Processing tomatoes (Lycopersicon esculentum Mill.) grown in field plots with soil infested with or free of Phytophthora parasitic Dastur. were furrow-irrigated for 4 to 8 hours every 14 days (normal irrigation), for 4 to 8 hours every 28 days (less frequent irrigation), or for 4 to 8 and 24 hours on alternate irrigations every 14 days (prolonged irrigation). Disease developed more rapidly and symptom severity was greater in inoculated plants that received prolonged irrigation, whereas disease onset was delayed in inoculated plants that were irrigated less frequently. Water extraction by tomato roots from well-irrigated and noninfested soil was usually greatest at shallow depths and decreased with depth. When disease was increasing and soil moisture was high, diseased plants extracted less total water from all depths and significantly less water at shallow depths. Plants in the drier soil profiles extracted the greatest amounts of water at depths below 90 cm, and diseased plants irrigated less frequently showed reductions in water extraction at shallow depths later in the season. Tomato root systems appeared to compensate for moderate levels of root disease at shallow depths by extracting more water from deeper in the profile.
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