Horticultural Characterization of Wild Hydrangea quercifolia Seedlings Collected Throughout the Species Native Range

Abstract

Oakleaf hydrangea (Hydrangea quercifolia Bartr.) is an understory shrub native to the southeastern United States. Hydrangeas are popular ornamental landscape plants; however, little is known about the diversity in horticulturally important traits for oakleaf hydrangea. Information regarding the variation in important traits could guide future breeding efforts for the species. Seed was collected from 55 populations throughout the range of the species for the purpose of conducting a horticultural characterization of the species compared with select cultivars. Plant architecture was characterized as plant height, number of nodes, internode length, number of branches, and plant width. Plant architecture was measured for container-grown and field-grown plants in two locations (Minnesota and Tennessee). Tolerance to leaf spot (Xanthomonas campestris L.) was characterized for wild-collected seedlings and cultivars by measuring disease severity under exposure to ambient inoculum. Cold hardiness was characterized during two winters with a controlled freezing experiment. During the first winter, seedlings were tested in January; during the second winter, seedlings and cultivars were tested monthly from October through April. Plant architecture varied by environment, with plants growing larger in Tennessee than in Minnesota. The heights of container-grown and field-grown plants were correlated with the collection site latitude (r = −0.66), with populations from the northeastern extent of the range of the species being the most compact, and populations from Florida being the tallest. Leaf spot severity varied significantly among populations and cultivars and was also correlated with latitude for the seedlings (r = 0.70). Two populations in Florida were identified as sources of high tolerance to leaf spot, whereas ‘Flemygea’ and ‘Alice’ were identified as having moderate tolerance to leaf spot. Cold hardiness varied among populations and cultivars and among months of the winter. The overall maximum cold hardiness was observed in February [mean lethal temperature (LT50) = −33.7 °C], and several populations maintained an extreme level of cold hardiness into late winter. Midwinter cold hardiness also varied by latitude (r = −0.65), with northern populations showing higher levels of cold hardiness. These results indicate that certain wild oakleaf hydrangea populations will be useful for introgressing novel variation into breeding programs.

Precipitation, Temperature, and Population Structure Influence Genetic Diversity of Oakleaf Hydrangea Throughout Its Native Range

“…Plants in a location with a high range in temperature need to withstand both extreme heat and cold, which is a more complex selection pressure than either high or low temperature alone. Consistent with the effect of temperature on genetic diversity, tolerance to low temperatures in winter has been found to vary throughout the native range of H. quercifolia, with cluster three (Florida panhandle) having the least tolerance to low winter temperatures and populations having the greatest tolerance to low winter temperatures being from the northern portions of the species range [cluster one and the northern extent of cluster five (Sherwood et al 2021)]. Future abiotic stress tolerance research could further the understanding of the effects of climatic conditions on H. quercifolia growth, reproduction, and native range expansion/contraction.…”

“…Cluster three is the only one without any overlap and therefore represents a completely unique ecotype for the species. Furthermore, these populations from Florida have been previously determined to have an increased tolerance to leafspot [Xanthomonas campestris (Sherwood et al 2021)], which is likely due to this unique climate experienced by these populations. The adaptation to the unique climatic conditions in Florida makes cluster three a conservation priority.…”

Development of an interspecific hybrid between Hydrangea arborescens ‘Magical Pinkerbell’ and H. quercifolia JNHQ01

“…H. quercifolia의 품종 개발은 주로 자연 방임 수분에 의해 형성된 종자에서 선발되어진 것으로 알려져 있다 (Mallet et al, 1994;Lawson-Hall and Rother, 1995). 게다가 H. quercifolia는 원산지의 분포 범위가 매우 좁고 유전적 다양성에 대해 알려진 바도 매우 드물어 (Sherwood, 2021), 다양한 교배가 시도되지 못해 유전적으로 다양하지 못하다. 이를 극복하여 유전적 다양성을 증가시키고 매력적인 형질의 품종을 만들기 위해 종간 교배를 통한 다양한 교배가 시도되어야 하지 만 종간 교잡은 모부본의 유전체 크기와 염색체 수의 차이로 인해 매우 어렵다 (Rinehart et al, 2006).…”