Embryology of Eucalyptus Spathulata and E. platypus (Myrtaceae) Following Selfing, Crossing and Reciprocal Interspecific Pollination

Abstract

Embryology of Eucalyptus spathulata Hook. and E. platypus Hook. (subgenus Symphyomyrtus, section Bisectaria) was investigated by bright field microscopy to determine the cause of ovule failure at 2 months following selfing, crossing and reciprocal interspecific pollination. Eucalyptus spathulata retained more capsules and produced more seeds following cross- than self-pollination, whereas there was no difference between selfing and crossing for E. platypus. Both species produced seeds following interspecific pollination, but germination was low. Highest ovule penetration by a pollen tube, and ovule growth at 2 months, was observed following crossing of E. spathulata and following interspecific pollination of E. platypus. Most self-pollinated ovules of both species were degenerating and were either unfertilised or had undivided zygotes and free nuclear endosperm. Muticellular pro-embryos were more common in cross-pollinated and interspecific pollinated ovules than following selfing. It was concluded that ovule degeneration of E. spathulata and E. platypus following selfing resulted from low levels of pollen tube penetration and fertilisation, and that in those ovules which were fertilised, the zygote generally failed to divide. Degeneration following cross-pollination of E. spathulata also resulted from failure of the zygote to divide, and in E. platypus additional reasons were low levels of pollen tube penetration and fertilisation, and lack of cellularisation of the endosperm. Ovule degeneration of both species following interspecific pollination included failure of the zygote to divide, but in E. spathulata it also resulted from slower embryo development and reduced cellularisation of the endosperm.

Pollen tube growth and early ovule development following self- and cross-pollination in Eucalyptus nitens

“…This result is consistent with findings from other eucalypt species (e.g. Sedgley and Granger 1996). There was variation in the number of pollen tubes present in styles between trees, but as the mean number of pollen tubes was greater than the mean number of ovules per flower (10.7 ovules/locule vs 32.1 ovules/flower), pollen tube numbers were not found to limit seed set.…”

“…Late pre-zygotic control of selfpollinated seed production occurs in Eucalyptus woodwardii (Sedgley 1989;, whereas post-zygotic abortion of self-pollinated seed occurs in E. regnans ), E. cladocalyx and E. leptophylla (Ellis and Sedgley 1992). E. spathulata and E. platypus have both pre-and post-zygotic barriers to selfpollinated seed production as pollen tube penetration of ovules and ovule fertilisation was reduced following selfcompared with cross-pollination, and few self-fertilised ovules developed past zygote division (Sedgley and Granger 1996). E. globulus has also shown both preand post-zygotic barriers to self-pollinated seed production, with slightly fewer ovules penetrated by pollen tubes following self-compared with cross-pollination, and the majority of ovule abortion occurring after fertilisation (Pound et al 2002a(Pound et al , 2002b.…”

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

“…While strong barriers prevent hybridisation between Corymbia and other genera of Myrtaceae such as Eucalyptus (Griffin et al, 1988), partial or complete barriers within Corymbia may also exist. These barriers may occur due to pollen tubes being unable to germinate and grow the length of the style and reach the ovules, to penetrate ovules and allow fertilisation or due to abnormalities in zygote and seed development (Gore et al, 1990;Ellis et al, 1991;Sedgley and Granger, 1996;Delaporte et al, 2001).…”

Pre-dispersal seed predation and abortion in species of Callisthene and Qualea (Vochysiaceae) in a Neotropical savanna

“…In addition to resource limitation and environmental stress, seed abortion and loss of mature seeds can be caused by pollen limitation and inbreeding (Wiens et al 1987); breeding system incompatibility (Dhar et al 2006); by genetic load (Wiens et al 1987;Bawa et al 1989;Porcher & Lande 2005); and by abnormalities during ovule ontogeny (Palser et al 1990;Sedgley & Granger 1996). Therefore, seed abortion is the main mechanism of post-zygotic selection in plants, allowing resource allocation to be optimized and pre-dispersal seed predation to be avoided (Gribel & Gibbs 2002;Ward et al 2005;Chacoff et al 2008;Ghazoul & Satake 2009).…”