Pygmaeomycetaceae, a new root associated family in Mucoromycotina from the pygmy pine plains

ABSTRACTA new genus, Pygmaeomyces, and two new species are described based on phylogenetic analyses, phenotypic and ecological characters. The species delimitation was based on concordance of gene genealogies. The Pygmaeomyces cultures were isolated from the roots of mountain laurel (Kalmia latifolia) and pitch pine (Pinus rigida) from the acidic and oligotrophic New Jersey Pygmy Pine Plains; however, they likely have a broader distribution because their internal transcribed spacer (ITS) sequences have high similarity with a number of environmental sequences from multiple independent studies. Based on the phylogeny and phenotypical characters, a new family Pygmaeomycetaceae is proposed to accommodate this new lineage in Mucoromycotina. Pygmaeomycetaceae corresponds to Clade GS23, which was identified based on a sequence-only soil fungal survey and was believed to be a distinct new class. Compared to the culture-based methods, we observed that sequence-only analyses tend to over-estimate the taxonomic level. Results from this work will facilitate ecological and evolutionary studies on root-associated fungi.

Evaluation of Twenty-one Mountain Laurel Cultivars for Container and Landscape Performance in the Southeastern United States

Mountain laurel (Kalmia latifolia) is an outstanding ornamental shrub due to its attractive foliage and showy inflorescences. Breeding efforts have led to improved selections that have predominantly been developed and evaluated in the northeastern United States. Consequently, most cultivars have largely been dismissed as incompatible for the southeastern U.S. environmental conditions by nursery growers and consumers. This study was conducted over a 4-year period to evaluate 21 popular mountain laurel cultivars, primarily developed in the northeastern United States, for container and field performance in Georgia. All cultivars yielded considerable growth in the first year of container trials, indicating production of mountain laurel as a 1-year container crop is feasible. Cultivars displayed significantly different total growth index throughout the container trial. Fast-growing cultivars such as Bullseye and Ostbo Red yielded more than 100, 150, and 250 cm of growth index in 1, 2, and 4 years, respectively. Conversely, cultivars that grew slower, such as Firecracker and Tinkerbell, had less than 80, 115, and 180 cm in 1, 2, and 4 years, respectively. Cultivars were classified into five groups, using principal component analysis, that included dwarf habit with pink flower, dwarf habit with nonpink flower, nondwarf habit with green stem and white flower, nondwarf habit with pigment-patterned flower, and nondwarf habit with pink flower. In a field study, performance rating of 21 cultivars ranged from 2.0 to 4.8 (out of 5.0) in 2014 and from 2.0 to 5.0 in 2015. Ten cultivars that received the highest ratings over these 2 years were selected for a subsequent field trial in 2016. Cultivars showed overall decreased ratings (1.0–3.3) from the previous 2 years because of late spring planting. ‘Ostbo Red’, ‘Pristine’, and ‘Tinkerbell’ had higher performance ratings, more net growth, and less decrease in maximum quantum yield, which indicated suitable adaptation to southeastern U.S. environmental conditions. Nursery growers and consumers should benefit from regional cultivar trial information derived from this study. ‘Ostbo Red’, ‘Pristine’, and ‘Tinkerbell’ performed well across trials and therefore are recommended for southeastern U.S. landscapes based on superior container and field performance, leaf spot (caused by Mycosphaerella colorata) tolerance, and morphologic distinctions.

In Vitro Seed Germination of Kalmia latifolia L. Hybrids: A Means for Improving Germination and Speeding Up Breeding Cycle

Kalmia latifolia L. (mountain laurel), a member of Ericaceae, is a beautiful ornamental shrub native to the eastern United States. The plant is not common in the southeastern United States landscapes because of the limited heat tolerance of most commercial cultivars. Breeding of heat-tolerant cultivars can be achieved by cross hybridization, but is often challenged by low germination percentage, long germination time, and potential abortion of cross-hybridized seeds. We used in vitro seed germination to enhance germination and shorten germination time and investigated the appropriate collecting time, optimal basal medium, and pH for this approach. Collecting time affected in vitro seed germination, with more mature hybrid seeds [collected 4–5 months after pollination (MAP)] having higher germination rate (90% in 4 weeks) than the less mature seeds collected in 2 MAP (20% in 7 weeks). Seedlings from the mature seeds also produced two true leaves on average after 8 weeks of culture, whereas seedlings from the less mature seeds had no true leaves. Woody Plant Medium (WPM) better enhanced in vitro seed germination compared with Murashige and Skoog (MS) or Gamborg’s B5 (B5) medium. WPM yielded higher germination (98%) than MS (90%) and significantly greater total leaf area per seedling (67 mm3) than MS (50 mm3) and B5 (52 mm3) for seeds of ‘Firecracker’ × ‘Snowdrift’. Similar effects had been observed on seeds from ‘Little Linda’ × ‘Starburst’ and ‘Pristine’ × ‘Peppermint’. The pH ranging from 4.2 to 5.4 did not affect seed germination and seedling development of mountain laurel hybrids. Our protocol enabled early collection of mountain laurel hybrid seeds 1 month before their full maturation and permitted seeds to germinate in 4 weeks on WPM, which shortened the period from crossing to the seedling stage from up to 15 to 6 months and enhanced germination percentage from 30% to more than 90% compared with traditional seed germination. This protocol should be applied to promote the breeding and selection of new mountain laurel cultivars for the southeastern United States landscapes.

Forest dynamics and climate sensitivity of an endangered Carolina hemlock community in the southern Appalachian Mountains, USA

During the last century, the eastern United States has functionally lost two major tree species (American chestnut and American elm), two more, eastern and Carolina hemlock, will likely be functionally extinct during much of their ranges by 2050. Carolina hemlock forests are geographically limited to high elevations in the southern Appalachian Mountains and are considered to be endangered. We collected forest stand, composition, and tree age data at the beginning of a hemlock woolly adelgid (HWA) infestation. Prior to the arrival of HWA, Carolina hemlocks were healthy and densely populated in the overstory and understory. While Carolina hemlock regenerated successfully and continuously from 1850 to 2010, the development of this Carolina hemlock forest will be altered by the HWA and may result in an increase in the density of northern red oak, white oak, mountain laurel, and Catawba rhododendron. Carolina hemlocks prefer cool, wet summers with older trees experiencing greater reductions in radial growth than younger trees during droughts. This study demonstrates that dendrochronological techniques can provide critical annual information on Carolina hemlock forest development and tree age–climate response. Our results provide a multicentury perspective for conservation efforts and management of Carolina hemlock forests in the southern Appalachian Mountains.