Judit Komáromi

New Insights into the Life Cycle of the Wheat Powdery Mildew: Direct Observation of Ascosporic Infection in Blumeria graminis f. sp. tritici

Although Blumeria graminis is an intensively studied pathogen, an important part of its life cycle (namely, the way ascospores initiate primary infections on cereal leaves) has not yet been explored in detail. This study reports, for the first time, the direct observation of this process in B. graminis f. sp. tritici using light and confocal laser-scanning microscopy. All the germinated ascospores produced a single germ tube type both in vitro and on host plant surfaces; therefore, the ascosporic and conidial germination patterns are markedly different in this fungus, in contrast to other powdery mildews. Germinated ascospores penetrated the epidermal cells of wheat leaves and produced haustoria as known in the case of conidial infections. This work confirmed earlier studies reporting that B. graminis chasmothecia collected from the field do not contain mature ascospores, only asci filled with protoplasm; ascospore development is induced by moist conditions and is a fast process compared with other powdery mildews. Although ascosporic infections are frequent in B. graminis f. sp. tritici in the field, as shown by this study and other works as well, a recent analysis of the genomes of four isolates revealed the signs of clonal or near-clonal reproduction. Therefore, chasmothecia and ascospores are probably more important as oversummering structures than genetic recombination factors in the life cycle of this pathogen.

Genetic diversity and host range of powdery mildews on Papaveraceae

Because of the strong morphological similarity of the powdery mildew fungi that infect papaveraceous hosts, a total of 39 samples were studied to reveal the phylogeny and host range of these fungi. ITS and 28S sequence analyses revealed that the isolates identified earlier as Erysiphe cruciferarum on papaveraceous hosts represent distinct lineages and differ from that of E. cruciferarum sensu stricto on brassicaceous hosts. The taxonomic status of the anamorph infecting Eschscholzia californica was revised, and therefore, a new species name, Erysiphe eschscholziae, is proposed. The taxonomic position of the Pseudoidium anamorphs infecting Glaucium flavum, Meconopsis cambrica, Papaver dubium, and Stylophorum diphyllum remain unclear. This study revealed that Erysiphe macleayae exhibits a specific host range different from that of E. cruciferarum, the common pathogen of papaveraceous hosts. Although E. macleayae occurred naturally on Macleaya cordata, Macleaya microcarpa, M. cambrica, and Chelidonium majus only, our inoculation tests revealed that the fungus was capable of infecting Argemone grandiflora, Glaucium corniculatum, Papaver rhoeas, and Papaver somniferum, indicating that these plant species may also be taken into account as potential hosts. Erysiphe cruciferarum originating from P. somniferum was not able to infect A. grandiflora, C. majus, E. californica, M. cordata, and P. rhoeas. The emergence of E. macleayae on M. microcarpa is reported here for the first time from the Czech Republic and Slovakia. The appearance of chasmothecia of E. macleayae on C. majus in Slovakia was reported, as well. Erysiphe cruciferarum was identified on G. corniculatum and reported here for the first time from Slovakia.

Identification of wheat genotypes with adult plant resistance to powdery mildew

As in the case of other wheat diseases, adult plant resistance (APR) to powdery mildew remains effective longer than monogenic hypersensitive resistance, so the objective was to identify winter wheat genotypes with this type of resistance. Field and greenhouse tests conducted on 41 varieties and breeding lines indicated that 36 were susceptible in the seedling stage, and only five were resistant in all stages of development. It is probable that these latter genotypes contain major resistance genes. The area under the disease progress curve was the same for most of the wheat genotypes as for the APR control variety Massey, but varieties and lines with significantly better resistance were also identified. Among the genotypes in the Martonvasar breeding stock, Mv Taltos and the line Mv07-03 were found to have excellent adult plant resistance.

Study of Fusarium head blight resistance in wheat using microsatellite markers

Investigations on Fusarium head blight (FHB) in wheat are gaining importance throughout the world. This can be attributed to the fact that Fusarium species not only cause yield losses, but also produce mycotoxins in infected plant tissues, the accumulation of which makes the grain unsuitable for both human and animal consumption (Larsen et al. 2004). Nowadays spring genotypes of Far Eastern origin are considered to have the best resistance, so these are generally used as basic material in studies on the genetic background of resistance. Several types of resistance have been described in wheat on the basis of the plants defence mechanisms (Mesterhdzy et al. 1999), but in most cases genetic analysis is focussed on Type II resistance, i.e. resistance to the spread of the fungus within the spike, since the use of point inoculation allows it to be examined separately from Type I resistance, which prevents the penetration of the fungus into the spike tissue. (Schroeder and Christensen 1963). The other method used to investigate FHB resistance is spray inoculation (Buerstmayr et al. 2003, Schmolke et al. 2005), but the infection data only allow conclusions to be drawn on field resistance, i.e. on the joint effect of the two main types of resistance (Miedaner et al. 2003). Although this inoculation method is used less frequently in the phenotypic analyses required for genetic research, its role should not be underestimated. The present experiments involved the genetic analysis of field resistance in the moderately resistant Chinese line Ning8331 and the moderately susceptible variety Martonvasari 17.