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Vegetative phase change, or the transition from juvenile vegetative to adult vegetative tissues, is essential to the lifecycle of higher plants. In maize (Zea mays L.), juvenile and adult vegetative tissues have distinctly different traits that may confer differing amounts of resistance to disease and insect infestations. Vegetative phase change has been linked to resistance to insects and common rust (Puccinia sorghi Schwein.). Seven cycles of divergent recurrent selection for early and late phase change were evaluated to determine effects of selection on phase change, insect resistance, and agronomic traits. Last leaf with juvenile wax, a trait indicative of the timing of phase change, was the selected trait. Divergent recurrent selection was effective in creating populations that underwent vegetative phase change at distinctly different developmental stages. Last leaf with juvenile wax moved from leaf 8.70 in the original population to leaf 14.48 in the late direction and 6.04 in the early direction. First leaf with adult wax moved from leaf 6.36 in the original population to leaf 8.15 in the late direction and 5.28 in the early direction. Several agronomic traits were also significantly altered by selection including plant and ear height, leaf number, kernel row count, and days to silking. C7Late plants averaged four more leaves and were taller and later flowering than C7Early plants. European corn borer (Ostrinia nubilalis Hubner) feeding damage on the second leaf above the ear was significantly greater in the late phase change direction, and significantly correlated with last leaf with juvenile wax. Most ear traits and European corn borer stalk damage resistance were not altered in a consistent way by selection.

Several states in the Midwestern United States are using risk assessment to determine the invasiveness of introduced plant species, and each assessment process is different. This may lead to differences in results for the same species between states, creating concern about credibility by those using the assessments. In this study, risk assessments for six Midwestern states were compared, examining format, content, and assessment committee membership. Case studies were conducted for four species for which at least five of the six states in the study completed a risk assessment; results were compared in the context of general differences in assessment content and those specific to each species. Furthermore, 14 species for which only four of the six states completed assessments were briefly examined for outcome differences only, and possible reasons for these inconsistencies. Overall, differences in assessments did not result in incompatible conclusions for the species compared, suggesting that unique assessments in each state can provide consistent and credible results. We propose that these Midwestern states share species resources with each other to further improve consistency between the assessments.

Palmer amaranth–a fast-growing, challenging to control noxious weed that significantly reduces crop yields—was first found in Minnesota in September 2016 in conservation plantings sown with Palmer amaranth contaminated seed mixes. Minnesota Department of Agriculture (MDA) designated Palmer amaranth as a Prohibited Noxious Weed in 2015 and listed it as a Noxious Weed Seed in 2016 by emergency order. A genetic test to identify Palmer amaranth was simultaneously developed by multiple labs providing a tool to limit its spread as a contaminant in seed. Seed companies adopted genetic testing methods for labeling seed for sale reducing introductions via the seed pathway. Additionally, MDA determined that manure spread on crop fields from contaminated screenings fed to livestock resulted in new infestations. Limiting spread via these and other potential pathways was critical to successfully reducing the impact of Palmer amaranth. MDA, University of Minnesota (UMN) Extension, Conservation Corps Minnesota and Iowa (CCMI), farmers, and other partners are working to eradicate these infestations before they can spread. In 2016, 35 sites were sown with Palmer amaranth contaminated seed mixes. Palmer amaranth was found at eight (23%) of these sites. Management with intensive scouting, torching, prescribed burning, and herbicide application was implemented in 2016 and 2017. By 2018, no Palmer amaranth was found at any of these sites. Similar success to newer infestations in 2018, 2019, and 2020 was achieved using the same methods. MDA recorded management activities and documented a comprehensive timeline of Palmer amaranth in Minnesota. This timeline provides a story of success and challenges in combating and eradicating Palmer amaranth.

In maize, timing of vegetative phase change has been implicated in the response to certain pests and environmental stresses. Common rust is the most serious disease of sweet corn in the north central United States. Sweet corn hybrids differing for resistance to common rust were evaluated for vegetative phase change traits. There were significant differences among hybrids for all vegetative phase change traits measured, as well as resistance to common rust. Certain hybrids displayed rapid transition (within two leaves) from juvenile to adult vegetation, while others displayed prolonged transition (within four leaves). There were no significant correlations between vegetative phase change traits and common rust severity among the commercial sweet corn hybrids evaluated in this experiment.

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Clasen, B. M., Moss, N. G., Chandler, M. A. and Smith, A. G. 2011. A preliminary genetic structure study of the non-native weed, common tansy (Tanacetum vulgare). Can. J. Plant Sci. 91: 717–723. Common tansy is an herbaceous perennial member of the Asteraceae and is considered a weed in North America. Common tansy was introduced deliberately for use as a funerary herb, medicine, preservative, and animal and insect repellent. It is known to escape cultivation and invade disturbed areas, spreading both sexually and asexually. This paper reports a preliminary analysis of the genetic structure of 10 invasive common tansy populations in Minnesota and Montana, USA, and Alberta, Canada. Ninety polymorphic loci were found using six inter simple sequence repeat (ISSR) primers used to amplify DNA from 40 individuals from 10 discrete populations. The diversity within and among populations was assessed using the Dice coefficient of similarity and AMOVA. The AMOVA showed that diversity within populations was generally high and that there was relatively small variation among populations. An unweighted pair-group with arithmetic mean (UPGMA) dendrogram was constructed based on the distance between populations, and demonstrated substantial and distinct clustering of a population from Ramsey County, Minnesota. A principal coordinates analysis clustered all individuals from Ramsey County distinctly from other individuals, indicating a possible limited gene flow among this population and the other populations sampled in this study. Understanding genetic diversity and the distribution of diversity within and among populations may help predict the potential for successful management of common tansy populations in North America.