Magnaporthe Research Articles

Rice blast forecasting models and their practical value: a review

Rice, after wheat, is the second largest cereal crop, and is the most consumed major staple food for more people than any other crop. Rice blast (caused by Pyricularia oryzae, teleomorph Magnaporthe grisea ) is the most destructive of all rice diseases, causing multi-million dollar losses every year. Chemical control of this disease remains the most effective rice blast management method. Many attempts have been made to develop models to forecast rice blast. A review of literature of the rice blast forecasting models revealed that 52 studies have been published, with the majority capable of predicting only leaf blast. The most frequent input variable has been air temperature, followed by relative humidity and rainfall. Critical factors for the pathogenesis, such as leaf wetness, nitrogen fertilization and variety resistance have had limited integration in the development of these models. This review reveals low rates of model application due to inaccuracies and uncertainties in the predictions. Five models are part of current operational forecasting systems in Japan, Korea and India. Development of in-field rice-specific weather stations, along with integration of leaf wetness and end-user interactive inputs should be considered. This review will be useful for modelers, users and stakeholders, to assist model development and selection of the most suitable models for the effective rice blast forecasting.

Diversity and bioprospecting potential of rhizo and endophytic bacteria from two mangrove plants in Saudi Arabia

Mangrove plants are located on coastal area of sea and harbor diverse communities of microorganisms. The aim of our present study was to isolate bacteria from two different mangroves collected from the coastal area of Thuwal, Saudi Arabia and to further screen them for their antimicrobial activities. We have isolated 317 different rhizo and endophytic bacteria from mangroves using soil, roots and leave tissues. Bacteria were screened for their antifungal activities against oomycetes pathogens, Phytophthora capsici, Pythium ultimum. Only 25 bacterial strains found to be active against oomycetes fungal pathogens. These bacteria were tested further against other fungal pathogens like Magnaporthe grisea, Altenaria malli, and Fusarium oxysporum. Antagonistic bacteria were further screened for antibacterial activities against human pathogenic bacteria. Only few isolates exhibited antagonistic activity against these pathogenic bacteria. Hydrolytic enzymes production (cellulase, protease, lipase, and amylase) was also assessed. Most of the active isolates exhibited amylase and protease activities. Identification based on 16S rRNA gene revealed 92.8 to 99.9% sequence, similar to type strains of related species. Antagonistic bacteria belong to 5 different classes that is Gammaproteobacteria (γ-Proteobacteria), Alphaproteobacteria (α-Proteobacteria), Firmicutes, Bacteroidetes and Actinobacteria. Our results provide evidence that, mangroves plants harbor potentially useful bacteria producing active metabolites and enzymes. Key words: Mangrove plants, antagonistic bacteria, enzymatic activities, 16S rRNA gene sequence, phylogenetic analysis.

DIFFERENT RICE BLAST RESISTANCE GENES CONTRIBUTING TO THE BROAD-SPECTRUM RESISTANCE IN ELITE MALE STERILE AND RESTORER LINES FOR HYBRID RICE BREEDING

Rice blast is one of the most destructive diseases of rice worldwide. Three-line hybrid rice provides a high efficacy system to exploit heterosis that contributes to the yield increase in the past decades. A disease-resistant breeding program has released two elite male sterile lines, Gang-Xiang 1A (GX1A) and D-Xiang 4A (DX4A), and an elite restorer line, Shuhui 707 (SH707), which showed resistance to 102 isolates of Magnaporthe oryzae. To address the question whether the sterile lines and the restorer line contained different resistance genes, expression levels of the functionally cloned blast resistance genes were examined by real-time PCR (RT-PCR). Our data demonstrated that Pikm, Pia, Pid2, Pi-ta, and Pi5 were the candidate contributors of resistance in GX1A, DX4A and/or SH707, because of their high expression. Resistant spectrum assay and sequence polymorphism analysis narrowed down the potentially resistant contributors to Pikm and Pid2 in GX1A and DX4A, and Pi-ta, Pi5 and Pid2 in SH707, respectively. These data indicate that the male sterile lines and the restorer line possess different resistance genes and are highly valuable in disease-resistant breeding programs for developing new male sterile and restorer lines. Therefore, hybrid rice has the advantage to pyramid multiple disease resistance genes by introduction of different resistance genes into the parental male sterile lines and restorer lines.

