Evaluation of genetic diversity of flowering dogwood (Cornus florida L.) in the eastern United States using microsatellites.

Flowering dogwood (Cornus florida L.) populations have experienced severe declines caused by dogwood anthracnose in the past three decades. Mortality has ranged from 48 to 98%, raising the concern that genetic diversity of this native tree has been reduced significantly. Microsatellite data were used to evaluate the level and distribution of genetic variation throughout much of the native range of the tree. In the first conducted study, we found that genetic variation in areas affected by anthracnose was as high as or higher than areas without die-offs. We found evidence of four widespread, spatially contiguous genetic clusters. However, there was little relationship between geographic distance and genetic difference. These observations suggest that high dispersal rates and large effective population sizes have so far prevented rapid loss of genetic diversity. The effects of anthracnose on demography and community structure are likely to be far more consequential than short-term genetic effects. The second study examined levels and distribution of genetic variation of C. florida throughout Great Smoky Mountains National Park (GSMNP). Significant genetic structure at both landscape and local levels were found. We infer that two genetic clusters exist within the park, mostly separated by the main dividing ridge of the Great Smoky Mountains. The differentiation is statistically significant, but subtle, with gene flow evident through low-elevation corridors. It seems unlikely that recent demographic dynamics have resulted in a depletion of genetic variation in flowering dogwoods

In Vitro Regeneration of Cladrastis kentukea (American yellowwood) and Cornus kousa (kousa dogwood)

Selection of superior individuals followed by clonal vegetative propagation is a very important strategy for plant improvement. Cloning via tissue culture can produce a population of an identical genotype without limits. A single specimen tree of Cladrastis kentukea and five different Cornus kousa cultivars were selected for tissue culture studies. These trees exhibited superior performance in horticultural trials, including disease resistance and drought tolerance, which are highly important to the green industry. Axillary buds from a single C. kentukea tree were initially cultured on either Woody Plant Medium (WPM) or Murashige and Skoog (MS) containing 0, 1, 2, or 4 μM 6–benzylaminopurine (BA). Cultures were transferred to fresh medium every four weeks. Elongated shoots were harvested after thirty-nine weeks and transferred to half-strength MS medium supplemented with following concentrations of IBA: 0, 3, 30, 100, and 300 μM for three days then returned to half-strength MS without growth regulators. Explants exposed to 300 μM of IBA produced significantly more roots (75%) compared to explants exposed to other treatments. Fifty- four and forty- six percent of the microshoots rooted when exposed to 100 and 30 μM IBA, respectively. Only 4% of the microshoots rooted when exposed to 3 μM IBA and none of the microshoots in the control treatment (0 IBA) rooted. Although 300 μM treatment yielded the most rooted plantlets, there was significantly higher terminal meristem abortion compared to other treatments. There were no statistical differences between the numbers of roots and total root length among all treatments. Additionally, all microshoots that rooted had lenticels, suggesting that presence of lenticel cambial activity can possibly predict rooting abilities of selected microshoots. Rooted microshoots were gradually acclimatized to non-sterile environment. Axillary and apical buds from five Cornus kousa cultivars (‘Little Beauty’, ‘Samaritan’, ‘Heart Throb’, ‘Rosabella’ and ‘Christian Prince’) were initially established on either WPM or one-half Woody Plant Medium/Broad Leaved Tree Medium (BW), amended with the following concentrations of 6–benzylaminopurine (BA): 0, 2, 4, and 8 μM. After explants were transferred at four-week intervals for 28 weeks beginning in April, only microshoots of ‘Samaritan’, ‘Heart Throb’, and ‘Rosabella’, were harvested from proliferating cultures and placed on rooting media. ‘Little Beauty’ and ‘Christian Prince’ did not perform well in multiplication phase of tissue culture and were excluded from further studies. Rooting media contained WPM or BW supplemented with either 1- naphthaleneacetic acid (NAA), indole-3-butyric acid (IBA), or indole-3-acetic acid (IAA) at the following concentrations: 0, 0.5, 1.5, 4.5, and 13.5 μM. Six weeks following rooting experiment, preliminary data was collected and results indicated a total of nine plants rooted on both WPM and BW media supplemented with IBA, 17 plants rooted on media supplemented with NAA, and 14 plants rooted plants supplemented with IAA. NAA and IAA appeared to be better for root production on C. kousa cultivars microshoots than IBA. Moreover, both WPM and BW media supported rooting of C. kousa microshoots. However, WPM appears to support more root production compared to BW. A greater number of ’Samaritan’ and ‘Heart Throb’ microshoots rooted on WPM amended with a wide range of NAA concentrations, whereas more ‘Rosabella’ microshoots rooted on BW medium amended with various concentrations of IAA. Since ‘Rosabella’ and ‘Heart Throb’ are very closely related and should have rooted with similar treatments, further research is needed to confirm this finding. Additionally, microshoots placed on either basal media supplemented with NAA produced significant amount of callus compared to microshoots exposed to other growth regulator treatments. The highest mean number of roots per rooted microshoot was recorded on ‘Samaritan’ when exposed to various NAA concentrations. In conclusion, the most and best rooting occurred with IBA treatments at lower concentrations, 0.5 and 1.5 μM, whereas NAA and IAA treatments were inconclusive

