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Abstract Background Rice blast is a devastating disease caused by Magnaporthe grisea, and it is not well controlled globally. As a Traditional Chinese Medicine, Artemisia argyi has been proven to have inhibitory effects on a variety of phytopathogenic fungi. Here, we used bioactivity-guided isolation method and transcriptomics to clarify the antifungal active compounds in A. argyi and their antifungal mechanisms. Results In vitro studies showed that the absolute ethanol extract (AEE) of A. argyi had a strong inhibitory effect on the growth of M. grisea, with a low EC50 value of 1.156 mg/mL, and could cause the destruction of hyphae cell membrane and the leakage of cell contents. To identify the active constituents, we fractionated the AEE using macroporous adsorption resin and silica gel column chromatography. The active fraction (Fr.F-1) was fractionated and had even higher antifungal activity than AEE. The results showed that both AEE and Fr.F-1 could impact primary metabolic pathways and reactive oxygen species homeostasis of M. grisea, decrease the content of reducing sugars and downregulate the expression of genes related to starch and sucrose metabolism. Further fractionation of Fr.F-1 led to the identification of two polymethoxylated flavonoids (eupatilin and 3,5,3ʹ-trihydroxy-7,8,4ʹ-trimethoxyflavone), both of which had antifungal activity and they worked synergistically in Fr.F-1. Finally, we also investigated the effect of AEE, Fr.F-1 and eupatilin on rice blast control. The results showed that AEE, Fr.F-1 and eupatilin application strongly enhanced rice resistance to M. grisea. Conclusion In brief, these findings indicate that Fr.F-1 subfraction from A. argyi and its main components polymethoxylated flavonoids confer inhibiting activities to M. grisea. This discovery can effectively alleviate the degradation pressure of A. argyi by-products, promote the healthy development of its industry, and provide new a strategy for the development of new botanical fungicides to control rice blast. Graphical Abstract

Rice blast is one of the most devastating biotic stresses that limits rice productivity. The North Eastern Hill (NEH) region of India is considered to be one of the primary centres of diversity for both rice and pathotypes of Magnaporthe grisea. Therefore, the present study was carried out to elucidate the genetic basis of leaf and neck blast resistance under Meghalaya conditions. A set of 80 diverse genotypes (natural population) and 2 F2 populations involving resistant parent, a wildtype landrace, LR 5 (Lal Jangali) and susceptible genotypes Sambha Mahsuri SUB 1 (SMS) and LR 26 (Chakhao Poireiton) were used for association analysis of reported major gene-linked markers with leaf and neck blast resistance to identify major effective genes under local conditions. Genotyping using twenty-five gene-specific markers across diverse genotypes and F2 progenies revealed genes Pi5 and Pi54 to be associated with leaf blast resistance in all three populations. Genes Pib and qPbm showed an association with neck blast resistance in both natural and LR 5 × SMS populations. Additionally, a set of 184 genome-wide polymorphic markers (SSRs and SNPs), when applied to F2-resistant and F2-susceptible DNA bulks derived from LR 5 × LR 26, suggested that Pi20(t) on chromosome 12 is one of the major genes imparting disease resistance. Markers snpOS318, RM1337 and RM7102 and RM247 and snpOS316 were associated with leaf blast and neck blast resistance, respectively. The genotypes, markers and genes will help in marker-assisted selection and development of varieties with durable resistance. [ABSTRACT FROM AUTHOR]

Eighteen blast isolates were obtained from hybrid combination Wuyou308 using the Magnaporthe oryzae pathogen isolation method. Race identification of these isolates was conducted based on seven Chinese blast differentials and 11 blast monogenic lines. The results indicated that the isolates were identified as the races of ZB13, ZB15 and ZC13, accounting for 66. 67%, 27. 78%, 5. 56%, respectively, and the resistance genes including Pi-ta2 and Pish, Pi-i were highly susceptible to these isolates, while the resistance genes like Pi-kh, Pi-1, Pi2, Pi-9 and Pi-50 showed good resistance to tested pathogens. All isolates were compatible to the original rice hybrid Wuyou308. Three isolates including GDHY-308-1401 were used for testing their pathogenicity to 45 local varieties. The results demonstrated that 13 varieties appeared highly susceptible to the tested isolates, accounting for 28. 89% ; two varieties appeared moderately susceptible to the tested isolates, accounting for 4.44% ; 30 varieties showed moderately/highly resistance, accounting for 66.67%. Among them, some of new hybrid combinations such as Wufengyou 9802, Wuyou 613, Wuyou 1179 showed good resistance to the inoculated strains, and they were recommended to be candidates in the rice region where Wuyou308 showed susceptibility. [ABSTRACT FROM AUTHOR]

Main conclusion: The investigation is the first report on genome-wide identification and characterization of NBLRR genes in pearl millet. We have shown the role of gene loss and purifying selection in the divergence of NBLRRs in Poaceae lineage and candidate CaNBLRR genes for resistance to Magnaporthe grisea infection. Plants have evolved multiple integral mechanisms to counteract the pathogens' infection, among which plant immunity through NBLRR (nucleotide-binding site, leucine-rich repeat) genes is at the forefront. The genome-wide mining in pearl millet (Cenchrus americanus (L.) Morrone) revealed 146 CaNBLRRs. The variation in the branch length of NBLRRs showed the dynamic nature of NBLRRs in response to evolving pathogen races. The orthology of NBLRRs showed a predominance of many-to-one orthologs, indicating the divergence of NBLRRs in the pearl millet lineage mainly through gene loss events followed by gene gain through single-copy duplications. Further, the purifying selection (Ka/Ks < 1) shaped the expansion of NBLRRs within the lineage of pear millet and other members of Poaceae. Presence of cis-acting elements, viz. TCA element, G-box, MYB, SARE, ABRE and conserved motifs annotated with P-loop, kinase 2, RNBS-A, RNBS-D, GLPL, MHD, Rx-CC and LRR suggests their putative role in disease resistance and stress regulation. The qRT-PCR analysis in pearl millet lines showing contrasting responses to Magnaporthe grisea infection identified CaNBLRR20, CaNBLRR33, CaNBLRR46 CaNBLRR51, CaNBLRR78 and CaNBLRR146 as putative candidates. Molecular docking showed the involvement of three and two amino acid residues of LRR domains forming hydrogen bonds (histidine, arginine and threonine) and salt bridges (arginine and lysine) with effectors. Whereas 14 and 20 amino acid residues of CaNBLRR78 and CaNBLRR20 showed hydrophobic interactions with 11 and 9 amino acid residues of effectors, Mg.00g064570.m01 and Mg.00g006570.m01, respectively. The present investigation gives a comprehensive overview of CaNBLRRs and paves the foundation for their utility in pearl millet resistance breeding through understanding of host–pathogen interactions. [ABSTRACT FROM AUTHOR]

