| Abstract | Sugarcane yield decline (YD) is characterised by poor root development ( a lack of fine root growth, root discolouration) and poor root health. Previous YD research implicated the involvement of unrecognised pathogens in the growth constraint. Research in this project attempted to determine the etiology of YD using various approaches. Electron miscroscopy highlighted the poor root surface characteristics in YD-affected roots and showed that soil pasteurisation greatly improved the root surface condition.. Transmission experiments demonstrated that very small quantities of either YD roots or soil extracts could lead to major growth depression and roots similar to YD, even in a non-degraded rainforest soil. Biocide studies showed that some general fungicided (mancozeb, maneb, zineb, benomyl, chlorothalonil, and anilazin) eliminated poor root health associated with YD, and implicated soil fungi in YD. Multiple regression analyses conducted on data from glasshouse experiments with diverse treatments also suggested that soil fungi were intimately involved in YD. Fungal isolates from sugarcane root systems and pathogenicity testing showed that dematiaceous and white sterile fungi could reduce sugarcane root growth and were probably significant contributing factors to YD. Studies into the unfluence of mycorrhizae (VAM) on sugarcane growth were initiated and VAM were shown to be common in sugarcane soils. A comparision was made between apple replant disease and YD and many Similarities observed. Research into other replant diseases should be accessed to assist YD investigations. Further research should seek to develop an assay for dematiaceous fungi and to study the influence of management strategies on these organisms. The effect of VAM on sugarcane growth at high P and the effect of various management strategies on the soil biological community are two important research areas. |