"Jumping Jack": Genomic Microsatellites Underscore the Distinctiveness of Closely Related Pseudoperonospora cubensis and Pseudoperonospora humuli and Provide New Insights Into Their Evolutionary Past

Downy mildews caused by obligate biotrophic oomycetes result in severe crop losses worldwide. Among these pathogens, Pseudoperonospora cubensis and P. humuli, two closely related oomycetes, adversely affect cucurbits and hop, respectively. Discordant hypotheses concerning their taxonomic relationships have been proposed based on host-pathogen interactions and specificity evidence and gene sequences of a few individuals, but population genetics evidence supporting these scenarios is missing. Furthermore, nuclear and mitochondrial regions of both pathogens have been analyzed using microsatellites and phylogenetically informative molecular markers, but extensive comparative population genetics research has not been done. Here, we genotyped 138 current and historical herbarium specimens of those two taxa using microsatellites (SSRs). Our goals were to assess genetic diversity and spatial distribution, to infer the evolutionary history of P. cubensis and P. humuli, and to visualize genome-scale organizational relationship between both pathogens. High genetic diversity, modest gene flow, and presence of population structure, particularly in P. cubensis, were observed. When tested for cross-amplification, 20 out of 27 P. cubensis-derived gSSRs cross-amplified DNA of P. humuli individuals, but few amplified DNA of downy mildew pathogens from related genera. Collectively, our analyses provided a definite argument for the hypothesis that both pathogens are distinct species, and suggested further speciation in the P. cubensis complex

Removing Systemic Barriers to Equity, Diversity, and Inclusion: Report of the 2019 Plant Science Research Network Workshop “Inclusivity in the Plant Sciences”

A future in which scientific discoveries are valued and trusted by the general public cannot be achieved without greater inclusion and participation of diverse communities. To envision a path towards this future, in January 2019 a diverse group of researchers, educators, students, and administrators gathered to hear and share personal perspectives on equity, diversity, and inclusion (EDI) in the plant sciences. From these broad perspectives, the group developed strategies and identified tactics to facilitate and support EDI within and beyond the plant science community. The workshop leveraged scenario planning and the richness of its participants to develop recommendations aimed at promoting systemic change at the institutional level through the actions of scientific societies, universities, and individuals and through new funding models to support research and training. While these initiatives were formulated specifically for the plant science community, they can also serve as a model to advance EDI in other disciplines. The proposed actions are thematically broad, integrating into discovery, applied and translational science, requiring and embracing multidisciplinarity, and giving voice to previously unheard perspectives. We offer a vision of barrier-free access to participation in science, and a plant science community that reflects the diversity of our rapidly changing nation, and supports and invests in the training and well-being of all its members. The relevance and robustness of our recommendations has been tested by dramatic and global events since the workshop. The time to act upon them is now

Colrado Wildflowers

Colorado wildflowers.https://trace.tennessee.edu/utiaphoto_2014/1480/thumbnail.jp

Yin and Yang of Our Work

Geosmithia morbida Canker on Black Walnut. Colorado 2013.https://trace.tennessee.edu/utiaphoto_2014/1703/thumbnail.jp

Collecting Oysters

Collecting oysters at Dewees Island, SC.https://trace.tennessee.edu/utiaphoto_2014/1622/thumbnail.jp

Austin, TX

Austin, TXhttps://trace.tennessee.edu/utiaphoto_2014/1442/thumbnail.jp

The Less Seen Cades Cove

This photo was taken near a trail that runs from Cades Cove to the Tail of the Dragon (US-129).https://trace.tennessee.edu/utiaphoto_2014/1470/thumbnail.jp