Academic literature on the topic 'Magnaporthe oryzae B. Couch'

Commercial rice crops (Oryza sativa L.) have been recently reintroduced to the Ord River Irrigation Area in northern Western Australia. In early August 2011, unusual leaf spot symptoms were observed by a local rice grower on rice cultivar Quest. A leaf spot symptom initially appeared as grey-green and/or water soaked with a darker green border and then expanded rapidly to several centimeters in length and became light tan in color with a distinct necrotic border. Isolations from typical leaf lesions were made onto water agar, subcultured onto potato dextrose agar, and maintained at 20°C. A representative culture was lodged in the Western Australian Culture Collection Herbarium, Department of Agriculture and Food Western Australia (WAC 13466) and as a herbarium specimen in the Plant Pathology Herbarium, Plant Biosecurity Science (BRIP 54721). Amplification of the internal transcribed spacer (ITS)1 and (ITS)2 regions flanking the 5.8S rRNA gene were carried out with universal primers ITS1 and ITS4 (4). The PCR products were sequenced and BLAST analyses used to compare sequences with those in GenBank. The sequence had 99% nucleotide identity with the corresponding sequence in GenBank for Magnaporthe oryzae B.C. Couch, the causal agent of rice blast, the most important fungal disease of rice worldwide (1). Additional sequencing with the primers Bt1a/Bt1b for the β-tubulin gene, primers ACT-512F/ACT-783R for the actin gene, and primers CAL-228F/CAL-737R for the calmodulin gene showed 100% identity in each case with M. oryzae sequences in GenBank, confirming molecular similarity with other reports, e.g., (1). The relevant sequence information for a representative isolate has been lodged in GenBank (GenBank Accession Nos. JQ911754 for (ITS) 1 and 2; JX014265 for β-tubulin; JX035809 for actin; and JX035808 for calmodulin). Isolates also showed morphological similarity with M. oryzae as described in other reports, e.g., (3). Spores of M. oryzae were produced on rice agar under “black light” at 21°C for 4 weeks. Under 30/28°C (day/night), 14/12 h (light/dark), rice cv. Quest was grown for 7 weeks, and inoculated by spraying a suspension 5 × 105 spores/ml onto foliage until runoff occurred. Inoculated plants were placed under a dark plastic covering for 72 h to maximize humidity levels around leaves, and subsequently maintained under >90% RH conditions. Typical symptoms of rice blast appeared within 14 days of inoculation and were as described above. Infection studies were successfully repeated and M. oryzae was readily reisolated from leaf lesions. No disease symptoms were observed nor was M. oryzae isolated from water-inoculated control rice plants. There have been previous records of rice blast in the Northern Territory (2) and Queensland, Australia (Australian Plant Pest Database), but this is the first report of M. oryzae in Western Australia, where it could potentially be destructive if conditions prove conducive. References: (1) B. C. Couch and L. M. Kohn. Mycologia 94:683, 2002; (2) J. B. Heaton. The Aust. J. Sci. 27:81, 1964; (3) C. V. Subramanian. IMI Descriptions of Fungi and Bacteria No 169, Pyricularia oryzae, 1968; (4) T. J. White et al. PCR Protocols: A Guide to Methods and Applications. M. A. Innis et al., eds. Academic Press, New York, 1990.

A field study was conducted during Kharif-2015 and 2016 on management of leaf and neck blast disease of rice caused by Magnaporthe oryzae under hill rice ecosystem. Different treatments including biological control agents like Trichoderma sp. and Pseudomonas sp. and chemical fungicides like tricyclozole, azoxystrobin and carbendazim were used at different growth stages of rice. Among the treatments, tricyclozole @ 0.06% was highly effective followed by azoxystrobin @ 0.1% with application immediately after appearance of disease. Trichoderma and Pseudomonas were not effective in reducing the disease pressure. Bangladesh J. Bot. 50(3): 713-716, 2021 (September)

