Floral reproduction in northern prickly ash (Zanthoxylum americanum Mill., Rutaceae)

Abstract

Zanthoxylum americanum floral reproductive biology was investigated in two Minnesota populations, concentrating on possible areas of interest for a future Zanthoxylum / citrus breeding effort. The study examined whether (1) Z. americanum pollen was viable, (2) autonomous apomixis was the predominant floral reproductive mechanism, (3) seedless fruits were produced, (4) instances of hermaphrodism occurred, and (5) citrus pollen showed any compatibility with Z. americanum pistils. Zanthoxylum americanum pollen viability was 95.8+/-0.3% (fresh) and 78.6+/-1.1% (stored 18 months at -12° C). Autonomous apomixis did not appear to be the primary floral reproductive mechanism. Seedless (stenospermocarpic) fruits occurred in 13% of the female fruit clusters examined. Hermaphrodism occurred sporadically in males but was not observed in females. Pollen from some citrus cultivars was sufficiently compatible with Z. americanum for pollen germination and pollen tube growth, but offspring from attempted Z. americanum x citrus crosses showed only Z. americanum morphology.