Development and Verification of an Interspecific Hybridization Protocol for Asclepias

Abstract

Milkweed (Asclepias sp.) is an important pollinator genus across North America and is a host plant for many butterfly species, notably the monarch butterfly (Danaus plexippus). Commercial production of Asclepias is limited to a few species, because most species lack commercial traits, with minimal branching habit, excessive height, and minimal color variation. This study used a commercially viable Asclepias species, butterfly weed (Asclepias tuberosa L.), as a maternal parent and trialed three different pollination methods in an attempt to create interspecific hybrids. Pollination methods included a traditional method, a pollen–solution-based method, and a novel inverted pollinia method. The inverted pollinia method increased pollination success rates 4-fold among intraspecific crosses of A. tuberosa. When pollination methods were optimized, A. tuberosa was used as the maternal parent, and one-way crosses were made to seven other Asclepias species using the inverted pollinia method. Of the seven species used as pollen donors, four developed hybrid seed successfully: green milkweed (Asclepias hirtella Woodson), purple milkweed (Asclepias purpurascens L.), showy milkweed (Asclepias speciosa Torr.), and common milkweed (Asclepias syriaca L.). As germination methods vary significantly among Asclepias species, three methods of germination were trialed on seed developed via interspecific hybridizations: direct seeded, cold–moist stratification, and embryo rescue. Of the three methods, cold–moist stratification was superior to direct seeding and embryo rescue. This research is the first documented case of a controlled interspecific hybridization event among these species.

Use of Flow Cytometry to Assess Total Genomic Content for Asclepias spp.

“…In a study by Lewis et al (2021), interspecific hybrids were attempted using A. tuberosa as the maternal parent and seven other species as pollen parents. Of seven pollen-donor species, only four successfully hybridized with A. tuberosa: A hirtella, A. purpurascens, A. speciosa, and A. syriaca.…”

“…These previously published studies indicate a division across the family into broadly geographic clades that could imply a high degree of relatedness among species within these clades. However, not all species within clades share the same affinity toward interspecific hybridization, raising questions as to what other factors are limiting interspecific compatibility (Lewis et al 2021). Although phylogenic relationships are tentative indicators of how genetically similar Asclepias spp.…”

Ornamental plant breeding is tools for new generation

“…Further examples are described in Marantaceae (Van Huylenbroeck et al, 2018) [19] Asclepias sp. (Lewis et al, 2021) [12] , Pavonia (Yue and Ruter, 2021) [25] , and various additional crops. In order for successful interspecific or extensive intergeneric crossing within a specific genus to occur (Eeckhaut et al, 2006) [31} , a number of hurdles must be overcome.…”

Ornamental plant breeding: entering a new era?

“…Other examples are described in Marantaceae Asclepias sp. (Lewis et al, 2021), Pavonia (Yue and Ruter, 2021), and many other crops. Asexual propagation makes it possible to propagate new types arising from interspecific hybridization even if they are sterile.…”