Summary of the final report on the Australian Flora Foundation funded project:

Boronia - survival or death in warmer climates - what you can't see is what is important. L. Tesoriero1, J. Lidbetter2, M. Terras1 & A. Drenth3
1NSW Agriculture EMAI, Camden NSW
2NSW Agriculture HRAS Gosford NSW
3 IRC 80 Meyers Rd Indooroopilly, Qld  Grant details  Send final report (PDF 21 KB)

This project looked for the reason growers are suffering severe plant losses in Boronia heterophylla grown for cut flower production. Boronia heterophylla and related hybrids are cultivated on the coast in South-Eastern NSW for the export cut flower market. Severe losses are experienced during the 5 year cropping period, particularly after the first pick of flowers (approximately 18 months after cutting grown tubestock are planted). Wilting and rapid death of plants are the most common symptoms associated with losses.

Surveys of wilting plants and taxonomic studies demonstrated that three Phytophthora species were consistently associated with field losses. They were: P. cinnamomi, P. cryptogea and P. drechslera. Greenhouse assays confirmed pathogenicity of the three Phytophthora species to B. heterophylla. P. cryptogea was the most aggressive species, causing 100% mortality in two trials when inoculated via the lower stem.

Thus this study determined that three Phytophthora species cause the root and crown rots of B. heterophylla and related hybrids.