Abstract Background The nucleotide binding site leucine rich repeat (NBLRR) genes significantly regulate defences against phytopathogens in plants. The genome-wide identification and analysis of NBLRR genes have been performed in several species. However, the detailed evolution, structure, expression of NBLRRs and functional response to Magnaporthe grisea are unknown in finger millet (Eleusine coracana (L.) Gaertn.). Results The genome-wide scanning of the finger millet genome resulted in 116 NBLRR (EcNBLRRs1-116) encompassing 64 CC-NB-LRR, 47 NB-LRR and 5 CCR-NB-LRR types. The evolutionary studies among the NBLRRs of five Gramineae species, viz., purple false brome (Brachypodium distachyon (L.) P.Beauv.), finger millet (E. coracana), rice (Oryza sativa L.), sorghum (Sorghum bicolor L. (Moench)) and foxtail millet (Setaria italica (L.) P.Beauv.) showed the evolution of NBLRRs in the ancestral lineage of the target species and subsequent divergence through gene-loss events. The purifying selection (Ka/Ks

Background: The nucleotide binding site leucine rich repeat (NBLRR) genes significantly regulate defences against phytopathogens in plants. The genome-wide identification and analysis of NBLRR genes have been performed in several species. However, the detailed evolution, structure, expression of NBLRRs and functional response to Magnaporthe grisea are unknown in finger millet (Eleusine coracana (L.) Gaertn.). Results: The genome-wide scanning of the finger millet genome resulted in 116 NBLRR (EcNBLRRs1-116) encompassing 64 CC-NB-LRR, 47 NB-LRR and 5 CCR-NB-LRR types. The evolutionary studies among the NBLRRs of five Gramineae species, viz., purple false brome (Brachypodium distachyon (L.) P.Beauv.), finger millet (E. coracana), rice (Oryza sativa L.), sorghum (Sorghum bicolor L. (Moench)) and foxtail millet (Setaria italica (L.) P.Beauv.) showed the evolution of NBLRRs in the ancestral lineage of the target species and subsequent divergence through gene-loss events. The purifying selection (Ka/Ks < 1) shaped the expansions of NBLRRs paralogs in finger millet and orthologs among the target Gramineae species. The promoter sequence analysis showed various stress- and phytohormone-responsive cis-acting elements besides growth and development, indicating their potential role in disease defence and regulatory mechanisms. The expression analysis of 22 EcNBLRRs in the genotypes showing contrasting responses to Magnaporthe grisea infection revealed four and five EcNBLRRs in early and late infection stages, respectively. The six of these nine candidate EcNBLRRs proteins, viz., EcNBLRR21, EcNBLRR26, EcNBLRR30, EcNBLRR45, EcNBLRR55 and EcNBLRR76 showed CC, NB and LRR domains, whereas the EcNBLRR23, EcNBLRR32 and EcNBLRR83 showed NB and LRR somains. Conclusion: The identification and expression analysis of EcNBLRRs showed the role of EcNBLRR genes in assigning blast resistance in finger millet. These results pave the foundation for in-depth and targeted functional analysis of EcNBLRRs through genome editing and transgenic approaches. [ABSTRACT FROM AUTHOR]

Rice blast is one of the most devastating biotic stresses that limits rice productivity. The North Eastern Hill (NEH) region of India is considered to be one of the primary centres of diversity for both rice and pathotypes of Magnaporthe grisea. Therefore, the present study was carried out to elucidate the genetic basis of leaf and neck blast resistance under Meghalaya conditions. A set of 80 diverse genotypes (natural population) and 2 F2 populations involving resistant parent, a wildtype landrace, LR 5 (Lal Jangali) and susceptible genotypes Sambha Mahsuri SUB 1 (SMS) and LR 26 (Chakhao Poireiton) were used for association analysis of reported major gene-linked markers with leaf and neck blast resistance to identify major effective genes under local conditions. Genotyping using twenty-five gene-specific markers across diverse genotypes and F2 progenies revealed genes Pi5 and Pi54 to be associated with leaf blast resistance in all three populations. Genes Pib and qPbm showed an association with neck blast resistance in both natural and LR 5 × SMS populations. Additionally, a set of 184 genome-wide polymorphic markers (SSRs and SNPs), when applied to F2-resistant and F2-susceptible DNA bulks derived from LR 5 × LR 26, suggested that Pi20(t) on chromosome 12 is one of the major genes imparting disease resistance. Markers snpOS318, RM1337 and RM7102 and RM247 and snpOS316 were associated with leaf blast and neck blast resistance, respectively. The genotypes, markers and genes will help in marker-assisted selection and development of varieties with durable resistance.

In the traditional method of the bio-fabrication of zinc oxide nanoparticles (ZnONPs), bacterial strains face metal toxicity and antimicrobial action. In the current study, an alkalescent nucleoside antibiotic was mixed with zinc hexanitrate to fabricate the ZnONPs. An integrated approach of DIAION HP-20 macroporous resin and sephadex LH-20 column chromatography was adopted to separate and purify alkalescent nucleoside AN03 from Streptomyces koyanogensis. Alkalescent nucleoside was confirmed by the Doskochilova solvent system. The bio-fabricated ZnONPs were characterized by using Fourier transform infrared (FTIR), X-ray diffraction (XRD), and transmission electron microscopy (TEM) analyses. The XRD spectrum and the TEM images confirmed the crystallinity and the spherical shape of the ZnONPs with an average size of 22 nm. FTIR analysis showed the presence of functional groups, which confirmed the bio-fabrication of ZnONPs from alkalescent nucleoside ANO3. In-vitro studies showed that 75 μg/mL of ZnONPs had a strong inhibitory zone (28.39 mm) against the Magnaporthe grisea and significantly suppressed the spore germination. SEM and TEM observations respectively revealed that ZnONPs caused breakage in hyphae and could damage the cells of M. grisea. Greenhouse experiments revealed that the foliar spray of ZnONPs could control the rice blast disease by 98%. Results also revealed that ZnONPs had positive effects on the growth of the rice plant. The present study suggested that ZnONPs could be fabricated from microbe-derived nucleoside antibiotics without facing the problems of metal toxicity and antimicrobial action, thus overcoming the problem of pathogen resistance. This could be a potent biocontrol agent in rice blast disease management. [ABSTRACT FROM AUTHOR]

Rice blast, caused by Magnaporthe grisea , is one of the most destructive diseases of rice worldwide. Mefentrifluconazole, a novel isopropanol triazole fungicide, exhibits excellent bioactivity to a wide range of fungi. However, its antifungal activity against M. grisea is not well studied. In this study, the sensitivity of 103 M. oryzae strains to mefentrifluconazole was determined by mycelial growth rate method, and the effect of mefentrifluconazole on the biochemical and physiological characteristers was examined. The results indicated that mefentrifluconazole exhibited excellent inhibitory activity against M. oryzae with EC 50 values of 103 M. oryzae strains tested ranging from 0.363 to 1.576 μg/mL, and the average EC 50 value of 0.958 ± 0.298 μg/mL. After mefentrifluconazole treatment, the apical branches of M. oryzae mycelia increased and the mycelia became distorted, twisted and ruptured. In addition, mefentrifluconazole increased relative conductivity, disrupted cell wall and membrane integrity, and significantly reduced ergosterol content. The expression levels of demethylation inhibitor resistance-associated genes Cyp51A , ABC6 and MFS1 were all significantly upregulated, suggesting an adaption response to mefentrifluconazole of M. oryzae. Furthermore, the results of pot experiment showed that mefentrifluconazole provided >70 % control efficacy against rice blast at 300 μg/mL, surpassing the performance of carbendazim, prochloraz and azoxystrobin at the same concentration. Overall, this study demonstrated the strong inhibitory activity of mefentrifluconazole against M. oryzae and the excellent efficacy in controlling rice blast, thus providing new sights into rice blast control as well as the practical application of mefentrifluconazole. • Baseline sensitivity of Magnaporthe grisea to mefentrifluconazole was established. • Mefentrifluconazole affected the morphology of M. grisea. • Mefentrifluconazole destroyed cell wall and membrane. • Mefentrifluconazole provided excellent control efficacy against rice blast. [ABSTRACT FROM AUTHOR]

