Natural field infections of wheat and triticale by fungi from the complex of fungi Stagonospora nodorum/Septoria tritici under climatic conditions of Poland.

Stagonospora nodorum and Septoria tritici are classified as necrotrophic fungi that cause glume and leaf blotch and speckled leaf blotch of cereals and grasses worldwide. Stagonospora nodorum blotch (SNB) and Septoria tritici blotch (STB) occur quite often in complexes and are classified among the most destructive diseases to their hosts, what also was found in the present study. The intensity of diseases caused on wheat and triticale in Poland is associated with weather and environmental conditions. Moderate temperatures in the range of 20 - 23 degrees C and high relative humidity are conducive for the occurrence and development of both, SNB and STB. Results of presently reported experiments confirm that species of Stagonospora nodorum and S. tritici complex on wheat and triticale occur naturally throughout the country. In addition, statistical tests proved that the natural infections of triticale and wheat varieties in field nurseries are statistically different between locations and within each location. Plants were subjected to phenotypic evaluation, taking into account the degree of infection of leaves and glumes (Poznan et al., 2011). The reported data are generally in coincidence with our previous findings, however, they need to be confirmed on multi annual basis.

A New Biotype of Phaeosphaeria sp. of Uncertain Affinity Causing Stagonospora Leaf Blotch Disease in Cereals in Poland.

A new Phaeosphaeria sp. biotype was isolated from winter ryes in Poland during 1995. Two isolates, Sn23-1 and Sn48-1, were obtained from diseased leaves of cvs. Motto and Dankowskie, respectively. The rye Phaeosphaeria sp. represented by isolate Sn48-1 has similar pycnidiospore morphology and induces disease symptoms in cereals similar to Phaeosphaeria nodorum, the causal agent of Stagonospora nodorum blotch disease (4). The pathogen (Sn48-1) produces hyaline, cylindrical pycnidiospores that are mostly three-septate and measure 12.8 to 23.7 × 2.1 to 3.2 µm (average size = 16 × 2.6 µm) on water agar. A molecular comparison of several genes in isolates Sn23-1 and Sn48-1 revealed that the rye Phaeosphaeria sp. was different from P. nodorum. In the conserved alpha-box sequence (1,93 bp) of the MAT1-1 gene, a four nucleotide difference occurred between the wheat-biotype P. nodorum and isolates Sn23-1 and Sn48-1 (GenBank Accession Nos. AY072933 and AF322008). In addition, the length of the internal transcribed spacer (ITS) region of the nuclear rDNA was the same for the wheat-biotype P. nodorum and the two rye Phaeosphaeria sp. isolates. However, a six nucleotide discrepancy was found in the ITS region (GenBank Accession Nos. U77362 and AF321323). The beta-glucosidase (bgl1) and beta-tubulin (tubA) genes differ in length between the wheat-biotype P. nodorum and two rye Phaeosphaeria sp. isolates (2,3). The main difference was due to the intron sizes of these two genes. One extra nucleotide was found in the intron2 of the bgl1 gene (GenBank Accession Nos. AY683619 and AY683620) and the intron1 of the tubA gene (GenBank Accession Nos. AY786337 and AY786331), respectively, in these two rye Phaeosphaeria sp. isolates. Disease severity on the fifth leaf (GS15) of Polish wheat (Alba, Begra, and Liwilla), triticale (Bogo and Pinokio), and rye (Zduno) cultivars was assessed with one (resistant) to nine (susceptible) scales 14 days after inoculation. Aggressiveness of wheat-biotype P. nodorum isolate Sn26-1 and rye Phaeosphaeria sp. isolate Sn48-1 was significant (P < 0.01) in five cultivars except in the moderately resistant wheat cv. Liwilla. The rye Phaeosphaeria sp. isolate Sn48-1 severely affected Polish rye Zduno (8.3) and two triticale cultivars (6.5), while the infection by isolate Sn26-1 was moderate (3-4). On the contrary, the wheat-biotype P. nodorum isolate Sn26-1 was more aggressive on wheat (4.1 on moderately resistant Alba and 6.2 on highly susceptible Begra) than the rye Phaeosphaeria sp. isolate Sn48-1, which had a scale of 2.2 and 4.3, respectively. Under laboratory conditions, the rye isolate Sn48-1 was able to cross with the wheat-biotype P. nodorum isolate Sn26-1 that has an opposite mating-type (MAT1-2) gene, but few viable ascospores were produced (1). References: (1) P. C. Czembor and E. Arseniuk. Mycol. Res. 104:919, 2000. (2) A. Malkus et al. FEMS (Fed. Eur. Microbiol. Soc.) Lett. 249:49, 2005. (3) E. Reszka et al. Can. J. Bot. 83:1001, 2005. (4) M. J. Richardson and M. Noble. Plant Pathol. 19:159, 1970.

