Effects of oxygen deprivation and pythium root rot on sugarcane red rot

The effects of oxygen deprivation or poor drainage and Pythium root rot on development of red rot, caused by Colletotrichum falcatum, and spring shoot population of sugarcane were evaluated under controlled and field conditions. Detached stalks of five cultivars were exposed to low atmospheric oxygen (0.5 to 2.7%), created by enclosing stalks in sealed chambers through which humidified nitrogen gas was passed for 0, 1, or 2 weeks. Stalks were then inoculated with C. falcatum and maintained for 6 weeks with humidified air flow. Red rot severity, assessed as four disease traits, was not increased by previous oxygen deprivation. In field experiments, inoculation of stalks of three cultivars with C. falcatum before planting resulted in a reduction in shoot populations the following spring. Poor drainage resulted in an additional reduction in shoot populations developing from inoculated stalks. Soil atmospheric oxygen was reduced in the root zone below planted stalks under poor drainage conditions. However, only minor reductions in oxygen were detected in the zone of elevated rows in which planted stalks were located. The detrimental effect of poor drainage on shoot populations from inoculated stalks was alleviated by metalaxyl application. Pythium root rot, caused by Pythium arrhenomanes, reduced the initial root system and growth of shoots in greenhouse experiments. The combination of P. arrhenomanes and C. falcatum inoculation increased dead bud percentage in one of two cultivars and red rot severity for both. The results suggest that spring shoot populations developing from red rot-affected stalks exposed to poor drainage can be reduced by the combined effects of red rot and Pythium root rot