Disease cycle of Stagonosporopsis tanaceti in pyrethrum plants

Abstract

Pyrethrum (Tanacetum cinerariifolium) is commercially cultivated in Australia for the production of pyrethrins. Ray blight caused by Stagonosporopsis tanaceti is considered a major limiting factor for pyrethrum production. Histopathology of infected pyrethrum plants identified the importance of crown infection where the infection hyphae were confined to the parenchyma cells of the epidermis, hypodermis and cortex without infecting the vascular tissues. Throughout the growth of pyrethrum plants, no vascular infection occurred in the petioles, flower stems and crowns. In infected leaf petioles and flower stems, pycnidia and extra-cellular anthocyanin material developed within 1–2 weeks of infection. The symptoms of infection included a dark brown discolouration or necrosis of infected cells caused by intra- or intercellular colonisation of hyphae. Secondary infection of leaves, flower stems and flower buds most likely occurred through wind, rain or water splash of pycnidiospores released from pycnidia in the leaves and petioles. Roots of the infected plants remained uninfected throughout the growth of the plants. Detailed understanding of the disease cycle of ray blight disease in pyrethrum plants will enable the development of more efficient, targeted control measures.