Guinea grass (Panicum maximum Jacq.) is an important C-4 perennial herbage in the southern part of Japan. In February 2002, a blast disease was found on the grass cultivated on the Okinawa Islands, the southern most region of Japan. Early symptoms appeared as small, round or ellipsoid lesions on leaves. Lesions later expanded to 2 to 5 × 1 to 2 mm and were spindle shaped and grayish white in the central area with dark brown margins. We obtained three single-conidia isolates of a Pyricularia-like fungus from the lesions and deposited them in the NIAS Genebank, Japan as MAFF306662, 306671, and 306672. The isolates were grown under near-UV light on V8 juice agar for 7 days to produce conidia, and guinea grass plants of the seven- to eight-leaf stage grown from seeds in a green house, five plants for each isolate, were inoculated by atomizing them with the conidial suspension of 105 conidia/ml. The same number of plants sprayed with sterilized distilled water served as the control. The experiments were repeated twice. All plants were covered with plastic bags for 24 h at 25°C to maintain high relative humidity. After 7 days, all inoculated plants showed symptoms identical to those observed in the field. Controls remained symptom free. The Pyricularia-like fungus was reisolated from lesions on inoculated leaves. The morphologies of the isolates were observed and described from the colonies grown under the condition described above. Conidiophores were pale brown, emerging singly or in small groups, straight or flexuous, geniculate toward the apex, and 36 to 197 × 2 to 5 μm. Conidia were obpyriform, straight, colorless to pale brown, smooth, and 19 to 30 × 5 to 10 μm with two to three septa. The morphologies were the same as those of the description of the genus Pyricularia. Previously, all Pyricularia isolates from Gramineae had been identified as P. grisea, except for those from rice (3,4). However, a new taxonomy of Pyricularia spp. based on DNA analyses was proposed by Couch and Kohn (1). Only the isolates from Digitaria were classified as P. grisea and those from C-3 grasses classified as P. oryzae. However, the species names for the isolates from the other C-4 grasses were not described. We analyzed the sequences of the rDNA-ITS region (ITS1-5.8s-ITS2) and β-tubulin gene of the isolates from guinea grass following Couch and Kohn (1). The sequences of rDNA-ITS (GenBank Accession No. AB512785) and β-tubulin (AB512786) of the isolate MAFF306672 matched the sequences of those of the Pyricularia sp. LS-group (AB274426 and AB274458, respectively) isolated from Leersia oryzoides. Hirata et al. (2) reclassified Pyricularia isolates from Gramineae by multilocus phylogenetic analysis and showed that non-P. oryzae and non-P. grisea isolates could be classified into two groups of the Pyricularia sp., a LS- and a CE-group, corresponding to those isolated from Leersia spp. and Setaria spp. or Cenchrus spp. of grasses, respectively. Since no Magnaporthe teleomorph was produced by the crossing tests using the isolates, we identified the isolates from guinea grass as the Pyricularia sp. LS-group on the basis of their morphology and the molecular phylogenetic analysis. To our knowledge, this is the first report of blast on guinea grass in Japan. References: (1) B. C. Couch and L. M. Kohn. Mycologia 94:683, 2002. (2) K. Hirata et al. Mycol. Res. 111:799, 2007. (3) K. D. Hyde. Australas. Plant Pathol. 22:73, 1993. (4) R. Sprague. Diseases of Cereals and Grasses in North America. Ronald Press Company, New York, 1950.

Magnaporthe oryzae, the fungus that causes rice blast, is the most destructive pathogen of rice worldwide. A number of M. oryzae mycoviruses have been identified. These include Magnaporthe oryzae. viruses 1, 2, and 3 (MoV1, MoV2, and MoV3) belonging to the genus, Victorivirus, in the family, Totiviridae; Magnaporthe oryzae. partitivirus 1 (MoPV1) in the family, Partitiviridae; Magnaporthe oryzae. chrysovirus 1 strains A and B (MoCV1-A and MoCV1-B) belonging to cluster II of the family, Chrysoviridae; a mycovirus related to plant viruses of the family, Tombusviridae (Magnaporthe oryzae. virus A); and a (+)ssRNA mycovirus closely related to the ourmia-like viruses (Magnaporthe oryzae. ourmia-like virus 1). Among these, MoCV1-A and MoCV1-B were the first reported mycoviruses that cause hypovirulence traits in their host fungus, such as impaired growth, altered colony morphology, and reduced pigmentation. Recently we reported that, although MoCV1-A infection generally confers hypovirulence to fungi, it is also a driving force behind the development of physiological diversity, including pathogenic races. Another example of modulated pathogenicity caused by mycovirus infection is that of Alternaria alternata chrysovirus 1 (AaCV1), which is closely related to MoCV1-A. AaCV1 exhibits two contrasting effects: Impaired growth of the host fungus while rendering the host hypervirulent to the plant, through increased production of the host-specific AK-toxin. It is inferred that these mycoviruses might be epigenetic factors that cause changes in the pathogenicity of phytopathogenic fungi.

