Wheat blast disease caused by Pyricularia grisea (telemorph Magnaporthe grisea) has become a serious restriction on increasing the area and production of the crop, especially in the tropical parts of the Southern Cone Region of South America. First identified in 1985 in the State of Paraná in Brazil, it has become an endemic disease in the low lying Santa Cruz region of Bolivia, south and south-eastern Paraguay, and central and southern Brazil in recent years. Severe infections have also been observed in the summer planted wheat crop in north-eastern Argentina. So far, only sporadic infections have been seen in Uruguay, especially during the wet and warm years. Spike infection (often confused with Fusarium head blight infection) is the most notable symptom of the disease and capable of causing over 40% production losses. However, under severe infection, the loss of production can be almost complete in susceptible varieties. Wheat blast is mainly a spike disease but can also produce lesions on all the above ground parts of the plant under certain conditions. Depending upon the point of the infection on the rachis, the disease can kill the spike partially or fully. The infected portion of the spike dries out without producing any grain which can be visibly distinguished from the healthy portion. While virulence diversity in the fungus has been reported in the literature and is under further exploration, genetic resistance in the host species has been more difficult to identify. Earlier, Brazilian cultivars such as BH 1146, CNT 8, several IAC and OCEPAR selections were credited as demonstrating different levels of field resistance, but this was not confirmed under artificial inoculation studies. However, other cultivars such as BR18, IPR 85, CD 113, have shown moderate levels of resistance over the years in many locations. Recently, several cultivars and advanced lines derived from the CIMMYT line, Milan, have been observed to carry a high level of resistance to blast disease throughout the endemic region. However, to date, the genetic basis of this resistance is not very clear due to extreme variation in the pathogen. Cultivars showing complete resistance against a few isolates under controlled conditions in the glasshouse, may or may not show field resistance in commercial cultivation. Due to an increase of the area under Milan based resistant wheat cultivars in Bolivia, Brazil and Paraguay, it needs to be combined with other sources of resistance urgently to prevent the selection of a virulent pathotype in the fungus. Besides genetic resistance, avoidance of early dates of seeding and chemical control can reduce the disease severity. Fungicides combining triazols with strobilurins can, under some situations, be effective in disease control at the heading stage. Even when all components of integrated disease management of wheat blast are not in place yet, it is seen as an essential strategy to reduce production losses in this region. Given the threat that the blast disease may pose to world wheat growin...

Seventy-two monoconidial isolates of Magnaporthe grisea were obtained from the States of Mato Grosso do Sul and Paraná. The isolates were inoculated on seedlings of 20 wheat (Triticum aestivum) cultivars under greenhouse conditions. The virulence diversity of M. grisea was assessed based on compatible and incompatible reactions of leaf blast on wheat cultivars. Fifty-four distinct virulence patterns were identified on test cultivars among the isolates collected from the two wheat growing States. Sixteen of these isolates corresponding to 22.2% showed similar virulence pattern. None of the wheat cultivars was resistant to all isolates of M. grisea, but the cultivars differed in degree of resistance as measured by the relative spectrum of resistance (RSR) and disease index (DI). Among the cultivars the RSR ranged from 0 to 53.3% and DI from 0.4662 to 0.9662 (0 to 1 scale). The wheat cultivar BR18 exhibited a broad resistance spectrum in relation to the rest of the tested cultivars to the isolates of M. grisea, and can be used in wheat resistance breeding.

Stemphylium is a genus of plant pathogens and saprobes in the Pleosporaceae (Pleosporales, Dothideomycetes, Ascomycetes). The teleomorphs of Stemphylium, where known, are in Pleospora, with Pleospora herbarum as the type. The goal of this study was to present a rigorous phylogenetic analysis of the relationships among Stemphylium isolates with particular emphasis on species delimitation in the P. herbarum clade, on possible new species and on the relationship of clades to cultures from type specimens. Our taxon sampling comprised 110 Stemphylium strains collected worldwide from various hosts and DNA sequences from four loci, from the ITS, the protein encoding GPD and EF-1 alpha genes and the intergenic spacer between vmaA and vpsA. A large EF-1 alpha intron delimited by noncanonical splice sites and encoding putative proteins was present in three unrelated isolates and was excluded from analyses. Isolates comprised 23 representatives derived from type strains, compared to type strains or otherwise connected to type material, 40 unnamed strains morphologically similar to the type P. herbarum, four strains from an outbreak of Stemphylium leaf blight of cotton in Brazil and eight strains collected in British Columbia mainly from nonagricultural hosts. Our findings provided strong support for the main groupings of Stemphylium obtained earlier and also revealed six possible new species. Other variation within morphological species might point to additional cryptic species. On the other hand, even with four loci, cultures ex-type of five species including P. herbarum were inseparable. We speculate that being self-fertile the clade including P. herbarum might represent a group of highly inbred, morphologically distinct lineages that have yet to accumulate detectable species-specific sequence variation. The lack of variation in P. herbarum clade contrasts with many other a priori defined morphological species where multigene phylogenetic analyses revealed new cryptic species.

Uredospore production per day and per sporulation period was measured under near-optimal conditions. Pustule density influenced time and rate of pustule opening, size of pustules, time of maximum sporulation, length of the sporulation period and the time and rate of tissue necrotisation. Within limits total dry weight of spores per leaf per sporulation period was independent of pustule density; it roughly equalled the dry weight of the spore producing leaf. The longest sporulation period observed was 65 days; at low pustule densities secondary pustules replaced exhausted primary pustules. Infectivity of the spores was normal up to 46 days after inoculation. The long sporulation period was epidemiologically interpreted as a survival mechanism.

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Genotypic and phenotypic variation among 16 isolates of Ramularia areola of Gossypium hirsutum collected from five different geographical regions of Brazil was studied through virulence spectrum on three cultivars in the glasshouse and through ERIC-and REP-PCR and ITS1-5.8S-ITS2 rDNA analysis. Difference in virulence spectrum and molecular analysis of some isolates was observed. ERIC-and REP-PCR showed similar results and revealed a high level of diversity among the isolates. A unique profile for both ERIC and REP was obtained for most isolates. On the other hand, the ITS rDNA analysis did not show different PCR-RFLP patterns. While some isolates differed among each other considering genotypic and phenotypic reactions, no clear cut evidence was found about the existence of genetic lineages of R. areola in Brazil. Identification of genetic variability among the R. areola isolates originated from different geographic regions would permit screening of Brazilian germplasm and achieve sources with a wide spectrum of resistance. This is the first report of the genotypic and phenotypic variability among the R. areola isolates originated from five cotton growing regions of Brazil.

The genetic diversity of the Stemphylium solani isolates from cotton was assessed by Enterobacterial Repetitive Intergenic Consensus (ERIC) and Repetitive Extragenic Palindromes (REP)-PCR fingerprinting. Twenty eight monosporic isolates of S. solani from cotton were used along with five isolates from tomato and one isolate of Alternaria macrospora from cotton for comparison. The dendrogram obtained revealed clear differences between the cotton and tomato isolates as well as between the tomato isolates from different geographic regions. The genetic relationships among S. solani isolates were also analyzed by sequencing the internal transcribed spacer (ITS) region of four isolates representing the three ERIC and REP groups. The tomato isolate from the State of São Paulo showed a distinct ITS sequence from that of the cotton isolates and tomato isolate from the State of Goiás, giving evidence that it belongs to a different genotype of S. solani. This is the first report of the entire sequence of the ITS1-5.8S-ITS2 regions of S. solani.