Update on the Occurrence of Yellow Leaf Syndrome in the South African Sugar Industry and Evidence for the Causal Organism

most commercial varieties in the cooler months will fade with In a survey of the South African and Swaziland sugarcane industries in 1997, symptoms of yellow leaf syndrome (YLS) were found in all areas and in a wide range of varieties. As in previous years, symptoms were present from late autumn to early summer. Symptoms were particularly common in the contrasting areas of the Midlands region of KwaZulu-Natal and the Mpumalanga lowveld, where the majority of stalks in whole fields often had symptoms. In the Midlands, widely grown variety N12, previously thought to have a degree of tolerance, invariably expressed conspicuous symptoms. In Mpumalanga, varieties N19 and N24 had more symptoms than other varieties. The usually wet conditions experienced over most of the industry in the winter months appear to have been conducive to the expression of YLS symptoms. A total of 265 samples of field grown sugarcane were collected to determine the presence of the putative causal agents of YLS. The phytoplasma ScYP was detected by PCR in 162 of 163 samples with typical symptoms of YLS from all areas. The luteovirus ScYLV, detected by enzyme-linked immunoassay (ELISA), was found to be mainly restricted to certain genotypes undergoing selection in northern KwaZuluNatal and Mpumalanga. The virus was not detected in commercial varieties in most of the sugar industry. This indicates that ScYLV is not a candidate casual agent for YLS as it commonly occurs in southern Africa. PCR and other evidence for the identity of the phytoplasma is presented.