Gene Flow Between Introduced and Native Eucalyptus Species: Morphological Analysis of Tri-Species and Backcross Hybrids Involving E. nitens

Abstract

Summary Morphometric analyses were conducted on second-generation tri-species and backcross hybrids in Eucalyptus. These hybrids were all produced using pollen from two E. nitens x cordata F1 hybrids and controlled pollination techniques. Tri-species hybrids were created with E. gunnii, E. ovata and E. viminalis as females, while backcrosses were produced with E. cordata. Multivariate analysis of seedling characteristics indicated that eighty percent of the backcross hybrids fell within the morphological range of E. cordata. All three cross combinations of the tri-species hybrids were biased away from E. nitens and towards their maternal parent and E. cordata. The inclusion of data for first-generation (F1) hybrids between the pure parental species in the current work showed the F1’s to be easily distinguishable from pure species, compared to second-generation hybrids. The use of morphology for detecting second-generation hybridisation involving exotic plantation species and native eucalypt populations will therefore be unreliable, and identifies a need for preventing second-generation hybrids from establish in the wild. The current work, nevertheless, provides further demonstration of the effectiveness of morphological identification of F1 hybrids. The easy recognition of F1 hybrids will be useful in identifying sites and species at risk of exotic gene flow and enable the development of weeding programs that focus on removing exotic hybrids in the wild.

Comparison of three pollination methods for Eucalyptus argophloia, a small-flowered eucalypt

“…Forestry breeding programmes could consider mass supplementary pollination (MSP) and nursery selection using screening-based morphological markers as an alternative method of producing improved seed set from crosspollination in small-flowered species (Abasolo et al 2012;Barbour et al 2002Barbour et al , 2003Barbour et al , 2007. Mass supplementary pollination is a method where the desired pollen parent is added to open-pollinated flowers and does not require style cutting, emasculation or bagging (Wallace et al 1996;Patterson et al 2004;Suitor et al 2008;Collins and Callister 2010).…”

The risk of pollen-mediated gene flow from exotic Corymbia plantations into native Corymbia populations in Australia

“…Producing this F 2 was also hampered by low seed set (D. Lee, personal communication). Similarly, despite limited assessments (de Assis, 2000;Barbour, 2004), three-way hybridisation is also expected to produce poor performing progeny (Barbour et al, 2007).…”

Assessing a Bayesian Approach for Detecting Exotic Hybrids between Plantation and Native Eucalypts

“…Hybrids have been reported based on morphology, with 1 typically being intermediate between the parental taxa [31,33,34]. The distinctive juvenile morphology of many species also makes identification of hybrids possible at an early age, and this characteristic has been widely used in studies investigating exotic gene flow in eucalypts [31,35,36].…”

“…As in other groups, identifying eucalypt hybrids can be problematic where species have similar morphology, or when there are advanced generation hybrids that resemble the backcross parent [35]. Additionally, in the context of E. globulus plantations, there are a range of native species that have similar seedling morphology to E. globulus, which could hybridise with other native species and produce hybrid seedlings resembling exotic hybrids.…”