Search Results (8)

Variance or complete loss of the avirulence gene (Avr) enables the pathogen to escape resistance protein (R) recognition. The field resistance effectiveness of the R gene is determined by its corresponding Avr gene in field isolates. To effectively deploy the rice blast R gene Pi54, the distribution, variation and evolution of the corresponding Avr gene, AvrPi54, were determined through PCR amplification, pathogenicity assay, gene sequences and evolutionary analysis. Among 451 Pyricularia isolates from rice and non-rice hosts, including Oryza rufipogon, Digitaria sanguinalis, Eleusine coracana, E. indica and Musa sp. in Yunnan province, the PCR amplification result showed that AvrPi54 alleles existed among 218 (48.3%) isolates including rice isolates, O. rufipogon isolates and E. coracana isolates. Pathogenicity assay showed that 336 (74.5%) isolates were avirulent to Tetep (holding Pi54). Five AvrPi54 haplotypes were identified among 142 isolates through the gene sequence. These haplotypes were determined to be avirulent to Pi54 through pathogenicity assay. Four novel haplotypes (H2 to H5) of the AvrPi54 gene would provide new target sites for rice blast control. Haplotype diversity analysis indicated that there existed a lower genetic diversity of AvrPi54 for P. oryzae populations (five haplotypes, H_d = 0.127, π = 2.9 × 10⁻⁴) in this study. Neutrality tests showed that AvrPi54’s genetic variation was affected by purified selection. Haplotype network and phylogeny analysis showed that H1 was an ancestral haplotype and was widely distributed in rice isolates and O. rufipogon isolates, while H5 diverged early and evolved independently. These results indicate that the gene evolves slowly and stably and is a comparatively conserved Avr gene. Full article

Cuban rice cultivars INCA LP-5 and INCA LP-7 are widely distributed in Cuba and Caribbean countries. Although there are studies about rhizospheric bacteria associated with these cultivars, there are no reports about their seed-associated bacteria. This study aimed to isolate endophytic bacteria from rice seeds and select those with the greatest plant growth-promoting traits. A total of nineteen bacterial strains from the genera Pantoea, Bacillus, Paenibacillus, and Pseudomonas were isolated from the husk and endosperm of rice seeds. The strains Pantoea sp. S5-1, Pseudomonas sp. S5-38, and Pseudomonas sp. S7-1 were classified as the most promissory to increase rice growth as they demonstrated the presence of multiple plant growth-promoting traits such as the production of auxins, phosphate, and potassium solubilization, the production of siderophores, and the inhibition of the phytopathogen Pyricularia oryzae. The inoculation of strains of Pantoea sp. and Pseudomonas spp. in rice improves the height, root length, fresh weight, and dry weight of the shoot and root after 21 days post-inoculation in hydroponic assays. This study constitutes the first report on Cuban rice cultivars about the presence of endophytes in seeds and their potential to promote seedling growth. Pantoea sp. S5-1, Pseudomonas sp. S5-38, and Pseudomonas sp. S7-1 were selected as the more promising strains for the development of bio-stimulators or bio-inoculants for Cuban rice crops. Full article

(1) Background: Pyricularia oryzae, the causal agent of rice blast disease, is one of the major rice pathogens. The complex population structure of P. oryzae facilitates the rapid virulence variations, which make the blast disease a serious challenge for global food security. There is a large body of existing genomics research on P. oryzae, however the population structure at the pan-genome level is not clear, and the mechanism of genetic divergence and virulence variations of different sub-populations is also unknown. (2) Methods: Based on the genome data published in the NCBI, we constructed a pan-genome database of P. oryzae, which consisted of 156 strains (117 isolated from rice and 39 isolated from other hosts). (3) Results: The pan-genome contained a total of 24,100 genes (12,005 novel genes absent in the reference genome 70-15), including 16,911 (~70%) core genes (population frequency ≥95%) and 1378 (~5%) strain-specific genes (population frequency ≤5%). Gene presence-absence variation (PAV) based clustering analysis of the population structure of P. oryzae revealed four subgroups (three from rice and one from other hosts). Interestingly, the cloned avirulence genes and conventional secreted proteins (SPs, with signal peptides) were enriched in the high-frequency regions and significantly associated with transposable elements (TEs), while the unconventional SPs (without signal peptides) were enriched in the low-frequency regions and not associated significantly with TEs. This pan-genome will expand the breadth and depth of the rice blast fungus reference genome, and also serve as a new blueprint for scientists to further study the pathogenic mechanism and virulence variation of the rice blast fungus. Full article

Blast is one of the most significant wheat diseases, causing high yield losses in susceptible varieties under favorable conditions in Latin America, Southeastern Asia and Eastern Africa. The disease is caused by the ascomycetous fungal pathogen Pyricularia oryzae Triticum lineage (PoTl). Chemical control with fungicides has been used as a management strategy; however, the effectiveness of the major classes of high-risk site-specific systemic fungicides has been reduced due to the widespread prevalence of resistance, especially in Brazil. Biological control is seen as a highly important and sustainable strategy to minimize the impact of yield losses associated with wheat blast in areas where fungicides are ineffective. In our study, we specifically aimed to determine the biological control potential of the three isolates of fluorescent Pseudomonas and three of Trichoderma as the antagonists of PoTl, both in in vitro and under greenhouse conditions. Additionally, we aimed to describe the ultrastructural interactions among the biocontrol agents and the pathogen in vitro by means of scanning electron microscopy (SEM). Fluorescent P. wayambapalatensis ‘Amana’ or Pseudomonas sp. nov. ‘Yara’, both from the P. putida group, and Trichoderma koningiopsis ‘Cachara’ significantly reduced PoTl in vitro mycelial growth and the blast disease severity on wheat plants. The SEM analyses revealed ultrastructural antagonistic mechanisms: biofilm formation, direct antagonism and mycoparasitism. Further research on the topic should include the development of stable formulations of the Pseudomonas- and Trichoderma-based biocontrol agents selected in our study for managing the wheat blast disease and the field tests of the biofungicide formulations obtained thereafter. Full article

