EFFECTS OF OXYGEN DEPRIVATION AND PYTHIUM ROOT-ROT ON SUGARCANE RED ROT

The effects of oxygen deprivation or poor drainage and Pythium root ro t on development of red rot, caused by Colletotrichum falcatum, and sp ring shoot population of sugarcane were evaluated under controlled and field conditions. Detached stalks of five cultivars were exposed to l ow atmospheric oxygen (0.5 to 2.7%), created by enclosing stalks in se aled chambers through which humidified nitrogen gas was passed for 0, 1, or 2 weeks. Stalks were then inoculated with C. falcatum and mainta ined for 6 weeks with humidified air flow. Red rot severity, assessed as four disease traits, was not increased by previous oxygen deprivati on. In field experiments, inoculation of stalks of three cultivars wit h C. falcatum before planting resulted in a reduction in shoot populat ions the following spring. Poor drainage resulted in an additional red uction in shoot populations developing from inoculated stalks. Soil at mospheric oxygen was reduced in the root zone below planted stalks und er poor drainage conditions. However, only minor reductions in oxygen were detected in the zone of elevated rows in which planted stalks wer e located. The detrimental effect of poor drainage on shoot population s from inoculated stalks was alleviated by metalaxyl application. Pyth ium root rot, caused by Pythium arrhenomanes, reduced the initial root system and growth of shoots in greenhouse experiments. The combinatio n of P. arrhenomanes and C. falcatum inoculation increased dead bud pe rcentage in one of two cultivars and red rot severity for both. The re sults suggest that spring shoot populations developing from red rot-af fected stalks exposed to poor drainage can be reduced by the combined effects of red rot and Pythium root rot.