The rust Puccinia arechavaletae, a potential biological control agent of balloon vine (Cardiospermum grandiflorum) in South Africa. II: Host range.
Cardiospermum grandiflorum (Balloon vine), a subtropical climber native to America, is rapidly increasing in importance as an invasive environmental weed in South Africa. It is a vigorous climber which invades forest margins and watercourses in sub-tropical areas such as coastal KwaZulu-Natal and Mpumalanga. Robust stems with tendrils enable C. grandiflorum to climb trees and form a dense canopy, completely smothering the underlying indigenous vegetation. Consequently it was targeted for biological control. The microcyclic rust fungus Puccinia arechavaletae was collected from Misiones, Argentina, and established under quarantine conditions in South Africa. Host specificity testing was carried out in the quarantine facilities. A total of 19 plant species were inoculated with the rust fungus, including representatives of 13 genera in the Sapindaceae which are native to southern Africa, three cultivars of the important crop plant Litchi chinensis, and all members of Cardiospermum that occurs in southern Africa. Other than C. grandiflorum, only C. corindum (of South African origin), C. pechuelii (native to Namibia), and C. halicacabum var. halicacabum (introduced weed in South Africa) were susceptible. Occasionally pustules developed on Allophylus natalensis, Dodonaea viscosa and Paullinia pinnata, but these are considered to be the result of the artificial high inoculum loads employed and not representing a susceptible host response. It is necessary to undertake a risk assessment of the potential risk posed to C. corindum and C. pechuelii before P. arechavaletae will be considered for the release as a biocontrol agent against balloon vine in South Africa.