Pyricularia oryzae causes rice blast, the major destructive disease in nearly all rice fields. In order to obtain highly active compounds against P. oryzae, four new 20-membered macrolides named venturicidins G–J (1–4) were isolated from the culture broth of Streptomyces sp. SN5452 along with two known ones, venturicidins A (5) and B (6). Their structures were determined by the cumulative analyses of nuclear magnetic resonance (NMR) spectroscopy and high-resolution electrospray ionization mass spectrometry (HRESIMS) data. All isolated compounds were evaluated for their antifungal activity against P. oryzae. Interestingly, these compounds exhibited obvious inhibition to mycelial growth and conidial germination of P. oryzae. Remarkably, the EC₅₀ values of venturicidins A (5), B (6), and I (3) against mycelial growth were 0.11, 0.15 and 0.35 µg/mL, and their EC₅₀ values of conidial germination were 0.27, 0.39 and 1.14 µg/mL, respectively. The analysis of structure-activity relationships (SARs) revealed that the methylated positions might be involved in the antifungal activity of venturicidins. These results indicate that the venturicidins are prospective candidates for novel fungicides that can be applied in controlling rice blast. Full article

Rhizosphere bacteria can positively influence plant growth by direct and indirect mechanisms. A total of 112 bacterial strains were isolated from the rhizosphere of rice and tested for plant beneficial activities such as siderophore production, cell-wall-degrading enzyme production, hydrogen cyanide (HCN) production and antifungal activity against rice blast disease fungus. The actinomycetes count was 3.8 × 10⁶ CFU/g soil. Streptomyces strains PC 12, D 4.1, D 4.3 and W1 showed strong growth inhibition of blast disease fungus, Pyricularia sp. (87.3%, 82.2%, 80.0% and 80.5%) in vitro. Greenhouse experiments revealed that rice plants treated with Streptomyces strain PC 12 recorded maximum plant height, root length and root dry weight compared to the control. Taxonomic characterization of this strain on the basis of 16S rRNA gene sequence led to its identification as Streptomyces palmae PC 12. Streptomyces palmae PC 12 may be used as biofertilizer to enhance the growth and productivity of commercially important rice cultivar RD6 and the biocontrol of blast disease fungus. Full article

Pseudomonas species are metabolically robust, with capacity to produce secondary metabolites including cyclic lipopeptides (CLPs). Herein we conducted a chemical analysis of a crude CLP extract from the cocoyam rhizosphere-derived biocontrol strain Pseudomonas sp. COW3. We performed in silico analyses on its whole genome, and conducted in vitro antagonistic assay using the strain and purified CLPs. Via LC-MS and NMR, we elucidated the structures of four novel members of the bananamide group, named bananamides D-G. Besides variability in fatty acid length, bananamides D-G differ from previously described bananamides A-C and MD-0066 by the presence of a serine and aspartic acid at position 6 and 2, respectively. In addition, bananamide G has valine instead of isoleucine at position 8. Kendrick mass defect (KMD) allowed the assignment of molecular formulae to bananamides D and E. We unraveled a non-ribosomal peptide synthetase cluster banA, banB and banC which encodes the novel bananamide derivatives. Furthermore, COW3 displayed antagonistic activity and mycophagy against Pythium myriotylum, while it mainly showed mycophagy on Pyricularia oryzae. Purified bananamides D-G inhibited the growth of P. myriotylum and P. oryzae and caused hyphal distortion. Our study shows the complementarity of chemical analyses and genome mining in the discovery and elucidation of novel CLPs. In addition, structurally diverse bananamides differ in their antimicrobial activity. Full article

Triazole pesticides are organic nitrogen-containing heterocyclic compounds, which contain 1,2,3-triazole ring. In order to develop potential glucosamine-6-phosphate synthase (GlmS) inhibitor fungicides, forty compounds of triazole derivatives were synthesized in an efficient way, thirty nine of them were new compounds. The structures of all the compounds were confirmed by high resolution mass spectrometer (HRMS), ¹H-NMR and ¹³C-NMR. The fungicidal activities results based on means of mycelium growth rate method indicated that some of the compounds exhibited good fungicidal activities against P. CapasiciLeonian, Sclerotinia sclerotiorum (Lib.) de Bary, Pyricularia oryzae Cav. and Fusarium oxysporum Schl. F.sp. vasinfectum (Atk.) Snyd. & Hans. at the concentration of 50 µg/mL, especially the inhibitory rates of compounds 1-d and 1-f were over 80%. At the same time, the preliminary studies based on the Elson-Morgan method indicated that the compounds exhibited some inhibitory activity toward glucosamine-6-phosphate synthase (GlmS). These compounds will be further studied as potential antifungal lead compounds. The structure-activity relationships (SAR) were discussed in terms of the effects of the substituents on both the benzene and the sugar ring. Full article