Flood Depth and Ethylene Interaction in Flood-Induced Rice Blast Field Resistance

Rice blast, caused by Magnaporthe grisea Cav., frequently limits rough rice yields and cultivar options in Arkansas rice production areas. Rice growers and researchers have long observed that susceptible rice plants are more blast resistant when growing in moisture saturated or flooded soil. In fact, Arkansas growers utilized flood-induced field resistance as their primary blast control measure while producing record rough rice yields in blast-susceptible cultivars ‘Wells’, ‘LaGrue’, and ‘Francis’ during the blast conducive years 2000 to 2003. Flood gradients and an ethylene inducer, ethephon, were utilized to induce blast field resistance in susceptible cultivars ‘M-201’, ‘Newbonnet’, LaGrue, ‘Mars’, and ‘Cypress’. When flood duration was 37 days, the blast disease indices (BIs) of all test cultivars except LaGrue were reduced by a threeand an eight-in. flood treatment. For all cultivars except M-201, two sequential 50 ppm ethephon applications increased blast field resistance of upland plants to levels comparable with that induced by a three-in. flood. Blast indices of combination flood-ethephon treatments were generally lower than those with flood treatment alone. Taken together, our results clearly show the value of increased flood depth and of flood-induced ethylene production as an essential component of the blast resistance-signaling pathways.