Is Eucalyptus Cryptically Self-incompatible?

Abstract

Background and aims: The probability that seeds will be fertilized from self- versus cross-pollen depends strongly on whether plants have self-incompatibility systems, and how these systems influence the fate of pollen tubes.

Methods: In this study of breeding systems in Eucalyptus urophylla and Eucalyptus grandis, epifluorescence microscopy was used to study pollen tube growth in styles following self- and cross-pollinations.

Key results: Pollen tubes from self-pollen took significantly longer than those from cross-pollen to grow to the base of the style in both E. urophylla (120 h vs. 96 h) and E. grandis (96 h vs. 72 h). In addition, both species exhibited reduced seed yields following self-pollination compared with cross-pollination.

Conclusions: The present observations suggest that, in addition to a late-acting self-incompatibility barrier, cryptic self-incompatibility could be a mechanism responsible for the preferential out-crossing system in these two eucalypt species.

Fig. 1.

Comparison of in vivo pollen tube growth after controlled self- and cross-pollinations in (A) Eucalyptus urophylla and (B) Eucalyptus grandis. Cross-pollinations were performed within each species (intraspecific).

Fig. 2.

Fluorescence micrographs of squashed Eucalyptus styles harvested after different pollination treatments and stained with aniline blue: (A) twisted pollen tubes after self-pollination in E. urophylla; (B) straight pollen tubes after cross-pollination in E. urophylla; (C–E) pollen tube pathway in an E. grandis cross 72 h after pollination where (C) shows pollen grains germinating on the stigma, (D) shows pollen tubes growing in the middle style and (E) shows pollen tubes at the cut end of the style (at the stylar base). Scale bars: (A, B) = 20 µm; (C–E) = 100 µm.