Self-incompatibility in Eucalyptus globulus ssp. globulus (Myrtaceae)

Abstract

Controlled pollinations with self- and cross-pollen were applied to individual flowers of five mature Eucalyptus globulus Labill. ssp. globulus trees to investigate the site of action of the self-incompatibility mechanism. Growth of pollen tubes in styles at 2 weeks after pollination and ovule penetration by pollen tubes at 2 and 4 weeks after pollination were investigated by fluorescence microscopy. Some pollinated flowers were left to develop to seed maturity, then harvested to quantify the level of self-incompatibility of each tree. Trees ranged from 76 to 100% self-incompatible. There was no significant difference in the number of pollen tubes in the style between treatments although variation was present between trees. The number of pollen tubes present was similar to the number of ovules present within flowers. Penetration of ovules by pollen tubes over all five trees combined revealed no difference between treatments at 2 weeks after pollination; however, there was slightly greater penetration by cross-pollen tubes at 4 weeks after pollination. This difference was not large enough to account for the near complete lack of selfed-seed production, suggesting late pre- or post-zygotic arrest of selfed ovules.

The effects of ethyl methanesulfonate treatment on Eucalyptus pollen behaviour in vitro

“…Though information on pollen germination and generative cell division of Eucalyptus pollen in vivo has not yet been published, the rates for Eucalyptus pollen tube elongation in vitro observed in this experiment are similar to those reported in vivo by Pound et al (2002). This supports the use of the in vitro assay of EMS on pollen treatment and use of doses of between 600 and 800 ppm, especially as there is no alternative assay that indicates the effectiveness of EMS treatment that is as quick or simple.…”

Breeding behaviour of Kunzea pomifera (Myrtaceae): self-incompatibility, intraspecific and interspecific cross-compatibility

“…In E. globulus ssp. globulus, four of five genotypes possessed greater than 99% self-incompatibility, but one individual was only 76% self-incompatible (Pound et al 2002). There appeared to be very little variation in the degree of self-incompatibility between accessions of K. pomifera in the present study, with all accessions producing fewer than 0.3 seeds per pollinated flower from self-, compared with 4.6 seeds from cross-pollinated flowers (Fig.…”

“…Such a mating system would be of advantage in highly fragmented natural populations, where seed production may still be possible in the total absence of 'outcross' pollen. Instances of late-acting pre-zygotic SI, similar to that found in K. pomifera, include tight coiling of self pollen-tubes at the base of the style as observed in Melaleuca capitata and M. nematophylla (Barlow and Forrester 1984), pollen-tube rejection near the micropyle as in Thryptomene calycina (Beardsell et al 1993a), and reduction in growth towards the base of the style or in the ovary before ovule penetration, as seen in Vaccinium corymbosum (El-Agamy et al 1981) and several species of Eucalyptus (Pound et al 2002;Horsley and Johnson 2007).…”

“…This phenomenon may also explain why many Eucalyptus species are described as having a mixed, but primarily allogamous, or preferential outcrossing, breeding system (Griffin 1982;Sedgley 1985;Griffin et al 1987;Ellis and Sedgley 1992;Eldridge et al 1993;Pound et al 2002). In Eucalyptus regnans, no difference was observed in levels of self-and out-crossing, with both modes of reproduction being frequently observed within individual open pollinated flowers (Griffin et al 1987).…”

“…Beardsell et al (1993b) proposed that self-incompatibility was prevalent in the family Myrtaceae. It has been established that a mixed, but primarily allogamous, or preferential outcrossing, breeding system is widespread in the genus Eucalyptus (Griffin 1982;Sedgley 1985;Ellis and Sedgley 1992;Pound et al 2002).…”