Resistance of Brazilian wheat cultivars to blast under controlled condition

ABSTRACT: The first report of wheat blast in the world was in Brazil, in 1986. Since then, a great effort has been made towards the development of wheat cultivars resistant to this disease, which is caused by the fungus Pyricularia oryzae Triticum (PoT). The objective of this research was to (i) evaluate the resistance of wheat genotypes to blast and (ii) verify the correlation between disease severity on wheat spikes and sporulation rate of PoT on spike rachises. Plants of 40 cultivars grown in pots, at the flowering stage (stage 65 on the Zadoks scale), were inoculated with a suspension of conidia of a PoT isolate representative of the main variant of the fungus reported in Brazil. Severity of blast on the spikes at 5 and 7 days after inoculation (dai) and the rate of sporulation of the fungus on the rachis (conidia per g of rachis) were evaluated. Eighty percent of the cultivars that were classified in the group with the lowest sporulation rate were also classified in the group with the highest resistance at 7 dai. However, the correlation coefficients of the analysis established between the cultivar severity at 5 and 7 dai averages and the PoT sporulation rate averages were not significant (r=0.2464 and r=0.2047, respectively). Results obtained represent the updated characterization to blast of wheat cultivars in Brazil and constitute an important exploratory framework for the evaluation of the reaction of wheat genotypes based on the sporulation rate of PoT on their tissues.

In Vitro Evaluation of Herbicides on Beneficial and Pathogenic Microorganisms

An experiment was conducted in the laboratory to evaluate the effect of herbicides on beneficial and pathogenic microorganisms. Eighteen treatments included six herbicides at three different doses viz., cyhalofop-butyl (80, 160 and 240 ppm), cyhalofop-butyl + penoxsulam (150, 300 and 450 ppm), bispyribac-sodium (25, 50 and 75 ppm), fenoxaprop-p-ethyl (60, 12 and 180 ppm), carfentrazone-ethyl (20, 40 and 60 ppm) and chlorimuron-ethyl + metsulfuron-methyl (4, 8 and 12 ppm) evaluated on beneficial microbial bioagents (Trichoderma viride and Pseudomonas fluorescens) and pathogenic microorganisms (Rhizoctonia solani, Pyricularia oryzae and Xanthomonas oryzae pv. oryzae). Results revealed that bispyribac-sodium and cyhalofop-butyl + penoxsulam had greatest inhibitory effect on pathogenic microorganisms Rhizoctonia solani (47.76 and 54.40%) and Pyricularia oryzae (49.07 and 61.12%), but showed no effect on Xanthomonasoryzaepv. oryzae, and were less harmful to biocontrol agents Trichoderma viride and Pseudomonas fluorescens at recommended doses, which were effective in control of broad spectrum of weed flora in rice ecosystem.

Disease resistance of improved MR220 lines against Pyricularia oryzae Cavara and their preliminary agronomic performance

Blast disease caused by Pyricularia oryzae is one of the most destructive fungal diseases of rice in Malaysia. Utilisation of resistant varieties is the most efficient management approach towards reducing yield losses. The line IRTP21683 with the Pi9 gene has shown strong resistance against the isolate MPO988.3 of pathotype P_0.0, the most prevalent P. oryzae pathotype in Malaysia. Crossing of IRTP21683 was undertaken with the recurrent parent MR220, a susceptible elite Malaysian rice variety, using a marker assisted backcrossing technique with two simple sequence repeat markers, RM19776 and RM7311, as the tag for the Pi9 gene. Twenty BC₃F₄ lines with the Pi9 gene were resistant when challenged with MPO 988.3. The cluster analysis based on seven agronomic parameters showed that the resistant BC₃F₄ lines could be divided into four groups, of which the members in group 1 and 2 have shown comparable or better performance than MR220. Five lines in group 1, B220PI9-3-48, B220PI9-3-76, B220PI9-3-77, B220PI9-3-79 and B220PI9-3-82 showed outstanding yield performance with early maturation.

