Three species of the Old World genus Dipsacus L. are considered invasive in the Americas, yet they may differ in how they spread and reproduce and in their genetic diversity. Differences in invasion method may suggest that different management techniques are needed for each species. We performed genetic analyses on 572 plants in 69 populations from the United States, Argentina, and Eurasia with the goals of analyzing taxonomy, diversity, mode of reproduction, population structure, and founder effect of each of these species’ invasions, as well as looking for evidence of recent or ongoing hybridization. We found Indian teasel [Dipsacus sativus (L.) Honck.] to be lowest in diversity and possibly reliant on self-pollination more than the other species, Fuller’s teasel (Dipsacus fullonum L.) and cutleaf teasel (Dipsacus laciniatus L.). We found no evidence of hybridization within the invasions and no support for D. sativus as a subspecies of D. fullonum. The closest genetic matches of D. fullonum from the United States to the native range were with Hungary and Spain, while the closest match for D. fullonum between Argentina and the native range was with Spain. Dipsacus laciniatus from the United States most closely matched with samples from Russia. Population structure information regarding these three weedy Dipsacus species can help us understand their invasive processes as well as give insight into their management and the development of a biological control program.

Cosmopolites sordidus (Germar), commonly known as banana corm weevil, is an important economic pest in Asia that can cause severe yield loss depending upon the stage at which infestation occurs. In spite of its economic importance, little is known about the population structure of this pest in India. Random amplified polymorphic DNA (RAPD) and amplified fragment length polymorphism (AFLP) were used to characterize the population genetic structure of C. sordidus collected from five hot spot locations in India. Nineteen RAPD primers and five selective AFLP primer combinations generated 147 and 304 amplification products, respectively. UPGMA dendrograms generated with both marker systems failed to reveal populations clustered based on geographic distance, which was confirmed by the Mantel test, which did not show a strong correlation between genetic distance and geographic distance. Values of indices of genetic identity showed that the populations were closely related. Though the gene flow estimate (Nm) between the populations was 0.469, suggesting restricted gene flow, the populations are not genetically distinct. These observations suggest that the range expansion of this banana pest in India has taken place through transport of infested corms and plant material, resulting in genetically close populations that are geographically distinct. These results provide important information on the population structure of this pest in India, which will aid in designing suitable strategies for its control and management, especially with respect to insecticide resistance.

Genetic markers have been used in horticulture and conservation biology to identify breeding lines, assess genetic diversity, and examine gene flow. In weed science, analysis of genetic markers is not as common, as the focus often lies in the development of control methods. This is unfortunate, because advances in genetic marker techniques may lead to innovative methods in controlling weedy plants. Microsatellites, random amplified polymorphic DNA (RAPDs), intersimple sequence repeats (ISSRs), amplified fragment length polymorphisms (AFLPs), DNA sequences, single nucleotide polymorphisms (SNPs), and derived cleaved amplified polymorphic sequences (dCAPS) have been used in studying genetics of weedy plants. Beyond assessing genetic diversity of weeds, markers have been used to examine gene flow, patterns of dispersal, ploidy levels, and relationships of weedy and nonweedy species, as well as identifying founder populations. Identification of closely related species may indicate the potential for hybridization, cross reactivity of chemical applications, or nontarget biological control effects. Furthermore, markers have been used in identification of mutations conferring herbicide resistance and identification of regions correlating fitness of weedy and hybrid plants in new habitats. Knowledge from genetic markers provides fundamental information that can be used in advancing chemical and biological control in weed management. This article serves as a review of these marker types and their application to weed science.

Andean arracacha (Arracacia xanthorrhiza Bancr.) is a valuable but poorly known vegetatively reproduced root crop whose origin is still unresolved. Wild tuberous forms are present in the presumed areas of domestication and have a perennial or monocarpic life history. To elucidate the origin of the cultivated form, we surveyed a molecular analysis with amplified fragment length polymorphisms (AFLPs) in a representative sample of this crop and its wild relatives from Ecuador and Peru, the presumed areas of domestication. Wild species with tuberous and non-tuberous roots were included, as well as the perennial and monocarpic forms of the presumed wild ancestor. While the two wild varieties of A. xanthorrhiza were closest to the cultivars, they were distinguished by AFLPs. Unexpectedly, two clearly distinct groups were formed among the cultivars, one of which was significantly closer to the monocarpic wild form. However, the chloroplast DNA survey revealed greater similarity between all of the cultivars and the wild perennial A. xanthorrhiza. These results combined with the morphological and life history features, confirms the hypothesis that arracacha domestication started from the wild perennial form. We suggest this scenario of domestication followed by an unsuspected introgression in the cultivation, resulting in two cryptic genetic groups, well distinguished at the molecular level. This is an important revelation with implications in genetic resource conservation and breeding standpoints in this promissory crop.

Amplified fragment length polymorphisms (AFLPs) offer a reproducible, multiplex DNA assay by which to genotype mapping populations. We have evaluated physiological traits in barley seedlings grown in an hydroponic system and given a salt treatment. Multiple regression was used to show associations between AFLPs and quantitative traits. Effects at different loci were detected in stress treatments in comparison to the control implying that either novel gene action was induced by salt stress or that normal activity was reduced to a low level where alternate gene action is revealed. The QTLs occurred on all chromosomes but there appeared to be clusters of loci on chromosomes 1 (7H), 4 (4H), 5 (1H) and 6 (6H). The significance of our results is discussed in the context of studies to explore the barley genome and the application of the results of these genetical analyses to barley breeding.