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In order to determine the influence of various flooding episodes on the severity of root rot and crown rot of peach caused by Phytophthora spp., one-mo-old seedlings were grown for two months in potting mix artificially infested with P. cinnamomi, P. megasperma, or an unidentified Phytophthora sp. (isolate SJ45). The soil matric potential (ym) was maintained constant at -20 millibars (mb) using Büchner funnels as tension plates, or it was interrupted once every two weeks by flooding periods (ym = 0) of 6, 12, 24, or 48 h. At constant soil ym = -20 mb, P. cinnamomi caused 48% root rot, but P. megasperma and the unidentified Phytophthora sp. caused no measurable disease. P. megasperma caused virtually no disease when soil was flooded (ym = 0) for 6 or 12 h; however, it caused 62% root rot and 0.7 crown rot index when the soil was flooded for 24 h, and 100% root rot and 2.8 crown rot index when the soil was flooded for 48 h. The severity of the disease caused by the unidentified Phytophthora sp. increased gradually as the flooding periods lengthened; it caused 36, 45, 74, and 100% root rot when the soil was flooded for 6, 12, 24, and 48 h, respectively, and caused crown rot only when 48 h floodings were imposed. The respective root rot caused by P. cinnamomi when seedlings were grown in soil flooded for 6, 12, 24, and 48 h was 55, 69, 91, and 100%. When peach leaf disks were used as bait for zoospores in flooded soil, the mean percentages of disks infected by P. cinnamomi zoospores at the baiting intervals of 0-2, 0-4, 20-24, and 44-48 h after onset of flooding were 67, 78, 60, and 31%, respectively. At these same baiting intervals, the incidence of disk infection by P. megasperma was 26, 68, 77, and 56%, and by the unidentified Phytophthora sp. was 23, 73, 98, and 95%. These data suggest that careful soil-water management should minimize losses of peach trees due to root and crown rot caused by Phytophthora sp. and P. megasperma, but it would be less effective when the disease is caused by P. cinnamomi.

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Universidad Autónoma del Estado de México
Sistema de Información Científica Redalyc ®
Versión 3.0 | 2018
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