Simple Summary: Rice is often attacked by several herbivores and plant pathogens at the same time. Public research has mainly focused on enhancing rice resistance against these biotic stresses by selecting rice lines with resistance genes during breeding programs. However, rice resistance to biotic stresses is also affected by soil nutrients, including available nitrogen and silicon. Nitrogen tends to reduce resistance, but silicon can increase resistance. We assessed the effects of combining soil silicon with host plant resistance against rice planthoppers, blast disease, and bacterial blight disease. We used pure silicon (SiO2) to avoid the confounding effects of nutrients associated with silicates. We also assessed the effects of nitrogenous fertilizer on silicon-augmented resistance to planthoppers. We found that high nitrogen diminishes the capacity of soil silicon and host resistance to reduce planthopper fitness (i.e., nitrogen was antagonistic); but that silicon counters nitrogen-related reductions in rice antixenosis defenses (e.g., repellency) against gravid female planthoppers (i.e., an additive effect of silicon and resistance). Silicon augmented resistance against blast and bacterial blight, but the effects were most apparent on susceptible varieties. Plants infected with bacterial blight generally grew larger in silicon amended soils. We discuss how silicon improves seedling quality by augmenting broad-spectrum resistance. Soil silicon enhances rice defenses against a range of biotic stresses. However, the magnitude of these effects can depend on the nature of the rice variety. We conducted a series of greenhouse experiments to examine the effects of silicon on planthoppers (Nilaparvata lugens [BPH] and Sogatella furcifera [WBPH]), a leafhopper (Nephotettix virescens [GLH]), blast disease (Magnaporthe grisea) and bacterial blight (Xanthomonas oryzae) in susceptible and resistant rice. We added powdered silica gel (SiO2) to paddy soil at equivalent to 0.25, 1.0, and 4.0 t ha−1. Added silicon reduced BPH nymph settling, but the effect was negligible under high nitrogen. In a choice experiment, BPH egg-laying was lower than untreated controls under all silicon treatments regardless of nitrogen or variety, whereas, in a no-choice experiment, silicon reduced egg-laying on the susceptible but not the resistant (BPH32 gene) variety. Stronger effects in choice experiments suggest that silicon mainly enhanced antixenosis defenses. We found no effects of silicon on WBPH or GLH. Silicon reduced blast damage to susceptible and resistant (Piz, Piz-5 and Pi9 genes) rice. Silicon reduced damage from a virulent strain of bacterial blight but had little effect on a less virulent strain in susceptible and resistant (Xa4, Xa7 and Xa4 + Xa7 genes) varieties. When combined with resistance, silicon had an additive effect in reducing biomass losses to plants infested with bacterial blight (resistance up to 50%; silicon 20%). We discuss how silicon-containing soil amendments can be combined with host resistance to reduce biotic stresses in rice. [ABSTRACT FROM AUTHOR]

Rice blast is a major threat to the rice crop in rice-growing areas around the globe. However, synthetic fungicides are injurious for the ecosystem and the existing bio-control agents facing the resistance from the pathogens. In this study, an isolated novel Streptomyces strain (TA-47), from the rice field was identified by culturing on different media, physiological tests, biochemical tests, chemo-taxonomy and molecular biological approaches. In-vitro and in-vivo bio-control activity of the isolated strain was evaluated. Growth on the media, spore production, utilization of sole carbon and nitrogen sources, presence of diaminopimelic acid (DAP) in the cell wall of the strain and fatty acid production were observed.16S rRNA (gene sequence) and a neighbour-joining hood tree indicated that the strain TA-47 is Streptomyces koyanogensis. In-vitro inhibition zone of 29 mm against the M. grisea showed the antagonistic potential of the novel strain TA-47. On the other hand, in the in-vivo studies, strain TA-47, showed the strong bio-control effect, as disease severity decreased to 19.66 ± 1.6%, while in the non-treated sample the disease severity was recorded as 44.66 ± 5.249%. Moreover, after the treatment of the strain, effects on the growth, such as increased height and root length by 72.22 and 16.54 cm, respectively, were also recorded. In conclusion, rhizosphere Streptomyces TA-47, was a novel Streptomyces koyanogensis strain. The study found that the strain had strong bio-control and growth-promoting abilities. Abbreviation: M Grisea, Magnaporthe grisea; ISP, International Streptomyces Project; PDA, Potato Dextrose AgarSEM, Scan Electron Microscope; TLC, Thin Layer Chromatography; GC-MS, Gas Chromatography Mass Spectrum

Rice blast (Magnaporthe grisea) is first reported in China and then in Africa in1922. The disease is now the most widespread and devastating rice disease in all rice producing areas of the world. The disease can cause from mild yield reduction to total crop loss as depends on the variety and severity level. The rice blast isolate is closely related to the isolate of other blast like fungus and distinctly described as Magnaporthe grisea. Rice blast fungus starts the infection cycle after a three-celled conidium lands on the rice leaf surface. Thousands of spores can be produced from a single lesion within 15 days after infection. Symptoms on leaves start as small brown necrotic lesions that evolve to larger elliptical or spindle-shaped lesions, colored whitish to gray with darker borders while infected seeds display brown spots, which may result from the infection of the florets as they matured into seeds. The rice blast needs at least a 12-hour period of moderate temperatures (25 to 30 °C), high relative humidity (90-92 %), and high moisture which are conducive for its development. The disease can be managed by using resistant varieties, using integrated disease management options and nutrient managements like application of recommended nitrogen fertilizers and application of silicon fertilizers. The rice plant responds differently for reducing the occurrence and damage of the disease either fungus is incapable causing sporulating lesions on the plant or the plant develop residual resistance that remains when complete resistance has been overcome by the pathogen. [ABSTRACT FROM AUTHOR]

Rice blast disease caused by Magnaporthe grisea (Hebert) Barr is a serious biotic stress causing worldwide yield loss in cultivated rice. As high as 75% to 100% crop damage has been recorded in India. The disease is manifested by the appearance of lesions of various colours, size and spore liberation ability. The pathogen also infects 50 other hosts including weeds and grasses as secondary hosts. Information on genetic diversity, host specificity and phenotypic characters of the pathogens needs to be explored for better management of the disease. Therefore, fourteen M. grisea isolates from rice host and six isolates from weed host Echinochloa colonum were collected from three locations of coastal Odisha. Culture studies revealed that most isolates from virulent lesions had both black colour mycelia and pigmentation (B/B pattern). All the twenty M. grisea isolated produced bigger conidia with size ranged from 21.1–33.0µm to 7.6–12.7µm (length and breadth). Isolates from virulent lesions produced higher number of conidia. Isolates from weed had long and slender type conidia. Molecular genetic studies based on repetitive element Pot2 and random amplified polymorphic DNA (RAPD) could separate isolates on the basis of host plant and virulence of source lesion. Isolates from weed were consistently placed in separate group where presence and absence of bands specific to this group were observed. Rep‐PCR based on Pot2 amplified polymorphic DNA fragments where bands at 1750bp were specific to isolates from weed. Similarly, amplification specific to weed isolates was obtained at 1200bp by primer OPB10 in RAPD PCR. Amplification at these base pairs may be used for the development of markers to distinguish M. grisea from rice and weed. This is the first report of utilization of rep‐PCR and RAPD to distinguish M. grisea among rice and Echinochloa colonum in this region. [ABSTRACT FROM AUTHOR]

