Protocol for Producing Synthetic Polyploid Oats

A protocol to produce synthetic oats by introducing alien genetic variations into cultivated oats is proposed based on suitable genetic relationships between Avena species. Furthermore, artificial hybridization procedures between different ploidy species are explained. Amphiploids can be produced by rescuing aborted embryos and treating the F₁ hybrids with colchicine to overcome sterility between interspecific plants. Furthermore, I present the cytological methods for observing somatic and meiotic chromosomes in the treated hybrids.

Screening Wild Oat Accessions from Morocco for Resistance to Puccinia coronata

Here, we report the screening of 332 new accessions of 11 different wild oat (Avena) species from the United States Department of Agriculture National Small Grains Collection in Aberdeen, ID, for resistance to crown rust disease, caused by Puccinia coronata f. sp. avenae. This collection originated from Morocco and includes Avena agadiriana, A. atlantica, A. barbata, A. damascena, A. eriantha, A. hirtula, A. longiglumis, A. magna, A. murphyi, A. sterilis, and A. wiestii. After screening this collection with a highly diverse population of P. coronata f. sp. avenae, 164 accessions (49%) were rated moderately resistant to resistant in the preliminary screen at the seedling stage and 181 accessions (55%) rated moderately resistant to highly resistant in the adult plant stage. Although none of the accessions showed a highly resistant response consistently in the seedling stage, 20 accessions did display a highly resistant response in the adult plant stage. Both seedling as well as adult plant resistance was found in 150 (45%) of the accessions. Virulence in P. coronata has been reported to all resistance genes currently being used in North American oat cultivars. The new resistance sources presented here are potentially new sources for future breeding. The resistance found in 52 accessions of A. magna and A. murphyi with the AACC genome is especially valuable because these should be relatively easy to transfer into hexaploid A. sativa.

Tall oatgrass mosaic virus (TOgMV): a novel member of the genus Tritimovirus infecting Arrhenatherum elatius

A novel tritimovirus of the family Potyviridae was isolated from tall oatgrass, Arrhenatherum elatius, exhibiting mosaic symptoms. The virus, for which the name tall oatgrass mosaic virus (TOgMV) is coined, has a filamentous particle of 720 nm and is associated with pinwheel inclusion bodies characteristic of members of the family Potyviridae. The virus was mechanically transmitted to tall oatgrass seedlings, which subsequently exhibited mosaic symptoms. The experimental host range was limited to a few monocot species. The complete genome sequence of TOgMV was determined to be 9359 nucleotides, excluding the 3' polyadenylated tail. The viral RNA encodes one large putative open reading frame of 3029 amino acids with a genome organization typical of monopartite potyvirids. Pairwise comparison of putative mature proteins and proteinase cleavage sites indicated that TOgMV is most closely related to members of the genus Tritimovirus. Phylogenetic analysis of the complete polyprotein and CP sequences of representative members of the family Potyviridae indicate that TOgMV is a distinct tritimovirus naturally infecting tall oatgrass.

Additional Sources of Broad-Spectrum Resistance to Puccinia coronata f. sp. avenae from Canadian Accessions of Avena barbata

Crown rust (Puccinia coronata f. sp. avenae) is considered the most damaging disease of oat and the use of race-specific seedling (Pc) genes for resistance has been the primary means of control. As these resistance genes from cultivated oat, Avena sativa, and the wild hexaploid animated oat, A. sterilis, were deployed in oat cultivars, corresponding virulence in the U.S. crown rust population increased rapidly, such that the effective lifespan of a resistant cultivar in the United States is now 5 years or less. Introgression of resistance from diploid and tetraploid Avena spp. into hexaploid oat has been difficult due to the difference in ploidy levels and the lack of pairing of homeologous chromosomes between species. The wild tetraploid slender oat, A. barbata, has been a source of powdery mildew and stem rust resistance in cultivated oat but has largely been unexploited for crown rust resistance. A relatively high percentage of A. barbata accessions from the United States Department of Agriculture (USDA) National Small Grains Collection were resistant to a highly diverse crown rust population in recent tests. Tests of 1,099 A. barbata accessions from the Canadian Plant Gene Resources Center not represented in the USDA collection revealed that a similar percentage (11.4%) were at least moderately resistant at the seedling and adult plant stage when tested with a highly diverse bulk inoculum derived from the St. Paul buckthorn nursery. Eighteen accessions were rated as highly resistant or a mix of highly resistant and resistant plants in both seedling and adult plant tests. Three accessions (CN21531 from Italy and CN26271 and CN26305 from Spain) displayed a unique "blotchy" resistant reaction as adult plants. Resistant accessions were found from throughout much of the natural range of A. barbata but the Western Mediterranean and Lebanon had the highest frequency of accessions with broad-spectrum resistance.

Broad-Spectrum Resistance to Crown Rust, Puccinia coronata f. sp. avenae, in Accessions of the Tetraploid Slender Oat, Avena barbata

The use of race-specific seedling genes for resistance has been the primary means of controlling crown rust of oat (Puccinia coronata). As resistance genes from hexaploid cultivated oat, Avena sativa and, later, the wild hexaploid animated oat, A. sterilis, were deployed in oat cultivars, corresponding virulence in the crown rust population increased rapidly, such that the effective lifespan of a resistant cultivar in the United States is now 5 years or less. Introgression of resistance genes from diploid and tetraploid Avena spp. into hexaploid oat has been difficult due to differences in ploidy levels and the lack of homology of chromosomes between the two species. The wild tetraploid slender oat, A. barbata, has been a source of powdery mildew and stem rust resistance in cultivated oat but has largely been unexploited for crown rust resistance. In total, 359 accessions of A. barbata from the National Small Grains Collection were evaluated in seedling greenhouse tests. Of these accessions, 39% were at least moderately resistant when inoculated with a crown rust race with low virulence (DBBC). When tested further with a highly diverse bulk inoculum from the 2006 and 2007 St. Paul buckthorn nursery, 48 accessions (approximately 13%) were resistant. Many of these accessions were heterogeneous in reaction, but two accessions (PI320588 from Israel and PI337893 from Italy) were highly resistant (immune) and two others (PI337886 from Italy and PI367293 from Spain) consistently produced resistant reactions (chlorotic flecks) in all tests. Resistant accessions were found from throughout much of the natural range of A. barbata. Crosses of some of the better accessions have been made to cultivated oat.