The rust fungus Puccinia arechavaletae, a potential biological control agent of balloon vine (Cardiospermum grandiflorum) in South Africa. I: Biology

Abstract

Studies on the rust fungus Puccinia arechavaletae, were conducted to determine its potential for use as a classical biological control agent against the alien environmental weed Cardiospermum grandiflorum in South Africa. The production of basidiospores is a crucial stage in the life cycle of this microcyclic rust species, and was determined to optimally occur at 20 °C, under high relative humidity (above 90%), in the presence of free water. The first basidiospores were released from mature telia after being incubated for 4 h under optimum conditions, reaching a peak of production after 24 h. Germination of basidiospores optimally occurred at 20 °C, and they were extremely vulnerable to desiccation. Germinating basidiospores directly penetrated epidermal cells of South African C. grandiflorum within which a vesicle formed, followed by rapid radial colonization of the leaf tissue by fungal mycelium. The first symptoms observed were small chlorotic spots on the leaves from 14 days onwards, with telial pustules appearing between 14 and 21 days post inoculation. The rust P. arechavaletae was shown to be highly pathogenic towards South African C. grandiflorum, causing severe disease symptoms with a detrimental effect on plant health and vigor.