Background: Seed borne endophytic fungi play an important role in seed germination and plant health. There are ubiquitous and have been found associated in every plant species investigated so far. They colonize plant seeds without causing any disease and are often vertically transmitted. Despite their occurrence, seed borne endophytic fungi are poorly investigated and their role for application in agriculture is still to be elucidated. Methods: In the present study endophytic fungi associated with seeds of some indigenous rice varieties of North East, India was investigated. The isolates were determined for IAA activity in-vitro and antifungal activity against rice pathogen, Magnaporthe grisea. Crude metabolites obtained from potent isolates were characterized by GCMS analysis to reveal the presence of bioactive compounds. Result: Our result indicated that commonly isolated fungal genera were Aspergillus, Fusarium, Gliocladium, Mucor, Penicillium, Bipolaris, Basidiobolus and Mycelia sterilia. Amongst them, colonization frequency (CF %) of Fusarium (8.8%) was found to be highest and was isolated from seeds of almost all the varieties. It was observed that four isolates of Fusarium showed good IAA production in the medium amended with tryptophan. The isolates also displayed antifungal activity against Magnaporthe grisea. GCMS analysis of the metabolites indicated presence of several bioactive compounds. The study suggests that seed borne endophytes can be explored as bio-inoculants for crop improvement in future research program. [ABSTRACT FROM AUTHOR]

Rice is the world's most important food crop as it provides nutrition to the two third of its population. The improvement in yield of this crop is challenged by several biotic and abiotic factors. Among the biotic stresses, rice blast is a serious production constraint for rice in Kashmir conditions. Keeping in view the above fact, an investigation was carried out at two locations viz, Anantnag and Pulwama using Randomised Block Design (RBD) with three replications during Kharif 2018-2019 to check the efficacy against leaf and neck blast disease of rice variety K-448 with Tricyclazole (75WP) 1g l-1, Hexaconazole (5EC) 2.5ml l-1 and Mancozeb (45WP) 1g l-1 as chemical fungicides, Trichoderma harzianum as biocontrol agent and leaf extracts of Datura stramonium and Cannabis sativa (15%) as botanicals in experimental plots. The treatments were applied three times in the field at tillering, booting and neck blast stages. Leaf and neck blast percent disease intensity and total yield were recorded using Standard Evaluation System for rice (SES 0-9). All the spray treatments proved effective and reduced leaf and neck blast intensity and significantly increased the yield parameters. Among all treatments, Tricyclazole (beam) was found significantly superior and recorded minimum leaf blast intensity (8.54%), neck blast intensity (21.20%) and remarkably significant increase in grain and straw yield (3303kgh-1 and 6001kgh-1). The next best treatment was T.harzianum which registered leaf blast intensity (13.06%) and (34.43%) neck blast intensity at both locations and was found statistically at par with Hexaconazole (14.17% and 36.94%) followed by Mancozeb (19.11% and 42.02%) and Datura stramonium (25.65% and 46.13%). Maximum leaf and neck blast (40.15% and 57.97%) was observed with Cannabis sativa leaf extract but showed numerically higher grain (2069 kg/ha) and straw yield (4509 kg/ha) as compared to untreated control. [ABSTRACT FROM AUTHOR]

Soil silicon enhances rice defenses against a range of biotic stresses. However, the magnitude of these effects can depend on the nature of the rice variety. We conducted a series of greenhouse experiments to examine the effects of silicon on planthoppers (Nilaparvata lugens [BPH] and Sogatella furcifera [WBPH]), a leafhopper (Nephotettix virescens [GLH]), blast disease (Magnaporthe grisea) and bacterial blight (Xanthomonas oryzae) in susceptible and resistant rice. We added powdered silica gel (SiO2) to paddy soil at equivalent to 0.25, 1.0, and 4.0 t ha−1. Added silicon reduced BPH nymph settling, but the effect was negligible under high nitrogen. In a choice experiment, BPH egg-laying was lower than untreated controls under all silicon treatments regardless of nitrogen or variety, whereas, in a no-choice experiment, silicon reduced egg-laying on the susceptible but not the resistant (BPH32 gene) variety. Stronger effects in choice experiments suggest that silicon mainly enhanced antixenosis defenses. We found no effects of silicon on WBPH or GLH. Silicon reduced blast damage to susceptible and resistant (Piz, Piz-5 and Pi9 genes) rice. Silicon reduced damage from a virulent strain of bacterial blight but had little effect on a less virulent strain in susceptible and resistant (Xa4, Xa7 and Xa4 + Xa7 genes) varieties. When combined with resistance, silicon had an additive effect in reducing biomass losses to plants infested with bacterial blight (resistance up to 50%; silicon 20%). We discuss how silicon-containing soil amendments can be combined with host resistance to reduce biotic stresses in rice.

Foliar blast disease in pearl millet (Pennisetum glaucum (L.) R. Br.) caused by Magnaporthe grisea once considered as a minor disease, has become major threat for pearl millet cultivation during recent decade in almost all pearl millet growing areas. The present study is an attempt to understand the inheritance of foliar blast resistance in pearl millet against the natural inoculum of Magnaporthe grisea and also against artificial inoculum of its devastating strain PMg_DI. The experiment was conducted at ICRISAT, Hyderabad and IARI, New Delhi during 2017-19. F2 and backcross populations derived from a susceptible genotype ICMB 95444 and two resistant lines PPMI-10018 and PPMI-2464 were used. Screening of individual plant in F1s, F2s, BCP1s (susceptible parent × F1) and BCP2s (resistant parent × F1) under field and controlled conditions indicated that the resistance is governed by a single dominant gene. The test of allelism was conducted by crossing the resistant parents. No segregation for resistance was observed in F2 generation when screened against the natural inoculum of Magnaporthe grisea and its strain PMg_DI. This indicates that both the resistant parents possess the same gene.

A principal doença da cultura do arroz é a brusone, causada pelo fungo Pyricularia grisea (Cooke) Sacc., que pode apresentar variabilidade genética tanto entre cepas isoladas de diferentes locais ou lesões quanto entre cepas oriundas de uma mesma lesão, indicando o potencial mutativo desse fungo. Por meio de Rep-PCR, baseada no elemento repetitivo Pot-2, foi levantada a variabilidade genética de 64 isolados de P. griseaoriginados de lesões de seis panículas de arroz ‘Epagri 108’. Não houve diferenças genéticas intralesão, porém houve varia bilidade genética interlesão para isolados de uma das panículas, que apresentaram três padrões moleculares distintos, indicando a coexistência, em um mesmo genótipo de arroz, de várias cepas do fungo. Isto pode ter implicações em levantamentos de ocorrência de raças, bem como em trabalhos de melhoramento genético da cultura do arroz para resistência à brusone.