Identity and conservation of mating type genes in geographically diverse isolates of Phaeosphaeria nodorum.

Mating type idiomorphs (MAT1-1 and MAT1-2) were identified from the heterothallic loculoascomycete Phaeosphaeria nodorum (wheat biotype) using DNA from a pair of isolates from Poland and Georgia, USA that are known to mate. MAT predicted proteins of P. nodorum are similar in sequence and in phylogenetic relationship to those described for other loculoascomycetes such as Cochliobolus spp., Alternaria alternata, and Didymella zeae-maydis. The organization of the MAT locus of the P. nodorum differs from these species in that its idiomorph begins within an adjacent upstream conserved ORF of unknown function. MAT-specific primers were used to identify isolates of both mating types in field populations, demonstrating that an absence of either mating type is not the reason that the teleomorph has not been found in New York. Portions of MAT1-1 and MAT1-2 were sequenced from geographically diverse isolates, including those from regions where the teleomorph has been reported. MAT was highly conserved and no significant differences in sequence were found.

Seasonal Patterns of Spore Dispersal of Phaeosphaeria spp. and Stagonospora spp.

The spatial and temporal patterns of discharge and dissemination of airborne spores of Phaeosphaeria spp. and Stagonospora spp. were studied. Both ascospores and pycnidiospores of the pathogens were deposited at various densities on microscope slides used as spore samplers. The maximum deposition of the spores was observed during the period of August to October. A multiple regression analysis was used to determine which weather factors significantly explained the variation measured in the numbers of ascospores that settled on microscope slides. Rainfall, air temperature, and relative air humidity were influential in the release of Phaeosphaeria spp. ascospores into the air. The amount of airborne ascospores was a function of the variables and remained largely under their control. The liberation of ascospores was favored by air temperature above 0°C, rainfall greater than 1 mm, and high relative humidity. The range of atmospheric conditions stimulating air dispersal of ascospores was wider than that for pycnidiospores. Pycnidiospores were sampled only during rainy days. Their release was affected adversely by air temperature below 5°C. Multiple regression models based on weather data were developed and verified for their predictive ability and accuracy by jackknife and cross-validation procedures, as well as by comparisons of observed and predicted mean numbers of deposited ascospores per microscope slide after a substitution of each period data set with a set of data of the other respective time interval. The numbers of airborne ascospores predicted by the regression models were in a good agreement with the observed values. The jackknife and cross-validation techniques allowed use of the limited data sets for both the parameter estimation and validation processes in a development of simulation models. The airborne inoculum appeared to be omnipresent over cereal areas year round, except during periods with freezing temperatures and a snow cover. Such an omnipresence of inoculum of the pathogens poses a danger to crops and could be of importance in the epidemiology of Stagonospora (= Septoria) blotches under the climatic conditions of central Poland.

Pathogenicity of seed transmittedFusarium spp. to triticale seedlings.

In the conducted studies 13 species ofFusarium were isolated into pure culture from triticale seed. Their pathogenicity was assessed under laboratory and greenhouse conditions. Most of the species studied were highly pathogenic to the first leaf see-dlings of triticale 'Grado' and 'Lasko' under both sets of conditions. It was shown, that seed-transmitted Fusarium spp. considerably reduced the ability of seeds to germinate and incited seedling blight. On average, triticale 'Lasko' was more resistant toFusarium spp. than 'Grado', but in some instances a reverse reaction was observed.