RATOON STUNTING DISEASE RESISTANCE OF AUSTRALIAN SUGARCANE VARIETIES

NEW SUGARCANE VARIETIES are screened for resistance to ratoon stunting disease (RSD) by BSES to provide additional information to growers and industry advisors. This paper reports on the RSD resistance of twenty-seven varieties, including eight standard varieties, in a plant and first ratoon crop. Results of the plant crop have been published previously. The varieties were inoculated by spraying the secateurs and cut end of oneeye setts with juice from infected stalks as the setts were cut. The plant crop was harvested with a commercial harvester, which spread the disease further within the trial. In the plant crop, the intensity of the colour reaction (absorbance) of samples processed with the enzyme-linked immunosorbent assay (ELISA) was measured and the percent infected vascular bundles in leaf sheaths was determined with a tissue blot assay. In the first ratoon crop, these measurements were repeated and, in addition, the percent infected vascular bundles in stalks was measured with a tissue blot assay. The average ELISA reading increased by more than three times in the first ratoon crop compared to the plant crop. There were highly significant correlations between the absorbance from the ELISA and the percent infected vascular bundles in the leaf sheaths and stalks in the plant and first ratoon crops. The varieties Empire, Q208A and MQ239A were rated highly resistant with the ELISA method. Eight varieties were rated resistant; KQ236A, Q117, Q200A, Q230A, Q231A, Q237A, Q240A and Q243A. Five varieties were rated susceptible; Q110, Q138, KQ228A, Q235A and Q242A. This paper compares the three methods for rating varieties for resistance, the reaction of the varieties in the plant and first ratoon crops and discusses the implications of the RSD resistance ratings for control of the disease.