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

Abstract

Controlled self-and cross-pollinations were conducted on flowers of five mature Eucalyptus nitens trees. Levels of self-sterility of the trees ranged from 25.8 to 93.6%. Pollen tube numbers in styles and ovule penetration by pollen tubes was investigated 2 weeks after pollination by fluorescence microscopy. There were no significant differences between treatments in the number of pollen tubes present in styles or in the percentage of ovules penetrated by pollen tubes. Embryology of material harvested 2 and 4 weeks after pollination was investigated by bright-field microscopy. Fertilisation had taken place by 2 weeks after pollination with nearly every ovule showing evidence of fertilisation. Cross-pollination resulted in a greater proportion of healthy, developing ovules, at both 2 and 4 weeks after pollination, compared with self-pollination. The proportion of degenerating ovules increased from 2 to 4 weeks after pollination. The reduced ability of E. nitens to set self-pollinated seed compared with cross-pollinated seed appears to be controlled by a post-zygotic mechanism. Differences in ovule size may potentially assist in the identification of trees incapable of setting self-pollinated seed.

A comparison of the effect of genetic improvement, seed source and seedling seed orchard variables on progeny growth in Eucalyptus nitens in South Africa

“…There is little research on the breeding system of E. nitens, but Moncur et al (1995) estimated a 75% outcrossing rate in this species, and Pound et al (2003) found that levels of self-incompatibility in E. nitens ranged from 25.8 to 93.6%. Self-pollination is definitely possible in E. nitens (Griffin et al 1987;Tibbits 1988), particularly in areas where the presence of natural pollinators is low, and pollen load is poor.…”

“…The reticent or shy flowering of E. nitens has hindered the breeding programme and the production of improved seed, for plantation establishment. Globally, the species is known as a light and infrequent flowerer and produces small seed crops (Pound et al 2003). In South Africa, the species often only becomes reproductively mature at 10 to 15 years of age if grown in a plantation situation (Eldridge et al 1993; and requires winter chilling, or hormonal treatments to replace the chilling, if flowering is to occur earlier (Gardner and Bertling 2005).…”

An investigation of assumptions made in estimating genetic parameters and predicting genetic gain in a Eucalyptus nitens breeding programme in South Africa

“…It is thought that outcrossing is high in E. nitens due to successful late-acting selfincompatibility mechanisms in the species (Hodge and White 1993;Pound et al 2003).…”

“…Moncur et al (1995) estimated that outcrossing was at a level of 75% in an E. nitens seed orchard, and Pound et al (2003) found that levels of self-incompatibility in E. nitens ranged from 25.8 to 93.6%. The species demonstrates preferential outcrossing and appears to have a late-acting selfincompatibility system operating to reduce the production of selfed seed (Pound et al 2003;Tibbits 1989).…”

“…Moncur et al (1995) estimated that outcrossing was at a level of 75% in an E. nitens seed orchard, and Pound et al (2003) found that levels of self-incompatibility in E. nitens ranged from 25.8 to 93.6%. The species demonstrates preferential outcrossing and appears to have a late-acting selfincompatibility system operating to reduce the production of selfed seed (Pound et al 2003;Tibbits 1989). The assumption of > 70% outcrossing made by many authors (Butcher and Williams 2002;Grosser et al 2010;Hodge et al 1996;Moncur et al 1995;Moran et al 1989), may not be true of these F1 E. nitens seed orchards, due to poor flowering.…”