The gall rust fungus Prospodium transformans, a potential agent for use against Tecoma stans, fails to establish in South Africa.
Tecoma stans var. stans (Bignoniaceae) is emerging as an important invasive alien tree in South Africa. Host-specificity testing of the gall rust fungus, Prospodium transformans (Pucciniales) demonstrated that this potential agent was highly host-specific, and safe for release. Following permission being granted by the relevant authorities for release of this rust fungus, attempts to establish it in the field were initiated in November 2010, using a mix of three different isolates originating from Mexico. Field inoculations were carried out in the Durban area, KwaZulu-Natal (3 sites, twice), the Nelspruit area, Mpumalanga (5 sites, thrice), and Pretoria, Gauteng (1 site, once), during the summer rainy seasons of 2010/11 and 2011/12. On two occasions, air temperature was much higher than the optimal temperature for teliospore germination, and no infection occurred. However on all other occasions galls developed on leaves and occasionally stems, but none sporulated except for a few galls at only one site on one occasion at Nelspruit. Despite P. transformans readily developing sporulating galls in glasshouses under quarantine conditions it is likely that the isolates used are not fully compatible with the biotype of T. stans in South Africa. Thus this biotype can be considered as falling within the fundamental, but not the realized, host range of P. transformans.