tritici succeed to infect barberry, while Urediniospores are blocked by non-host resistance

Stripe rust (Yellow rust) caused by Puccinia striiformis f. sp. tritici (Pst) is a major disease of wheat worldwide. The use of resistant cultivars to control Pst has been very effective, low-cost, and ecologically sound. However, virulence patterns of Pst can quickly change, which may render resistant cultivars susceptible. The discovery of infection of Berberis spp. by basidiospores of Pst in 2010 raised important concerns about the evolution of new virulent races of the pathogen. Little is known about the infection process of Berberis spp. by basidiospores of Pst and the interaction between Berberis spp. and asexual urediniospores. In this study, the interaction between Pst urediniospores and Berberis spp. was investigated at histological and cytological levels. Our results indicate that Berberis spp. expresses a continuum of layered defenses comprised of structural and chemical changes in the cell wall as well as post-haustorial hypersensitive responses to urediniospore infection. Our study also re-examines in detail the infection process of Pst basidiospores on Berberis spp. and provides useful information for further research on the molecular mechanisms governing the interaction between Berberis spp. and Pst.

Three-dimensional surface reconstruction and in situ site-specific cutting of the teliospores of Puccinia miscanthi causing leaf rust of the biomass plant Miscanthus sinensis

The rust fungus Puccinia miscanthi on the naturally infected leaves of eulalia grass were investigated by light and electron microscopy. Many black telia were present on both the adaxial and abaxial leaf surfaces. The telia were often confluent, protruding distinctly from the leaf surface, and had numerous teliospores. Light microscopy revealed that the teliospores were club-like in shape (clavate), chestnut brown, and produced pedicels from one end. They were measured to be approximately 45 μm × 20 μm in size, and slightly constricted at the septa. Using stereo imaging, it was possible to generate images with more three-dimensionality than conventional scanning electron micrographs. Without the need for the mechanical sectioning of telia, the height of telia from the leaf epidermis could be measured at approximately 230 μm using three-dimensional surface reconstruction. Urediniospores were also found on the leaf surface, and possessed spines on the surface (echinulate). The internal features of the nonembedded teliospores could be unveiled using a focused ion beam system with a field emission scanning electron microscope, allowing for the in situ site-specific cutting of the non-embedded teliospores. These results show that three-dimensional surface reconstruction and targeted cutting are a potential alternative to mechanical sectioning of resin-embedded blocks, and have the potential to eliminate the uncertainty involved in selecting the region of interest.