Rice blast is a major threat to the rice crop in rice-growing areas around the globe. However, synthetic fungicides are injurious for the ecosystem and the existing bio-control agents facing the resistance from the pathogens. In this study, an isolated novel Streptomyces strain (TA-47), from the rice field was identified by culturing on different media, physiological tests, biochemical tests, chemo-taxonomy and molecular biological approaches. In-vitro and in-vivo bio-control activity of the isolated strain was evaluated. Growth on the media, spore production, utilization of sole carbon and nitrogen sources, presence of diaminopimelic acid (DAP) in the cell wall of the strain and fatty acid production were observed.16S rRNA (gene sequence) and a neighbour-joining hood tree indicated that the strain TA-47 is Streptomyces koyanogensis. In-vitro inhibition zone of 29 mm against the M. grisea showed the antagonistic potential of the novel strain TA-47. On the other hand, in the in-vivo studies, strain TA-47, showed the strong bio-control effect, as disease severity decreased to 19.66 ± 1.6%, while in the non-treated sample the disease severity was recorded as 44.66 ± 5.249%. Moreover, after the treatment of the strain, effects on the growth, such as increased height and root length by 72.22 and 16.54 cm, respectively, were also recorded. In conclusion, rhizosphere Streptomyces TA-47, was a novel Streptomyces koyanogensis strain. The study found that the strain had strong bio-control and growth-promoting abilities. [ABSTRACT FROM AUTHOR]

The fungal species contain diverse transposable elements and repetitive sequences up to ~10% of their genome. It has been reported that distribution of transposable elements tends to correlate with the host range of the pathogen. Moreover, transposable elements cause the loss of an avirulence gene in the pathogen, which resulted in disease on a resistance cultivar. Thus, the transposable elements in the fungal pathogens may be one of the key factors driving the plant-fungus interactive evolution. In this article, we reviewed classification and biological functions of transposable elements in Magnaporthe species.

In order to understand rice blast resistance gene patterns in rice landraces from Myanmar and Laos, we analysed the Pita, Pib, Pikh, Pi9 and Pi5 genes in 80 landraces through the use of functional molecular markers and functional fragment sequencing. These landraces were separated into four haplotypes (H1–H4) based upon three mutations identified in the Pita sequence. All four haplotypes were detected among landraces from Myanmar, whereas only the H1 and H2 haplotypes were detected among landraces from Laos. We additionally grouped landraces carrying 0–4 resistance genes into 18 genotypes based upon their resistance-susceptibility patterns and found that 16 of these genotypes were detected among Myanmar landraces at relative frequencies ranging from 2.50–12.50%, while 10 were detected among landraces from Laos at relative frequencies of 2.50–42.50%. The 'Pib(+) pikh(−) pi9(−) pi5(−) pita(−)' genotype was found to be dominant, accounting for 12.5 and 42.5% of landraces from Myanmar and Laos, respectively. The Pib, Pikh, Pi5 and Pita genes were detected in 52.50, 32.50, 37.50 and 30.00% of landraces from Myanmar respectively, whereas they were detected in 52.50, 12.50, 30.00 and 17.50% of landraces from Laos, respectively. The Pi9 gene was rarely detected among analysed landraces and was particularly rare in those from Laos. These findings suggest that rice landraces from Myanmar are more genetically diverse than those from Laos, with clear differences in blast resistance gene patterns between landraces from these two countries. [ABSTRACT FROM AUTHOR]

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This research took place at the Provincial Plant Sanitation Laboratory, in Camaguey, Cuba, between September 2013 and September 2015. The in vitro compatibility and antagonistic capacity of Trichoderma harzianum Rifai (strain A-34) on rice pathogens (Bipolaris oryzae Breda de Haan, Sarocladium oryzae (Sawada) w., Gams and D. Hawksworth and Magnaporthe grisea (Hebert Barr), was determined against pesticides used on rice. Assessment using traditional methods of microbiological isolation of mycelial growth, sporulation and conidial germination of the antagonist, to determine if the action mechanisms (antibiosis, competence, parasitism) against fungal pathogens, was made between 24 and 216 hours of application. A bifactorial design in dual culture was used for statistical analysis, along with scales for determination of microbial antagonistic capacity. Active ingredients tebuconazol + procloraz, trifloxistrobin+ ciproconazole, and epoxiconazole + kresoxim-methyl, affected mycelial growth of the antagonist. Moreover, the antagonist against active ingredients carbendazim, copper oxychloride, azoxystrobin and tebuconazo + triadimenol showed mycelial growth, sporulation and pathogen interaction, affecting their growth by means of coiling, penetration, granulation, and cell lysis, between 96 and 216 hours.

The probenazole fungicide is used for controlling rice blast (Magnaporthe grisea) primarily by inducing disease resistance of the plant. To investigate the mechanism of induced plant defense, rice seedlings were treated with probenazole at 15 days post emergence, and non-treated plants were used for the control. The plants were infected with M. grisea 5 days after chemical treatment and incubated in a greenhouse. After 7 days, rice seedlings were sampled. The metabolome of rice seedlings was chemically extracted and analyzed using gas chromatography and mass spectrum (GC-MS). The GC-MS data were processed using analysis of variance (ANOVA), principal component analysis (PCA) and metabolic pathway elucidation. Results showed that probenazole application significantly affected the metabolic profile of rice seedlings, and the effect was proportionally leveraged with the increase of probenazole concentration. Probenazole resulted in a change of 54 metabolites. Salicylic acid, γ-aminobutyrate, shikimate and several other primary metabolites related to plant resistance were significantly up-regulated and some metabolites such as phenylalanine, valine and proline were down-regulated in probenazole-treated seedlings. These results revealed a metabolic pathway of rice seedlings induced by probenazole treatment regarding the resistance to M. grisea infection.

Tolprocarb developed by Mitsui Chemicals Agro, Inc. (Tokyo, Japan) was discovered as a new oomycete fungicide. However, its antifungal spectrum and action mechanisms against fungi are completely different from those of the original compound, iprovalicarb. Tolprocarb has a potent and highly controlled effect on a rice blast fungus Magnaporthe grisea, and its mode of action was revealed to be the inhibition of polyketide synthase in the melanin biosynthesis pathway. In addition, tolprocarb induced systemic acquired resistance in Arabidopsis thaliana and rice (Oryza sativa L.). Owing to these double modes of action, tolprocarb can effectively control not only rice blast but also bacterial diseases, and has a low risk of developing fungicide-resistant isolates. Tolprocarb also provides long-term residual activity. A meta-analysis was performed in order to demonstrate tolprocarb's superior control against panicle blast in paddy fields. In addition, tolprocarb did not show cross-resistance against the fungi that are resistant to dehydratase inhibitor in melanin biosynthesis (Melanin Biosynthesis Inhibitor-Dehydratase; MBI-D) or respiratory complex III: cytochrome bc1 at Quinone outside site inhibitor (Quinone outside Inhibitor; QoI). Owing to its stable effects, tolprocarb appears to be a suitable choice for practical use against fungi in the rice production field. [ABSTRACT FROM AUTHOR]

