Didymella fabae (leaf and pod spot).

Ascochyta blight is the most severe disease of cool-season pulses (Davidson and Kimber, 2007). D. fabae (anamorph: Ascochyta fabae) attacks Vicia faba and can survive and reproduce in and spread from crop debris or be transported in infected seed. Introduction on infected seed occurred in Australia and Canada in the 1970s, and was probably the means for the pathogen's original spread to countries outside southwestern Asia. Ascospores are disseminated by wind from the debris as primary inoculum and secondary cycles are initiated by conidia spread by rain splash from plant lesions. The fungus is host-specific in causing disease, but may be able to survive in non-host plants and reproduce on their debris. It is not treated as a phytosanitary risk or listed as an invasive pathogen by major organizations. Seed certification is the primary means of preventing its spread to new areas and the importation of new genotypes of the fungus to areas already infested.

Meeting on September 16, 1892

A. Martin (Berlin), speaker. The ethiology of ectopic pregnancy is still very dark. Existing hypotheses explain only a few isolated cases, and that is far from perfect. We will not solve this issue satisfactorily and accurately until the physiology of impregnation (seed introduction) is clarified.

Low genetic divergence and variation in coastal dune populations of the widespread terrestrial orchid Epipactis helleborine

Reconstructing the early history of species divergence and quantifying the level of standing genetic variation in diverging populations are central to our understanding of ecotype formation and ultimately speciation. In this study, we used single nucleotide polymorphisms to reconstruct the evolutionary history of species divergence in coastal dune populations of the widespread terrestrial orchid Epipactis helleborine and to investigate the level of standing genetic variation in 29 coastal dune populations in a fragmented dune landscape along the Belgian and French coast. Additionally, we used seed introduction experiments to assess the potential for gene flow into existing populations after long-distance seed dispersal and the ability to colonize vacant sites. Our results showed that coastal dune populations diverged only recently from inland populations, went through a significant bottleneck and were most probably the result of a single colonization event. Current levels of population genetic diversity are low and not related to population size or spatial isolation. The sampled dune populations also showed little genetic differentiation, and no apparent spatial genetic structure was observed. Seed introduction experiments showed that seeds of coastal dune populations germinated easily in both occupied and unoccupied sites in dune habitat, indicating that the availability of suitable mycorrhizal fungi is not limiting the distribution of coastal dune populations and that gene flow through seeds has probably contributed to the observed low levels of genetic differentiation. Overall, these results are consistent with a process of genetic divergence after a single, recent colonization event, followed by extensive gene flow among populations.

Palmer Amaranth (Amaranthus palmeri) Damage Niche in Illinois Soybean Is Seed Limited

Palmer amaranth, a dioecious summer annual forb, originating in Sonoran desert washes, compromises crop yields in much of the southern United States and its range is expanding northward. Appropriate tactics for managing this weed proactively in the Upper Midwest will depend on characterizing its damage niche, the geographic range in which it can reduce crop yields. We implemented a common garden study in 2011 and 2012, planting eight accessions of Palmer amaranth from the southern and midwestern United States, into soybean crops in southern, central, and northern Illinois, at a population density of 8 plants m−2with a biocontainment protocol. Once Palmer amaranth plants initiated flowering, they were removed and burned. Weed survival, flowering, and weed biomass were measured, in addition to soybean yield and weather data. Analyses indicated that Palmer amaranth's damage niche in Illinois soybean was independent of weed genotype or maternal environment. Despite competing only briefly, Palmer amaranth reduced soybean yields in all site–years, indicating its damage niche in Illinois, and much of the Midwest, is limited primarily by seed immigration rate. These results highlight the urgent need for weed managers to learn Palmer amaranth identification, prevent seed introduction, and maintain a policy of zero seed return.