Rathayibacter toxicus, a Select Agent in the United States, is one of six recognized species in the genus Rathayibacter and the best known due to its association with annual ryegrass toxicity, which occurs only in parts of Australia. The Rathayibacter species are unusual among phytopathogenic bacteria in that they are transmitted by anguinid seed gall nematodes and produce extracellular polysaccharides in infected plants resulting in bacteriosis diseases with common names such as yellow slime and bacterial head blight. R. toxicus is distinguished from the other species by producing corynetoxins in infected plants; toxin production is associated with infection by a bacteriophage. These toxins cause grazing animals feeding on infected plants to develop convulsions and abnormal gate, which is referred to as “staggers,” and often results in death of affected animals. R. toxicus is the only recognized Rathayibacter species to produce toxin, although reports of livestock deaths in the United States suggest a closely related toxigenic species may be present. A closely related but undescribed species, Rathayibacter sp. EV, originally isolated from Ehrharta villosa var. villosa in South Africa, is suspected of producing toxin. Many of the diseases caused by Rathayibacter species occur in arid areas and the extracellular polysaccharide they produce is believed to aid in their survival between crops. For example, R. “agropyri” was isolated from infected plant material after being stored for 50 years in a herbarium. Similarly, the anguinid vectors associated with these bacteria form seed galls in infected plants and are capable of surviving for very long periods of time under dry conditions. The addition of R. toxicus to the list of Select Agents has raised concern over its potential introduction and a realization that current diagnostic methods are inadequate to distinguish among Rathayibacter species. In addition, little is known about the Rathayibacter species and their seed gall nematode vectors present in the United States.

Annual wheat displays monocarpic senescence, but amphiploids between wheat and its wild perennial relatives in the genus Thinopyrum generally display a polycarpic, perennial growth habit. In order to determine the chromosomal basis of this phenomenon, life-history characteristics were examined using Chinese Spring wheat and a complete Thinopyrum elongatum (2n=2x=14) chromosome addition series in a Chinese Spring background. Both monosomic and disomic additions and substitutions of Th. elongatum chromosome 4E conferred a polycarpic life history to annual Chinese Spring wheat. Disomic addition lines were found to be perennial under field conditions. This is the first report of a single alien chromosome conferring a polycarpic growth habit to a monocarpic species. Chromosome 4E altered the timing of tiller initiation, such that two growth phases could be clearly identified, the first phase being indistinguishable from the growth of euploid Chinese Spring, followed by a second phase of tiller initiation after the sexual cycle of the first phase tillers was complete (post-sexual cycle regrowth).

Perennial wheat offers a new solution to the long-standing problems of soil erosion and degradation associated with conventional annual small-grain cropping systems in the Pacific Northwest region. Using classical breeding methods, new types of wheat have been developed that maintain the key characteristics of annual wheat, but continue to grow after harvest. Following dormancy in the winter, growth is initiated from the roots or crowns in the spring, allowing a crop to be harvested every fall. By retaining constant soil cover over multiple years, wind and water erosion would be dramatically reduced. In addition, the costs associated with annual seeding and tillage would be minimized, and unlike many reduced tillage systems, it is expected that standard seeding equipment would be suitable for stand establishment. Other potential benefits of perennial wheat include improved wildlife habitat, more efficient use of available water, provision of a potent carbon sink, and the possibility of integrating straw retrieval into a small grains cropping system. Past attempts in the first half of the last century failed to develop perennial wheat as a viable crop, primarily because of low yields, and the research was ultimately abandoned. Perennial wheat production may now be viewed as acceptable for highly erodible land or for obtaining carbon sequestration credits. This paper presents an overview of solutions to the obstacles encountered by previous researchers, introduces some of the newly developed perennial wheat lines, and discusses considerations for management practices.

Plants grown through the winter are subject to selective pressures that vary with each year’s unique conditions, necessitating tolerance of numerous abiotic and biotic stress factors. The objective of this study was to identify molecular markers in winter wheat (Triticum aestivum L.) associated with tolerance of two of these stresses, freezing temperatures and snow mold—a fungal disease complex active under snow cover. A population of 155 F_2:5 recombinant inbred lines from a cross between soft white wheat cultivars “Finch” and “Eltan” was evaluated for snow mold tolerance in the field, and for freezing tolerance under controlled conditions. A total of 663 molecular markers was used to construct a genetic linkage map and identify marker-trait associations. One quantitative trait locus (QTL) associated with both freezing and snow mold tolerance was identified on chromosome 5A. A second, distinct, QTL associated with freezing tolerance also was found on 5A, and a third on 4B. A second QTL associated with snow mold tolerance was identified on chromosome 6B. The QTL on 5A associated with both traits was closely linked with the Fr-A2 (Frost-Resistance A2) locus; its significant association with both traits may have resulted from pleiotropic effects, or from greater low temperature tolerance enabling the plants to better defend against snow mold pathogens. The QTL on 4B associated with freezing tolerance, and the QTL on 6B associated with snow mold tolerance have not been reported previously, and may be useful in the identification of sources of tolerance for these traits.