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

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, contributes to the low fruit set in this species. Interspecific compatibility 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.

Unique growth paths of heterospecific pollen tubes result in late entry into ovules in the gynoecium of Sagittaria (Alismataceae)

“…Heterospecific pollen may not germinate on the stigma, or the growth of pollen tubes following germination may be prematurely terminated, such as is seen for interspecies hybridization between Kunzea pomifera and K. ericoides (Myrtaceae) (Page et al . ). In our study, pollen from S. trifolia germinated on the stigma of S. pygmaea , and heterospecific pollen tubes passed through the basal opening of the carpel and the surface tissue layer of the receptacle to finally enter into nearby ovaries.…”

Pollen–pistil interactions in reproductive interference: comparisons of heterospecific pollen tube growth from alien species between two native Taraxacum species

“…Harder, Cruzan & Thomson ; Onus & Pickersgill ; Page et al . ), implying some association with a recognition system during the pollen–pistil interaction (but see Liedl, McCormick & Mutschler ). The two native dandelions in our study are both self‐incompatible and always require pollen by another individual.…”

The Expression of Self-Incompatibility in Angiosperms Is Bimodal

“…The literature is replete with reports of seedless virgin fruits set through parthenocarpy. For example, in a recent study of the breeding system in Kunzea pomifera (Myrtaceae), Page et al (2010) find substantial fruit set in unpollinated controls (44% in one plant), with no or low seed set. In Styrax japonicus (Styracaceae), Reed (2003) finds the mean fruit set declining from 22% one month after pollination to 0% two months later.…”