La investigación se realizó en el Laboratorio Provincial de Sanidad Vegetal en Camagüey, en la etapa comprendida de septiembre de 2013 a septiembre de 2015, en condiciones in vitro donde se determinó la compatibilidad y capacidad antagónica frente a pesticidas usados en el arroz, de Trichoderma harzianum Rifai cepa A-34 sobre los patógenos del arroz (Bipolaris oryzae Breda de Haan, Saracladium oryzae (Sawada) w. Gams & D.Hawksworth y Magnaporthe grisea (Hebert) Barr). Las evaluaciones mediante métodos tradicionales de aislamiento microbiológico del crecimiento micelial, la esporulación y la germinación conidial del antagonista para determinar si ejerce los mecanismos de acción de antibiosis, competencia, y parasitismo ante los patógenos fúngicos se efectuaron a partir desde las 24 hasta las 216 horas empleando. Para el análisis estadístico se empleó un diseño bifactorial en el cultivo dual, además de las escalas para la determinación de la capacidad antagónica de los microorganismos. Los ingredientes activos tebuconazol + procloraz, trifloxistrobin+ ciproconazol, y epoxiconazol + kresoxim- metil, afectaron el crecimiento micelial del antagonista, por otra parte el antagonista frente a los ingredientes activos carbendazim, oxicloruro de cobre, azoxistrobina y tebuconazol + triadimenol tuvo crecimiento micelial, esporulación e interacción con los patógenos afectándose el crecimiento de los mismos a través de los mecanismos de acción de enrollamiento, penetración, granulación , y lisis celular desde las 96 hasta las 216 horas.

This research took place at the Provincial Plant Sanitation Laboratory, in Camaguey, Cuba, between September 2013 and September 2015. The in vitro compatibility and antagonistic capacity of Trichoderma harzianum Rifai (strain A-34) on rice pathogens (Bipolaris oryzae Breda de Haan, Sarocladium oryzae (Sawada) w., Gams and D. Hawksworth and Magnaporthe grisea (Hebert Barr), was determined against pesticides used on rice. Assessment using traditional methods of microbiological isolation of mycelial growth, sporulation and conidial germination of the antagonist, to determine if the action mechanisms (antibiosis, competence, parasitism) against fungal pathogens, was made between 24 and 216 hours of application. A bifactorial design in dual culture was used for statistical analysis, along with scales for determination of microbial antagonistic capacity. Active ingredients tebuconazol + procloraz, trifloxistrobin+ ciproconazole, and epoxiconazole + kresoxim-methyl, affected mycelial growth of the antagonist. Moreover, the antagonist against active ingredients carbendazim, copper oxychloride, azoxystrobin and tebuconazo + triadimenol showed mycelial growth, sporulation and pathogen interaction, affecting their growth by means of coiling, penetration, granulation, and cell lysis, between 96 and 216 hours.

El brusone del trigo causado por Magnaporthe grisea (T.T. Hebert) M.E. Barr (anamorfo Pyricularia grisea Sacc.), tuvo su primera epidemia en Paraguay en 2002, causando pérdidas de más del 70% en campos sembrados en la primera quincena de abril. Este hongo presenta una amplia gama de hospederos entre los cuales se destacan el arroz y el trigo, así como otras gramíneas cultivadas, nativas y malezas. Hasta el momento no se conocen los hospederos alternativos de este hongo en Paraguay o la importancia del inóculo procedente de los mismos para el cultivo del trigo. El objetivo de este estudio es identificar los posibles hospederos alternativos de Magnaporthe grisea en el Centro de Investigación Capitán Miranda, Itapúa, y en el Campo Experimental Yhovy, Canindeyú, durante los ciclos 2013 y 2014. Para ello, muestras de malezas, con síntomas característicos del ataque del hongo, fueron recolectadas en ambas localidades. Estas muestras fueron puestas en cámara húmeda y sembradas sobre medio de cultivo PDA, e incubadas durante 5 días a 25ºC en el laboratorio de Fitopatología del Centro de Investigación Hernando Bertoni, Caacupé. Posteriormente se realizó la identificación del hongo mediante observación al estereoscopio y microscopio. De las 21 especies recolectadas se constató la presencia del hongo en: Bromus catharticus, Brachiaria sp., Chloris gayana, Cyperus diffusus, Digitaria horizontalis y Lolium multiflorum. Así también se realizaron pruebas de patogenicidad con los aislados de Bromus catharticus, Digitaria horizontalis y Lolium multiflorum las cuales confirmaron la patogenicidad de dichos aislados sobre trigo.

To relieve the environmental pressure from overusing conventional pesticides formulations, the study of a new environmentally friendly and multifunctional formulation is so very urgent. Here, we firstly reported a lanthanum-modified chitosan oligosaccharide nanoparticles (Cos-La) prepared by a simple ionic cross-linking method to load avermectin (AVM). The loading capacity of AVM-loaded Cos-La was up to 46.3%. As a water-based formulation, Cos-La could effectively improve the persistence of AVM over 25% and reduce the photolysis rate of AVM around 20%. Furthermore, different concentrations of Cos-La were used to cultivate rice. The treated rice exhibited growth promotion effects in terms of plant height and fresh weight. With the increase in the treating concentration of Cos-La nanoparticles, the wettability of rice tended to reduce, which indicated it might lower the risk of plant diseases and pests. Further, Cos-La treated rice showed significant defense response for rice blast and the effect was two times more than equivalent Cos and LaCl 3 ·7H 2 O mixture solution. These results showed that Cos-La not only could improve the stability and persistence of pesticides, but also could effectively promote the growth and improve the disease resistance of crops. Cos-La nanoparticles would be a promising and environmentally friendly nanocarrier of pesticides in agricultural scenarios. [ABSTRACT FROM AUTHOR]

In the last few years resistance to azole fungicides has appeared in infected crops and has become more serious. Our aim was to analyse the reasons underlying the progressive decrease in the effectiveness of azole fungicides in controlling Magnaporthe grisea, the causal agent of rice blast. Forty-nine isolates of M. grisea were isolated from Hubei, Hunan, Jiangsu and Heilongjiang provinces in China. Their sensitivity to five sterol demethylation inhibitors, such as diniconazole, tebuconazole, triadimenol, triadimefon and propiconazole was measured. Three insensitive isolates (HM2, CY3 and CY6) and three hypersensitive isolates (CY8, YA10 and 101301) were characterised to elucidate the sensitivity mechanism to triazoles. Through a comparison of M13 fingerprinting, CYP51 sequences and expression, the results indicated that the genetic background of M. grisea isolates and CYP51 expression are conserved. However, the substitution of S312L in SRS4 of M. grisea CYP51F2 may contribute to the sensitivity difference of M. grisea to triazoles. [ABSTRACT FROM AUTHOR]

In order to find a natural alternative to the synthetic fungicides currently used against the devastating rice blast fungus, Magnaporthe grisea, this study explored the antifungal potential of citral and its mechanism of action. It was found that citral not only inhibited hyphal growth of M. grisea, but also caused a series of marked hyphal morphological and structural alterations. Specifically, citral was tested for antifungal activity against M. grisea in vitro and was found to significantly inhibit colony development and mycelial growth with IC50 and IC90 values of 40.71 and 203.75 μg/mL, respectively. Furthermore, citral reduced spore germination and germ tube length in a concentration-dependent manner. Following exposure to citral, the hyphal cell surface became wrinkled with folds and cell breakage that were observed under scanning electron microscopy (SEM). There was damage to hyphal cell walls and membrane structures, loss of villous-like material outside of the cell wall, thinning of the cell wall, and discontinuities formed in the cell membrane following treatment based on transmission electron microscopy (TEM). This increase in chitinase activity both supports the morphological changes seen in the hyphae, and also suggests a mechanism of action. In conclusion, citral has strong antifungal properties, and treatment with this compound is capable of causing significant damage to the hyphal cell walls of M. grisea.