Understanding the toxic effect of Magnaporthe oryzae on rice to breed resistant varieties is important for environment protection. The effects of four M. Oryzae physiological races were conducted on the photosynthesis and photosynthetic pigment contents relating to hybrid rice. The results suggest that Pn、E、chl a/chl b and Car content at all growth stages, Ci and Gs at tillering stage, the content of Chl a, Chl b, Chl (a+b) at tillering stage and jointing stage are decreased significantly by the M. oryzae toxins , while Ci and Gs at jointing stage and booting stage, the content of Chl a, Chl b and Chl (a+b) at booting stage show a significant increase in their values. Photosynthesis of rice are inhibited by stomatal and non-stomatal factors in rice treated by M. Oryzae toxins. The response of rice at different growth stages is statistically different for various M. Oryzae physiological races.

Correction for ‘Effects of UV-B radiation on the infectivity of Magnaporthe oryzae and rice disease-resistant physiology in Yuanyang terraces’ by Xiang Li et al., Photochem. Photobiol. Sci., 2018, 17, 8–17.

Rice yield is greatly reduced owing to rice blast, a polycyclic fungal disease caused by the ascomycete Magnaporthe oryzae. Previously, Bacillus cereus HS24, isolated from a rice farm, showed a strong antimicrobial effect toward M. oryzae. To better exploit it as a biocontrol agent, HS24 was studied for the mechanism that it uses to suppress rice blast. Conidium germination in M. oryzae was significantly inhibited by HS24, whereby inhibition reached 97.8% at the concentration of 107 CFU/ml. The transcription levels of Ca2+/calmodulin-dependent protein kinase II, PMC1, and CCH1, key genes involved in the M. oryzae Ca2+ signaling pathway, were significantly decreased in HS24-treated conidia at high concentration. The treatment of M. oryzae with the corresponding Ca2+ signaling pathway inhibitors KN-93, verapamil, and cyclopiazonic acid significantly reduced conidium germination. This inhibitory effect was found to be concentration dependent, similar to the HS24 treatment. We also found that HS24 was able to decrease the intracellular free Ca2+ concentration in M. oryzae conidia significantly. The addition of exogenous Ca2+ did not diminish the inhibitory effect of HS24 on the reduction of intracellular free Ca2+ concentration and the level of conidium germination. In conclusion, B. cereus HS24 at high concentration prevents extracellular Ca2+ from entering the conidia in M. oryzae, causes a significant reduction of intracellular free Ca2+ concentration, and results in the inhibition of conidium germination.

Wheat blast, caused by Magnaporthe oryzae, is an important disease across central and southern Brazil. Control has relied mainly on strobilurin fungicides (quinone-outside inhibitors [QoIs]). Here, we report the widespread distribution of QoI resistance in M. oryzae populations sampled from wheat fields and poaceous hosts across central and southern Brazil and the evolution of the cytochrome b (cyt b) gene. Sequence analysis of the cyt b gene distinguished nine haplotypes, with four haplotypes carrying the G143A mutation associated with QoI resistance and two haplotypes shared between isolates sampled from wheat and other poaceous hosts. The frequency of the G143A mutation in the wheat-infecting population increased from 36% in 2005 to 90% in 2012. The G143A mutation was found in many different nuclear genetic backgrounds of M. oryzae. Our findings indicate an urgent need to reexamine the use of strobilurins to manage fungal wheat diseases in Brazil.

