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The genetic structure of Mycosphaerella musicola has never been investigated in Brazil to address epidemiologically related questions associated with yellow sigatoka. A total of 223 single-conidium isolates from four regions (North, South, Zona da Mata and Triângulo Mineiro) of Minas Gerais State, Brazil, were used to assess the population genetic structure of M. musicola. Isolates were characterized regarding the frequency of the MAT1-1-1 or MAT1-2-1 idiomorphs and polymorphism at nine microsatellite loci. The mating-type ratio in three of the four subpopulations was c. 1:1. A total of 87 alleles and 216 multilocus genotypes were identified. The overall population was in linkage equilibrium. Most (93.9%) genetic variation was detected within the subpopulations and there was weak differentiation between them. In total, eight genetic groups were detected and isolates of seven groups were present in all regions. The population of M. musicola in Minas Gerais seems to have high evolutionary potential: it is panmictic and both sexual reproduction and gene flow affect genetic variability. Strategies to avoid fungicide resistance should be enforced and breeding programmes need to consider quantitative resistance in the banana cultivars.

An understanding of the progression of a disease is important in the adoption of control strategies as well as the evaluation of their efficacies. Temporal analysis is especially useful because it integrates the evolution of the interaction between the components of the pathosystem, as expressed by the accumulated data on the incidence and severity of disease and depicted by the disease progression curve. Within a given patho-system, the dispersed airborne spores are important components in the progress of plant disease epidemics. Our aims were to evaluate the temporal dynamics of yellow Sigatoka in a banana plantation located in Coronel Pacheco, MG, Brazil, and to assess the aerobiology of Mycosphaerella musicola spores throughout the year. During the rainy season, we observed intense disease progression concomitant with high rates of leaf emission, which caused rapid reversal of the severity peaks after the maximum rates were reached. The yellow Sigatoka progress curve showed two peaks of extreme severity. The first, which occurred during the rainy season, was predominantly caused by a high concentration of conidia. The second, which occurred during the dry season, was predominantly caused by a high concentration of ascospores in the air. The ascospore concentrations were correlated with the severity of the disease 29 days later, indicating the average latency period of the disease in that region. The patterns of the severity curves for both peaks fit the monomolecular model, and the progression rates were higher during the rainy season than the dry season. The spore concentrations were the same at the two evaluated heights. In all evaluations, it was observed a higher concentration of ascospores than of conidia, with the greatest ascospore concentrations occurring during the early hours of the day and the greatest conidia concentrations occurring later, after the dew has dropped from the leaves.

BACKGROUND: The physico-chemical characteristics of a new banana triploid hybrid (FLHORBAN 920 cultivar, AAA group), partially resistant to Yellow Sigatoka and Black Leaf Streak diseases, were measured throughout ripening and compared with those of the Cavendish banana. RESULTS: The greatest differences between FLHORBAN 920 (F920) and the Cavendish variety were observed at intermediate maturity, when bananas were yellow with green tips or yellow. The F920 bananas have more dry matter and starch than those of Cavendish. The total polyphenol contents of F920 bananas were three-fold higher than Cavendish. The sucrose contents were 1.5-fold higher in F920 fruits, whereas glucose and fructose contents were two-fold higher in Cavendish fruits. The F920 fruits had fewer esters, carbonyls and phenolic ethers than Cavendish. The two varieties differed in the composition in methyl-branched (alcohols and esters) and phenolic ether volatile compounds. CONCLUSION: These characteristics, coupled with resistance to the principal banana diseases, suggest that the F920 variety should be developed further. c � 2008 Society of Chemical Industry

