Finding the best match – use of the rust fungus Maravalia cryptostegiae for control of Cryptostegia madagascariensis in Brazil

• Invasive Cryptostegia populations in Brazil identified as C. madagascariensis. • Brazilian populations most closely related to populations from northern Madagascar. • Strain of rust ex northern Madagascar most compatible with Brazilian populations. • Great potential for biological control of Cryptostegia madagascariensis in Brazil. Cryptostegia madagascariensis is a fast-growing woody vine, native to the western coast of Madagascar. Originally introduced as an ornamental, this prolific invader has escaped cultivation and encroached onto semi-arid regions of north-eastern Brazil. Whilst the invasion is believed to be in its early stages, dense infestations can negatively affect whole ecosystems; plants can aggressively smother native vegetation causing canopy collapse and are threatening the unique Caatinga ecosystem. Current methods of control rely on the use of mechanical or chemicals means which are labour intensive, time consuming and require frequent follow up treatment. In 2018 the decision was made to evaluate the potential for classical biological control of C. madagascariensis in Brazil, piggy-backing on the success of the programme against the congeneric species Cryptostegia grandiflora in Australia. Surveys sourced 22 strains of the highly damaging rust fungus, Maravalia cryptostegiae , which were screened for their compatibility and virulence towards Brazilian populations of the weed. Molecular analyses of plant populations from both the native and introduced range were also conducted, to confirm the identity of the invasive species in Brazil and if possible, determine from where in Madagascar the introduction originated. Both molecular and rust-susceptibility studies corroborate with each other that the Cryptostegia populations in Brazil assessed are homogenous and closely related to a geographically isolated population of C. madagascariensis in northern Madagascar. Brazilian populations of the weed were highly susceptible to selected strains of the rust, making the invasive vine an ideal candidate for a classical biological control programme.