Date of Award

Summer 8-10-2018

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Horticulture

Advisor

Bryan Peterson

Second Committee Member

Michael Day

Third Committee Member

Stephanie Burnett

Abstract

The honeysuckles, or Lonicera, represent a circumboreally-distributed genus in the Caprifoliaceae family. A diverse assortment of vines, lianas, and shrubs comprise the genus, and honeysuckles have long been a staple of the horticultural industry, prized for their robustness as much as their sweet-scented flowers and colorful fruits. However, many cultivated honeysuckles of Eurasian origin have proven invasive outside of their native range, displacing native species and reducing overall diversity and ecosystem health. Planting of Eurasian Lonicera taxa is now often discouraged or banned throughout much of North America. Conversely, native North American Lonicera species are often sparsely distributed and of conservation concern throughout their native range. Given the historic popularity of Eurasian honeysuckles in cultivation in North America, their tendency to become invasive pests, and the sparse populations of native Lonicera, we identified two avenues of inquiry: 1) to identify means of efficiently propagating native Lonicera species, for potential conservation or industry application, and 2) to screen Eurasian honeysuckle species and cultivars for invasiveness.

First, we conducted parallel studies evaluating the feasibility of propagating the North-American native wetland shrub Lonicera villosa, found throughout much of Canada and sparsely in New England and the Great Lakes regions of the United States, by stem cuttings. In 2017, we collected softwood cuttings from a native population in Maine, wounded them on one side, treated them with 0, 4000, 8000, or 12000 mg·L1 of K-IBA in water, and stuck the cuttings in rooting media composed of 1:1, 1:3, or 0:1 peat:perlite by volume. In one study, cuttings were irrigated by overhead mist, while the other utilized a simple subirrigation system. Rooting percentages were high in both systems and were not found to vary significantly with treatments. Root quality significantly improved with the addition of K-IBA and with increasing proportions of perlite in the media but did not improve significantly with increasing K-IBA application rates. These findings indicate that L. villosa can be propagated to the high standards necessary for commercial production or conservation purposes.

Second, we conducted two comparative studies contrasting the growth of Lonicera caerulea cultivars, bred from Eurasian genotypes and marketed as an agricultural crop in North America, with the regionally invasive congeners L. tatarica and L. xylosteum, and the regionally native L. villosa. The first study evaluated the comparative growth of these honeysuckles (sans L. xylosteum) across five levels of applied slow-release fertilizer. Lonicera caerulea produced significantly more dried biomass than L. villosa at all but the highest rates of fertilizer application, and less dried biomass than L. tatarica, yet resembled L. tatarica more strongly in height and leaf area. In a second study, the four honeysuckle taxa were co-planted in large 20-gallon pots and subjected to either flooded, container capacity, or drought moisture treatment regimes. Lonicera caerulea significantly outperformed L. villosa and compared favorably with its invasive congeners in terms of dried biomass, height, and leaf area. Taken together, these studies suggest that the non-native Lonicera caerulea cultivars are not functionally equivalent to their related native taxa and we advise caution and further screening for invasiveness prior to their widespread release.

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