Black Sigatoka caused by Mycosphaerella fijiensis Morelet is the most dangerous and devastating disease of banana around the world. Disease control is carried out by integrating cultural, genetic and chemical measures. Mycosphaerella musicola has been replaced by M. fijiensis wherever Black Sigatoka has been introduced in America and elsewhere, and remains as a significant problem at sites located at relatively high altitudes. To optimize fungicide applications for disease management a presymptomatic quantification of fungal proteins in leaves is desirable. In this study, we describe the generation of a mouse monoclonal antibody (Mab) reactive to a high-molecular weight antigens from M. fijiensis mycelial single ascospore in vitro culture, but not reactive to mycelial antigens from M. musicola, M. musae and M. minima single ascospore cultures. A rabbit-specific polyclonal antibody against the same M. fijiensis antigen, reactive also to fungal secreted proteins, was able to discriminate naturally M. fijiensis infected from healthy leaves as well as other concomitant fungi. The Mab was used as a capturing reagent and the polyclonal preparation as a second antibody for a triple antibody enzyme-linked immunosorbent assay able to quantify mycelial protein antigens in a range of 10–40 μg / ml and differentiate it from healthy banana leaf extracts. The aim of this study was the analytical setting up of a Mab-based immunoassay for the quantification of mycelial and secreted proteins of M. fijiensis. It is intended for the further establishment and optimization of an asymptomatic leaf assay for an improved forecast and warning system applied to Black Sigatoka disease management.

The worldwide destructive epidemic of the fungus Mycosphaerella fijiensis on banana started recently, spreading from South-East Asia. The founder effects detected in the global population structure of M. fijiensis reflected rare migration events among continents through movements of infected plant material. The main objective of this work was to infer gene flow and dispersal processes of M. fijiensis at the continental scale from population structure analysis in recently invaded regions. Samples of isolates were collected from banana plantations in 13 countries in Latin America and the Caribbean and in Africa. The isolates were analysed using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and microsatellite molecular markers. The results indicate that a high level of genetic diversity was maintained at the plantation and the plant scales. The loci were at gametic equilibrium in most of the samples analysed, supporting the hypothesis of the existence of random-mating populations of M. fijiensis, even at the plant scale. A low level of gene diversity was observed in some populations from the Africa and Latin America-Caribbean regions. Nearly half the populations analysed showed a significant deviation from mutation-drift equilibrium with gene diversity excess. Finally, a high level of genetic differentiation was detected between populations from Africa (FST = 0.19) and from the Latin America-Caribbean region (FST = 0.30). These results show that founder effects accompanied the recent invasion of M. fijiensis in both regions, suggesting stochastic spread of the disease at the continental scale. This spread might be caused by either the limited dispersal of ascospores or by movements of infected plant material.

Single-copy restriction fragment length polymorphism (RFLP) markers were used to determine the genetic structure of the global population of #Mycosphaerella musicola#, the cause of Sigatoka (yellow Sigatoka) disease of banana. The isolates of #M. musicola# examined were grouped into four geographic populations representing Africa, Latin America and the Caribbean, Australia and Indonesia. Moderate levels of genetic diversity were observed for most of the populations (H = 0.22-0.44). The greatest genetic diversity was found in the Indonesian population (H = 0.44). Genotypic diversity was close to 50% in all populations. Population differentiation tests showed that the geographic populations of Africa, Latin America and the Caribbean, Australia and Indonesia were genetically different populations. Using tests, very high levels of genetic differentiation were detected between all the population pairs (Fst > 0.40), with the exception of the Africa and Latin America -Caribbean population pair. These two populations differed by only 3% (Fst = 0.03), and were significantly different (P < 0.05) from all other population pairs. The high level of genetic diversity detected in Indonesia in comparison to the other populations provides some support for the theory that #M. musicola# originated in South-east Asia and that #M. musicola# populations in other regions were founded by isolates from the South-east Asian region. The results also suggest the migration of M. musicola between Africa and the Latin America-Caribbean region.