The GEMO project: Hitchhiking DNA in Magnaporthe oryzae

The GEMO project: Hitchhiking DNA in Magnaporthe oryzae

EXPLORING MECHANISM OF RESISTANCE TO ISOPROTHIOLANE IN MAGNAPORTHE ORYZAE, THE CAUSAL AGENT OF RICE BLAST

The fungicide isoprothiolane (IPT) has widely been used to control the rice blast fungus Magnaporthe oryzae for decades. However, the molecular mechanism of resistance is still unexplained and was only believed to be associated with transmethylation in the biosynthesis of phosphatidylcholine. In this study we tested IPT sensitivity of hundreds of M. oryzae isolates collected from Yunnan and Hubei provinces of China. Three IPT-resistant mutants were generated by exposing the mycelium to increasing concentrations of IPT. No fitness penalty was observed in these resistant mutants. In consideration of the role on transmethylation in the biosynthesis of phosphatidylcholine, three candidate genes, PEAMT, CHO2, and OPI3, were sequenced, and their expression profile determined. There was no significant difference in the expression of these genes between resistant mutants and sensitive parental isolates. Additionally, Solexa sequencing was conducted to screen potential target genes. MGG_09793 was the most frequently changed gene between resistant mutant H08-1a_mut and sensitive parental isolate H08-1a after IPT treatment. After knockout, this gene in H08-1a_mut and H08-1a, resistance status did not change. This study indicates that the expected PEAMT, CHO2 and OPI3 genes were not responsible for IPT resistance. Interestingly, the DJ-1/PfpI family protein MGG_09793 was specifically and strongly induced by IPT treatment in sensitive isolates.

Characterization and Evaluation of Native Pseudomonas Spp. of South Gujarat against Leaf Blast in Finger Millet

Seven Pseudomonas isolates were isolated from different locations of south Gujarat. Based on the morphological, biochemical and physiological characterization of these isolates, four bacterial isolates were identified as Pseudomonas aeruginosa (PaWP, PaWS, PaRS and PaNS) and three as P. fluorescens (PfWN, PfRB and PfNC). All the isolates were able to grow in 2 to 10% NaCl but, failed to grow at 12% concentration and recorded growth from 10 to 42°C temperature. All the isolates grew in 6 to 8 pH range but failed to grow at 4, 5 and 10 pH. Bio-efficacy of the seven native strains of Pseudomonas spp. Was compared along with local commercial available biopesticides i.e. P. fluorescens (Aumgene, Pramukh and Pantnagar) and Hinosan. Three times spraying of P. aeruginosa Rambhas Strain at 0.6% (2×109 cfu/ml) at 15 days interval, starting at 21 days of transplanting was found significantly effective in the management of the leaf blast of finger millet ( Magnaporthe grisea (Cke) Sacc.) by lowering disease intensity and increasing grain yield as well as fodder.

Period, subculture number and culture color influence on the isolated Magnaporthe oryzae sporulation at the Tocantins State

El hongo Magnaporthe oryzae , causante de lo anublo del arroz (Bruzone), presenta una serie de limitaciones a los cultivos bajo condiciones controladas. Algunas caracteristicas pueden ser variables, incluso para un mismo aislado y requieren innovaciones por los investigadores para permitir lo desarrollo de las pruebas. Este estudio tuvo como objetivo verificar, en esporas aislados M. oryzae raza IA-1 recogidas en el Proyecto Rio Formoso, municipalidad de Formoso do Araguaia, la durabilidad de los cultivos almacenados en el laboratorio, la cantidad maxima de repicagens para mantener la produccion satisfactoria de las conidias por las colonias y la relacion de diferentes colores de las culturas en medio BDA con la produccion de conidias. Con este fin, se llevo a cabo tres experimentos en el diseno completamente al azar. En el estudio I, se utilizaron las culturas con 10, 14, 18, 22, 26 y 30 dias despues de la repicagen. En el estudio II, se utilizaron las culturas con 0, 1, 2, 3 y 4 repicagens de la cultura original. En el estudio III, los cultivos fueron clasificados como Negro, centro Gris con bordes anchos, Gris, centro Gris con bordes Blancos estrechos y Blanco. Mayores esporulaciones de M. oryzae se obtuvieron a los 14 dias despues del trasplante, en la segunda repicagen y de la coloracion negra.

