Host range of xanthomonas sp., causal agent of the false red stripe of sugarcane, among grasses

Abstract

False Red Stripe (FRS), a new disease caused by Xanthomonas sp., is different from any other sugarcane disease already described. It is distributed throughout the main sugarcane areas of the CenterSouth of Brazil but has not been reported in the Northeast and North of Brazil or any other country. The present work determined the host range of the FRS bacterium among grasses crops and weeds, through artificial inoculation by injection and spraying of bacterial suspension. From the 31 different species inoculated with the FRS bacterium, only sorghum, maize and oat expressed symptoms 15 days after inoculation. Sorghum presented coalescent red stripes at the injection point. Under and above the injection point, at the adaxial face of the leaves, bacterial exudates were observed on the narrow red stripes (1 mm). The symptoms in sorghum were very similar to those observed in sugarcane; however, no yellowish flex were observed on the stripes. Maize plants presented a generalized discoloration of tissues near the inoculation point and the appearance long chlorotic stripes with 2-3 mm, but no bacterial exudation. Only oat plants expressed symptoms after inoculation by spraying. The FRS bacterium was recovered by re-isolation from the symptomatic leaves of sorghum, maize and oat and its identity was confirmed by serological and RepPCR tests. A survey of sorghum, maize and oat fields should be carried out in order to determine whether or not the FRS bacterium can infect these crops naturally.