Effect of Stalk Desiccation on Sugarcane Red Rot

The effect of drought conditions at planting time on sugarcane red rot, caused by Colletotrichum falcatum, was evaluated in experiments conducted under controlled conditions and in the field. For experiments under controlled conditions, detached and topped mature stalks of five cultivars were inoculated with conidia of C. falcatum, then exposed to a 3-week desiccation treatment, followed by 3 weeks without desiccation, or maintained for 6 weeks without desiccation. Disease severity, assessed as the number of nodes beyond which rot symptoms extended, number of nodes rotted, internode rot severity, and a rot severity index, was increased in five cultivars by exposure to desiccation. However, response of individual cultivars varied for some disease traits assessed. In field experiments, C. falcatum inoculation alone did not reduce spring shoot populations for seven cultivars. The lowest shoot populations occurred in plantings of inoculated stalks exposed to desiccation. Some cultivars were adversely affected by desiccation alone. These results demonstrate that red rot severity can be increased by the occurrence of drought conditions during the initial growth processes of vegetatively propagated sugarcane stalks.