THE CURRENT DISEASE SITUATION ON THE COMMERCIAL ESTATE OF RAMU SUGAR, PAPUA NEW GUINEA

PAPUA NEW GUINEA is the centre of origin for several Saccharum species, including S. officinarum, the original species used in commercial production. There are a number of endemic diseases that affect commercial sugar production in PNG on the commercial estate of Ramu Sugar Limited at Gusap, Madang Province. These include downy mildew, Ramu stunt and the leaf diseases orange rust, brown rust and yellow spot. Of these, downy mildew is of greatest significance. The disease has reduced the number of foreign varieties able to be grown commercially by up to 50% and also affects the selection of new clones in the Ramu breeding program. Ramu stunt has also had a very serious effect on crop production, particularly in the 1986 season when it caused very low yields in the variety Ragnar. Ramu stunt is only known from PNG and is transmitted by the plant hopper Eumetopina. Resistance screening trials are undertaken routinely for both downy mildew and Ramu stunt. In recent years, two previously exotic major diseases, leaf scald and ratoon stunting disease (RSD), have been identified on the estate and RSD is now a very serious problem for Ramu Sugar. Control programs are being established. Other diseases present on the estate include Fiji leaf gall, Ramu orange leaf and Ramu streak. Diseases will be of on-going importance for commercial sugar production in PNG.