Isolation and Identification of Antibacterial and Antifungal Compounds from Praxelis clematidea R. M. King & H. Robinson as an Effective Potential Treatment against Rice Pathogens

Bacterial leaf blight and blast diseases caused by the bacterium Xanthomonas oryzae pv. oryzae and the fungus Pyricularia oryzae, respectively, are among the most important infectious diseases affecting rice. We evaluated the antimicrobial effects of compounds derived from Praxelis clematidea on Xanthomonas oryzae and Pyricularia oryzae. The dried aerial parts of Praxelis clematidea were subjected to ethanol extraction, separated by solvent partitioning using hexane, chloroform, ethyl acetate, and water. In vitro assays demonstrated that the main antibacterial and antifungal activities were distributed in the ethyl acetate and chloroform fractions, respectively. These fractions were further separated using silica gel chromatography and reversed-phase chromatography. Finally, we isolated five compounds, 1–5, that inhibited the growth of Xanthomonas oryzae in vitro and four compounds, 6–9, that exhibited in vitro antifungal activity against Pyricularia oryzae. We evaluated their antimicrobial activities and identified their chemical structures by NMR and mass spectrometry analyses. This is the first study to isolate compound 2 (4,4′,4′′-nitrilotriphenol) as an alternative microbial from natural resources and evaluate its physiological activity. Moreover, this is the first report to demonstrate antibacterial activity in comparison with flavonoids. Praxelis clematidea extracts plausibly exert both antibacterial and antifungal effects, which should be further validated in field trials.

Antifungal Activities of Ageratum conyzoides L. Extract against Rice Pathogens Pyricularia oryzae Cavara and Rhizoctonia solani Kühn

Blast disease and sheath blight disease caused by infection with Pyricularia oryzae and Rhizoctonia solani, respectively, are serious fungal diseases in paddy fields. Although synthetic fungicides have been used to control these diseases, the development of ecologically friendly alternatives is required because fungicides can cause health problems and environmental pollution. Natural herbs possessing antifungal activities are among the candidates as alternatives. Ageratum conyzoides is known to contain antifungal compounds, such as precocene II and polymethoxyflavones. Here, we report the antifungal activities of five compounds isolated after ethanol extraction from Ageratum conyzoides against Pyricularia oryzae and Rhizoctonia solani in vitro. Further, we demonstrated the protective effect of the extract on rice from Pyricularia oryzae infection by field trial testing in a shaded net-house.

Tenuazonic acid production is dispensable for virulence, but its biosynthetic gene expression pattern is associated with the infection of Pyricularia oryzae

Tenuazonic acid (TeA) is a toxin produced by the rice blast fungus Pyricularia oryzae. Although knockout of the TeA biosynthetic gene TAS1 did not affect the virulence of P. oryzae, constitutive TAS1 expression suppressed its infection. TAS1 expression was induced alongside transition of P. oryzae infection behavior. The results suggested that controlling TeA biosynthesis is important for P. oryzae infection.

Transcriptomic and Ultrastructural Analyses of Pyricularia Oryzae Treated With Fungicidal Peptaibol Analogs of Trichoderma Trichogin

Eco-friendly analogs of Trichogin GA IV, a short peptaibol produced by Trichoderma longibrachiatum, were assayed against Pyricularia oryzae, the causal agent of rice blast disease. In vitro and in vivo screenings allowed us to identify six peptides able to reduce by about 70% rice blast symptoms. One of the most active peptides was selected for further studies. Microscopy analyses highlighted that the treated fungal spores could not germinate and the fluorescein-labeled peptide localized on the spore cell wall and in the agglutinated cytoplasm. Transcriptomic analysis was carried out on P. oryzae mycelium 3 h after the peptide treatment. We identified 1,410 differentially expressed genes, two-thirds of which upregulated. Among these, we found genes involved in oxidative stress response, detoxification, autophagic cell death, cell wall biogenesis, degradation and remodeling, melanin and fatty acid biosynthesis, and ion efflux transporters. Molecular data suggest that the trichogin analogs cause cell wall and membrane damages and induce autophagic cell death. Ultrastructure observations on treated conidia and hyphae confirmed the molecular data. In conclusion, these selected peptides seem to be promising alternative molecules for developing effective bio-pesticides able to control rice blast disease.