Magnaporthe grisea is the causal agent of rice blast disease, which is the most serious disease of cultivated rice. Aromatic polyketides are its typical metabolites and are involved in the infection process. In the search for novel lead compounds, chemical investigation of the fungus M. grisea M639 has led to the isolation of four new aromatic polyketides (salicylaldehyde skeleton bearing an unsaturated side chain), griseaketides A−D (1−4), as well as 15 known compounds (5−19). The structures of the new compounds were elucidated on the basis of extensive spectroscopic analyses, including HR-MS, 2D NMR. Compound 12 showed prominent activity that killed 94.5% of C. elegans at 400 ppm and 66.9% at 200 ppm over 24 h. This is the first report describing the nematicidal activity of this type aromatic polyketide.

Blast disease caused by the fungus, Magnaporthe grisea, is among the most damaging diseases of rice and ragi leading to heavy crop losses worldwide. To avoid losses, farmers resort to indiscriminate applications of plant protection chemicals that also harm the ecosystem and lead to resistance buildup in the phytopathogens. Therefore, alternative eco-friendly strategies need to be evolved and put in place. The present study was thus undertaken to identify competent rhizobacteria having promising biocontrol activity against M. grisea infecting ragi. A total of 70 rhizospheric pseudomonads were isolated from different annual plants, of which 10 isolates showed maximum inhibition of two test isolates of M. grisea. Pseudomonas fluorescens isolate Pf-30 exhibited maximum inhibition (81.25 and 88.43 %) against the test pathogen, followed by Pf-53. Of all, 19 isolates were prominent in chitinase production with Pf-30 showing maximum efficiency (218.18 %) for enzyme production. In general, 25 °C temperature and pH 5.0 were optimum for enzymatic activity, although maximum activity (15.42 IU ml) by Pf-30 was recorded at pH 6.5 and 35 °C, followed by Pf-53 (4.48 IU ml). In- planta evaluation in polyhouse revealed that different pseudomonads could suppress the disease significantly when given as seed treatment and foliar spray. Maximum disease suppression was exhibited by Pf-47 and Pf-53 (82.77 and 82.06 %, respectively). Effect of three-factor (pathogen, variety, and pseudomonads) interaction revealed that all interactions, except pathogen x variety, contributed significantly. [ABSTRACT FROM AUTHOR]

Genetic diversity among 26 rice genotypes was investigated using RAPD markers. The genotypes were screened for the leaf blastdisease reaction at two different environments. The average number of alleles amplified per primer was 9.03. Average number ofpolymorphic bands per primer was 6.80 with average polymorphism information content (PIC) of 0.264. Clustering based ondendrogram revealed two major clusters and 5 sub clusters. Principal Coordinate Analysis (PCoA) revealed three major groups.The first coordinate does not discriminate any of the genotypes based on the geographical origin, but the second and thirdcoordinates differentiated South East Asian and South Asian genotypes clearly. Genetic diversity analysis of rice genotypes withRAPD marker system and phenotypic screening for blast resistance revealed that White Ponni (susceptible) and Moroberekan(resistant) were one among the genetically distant and contrasting parents for leaf blast resistance. There is no cleardiscrimination of the markers to distinguish leaf blast resistant and susceptible genotypes into separate clusters by the principalcoordinate analysis.

In order to screen novel inhibitors against Magnaporthe grisea, substituted 2-nitro-1- arylethylene (2) and substituted 2-bromo-2-nitro-1-arylethylene derivatives (3) were rationally designed and synthesized based on the structural information of 1,3,8-trihydroxynaphthalene reductase (3HNR).In addition, Inhibition assay for 3HNR and antifungal activity to M. grisea are done, furthermore, the probable binding mode of 3HNR and target compound was analyzed by using Molecular Docking method. Results showed that most of target compounds possessed high inhibitory activity against 3HNR (IC50 < 5.0 μmol/L). In comparison, compounds 3a and 3b showed the highest inhibitory activity (IC50 = 0.53 μmol/L). Most of the compounds exhibited certain antifungal activity to M. grisea at 50 μg/mL, the inhibition rate of 2e, 3a and 3b exceeded 96%. Compound 3a and 3b exhibited excellent antifungal activity against M. grisea (EC50 = 16.4 μg/mL for 3a, EC50 = 11.6 μg/mL for 3b, respectively). Analysis result of Molecular Docking method indicated that nitrostyrene compounds showed strong interactions with 3HNR from M. grisea. The hydrogen bonds between the Br atoms of the compound 3 and two hydroxyl groups, separately from Tyr223 and Tyr178 of 3HNR explain the excellent inhibitory activity of compound 3. [ABSTRACT FROM AUTHOR]

1,3,8-Trihydroxynaphthalene reductase (3HNR) is an essential enzymes that is involved in fungal melanin biosynthesis. Based on the structural informations of active site of 3HNR, a series of β-nitrostyrene compounds were rationally designed and synthesized. The enzymatic activities of these compounds showed that most of them exhibited high inhibitory activities (<5.0 μM) against 3HNR; compound 3-2 exhibit the highest inhibitory activity (IC 50 = 0.29 μM). In particular, some of these compounds had moderate fungicidal activity against Magnaporthe grisea. Compound 3-4 showed high in vivo activities against M. grisea (EC 50 = 9.5 ppm). Furthermore, compound 3-2 was selected as a representative molecule, and the probable binding mode of this compound and the surrounding residues in the active site of 3HNR was elucidated by using molecular dock. The positive results suggest that β-nitrostyrene derivatives are most likely to be promising leads toward the discovery of novel agent of rice blast. [ABSTRACT FROM AUTHOR]

In order to study the effects of different physiological races of rice blast fungus on different resistance of rice materials of different yield traits, the sundry physiologic races of spores of Magnaporthe grisea were used to inoculate the restore line R725, R720 and R727 at booting stage of rice. The results showed that each of the physiological races of rice blast fungus could cause reduction of rice output. Among them, ZA5 had the greatest effect on the R725; ZC8 had the greatest effect on the R720; ZA17 had the greatest effect on R727. Multi factor regression equation showed that after inoculating the Magnaporthe grisea, setting percentage and 1000 grain weight was a major factor limiting the yield of rice. [ABSTRACT FROM AUTHOR]

