Diaporthe species associated with dieback on Cyclopia (honeybush)

The formal honeybush tea industry in South Africa is relatively new, and has tremendous growth potential. However, as with other cultivated crops, production and yield can be adversely affected by fungal diseases. A number of Diaporthe species are recognised as causal agents of plant disease symptoms such as dieback, twig blight and branch cankers. For the past few years, such symptoms have been observed on Cyclopia (honeybush) species in cultivated fields located in two districts in the Western Cape province of South Africa. In this study, Diaporthe species associated with honeybush dieback symptoms were identified. One hundred and fifteen isolates recovered from C. genistoides, C. longifolia and C. subternata exhibited cultural characteristics typical of Diaporthe. Representative isolates of the morphological groups were identified to species level, based on the sequence analysis of the rDNA internal transcribed spacer (ITS) region, β-tubulin (tub2), histone 3 (his3) and the translation elongation factor 1-alpha (tef1-α) genes. Seven Diaporthe species were found to be associated with honeybush, namely, D. aspalathi, D. cynaroidis, D. foeniculina, D. heterophyllae, D. inconspicua, D. nebulae and D. sojae. The isolates of each species used in the pathogenicity tests were all pathogenic on C. subternata. Diaporthe heterophyllae was the most virulent species, causing the longest internal lesions as well as typical dieback symptoms. Diaporthe nebulae was moderately virulent in comparison to D. heterophyllae, while the other species were significantly less virulent.