| Abstract | Chlorotic streak is a disease recognised since 1929 and is widespread through the cane growing countries of the world. Despite considerable research, particularly in the 1940-1970 period, the causal agent of the disease is still unknown. The disease is systemic and affects germination and crop yield. It is widespread through Queensland being favoured by high rainfall and/or poor drainage. The worst affected areas are the high rainfall wet tropics and poorly drained areas in other districts. This three-year project was initiated to gain a better understanding of the effects of the disease on yield; to screen commercial varieties for resistance; to research the distribution in parts of the Burdekin River Irrigation Area (BRIA); and to attempt to identify the causal agent. Yield loss trials were planted in the Tully and Herbert districts in 2000. Varieties ranging from resistant to susceptible were included to determine the relationship between resistance and yield loss. Plant crop harvests in 2001 revealed losses of up to 60% when crops planted with stalks showing diseased symptoms were compared with crops established with stalks exhibiting no symptoms. Yield effects therefore can be dramatic with the disease. Even some resistant canes suffered significant losses, suggesting farmers should obtain the cleanest planting material they can to establish new crops. One resistant variety (Q162) suffered negligible losses. Germination was slowed, and reduced overall, by chlorotic streak disease (CSD) with the main effect being on tonnes cane/ha rather than ccs (sugar content was largely unaffected by CSD). There was a significant relationship between varietal resistance and yield (r-squared 0.56) in the Herbert trial suggesting there is a correlation between resistance and yield. Surveys of the Invicta, Pioneer, Kalamia and Inkerman mill areas revealed the presence of a greater level of CSD than known previously. The greatest level of disease was found in Q127 though other varieties were also diseased. There was a link between irrigation water source and the area affected by the disease. Where channel water was used, higher disease levels resulted compared to fields irrigated with bore water. This is not surprising because drainage water from infested fields is known to carry the causal agent and channel water contains some drainage water. Transmission studies using hydroponics were commenced to provide suitable root material for molecular assay research into the causal agent. However, no disease transmission occurred and it is postulated that a soil-borne vector may be needed to aid transmission. PhD studies at the University of Adelaide have focused on light and electron microscopy, and molecular methods of pathogen detection. This project finishes in 2003 but so far no agents have been associated with diseased material. |
