Pollen contamination in Acacia saligna: assessing the risks for sustainable agroforestry

Abstract

Species developed for sustainable agroforestry may pose risks to remnant populations of closely related species via genetic contamination. Genetic contamination and the production of hybrid progeny may threaten the health and long-term viability of remnant populations. Acacia saligna is a native Western Australian species complex selected for further development for agroforestry in the agricultural areas of southern Australia.A. saligna shows great morphological, ecological, biological and genetic variation, and will be reclassified into a number of subspecies. This research aimed to develop genetic markers and use them to assess the levels and distances of gene flow via pollen dispersal between two of the proposed subspecies of Acacia saligna. Pollen dispersal from the abundantly flowering subsp. saligna into the poorer flowering subsp. lindleyi was high (32%). At the same site, pollen dispersal from subsp. lindleyi into subsp. saligna was much lower (14%). Most genetic contamination from subsp. saligna into subsp. lindleyi occurred at short distances (<300 m) although inter-subspecific pollen dispersal was detected over large distances of around 1600 m. The comparative levels of inter-subspecific pollen dispersal are influenced by the relative floral fecundity of the different variants. The results indicate that small remnant populations of subsp. lindleyi will be exposed to high levels of hybridisation when subsp. saligna is planted nearby for agroforestry. The effects of inter-subspecific hybridisation in A. saligna are unknown and until further investigated it is recommended as a management guideline that isolation distances of 1600 m or more be imposed between agroforestry plantings and native populations.

Applied phylogeography ofCyclopia intermedia(Fabaceae) highlights the need for ‘duty of care’ when cultivating honeybush

“…These demographic processes, and their impacts on intraspecific genetic diversity, are rarely considered when wild crop or medicinal plants are introduced to an agricultural setting. This has resulted in genetic divergence between neighbouring wild and cultivated populations ( Yuan et al, 2010 ; Otero-Arnaiz, Casas & Hamrick, 2005 ), creating opportunities for genetic pollution of wild populations ( Bredeson et al, 2016 ; Bartsch et al, 1999 ; VandenBroeck et al, 2004 ; Millar & Byrne, 2007 ) and potentially disrupting species boundaries through the formation of hybrid taxa ( Macqueen & Potts, 2018 ; Lexer et al, 2003a ; Lexer et al, 2003b ). For example, wild harvesting of the Chinese medicinal plant Scutellaria baicalensis (Lamiaceae) has resulted in rapid declines in population sizes and, subsequently, widespread cultivation was promoted to meet demands and reduce harvesting pressure on wild populations ( Yuan et al, 2010 ).…”

Estimating exotic gene flow into native pine stands: zygotic vs. gametic components

“…Contemporary exotic gene flow rates may depart from historical averages among natural populations due to recent human-mediated asymmetries in the size, density, age, fecundity and reproductive phenology of forest plantations vs. natural stands. Whether these factors tend to increase or decrease zygotic and gametic exotic gene flow remains unknown, because there are few assessments of gene flow from exotic forest plantations and, due to methodological constraints, they have focussed either on male gametic gene flow only (Millar & Byrne 2007;Robledo-Arnuncio et al 2009;Millar et al 2012), or on total gene flow irrespective of the dispersal vector (Smulders et al 2008;Meirmans et al 2010;Steinitz et al 2012).…”

Peer Review #1 of "Applied phylogeography of Cyclopia intermedia (Fabaceae) highlights the need for ‘duty of care’ when cultivating honeybush (v0.2)"

“…These demographic processes, and their impacts on intraspecific genetic diversity, are rarely considered when wild crop or medicinal plants are introduced to an agricultural setting. This has resulted in genetic divergence between neighbouring wild and cultivated populations (Yuan et al, 2010;, creating opportunities for genetic pollution of wild populations (Bredeson et al, 2016;Bartsch et al, 1999;Vanden Broeck et al, 2004;Millar and Byrne, 2007) and potentially disrupting species boundaries through the formation of hybrid taxa (Macqueen and Potts, 2018;. For example, wild harvesting of the Chinese medicinal plant Scutellaria baicalensis (Lamiaceae) has resulted in rapid declines in population sizes and, subsequently, widespread cultivation was promoted to meet demands and reduce harvesting pressure on wild populations (Yuan et al, 2010).…”