Two sigatoka leaf-spot diseases affect banana and plantain: yellow sigatoka and black sigatoka. These are caused by two closely related and morphologically similar species of fungi: yellow sigatoka by Mycosphaerella musicola, and black sigatoka by M. fijiensis. Correct identification of these pathogens is hampered by the ambiguity of symptoms on different cultivars, and the difficulty in successfully isolating the pathogens in pure culture. Subsequent identification relies on sporulation which may also be difficult to induce. A diagnostic test based on the polymerase chain reaction (PCR) was therefore developed for these pathogens. The internally transcribed spacer (ITS1) region of ribosomal DNA (rDNA) of several isolates of M. fijiensis, M. musicola, and M. musae was sequenced, and a 21-base oligonucleotide primer constructed for each species from a variable region identified in the sequences. These primers were used with primers in the conserved regions of the rDNA to produce a species-specific product for each of the three species using PCR. The primers also amplified a fungal product from single ascospores placed in the PCR reaction, and from DNA from banana leaf tissue showing disease symptoms. No PCR products were produced when DNA from other species commonly found on banana was amplified. The fungi have been detected in herbarium samples up to 3 years old. The technique is very sensitive, and is able to detect DNA in a 1:20000 dilution of DNA extracted from 50 mg of freeze-dried fungal mycelium.

The polymerase chain reaction (PCR)-based technique of random amplification of polymorphic DNA (RAPD) was used to differentiate DNA from species of the genus Mycosphaerella. DNA from two pathogens which cause Sigatoka leafspot diseases of banana, M. fijiensis and M. musicola, and two other Mycosphaerella species which are commonly found on banana, M. musae and M. minima, gave distinct RAPD banding patterns with all PCR primers tested. PCR, using primer RC07, amplified a 1250bp RAPD fragment from all isolates of M. fijiensis obtained from 11 geographical origins. This fragment was absent from the other species of Mycosphaerella. In Southern blots of genomic DNA, this band hybridized exclusively to DNA from M. fijiensis, and the pattern of hybridization suggested that it was binding to repeated DNA. A RAPD band amplified with primer PM06 obtained from M. musicola was also found to be species-specific. Southern analysis suggested that the fragment hybridized to a single-copy sequence in the M. musicola genome. Total genomic DNA from M. musicola was found to be a species-specific hybridization probe. Dot-blots confirmed the specificity of these probes, and could be used to identify isolates of Mycosphaerella which cause Sigatoka disease of banana in south-east Asia.

Yellow Sigatoka caused by the ascomycete Mycosphaerella musicola Leach, is one of the most severe banana diseases worldwide, which spread in most banana growing areas, until Black Sigatoka, a more aggressive disease caused by Mycosphaerella fijiensis, appeared. Because of the highly devastating nature of the latter pathogen, recent research almost exclusively focused on M. fijiensis. To close the gap of knowledge and to study the population structure of M. musicola in Yellow Sigatoka-infested areas, we cloned and characterized a versatile set of 26 polymorphic locus-specific microsatellite markers.

Agriculture in tropical countries produces many of the world's most valuable crops, but productivity is limited by a multiplicity of different diseases, many of which have been inadequately studied. Certain characteristics of tropical climates have a fundamental influence on the incidence and severity of many of these diseases. The main seasonal variations which control crop growth and disease epidemiology depend on differences in moisture availability rather than daylength and temperature differences. Marked dry seasons hinder the survival of many pathogens outside hosts unless they can produce drought-resistant spores. In many tropical areas continuous cropping throughout the year is possible, enabling disease epidemics to continue without interruption over long periods. Much agriculture in the tropics is at fairly high altitudes enabling temperate crops to be grown, but low temperatures may present special disease hazards. Violent storms are a feature of many tropical climates and have been implicated in the spread of many bacterial diseases. Drought is a factor which influences the severity of many root diseases. The various effects which moisture, as rain or dew, temperature and cropping cycle can have are illustrated by discussion of sigatoka disease of bananas (Mycosphaerella musicola Leach), South American leaf blight of rubber (Microcyclus ulei (R. Henn.) Arx) and coffee berry disease (Colletotrichum coffeanum Noack).