The development of new cultivars better adapted to specific growing conditions is a key strategy to meet an ever-increasing growing global food demand and search for more sustainable cropping systems. This is even more crucial in the context of a changing climate. Ecophysiological models and advanced computational techniques (e.g., sensitivity analysis, SA) represent powerful tools to analyze genotype (G) by environment (E) interactions, thus supporting breeders in identifying key traits for specific agro-environmental contexts. However, limits for the effective use of mathematical models within breeding programs are represented by the uncertainty in the distribution of plant trait values, the lack of processes dealing with resistance/tolerance traits in most ideotyping studies, the partial suitability of current crop models for ideotyping purposes, and the absence of modelling tools directly usable by breeders. The aim of this research was to address these issues improving methodologies already in use, proposing new paradigms for the development of crop models explicitly targeting ideotyping applications and developing tools that would encourage a deep interaction of the modelling and breeding communities. The focus was on rice, for its role as staple food for more than a half of world’s population, and on resistance/tolerance traits to biotic/abiotic stressors, for their central role in increasing crop adaptation. Moreover, current conditions and climate change projections were considered, to support the definition of strategies for breeding in the medium-long term. A standard procedure to quantify − and manage − the impact of the uncertainty in the distribution of plant trait values was developed, using the WARM rice model and the Sobol’ method as case study. The approach is based on a SA (generating sample of parameter distributions) of a SA (generating samples of parameters for each generated distribution) using distributions of jackknife statistics calculated on literature values to reproduce the uncertainty in defining parameters distributions. As a practical implication, the procedure developed allows identifying plant traits whose uncertainty in distribution can alter ideotyping results, i.e., traits whose distributions could need to be refined. Global SA was then used to identify rice traits putatively producing the largest yield benefits in five contrasting districts in the Philippines, India, China, Japan and Italy. The analysis involved phenotypic traits dealing with light interception, photosynthetic efficiency, tolerance to abiotic stressors, resistance to fungal pathogens and grain quality. Results suggested that breeding for traits involved with disease resistance and tolerance to cold- and heat-induced spikelet sterility could provide benefits similar to those obtained from improving traits affecting potential yield. Instead, advantages resulting from varying traits involved with grain quality were markedly frustrated by inter-annual weather variability. Since results highlighted strong G×E interactions, a new index to derive district-specific ideotypes was developed. Given the key role of biotic/abiotic stressors in determining actual yield and the deep impact of related G×E interactions, a study was carried out by explicitly focusing on the definition of rice ideotypes improved for their resistance to fungal pathogens and tolerance to abiotic constraints (temperature shocks inducing sterility). The analysis was carried out at district level with a high spatial resolution (5 km × 5 km elementary simulation unit), targeting the improvement of the most representative 34 varieties in six Italian rice districts. Genetic improvement was simulated via the introgression of traits from donor varieties. Results clearly showed that breeders should focus on increasing resistance to blast disease, as this appears as a factor markedly limiting rice yields in Italy, regardless of the districts and climate scenarios, whereas benefits deriving from improving tolerance to cold-induced sterility could be markedly affected by G×E interactions. To reduce the risk of discrepancies between in silico ideotypes and their in vivo realizations, both studies involved only model parameters with a close relationship with phenotypic traits breeders are working on. However, a long-term strategy to overcome limitations related with the partial suitability of available models would be building new ideotyping-specific models explicitly around traits involved in breeding programs. This proposal for a paradigm shift in model development was illustrated taking salt stress tolerance and rice as a case study. Dedicated growth chamber experiments were conducted to develop a new model explicitly accounting for tolerance traits modulating Na+ uptake and distribution in plant tissues, as well as the impact of the accumulated Na+ on photosynthesis, senescence and spikelet sterility. An ideotyping study was conducted at two sites (in Greece and California) characterized by different seasonal dynamics of salinity in field water. Results showed how, under different scenarios, traits assuring the largest contribution to the overall tolerance could refer to completely different physiological mechanisms: tissue tolerance in one case, sodium exclusion in the other. This encourages the development of explicit trait-based approaches to increase the integration of crop models within breeding programs. A parallel path to achieve this goal is the development of modelling platforms targeting breeders as final users, who does not have necessarily in-depth skills in crop modelling and IT. The platform ISIde, derived from a close collaboration between target users, biophysical modelers and IT specialists, represents the first prototype of a platform specifically developed for being used directly by breeders to evaluate in silico improved varieties at district level. This thesis demonstrated the usefulness of simulation models for the definition of ideotypes for specific agro-environmental conditions. Targeting ideotyping applications, new methodologies, paradigms for model development and modelling tools were developed, thus contributing to improve the potential of crop modelling to support breeding programs. Future developments will target researches aimed at overcoming the limits behind this study, i.e., (i) absence of explicit interactions between traits, (ii) no adaptation strategies considered, and (iii) lack of approaches for the simulation of the evolutionary potential of pathogens in response to long-term climate variations and increased host resistance.