A number of bacterial pathogens have previously been shown to cause blight and die-back of Eucalyptus species. These include Pantoea ananatis, Pseudomonas cichorii, Xanthomonas axonopodis and Xanthomonas dyei pv. eucalypti. In 2003 a newly established compartment of a Eucalyptus grandis clone in the Mtunzini area of South Africa showed extensive leaf blight and die-back. The plantation was located in an area where sugarcane is extensively cultivated. Bacteria were commonly found exuding from leaves and petioles. Numerous insects in the family Miridae were observed in the plantation and collected. Isolations from diseased material and mirid insects yielded two distinct bacterial species. The objectives of this study were to identify these bacterial species and determine their aetiology. Phenotypic methods as well as 16S rRNA and gyrB sequencing were performed on all isolates, confirming the presence of P. ananatis and Xanthomonas vasicola, of which the pathovar vasculorum (Xvv) is known to infect sugarcane and maize. Xanthomonas vasicola isolates from E. grandis and a strain of Xvv, previously isolated from sugarcane, were inoculated into the susceptible Eucalyptus clone and three sugarcane cultivars. All isolates were found to be pathogenic. This study thus suggests that X. vasicola has made a significant host jump from sugarcane to eucalypts in South Africa.

Detection of Leifsonia xyli subsp. xyli (Lxx) on a large scale is based on serological assays such as evaporative-binding enzyme-linked immunoassay (EB-EIA). These methods are time consuming and require well-equipped laboratories. This study presents the development of a loop-mediated isothermal amplification (LAMP) assay which allows detection of Lxx in 30 min at 65°C, using xylem sap as the template. The assay requires minimal laboratory equipment and could be used at near farm conditions, thus saving time and money required to transfer samples from remote areas to diagnostic laboratories. The LAMP method shows potential as an alternative detection method for RSD.

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In this study, beneficial relationships between Fusarium species in sugarcane and the stalk borer, Eldana saccharina (Lepidoptera: Pyralidae) were demonstrated in vitro. In addition, Fusarium species with antagonistic properties were found to inhabit sugarcane. Attenuated Fusarium isolates from sugarcane stalks collected across the South African sugar industry were incorporated into diet formulated to mass rear E. saccharina. Of the over 200 Fusarium isolates obtained, 10 that significantly improved the survival and development of E. saccharina larvae and considered to be beneficial were selected for further study, as were 10 that were detrimental or antagonistic to the stalk borer. Twelve of the selected isolates were identified as F. sacchari by direct sequencing of translation elongation factor-1α fragments, eight of which resulted in reduced numbers of surviving larvae and significantly lower larval masses. F. proliferatum isolates resulted in increased survival and mass of E. saccharina and three of the five isolates assigned to the F. pseudonygamai group enhanced E. saccharina development. Results from olfactory choice experiments suggested the production of attractive and repellent metabolites by certain isolates. Findings from this study may offer additional or alternative strategies for managing E. saccharina infestation of sugarcane.