Phytophthora cryptogea root rot of tomato in rockwool nutrient culture:

SUMMARY The effect of root temperature on growth and yield of rockwool‐grown tomato plants infected with Phytophthora cryptogea was investigated. Measurements of shoot and root growth were taken at high (25 o C) and low (15 o C) root temperatures during the generative phase of growth. The growth of roots of healthy and P. cryptogea‐infected tomato plants in rockwool blocks was higher in plants grown with roots at 25 o C than at 15 o C after 60 days and a similar effect was found in slabs after 98 days. Under sub‐optimal conditions for growth the disease became severe when root temperatures were low. Growth of roots was greatest when roots were maintained at a high temperature in combination with an ambient air temperature of c. 15 o C and the response was greater in cv. Counter than cvs Calypso and Marathon. Water‐soluble carbohydrates of roots were higher in those produced in blocks than slabs and were reduced by infection compared to healthy plants with roots at 15 o C and 25 o C. Reduced transpiration rates were found 17 days after inoculation in symptomless plants grown at a root temperature of 25 o C. Infection, regardless of the temperature of the roots or cultivar, led to reduced stem growth. The plants grown at 25 o C were taller than those with a root temperature of 15 o C. After 9 wk of harvest, the cumulative fruit yields in infected cvs Counter and Calypso grown at 25 o C were comparable to that in healthy plants grown at either temperature and cumulative fruit numbers followed a similar pattern. High root temperatures led to delayed fruit ripening between weeks 3–10 and a larger number of unripe fruit. The weight of unripe fruit from infected plants grown at 25 o C at the terminal harvest was higher than from healthy plants with roots maintained at 15 o C.