Lysobacter gummosus OH17 was able to enhance the ethylene levels in Oryza sativa ‘Nipponbare’ plants at the late interaction stages. In this work, L. gummosus OH17 was found to be capable of inducing the overexpression of relevant genes of the jasmonic acid and ethylene transduction pathways in Nipponbare plants, such as OsACC, OsACO, OsERF3, and OsLOX, which resulted in the up‐regulation of a number of pathogenesis‐related proteins. The observed metabolic effects enhanced the disease resistance of rice against the three most devastating rice pathogens: Magnaporthe oryzae causing rice blast, Rhizoctonia solani causing rice sheath blight, and Xanthomonas oryzae pv. oryzae causing bacterial leaf blight. Furthermore, it was shown that L. gummosus OH17 also enhanced ethylene production levels in other O. sativa varieties from both the japonica and indica subspecies. Here, we report for the first time the metabolic alterations produced by plant growth‐promoting rhizobacterium L. gummosus OH17 at the late interaction stages and how these alterations induce systemic resistance.

Crystal structure of rice defensin OsAFP1 and molecular insight into lipid-binding

Defensins are antibacterial peptides that function in the innate immune system. OsAFP1, a defensin identified from Oryza sativa (rice), exhibits antimicrobial activity against rice pathogens. Intriguingly, OsAFP1 was also shown to demonstrate potent antifungal activity against the human pathogenic fungus Candida albicans by inducing apoptosis in target cells, suggesting that OsAFP1 represents a potential new antibiotic candidate; however, further analyses, particularly at the structural level, are required to elucidate the mechanistic underpinnings of OsAFP1 antifungal activity. Here, we determined the three-dimensional structure of OsAFP1 using X-ray crystallography. OsAFP1 features the cysteine-stabilized αβ structure highly conserved in plant defensins and presents a dimeric structure that appears necessary for antifungal activity. Superimposition of the OsAFP1 structure with that of Nicotiana alata NaD1 complexed with phosphatidic acid indicated that the target molecule is likely trapped between the S2-S3 loops of each OsAFP1 dimer. In lipid-binding analyses performed using nitrocellulose membranes immobilized with various membrane lipid components, OsAFP1 was found to bind to phosphatidylinositols (PIPs) harboring phosphate groups, particularly PI(3)P. These results indicate that OsAFP1 exerts antifungal activity by binding to PI(3)P contained in the C.albicans cell membrane, thereby applying cellular stress and inducing apoptosis. Furthermore, the OsAFP1 structure and site-specific-mutation analyses revealed that Arg1, His2, Leu4, Arg9, and Phe10 play critical roles in OsAFP1 dimer formation. Thus, our study provides novel insights into the antifungal mechanism of OsAFP1.

Yeast Associated with Rice Phylloplane and Their Contribution to Control of Rice Sheath Blight Disease.

The phylloplane is an important habitat for yeasts and these yeasts may have antagonistic activities against pathogens and could be used as biocontrol agents. To investigate rice phylloplane yeasts, 282 strains were isolated from 89 rice leaf samples and identified as 15 known yeast species in the phylum Ascomycota and 35 known and two potential new species in the phylum Basidiomycota. The majority of rice phylloplane yeasts belonged to the phylum Basidiomycota. The evaluation of antagonistic activities of 83 yeast strains against rice pathogenic fungi Pyricularia oryzae, Rhizoctonia solani, Fusarium moniliforme, Helminthosporium oryzae and Curvularia lunata revealed that 14 strains inhibited these pathogens. Among the antagonistic strains, Torulaspora indica DMKU-RP31, T. indica DMKU-RP35 and Wickerhamomyces anomalus DMKU-RP25 inhibited all rice pathogens tested, and the production of volatile organic compounds, fungal cell wall degrading enzymes and biofilm were the possible antagonistic mechanisms against all rice pathogens tested in vitro. These yeast strains were evaluated for controlling rice sheath blight caused by R. solani in rice plants in the greenhouse and were found to suppress the disease by 60.0–70.3%, whereas 3% validamycin suppressed by 83.8%. Therefore, they have potential for being developed to be used as biocontrol agents for rice sheath blight.

Chitosan guar nanoparticle preparation and its in vitro antimicrobial activity towards phytopathogens of rice

The aim of the present study was to prepare chitosan guar nanoparticle (CGNP) with high antimicrobial activity to use as a bioprotectant against rice phytopathogens. Nanoparticles were prepared using sodium tripolyphosphate by the ionic gelation method. The physico-chemical properties of nanoparticles were characterized through DLS, FTIR, TEM, SEM, AFM and XRD. The application of CGNP to rice seeds stimulated seed germination and seedling growth. CGNP showed growth inhibition towards rice pathogens P. grisea and X. oryzae under in-vitro condition. Excised rice leaves treated with CGNP and challenged with P. grisea showed no blast disease symptom whereas control leaves showed very high blast disease symptom. The results of this study indicate that CGNP can be used as an antimicrobial agent to control blast, blight disease of rice.

Facile synthesis of asymmetric patchy Janus Ag/Cu particles and study of their antifungal activity

Asymmetric patchy Ag/Cu Janus nanoparticles (NPs) were synthesized via a “seed-mediated” approach. This is the first report of synthesis of nanometer sized metal-based Janus NPs without using complicated methods. Selective adsorption of the surfactant onto the seed NPs leads to the formation of Janus type structure. Subsequently the reduction potential of Ag+/Ag0 and Cu2+/Cu0 systems directs the formation of the “patch”. The patchy Janus NPs show significant antifungal activity towards a potent rice pathogen thus offering the prospect of future application in crop protection.

Silver Nanoparticles Synthesized by Using Bacillus cereus SZT1 Ameliorated the Damage of Bacterial Leaf Blight Pathogen in Rice.

Amongst serious biotic factors deteriorating crop yield, the most destructive pathogen of rice is Xanthomonas oryzae pv. oryzae (Xoo), which causes bacterial leaf blight (BLB) disease. This study involved targeted use of biogenic silver nanoparticles (AgNPs) to control BLB in order to cope with the disadvantages of chemical disease control. AgNPs were biologically synthesized from natively isolated Bacillus cereus strain SZT1, which was identified through 16S rRNA gene sequence analysis. Synthesis of AgNPs in bacterial culture supernatant was confirmed through UV-VIS spectroscopy. Fourier transform infrared spectroscopy (FTIR) confirmed that the existence of AgNPs was stabilized with proteins and alcoholic groups. X-ray diffraction (XRD) data revealed the crystalline nature and imaging with scanning electron microscopy (SEM) and transmission electron microscopy (TEM), showing the spherical shape of AgNPs with particle sizes ranging from 18 to 39 nm. The silver presence in AgNPs was further confirmed by energy dispersive spectra. Biogenic AgNPs showed substantial antibacterial activity (24.21 ± 1.01 mm) for Xoo. In a pot experiment, AgNPs were found to be effective weapons for BLB by significantly increasing the plant biomass with a decreased cellular concentration of reactive oxygen species and increased concentration of antioxidant enzyme activity.