Rice blast is considered the most devastating disease worldwide; since it is widely distributed, it affects the aerial parts of rice plants, reducing agricultural yields significantly, besides constituting a serious constraint to production. Knowing this antecedent, this work was developed for two years, with the aim of selecting resistant rice cultivars against Magnaporthe grisea Barr (Pyricularia grisea Sacc) with good agronomic performance, to be further used as progenitors in rice breeding programs. Results showed a significant interaction among genotype, location and year of cultivars against blast and yield. The usefulness of Biplot analysis was confirmed for selecting stable cultivars according to their proximity to the origin of coordinates, as well as those responsible for the significant genotype-environment interaction. Four cultivars were classified as more stable to rice blast resistance: '2077', 'IR 759-54-2-2', 'Tetep' and 'Moroberekan', and six cultivars for agricultural yield: 'Amistad'82', 'INCA LP-1', 'INCA LP-6', '6066', 'CP1C8' and 'IR 1529-430', characteristics that let them be used as progenitors for crosses in rice breeding programs of Cuba. [ABSTRACT FROM AUTHOR]

Although quantitative trait loci (QTL) underpin many desirable agronomic traits, their incorporation into crop plants through marker-assisted selection is limited by the low predictive value of markers on phenotypic performance. Here we used candidate defense response (DR) genes to dissect quantitative resistance in rice using recombinant inbred (RI) and advanced backcross (BC) populations derived from a blast-resistant cultivar, Sanhuangzhan 2 (SHZ-2). Based on DNA profiles of DR genes, RI lines were clustered into two groups corresponding to level of resistance. Five DR genes, encoding putative oxalate oxidase, dehydrin, PR-1, chitinase, and 14-3-3 protein, accounted for 30.0, 23.0, 15.8, 6.7, and 5.5% of diseased leaf area (DLA) variation, respectively. Together, they accounted for 60.3% of the DLA variation and co-localized with resistance QTL identified by interval mapping. Average phenotypic contributions of oxalate oxidase, dehydrin, PR-1, chitinase, and 14-3-3 protein in BC lines were 26.1, 19.0, 18.0, 11.5, and 10.6%, respectively, across environments. Advanced BC lines with four to five effective DR genes showed enhanced resistance under high disease pressure in field tests. Our results demonstrate that the use of natural variation in a few candidate genes can solve a long-standing problem in rice production and has the potential to address other problems involving complex traits.

Com o objetivo de identificar as raças fisiológicas de Pyricularia grisea que ocorrem em Minas Gerais, coletaram-se 23 amostras de folhas de arroz com sintomas da brusone em 15 municípios representativos do estado. Foram obtidos 138 isolados, oriundos das 23 amostras, sendo duas lesões por amostra e três monospóricas por lesão. Os 138 isolados foram inoculados na série Internacional de diferenciadoras e as raças, determinadas utilizando-se uma escala visual de notas de 0 a 9. Foram identificadas as raças IA-1, IA-9, IA-10, IA-13, IA-65, IA-73, IB-1, IB-9, IB-15, IB-41, IB-64, IC-9, IC-14, IC-16. A raça predominante foi a IA-9 em 41,18% dos isolados, seguida pela IA-1 em 18,37% e IB-9 em 16,92%.Diferentes raças fisiológicas de P. grisea foram identificadas nos isolados provenientes de uma única lesão, indicando alta variabilidade do fungo.With the objective of identifying the physiological races of Pyricularia grisea which occur in Minas Gerais, samples of rice leaves with blast lesions were collected from 15 locations. Three single spore isolates from each one of the two lesions obtained from 23 samples were analyzed. Races were identified according to the reaction pattern on eight standard international differentials utilizing the visual rating scale of 0 to 9. Races IA-1, IA-9, IA-10, IA-13, IA- 65, IA-73, IB-1, IB-9 IB-15, IB-1, IB-64, IC-9, IC-14, IC-16 were identified. The predominant race IA-9 was identified in 41.18% of the isolates , followed by IA-1 in 18.37% and IB-9 in 16.92%. Different physiological races of P. grisea were identified from isolates obtanied from a single lesion indicating high variability of the fungus.

Este trabalho teve como objetivos determinar as perdas na produtividade de arroz causadas pela brusone (Pyricularia grisea) e estabelecer as relações entre a severidade da doença e alguns componentes de produtividade, nas condições naturais de infecção no campo. Foram realizados dois experimentos em solos de cerrado, com e sem irrigação suplementar, com as cultivares melhoradas de arroz de terras altas (Bonança, Canastra, Caiapó e Primavera). O método de regressão múltipla foi utilizado, incluindo severidade de brusone nas folhas e de brusone nas panículas como variáveis independentes e produtividade como variável dependente, para estimativa das perdas na produtividade. No experimento com irrigação suplementar, a severidade de brusone nas folhas não contribuiu para variação da produtividade. No experimento sem irrigação, a perda média na produtividade das quatro cultivares, estimada com base na equação de regressão, foi de 59,6%, considerando as médias de 33,6% e 49,9% de brusone nas folhas e panículas, respectivamente. A perda estimada em biomassa, causada pela brusone nas folhas, foi de 28,6%. As relações entre severidade de brusone nas panículas e a porcentagem de espiguetas vazias foram lineares e positivas e resultaram em 5,0% e 43,9% de perdas, nos experimentos com e sem irrigação, respectivamente. A brusone nas panículas reduziu a massa de 100 grãos em 5,9% no experimento irrigado e em 47,8% no experimento não irrigado.

A adubação silicatada constitui uma das alternativas para diminuir o uso de fungicidas no controle da brusone em arroz. Foi realizado um experimento, durante 1999/2000 e repetido durante 2000/2001, com o objetivo de estudar a eficiência relativa de fontes de silício (Si) na redução da severidade da brusone nas folhas da cultivar Metica-1, em área de várzea. Os tratamentos foram três fontes de Si (silicato de alto forno; serpentinito, minério rico em Si e wollastonita, um metasilicato de cálcio natural), em cinco doses (0, 0,5, 1,0, 2,0 e 4,0 Mg ha-1) sem tratamento das sementes ou com tratamento das sementes com o fungicida pyroquilon 200 g de i.a. por 100 kg. A severidade da brusone diminuiu significativamente com o aumento de doses de silício. As relações entre a área sob curva de progresso da doença e as doses, tanto do silicato de alto forno quanto da wollastonita, foram lineares e negativas, com ou sem tratamento de sementes, em ambos os anos do experimento. Os resultados revelam o aumento da eficiência do tratamento das sementes com fungicida na redução da brusone nas folhas com a fertilização silicatada.Silicon fertilization of rice is one of the alternatives for reducing the use of fungicides in the control of rice blast. An experiment was conducted, during 1999/2000 and repeated in 2000/2001, in order to study the efficiency of sources of silicon (Si) to reduce leaf blast on rice cultivar Metica-1, cultivated in the low land. The treatments included three sources of Si (high furnace silicate slag, serpentinite ore rich in silicon and wollastonite ore, a native calcium metasilicate) at five doses (0, 0.5, 1.0, 2.0 and 4.0 Mg ha-1), with and without fungicide treatment (pyroquilon 200 g a.i. per 100 kg of seed). The blast disease severity decreased with increase in Si doses. The relationship between area under disease progress curve and doses of silicate slag as well as wollastonite were linear and negative, with and without seed treatment. Furthermore, the results show the increased efficiency of seed fungicide treatment in reducing blast severity, with silicon fertilization.