EFFECT OF LOCATION OF DRIP IRRIGATION EMITTERS AND POSITION OF PHYTOPHTHORA-CAPSICI INFECTIONS IN ROOTS ON PHYTOPHTHORA ROOT-ROT OF PEPPER

The effects of the location of drip irrigation emitters and the positi on of inoculum in roots on Phytophthora root rot of pepper were studie d on cultivars Yolo Wonder B (susceptible) and Adra (resistant). In fi eld plots infested with Phytophthora capsici, the location of emitters had major effects on incidence of diseased plants, severity of root s ymptoms, yield, shoot dry weight, level of soil moisture, and plant le af water potential. Disease levels were highest with emitters at the s oil surface and in the plant row. The subsurface (15 cm deep) position gave the most efficient control in the field without reducing yields in noninfested plots. Disease levels were more severe with cv. Yolo th an with cv. Adra. Results were similar in analogous greenhouse tests. In complementary experiments, when zoospores were placed onto tips oi roots that were 7 to 10 cm or 14 to IS cm long, inoculation at differe nt positions in the root system had no effect on the lesion growth rar e for either cultivar, but the progress of lesions on 'Yolo' was three to five times faster than on 'Adra'. Moreover, the rate of lesion gro wth declined with time on 'Adra', but remained constant in 'Yolo'. and above-ground symptoms of root rot on 'Yolo' were more severe when ino culum was placed higher in the soil profile. Phytophthora root rot of pepper can be reduced in low rainfall areas by positioning the drip em itters away from plant stems, with a subsurface location giving the be st results. The advantages of associating genetic resistance with a we ll-managed drip system were evident.