EFFECT OF SOIL-WATER MATRIC POTENTIAL AND PERIODIC FLOODING ON MORTALITY OF PEPPER CAUSED BY PHYTOPHTHORA-CAPSICI

Periodic flooding increased the mortality of pepper plants (Capsicum annuum L. 'Early Calwonder') grown in soil infested with 25 oospores of Phytophthora capsici per gram of soil as compared with those grown in infested soil at constant soil-water matric potentials of -2.5 and -12.5 kPa. Plant mortality increased as the number of 24-hr flooding periods at 10-day intervals increased. Plants grown in infested soil at a constant soil-water matric potential of -12.5 kPa were not infected 37 days after transplanting. However, when infested soil was periodically flooded, 20, 53, and 100% of the plants died after one, two, and three flooding periods, respectively. With a soil-water matric potential of -2.5 kPa, 0, 80, and 100% of the plants died after one, two, and three flooding periods, respectively. Only one of 15 plants was infected at a constant soil-water matric potential of -2.5 kPa. Our results support field observations associating heavy rainfall and subsequent flooding of the soil with increases in disease progress.