An epidemic of orange rust on sugarcane in Australia.
An epidemic of orange rust (Puccinia kuehnii) occurred in Queensland in cv. Q124 in the 2000 cropping season. Orange rust has been present in Australia for over one hundred years but had only previously caused significant losses in noble cultivars in the early 1900s. Q124 was previously resistant and it is suspected that a new race of P. kuehnii is responsible for the epidemic. Q124 comprised 45% of the Queensland crop and reductions in sugar yield due to the rust outbreak in the Central, Burdekin, Herbert, and Northern districts, where all fields of Q124 were severely affected, were estimated at between 30-40%. Losses occurred in both tonnes of cane and sugar content. The disease reduced fibre levels in the cane and mills had to purchase extra fuel to operate their boilers. Other susceptible commercial cultivars included Q173, Q178 and Q182. Overall losses were estimated at A$150-210 m, making this the most economically damaging disease epidemic in the history of the Australian sugar industry. Before the rust outbreak, Q124 yielded well compared with most other cultivars in many districts. However, in variety trials in 2000, when affected by orange rust, Q124 performed poorly. Fifteen percent of commercial cultivars and less than ten percent of clones in the BSES parent collection and clones in advanced stages of selection were susceptible to the new race of P. kuehnii. Breeding and selecting for resistance to this pathogen should be effective. Already resistant commercial and newly released cultivars are being planted. However, it will take at least another three years before all Q124 can be removed from production. A fungicide control strategy is being investigated to reduce economic losses in the short term.