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Effects of Furrow Irrigation Schedules and Host Genotyp on Phytophthora Root Rot of Pepper. A. C. CAFE-FILHO, Former Graduate Student, Department of Plant Pathology, University of California, Davis 95616. J. M. DUNIWAY, Professor, Department of Plant Pathology, University of California, Davis 95616. Plant Dis. 79:39-43. Accepted for publication 22 September 1994. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1995. DOI: 10.1094/PD-79-0039.

The effect of furrow irrigation regimes on Phytophthora root rot of pepper (Capsicum annuum) was studied at Davis, California, in the dry summer months of 1990 and 1991. Soil near the roots was artificially infested with inoculum of Phylophthora capsici when plants of susceptible cv. Yolo Wonder B were at the seven- or nine-leaf stage, and furrow irrigation was applied every 7, 14, or 21 days. In 1990, disease incidence was higher and onset of above-ground symptoms was earlier with more frequent irrigation. Yield in infested plots irrigated every 21 days did not differ from that in the corresponding noninfested controls, whereas yields in infested soil irrigated every 7 and 14 days were only 45 and 83% of the respective controls. Irrigation schedules in noninfested controls had no effect on yield and had minimal effects on plant water potential. In 1991, while the trend of reduced disease with longer irrigation intervals was conserved, disease level as a whole was higher and no effective root rot control was achieved. The levels of water stress attained in an additional treatment irrigated only once did not enhance disease. Contrary to the results in 1990, more frequent irrigation of noninfested soil in 1991 significantly increased yield and plant water potential. Evidence is presented that the differences in disease development and yield between years were related to temperature effects on plant development. In a separate experiment with genotypes varying in resistance to P. capsici. disease increased with irrigation in three genotypes (Yolo Wonder, Adra, and PH28). Three other genotypes (DK1, 2258, and CM328) developed little or no disease, even under extremely moist conditions. While the importance of other environmental factors was illustrated, frequency of irrigation is an important factor in epidemics of P. capsici root rot. Effective irrigation management and genetic resistance can reduce disease development significantly.