Fertility status of Magnaporthe grisea populations from finger millet

Two hundred twenty nine isolates of Magnaporthe grisea were collected from finger millet cultivars at 14 locations in north India (Uttarakhand) and two locations in south India (Tamilnadu&Karnataka). Each isolate was tested for the mating types (Male fertile and female sterile) using standard fertile testers. Per cent isolates that neither mated nor produced perithecia was high among isolates collected from south India than those from Uttarakhand. Male fertile and hermaphrodite isolates from cooler region showed greater efficiency to produce perithecia. Results revealed that distribution of mating type varied with geographical region. Male fertile and female sterile isolates segregated in 1:1 ratio among field isolates collected from both north and south India. Field isolates from north India showed equal probability of getting male fertile, female sterile and hermaphrodite isolates, which suggested that probability for sexual reproduction in the population of M. grisea existed in nature in the central Himalayas of India.

Blast fungus inoculation reduces accumulation and remobilization of pre-anthesis assimilates to rice grains

The importance of stored assimilates for grain development in cereals has been widely recognized, particularly in cereals exposed to stress during the grain filling period. This study was conducted to investigate the effect of the blast fungus Magnaporthe grisea on dry matter accumulation, remobilization and utilization in rice ( Oryza sativa L.) under field conditions. Four rice varieties with various levels of susceptibility to rice blast were grown in 2003 and 2004 under high and low disease intensity, caused by early inoculation and natural infection respectively. High disease intensity reduced plant height, dry matter accumulation, the harvest index and grain yield. Plants grown under high disease intensity translocated fewer stored assimilates to the grain than plants grown under low disease intensity. Dry matter translocation from the vegetative parts to the grain was significantly correlated with dry matter at anthesis (r=0.65, P l). High stress from early leaf blast caused by inoculation with the blast fungus affected overall plant growth and lowered the production of pre-anthesis assimilates, as well as causing severe levels of neck blast that resulted in a low translocation rate during the filling period, and therefore a lower grain yield than in naturally infected plants.

Identification and Mapping of the QTL Controlling Resistance to Blast (Magnaporthe grisea) Disease in Rice

The rice blast resistance of one hundred and sixty F(subscript 2)-derived lines from the TNG69 x KHK cross was evaluated in greenhouse inoculation and field tests. Results from both screening methods revealed that the resistance to rice blast was mainly controlled by two major and several minor QTLs (Quantitative trait loci). Broad-sense heritability (H²(subscript B)) was estimated according to the variance of combined analysis. The value was 85.4% in greenhouse inoculation and 73.7% in field test. The blast resistance phenotypes in six environments (2 methods x 3 years) were analyzed using Mapmaker-QTL program. All informative markers distributed within the R165-R750 interval of linkage group A (chromosome 12) were correlated with rice blast resistance. Except for slighter symptom in the field test during 1999, the phenotypic contribution of each detected QTL was ranged from 21.3% to 72.4% with LOD scores from 7.43 to 24.42 in all surveyed environments. Thus, it is suggested that a major resistance gene was located on chromosome 12. Our results not only have proved the efficiency of greenhouse test for rice blast resistance, and have located a major gene with resistance across the different environments. The DNA makers closely linked with QTL affecting blast resistance may provide a useful tool for marker-assistant-selection (MAS) in the near future.

Genetic Analysis of Virulence in the Rice Blast FungusMagnaporthe grisea

Genetic Analysis of Virulence in the Rice Blast Fungus<i>Magnaporthe grisea</i>