Generation of Doubled Haploid Barley by Interspecific Pollination with Hordeum bulbosum.

The generation of doubled haploid barley plants by means of the so-called "Bulbosum" method has been practiced for meanwhile five decades. It rests upon the pollination of barley by its wild relative Hordeum bulbosum. This can result in the formation of hybrid embryos whose further development is typically associated with the loss of the pollinator's chromosomes. In recent years, this principle has, however, only rarely been used owing to the availability of efficient methods of anther and microspore culture. On the other hand, immature pollen-derived embryogenesis is to some extent prone to segregation bias in the resultant populations of haploids, which is due to its genotype dependency. Therefore, the principle of uniparental genome elimination has more recently regained increasing interest within the plant research and breeding community. The development of the present protocol relied on the use of the spring-type barley cultivar Golden Promise. The protocol is the result of a series of comparative experiments, which have addressed various methodological facets. The most influential ones included the method of emasculation, the temperature at flowering and early embryo development, the method, point in time and concentration of auxin administration for the stimulation of caryopsis development, the developmental stage at embryo dissection, as well as the nutrient medium used for embryo rescue. The present protocol allows the production of haploid barley plants at an efficiency of ca. 25% of the pollinated florets.

The durable wheat disease resistance gene Lr34 confers common rust and northern corn leaf blight resistance in maize.

Maize (corn) is one of the most widely grown cereal crops globally. Fungal diseases of maize cause significant economic damage by reducing maize yields and by increasing input costs for disease management. The most sustainable control of maize diseases is through the release and planting of maize cultivars with durable disease resistance. The wheat gene Lr34 provides durable and partial field resistance against multiple fungal diseases of wheat, including three wheat rust pathogens and wheat powdery mildew. Because of its unique qualities, Lr34 became a cornerstone in many wheat disease resistance programmes. The Lr34 resistance is encoded by a rare variant of an ATP-binding cassette (ABC) transporter that evolved after wheat domestication. An Lr34-like disease resistance phenotype has not been reported in other cereal species, including maize. Here, we transformed the Lr34 resistance gene into the maize hybrid Hi-II. Lr34-expressing maize plants showed increased resistance against the biotrophic fungal disease common rust and the hemi-biotrophic disease northern corn leaf blight. Furthermore, the Lr34-expressing maize plants developed a late leaf tip necrosis phenotype, without negative impact on plant growth. With this and previous reports, it could be shown that Lr34 is effective against various biotrophic and hemi-biotrophic diseases that collectively parasitize all major cereal crop species.

Experimental approaches to investigate effector translocation into host cells in the Ustilago maydis/maize pathosystem.

The fungus Ustilago maydis is a pathogen that establishes a biotrophic interaction with Zea mays. The interaction with the plant host is largely governed by more than 300 novel, secreted protein effectors, of which only four have been functionally characterized. Prerequisite to examine effector function is to know where effectors reside after secretion. Effectors can remain in the extracellular space, i.e. the plant apoplast (apoplastic effectors), or can cross the plant plasma membrane and exert their function inside the host cell (cytoplasmic effectors). The U. maydis effectors lack conserved motifs in their primary sequences that could allow a classification of the effectome into apoplastic/cytoplasmic effectors. This represents a significant obstacle in functional effector characterization. Here we describe our attempts to establish a system for effector classification into apoplastic and cytoplasmic members, using U. maydis for effector delivery.