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  • Author or Editor: A. N. Roberts x
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The genus Cornus consists of many species, of which C. florida, C. kousa, C. mas, and C. stolonifera are four main ornamental species in North America, Asia, and Europe. For example, over 200 cultivars of C. florida alone have been developed for the nursery industry. Microsatellite loci, or SSR, are useful markers for studying genetic diversity and for creating linkage maps of the various species. The objective of this study was to investigate the genetic diversity between these four Cornus species and eight hybrids. Evaulation of the diversity will be useful in assessing the selection pressure of breeders and/or genetic drift of these dogwood cultivars/lines. Fifteen SSR primer pairs were selected to examine 56 Cornus cultivars and/or lines of the four species and hybrids. The study included 28 C. florida cultivars and lines, 15 C. kousa cultivars and lines, four C. stolonifera cultivars, one cultivar of C. mass and eight hybrids between various Cornus species. An exceptionally high level of diversity was detected among the 56 entries in both the number and size range of SSR alleles. A total of 95 alleles with an average of 7.8 alleles per loci were detected among these 56 genotypes. These selected Cornus cultivars and/or lines could be clustered into four to six subgroups. Some Cornus species were integrated into other species groups, suggesting gene flow between species via the breeding or evolution. SSR markers can contribute to the exploitation of genetic diversity for existing Cornus germplasm. For further study, examination of more SSR loci could explain more completely the diversity among these Cornus cultivars and lines.

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Sunn hemp, Crotalaria juncea L., is a warm-season legume that is planted before or after a vegetable cash crop to add nutrients and organic matter to the soil, for weed-growth prevention, and to suppress nematode populations. Sunn hemp flowers may also provide nectar and pollen for pollinators and enhance biological control by furnishing habitat for natural enemies. Despite these benefits, adoption in the United States has been limited because of restricted availability of seeds, particularly in temperate climates. Experiments were conducted in north-central Florida to compare flowering and seed production of domestic and foreign sunn hemp lines across different seeding rates and planting dates. Our objectives were to test whether a low seeding rate would result in the production of higher numbers of flowers and to test whether planting earlier in the season would also result in higher numbers of flowers. Our results over a 2 year period showed that the domestic cultivar AU Golden is capable of substantial flowering and seed production in the test region, confirming the compatibility of local environmental conditions. Seed costs suggest that ‘AU Golden’ is comparable with sunn hemp lines grown in foreign countries and is much less expensive than the standard cultivar Tropic Sun from Hawaii. The results demonstrate the potential economic viability of early flowering cultivars of sunn hemp as a cover crop alternative in Florida to improve soils in agricultural landscapes.

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The genus Chrysogonum is native to the eastern United States. Three entities have been recognized—either as three varieties of Chrysogonum virginianum or as two species, one of them with two varieties. The current study suggests that a fourth entity should be recognized. Several forms of the complex are in commercial trade as ornamentals. As very limited molecular information on Chrysogonum is available, we developed a set of genic simple sequence repeat markers (eSSRs) from de novo transcriptome sequencing. We tested a set of 17 eSSRs on a collection of C. virginianum genomic DNA samples from the three botanical varieties, and a new putative type observed in Tennessee, dubbed “Ocoee-type” for its geographic origin. The polymerase chain reaction and capillary electrophoresis analyses with downstream population genetics tools verified the usefulness of the eSSRs. By applying this approach, we showed recognizable variation within Chrysogonum, although it did not correspond exactly to previous infraspecific classifications. Finally, as demonstrated for the commercial cultivar Pierre included in the study, the eSSRs can be used for enhancing the future breeding or hybridization efforts of this ornamental plant.

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Root traits are an important component for productive plant performance. Roots offer immediate absorptive surfaces for water and nutrient acquisition and are thus critical to crop growth and response to biotic and abiotic stresses. In addition, roots can provide the first line of defense against soilborne pathogens. Watermelon crop performance is often challenged by inclement weather and environmental factors. A resilient root system can support the watermelon crop’s performance across a diverse range of production conditions. In this study, 335 four-day-old watermelon (Citrullus spp.) seedlings were evaluated for total root length, average root diameter, total root surface area, and total root volume. Total root length varied from 8.78 to 181 cm (20.6-fold variation), total surface area varied from 2 to 35.5 cm2, and average root diameter and total root volume had an 8- and 29.5-fold variation, respectively. Genotypes PI 195927 (Citrullus colocynthis) and PI 674448 (Citrullus amarus) had the largest total root length values. Accessions PI 674448 and PI 494817 (C. amarus) had the largest total root surface area means. Watermelon cultivars (Citrullus lanatus) had a relatively smaller root system and significantly fewer fibrous roots when compared with the roots of the other Citrullus spp. Positive genetic correlations were identified among total root length, total root surface area, and total root volume. This genetic information will be useful in future breeding efforts to select for multiple root architecture traits in watermelon. Germplasm identified in this study that exhibit superior root traits can be used as parental choices to improve watermelon for root traits.

Open Access