LAUSR

Orange rust caused by Puccinia kuehnii was observed in Mauritius in March 2018 on cultivar M 2705/06, under selection. Typical symptoms of cinnamon to yellowish brown lesions, with pustules protruding on the underside of leaves and occurring at times in patches were observed on the cultivar. The causal agent of orange rust was confirmed by light microscopy, PCR using Puccinia kuehnii specific primers and sequencing of PCR fragments. It could be distinguished from brown rust ( Puccinia melanocephala ) that has been present in Mauritius since 1978 by both light microscopy and PCR. An initial survey showed the disease was present in four experimental sites in the Centre and West of the island, where cultivar M 2705/06 was being evaluated. An island-wide survey carried out in May 2018 showed a rapid escalation of the disease all over the island with more pronounced infection in the North and East. The commercial variety R570 and cultivar R582, under selection were rated susceptible under natural inoculum pressure of orange rust. A reduction of 20.6% in sucrose content was noted in severely infected cultivar M 2705/06. There is no evidence on how and when the disease was introduced in the island, but its high incidence on R570, which occupies about 18% of area under cane, indicates a recent introduction. The insignificant level of infection in cultivar Q124 in the germplasm collection points towards a different strain of the pathogen present in Mauritius as the variety was found to be highly susceptible in Queensland, Australia. The evolution of orange rust in Mauritius will be followed in coming crop seasons.