Poster Presentation Science Protecting Plant Health 2017

A fresh look at the life cycle of powdery mildews infecting important crops (#322)

Levente Kiss 1
  1. University of Southern Queensland, Toowoomba, QLD, Australia

Although life cycles of powdery mildews infecting important crops have long been considered as well defined processes, our studies revealed new aspects of both asexual and sexual cycles. We detected microcyclic conidiogenesis (MC), i.e. production of conidia on a spore without any, or only a minimal, involvement of hyphal growth, in more than 10 species belonging to distinct phylogenetic lineages. In powdery mildews, MC means that germinated conidia can sometimes serve as sites for conidiogenesis: conidiophores can develop directly on the germinated conidial body and produce new conidia. If this happens in a young colony, established by the germinated conidium itself, MC will contribute to a quick propagation of the fungus because new conidia are produced quicker on microcyclic conidiophores than on the hyphae of the young mycelium.

In many powdery mildews, especially in temperate climate zones, ascospores coming from sexual fruiting bodies, called chasmothecia (formerly: cleistothecia), initiate the primary infections early in the host plant growth season. Although ascosporic infections have long been considered as the first step in the life cycle of the cereal powdery mildew pathogen, Blumeria graminis, this has been documented for the first time only very recently in our laboratory. Germinated ascospores penetrated the epidermal cells of wheat leaves and produced haustoria as known in the case of conidial infections. We confirmed earlier studies reporting that B. graminis chasmothecia do not contain mature ascospores int he field, only asci filled with protoplasm; ascospore development is induced by moist conditions and it is a fast process compared to other powdery mildews. Although ascosporic infections are frequent in B. graminis in the field, a genomic analysis revealed the signs of clonal or near-clonal reproduction. Therefore, ascospores are probably more important as dormant structures than genetic recombination factors in the life cycle of B. graminis.