ORIGINAL ARTICLE Breeding behaviour of Kunzea pomifera (Myrtaceae): self-incompatibility, intraspecific and interspecific cross-compatibility T. Page • G. M. Moore • J. Will • G. M. Halloran Received: 12 May 2007 / Accepted: 18 January 2010 / Published online: 11 February 2010 Ó Springer-Verlag 2010 Abstract To examine breeding system characteristics of the endemic Australian prostrate shrub Kunzea pomifera, artificial hybridisations were undertaken using thirteen different genotypes of K. pomifera, to elucidate: (1) self- incompatibility, (2) intraspecific cross-compatibility in the species and (3) interspecific cross-compatibility with each of K. ambigua and K. ericoides. K. pomifera exhibited very low self-compatibility, with the barrier to self-fertilisation being prevention of pollen-tube growth in the style or ovary. Following intraspecific pollination amongst a number of different genotypes of K. pomifera, 38.4% of pollinated flowers developed fruit; arrest of compatible pollen-tubes in the style, preventing fertilisation, contrib- utes to the low fruit set in this species. Interspecific com- patibility was examined between K. pomifera (pistillate parent) and K. ambigua (staminate parent) where seed set per pollinated flower (4.47) was not significantly different from intraspecific crosses (4.66). In crosses between K. pomifera (pistillate parent) and K. ericoides as staminate plant, 0.037% of pollinated flowers produced fruit, with 0.0075 seeds per pollinated flower. Reproductive barriers between these two species were evident in the style of K. pomifera, where the growing tips of the K. ericoides pollen-tubes swelled and ceased to grow. Keywords Hybridisation incongruity Á Interspecific crosses Á Kunzea ambigua Á Kunzea ericoides Á Kunzea pomifera Á Self-incompatibility Introduction Kunzea pomifera (Myrtaceae) is a prostrate Australian native shrub species that produces edible berries that were highly valued by Aboriginal people (Clarke 1998) and which are now considered to have commercial potential (Graham and Hart 1997; Ahmed and Johnson 2000). Substantial variation for important economic traits exists within this and other related species, which offers the opportunity for domestication and improvement. There- fore, knowledge of its breeding system and cross-compat- ibility with related species that are sources for potentially useful characters is important for the development of the species as a crop. Barriers to self-pollination within (de Nettancourt 1997) and hybridisation between species (Rieseberg and Carney 1998) have evolved in many plant species to maximise fitness in the progeny. Plant species that employ ‘strategies’ to ensure out-crossing typically exhibit a range of physical, developmental and/or chemical mechanisms to restrict inbreeding. Self-incompatibility (SI) systems are important to facilitate increased levels of outbreeding within a population, to maintain high degrees of heterozygosity and in the strictest sense may be defined Communicated by Andrew Stephenson. T. Page (&) Agroforestry and Novel Crops Unit, School of Marine and Tropical Biology, James Cook University, PO Box 6811, Cairns, QLD 4870, Australia e-mail: tony.page@jcu.edu.au G. M. Moore Á J. Will Melbourne School of Land and Environment, The University of Melbourne, Burnley College 500 Yarra Blvd, Richmond, VIC 3121, Australia G. M. Halloran Melbourne School of Land and Environment, The University of Melbourne, Parkville, VIC 3052, Australia 123 Sex Plant Reprod (2010) 23:239–253 DOI 10.1007/s00497-010-0133-0