FLORAL MORPHOLOGY AND BREEDING SYSTEM OF 3 SPECIES OF EUCALYPTUS, SECTION BISECTARIA (MYRTACEAE)

Aspects of the breeding system, floral morphology and pistil cytology were studied in three trees each of E. spathulata, E. cladocalyx and E. leptophylla. E. spathulata and E. leptophylla were found to be highly self incompatible, setting very low levels of seed from controlled self pollination. E. cladocalyx trees ranged from self compatible to self incompatible. Reductions were seen in both the number of capsules and the numbers of seeds per capsule, from self pollination. The mechanism of self incompatibility was investigated in the pistil by following the success of cross and self pollinations with fluorescence microscopy. In E. cladocalyx and E. leptophylla no reduction in ovule penetration was seen from self pollination while in E. spathulata a significant reduction was seen in two trees but not the third, indicating that the post-zygotic mechanism of self incompatibility operates in all three species, and with mixed pre-zygotic and post-zygotic mechanisms in E. spathulata. Floral architecture differed between the three species in the structure of the inflorescence units, flower morphology, and anther, pollen and ovule numbers per flower. Pistil cytology was similar for all three species but differed in the length of the stylar canal, degree of sclerotinisation, stigma morphology and volume of transmitting tissue. The implications of floral structure and of the location and extent of outcrossing control are discussed in relation to seed genotypes and seed output.