EFFECT OF INOCULUM DENSITY OF PYTHIUM-APHANIDERMATUM ON THE GROWTH AND YIELD OF CUCUMBER PLANTS GROWN IN RECIRCULATING NUTRIENT FILM CULTURE

The recirculation of hydroponic nutrient solutions in commercial green houses is being considered by cucumber sowers to reduce fertilizer use and to alleviate environmental problems that occur when waste nutrien t solutions are released into the environment. The potential rapid spr ead of root pathogens in recirculated solutions is of major concern. W e examined the effects of different inoculum densities of Pythium apha nidermatum on disease development in long English cucumber plants grow n in recirculating hydroponic culture. Cucumber plants in small recirc ulating culture systems were inoculated with P. aphanidermatum at leve ls ranging from 0.22 to 2 x 10(6) colony forming units per 100 L of nu trient solution. Plant growth and productivity were monitored. Pythium aphanidermatum readily spread through the nutrient solutions and caus ed browning of roots at all inoculum levels. At 2 x 10(6) cfu 100 L(-1 ), all plants died between 7 and 28 days after inoculation. Plants ino culated at low levels of inoculum did not die but showed reduced growt h and yield. Negative linear relationships were found between the log (concentration + 1) of inoculum of P. aphanidermatum in the nutrient s olutions and the dry weight of the plants, the number and weight of ma rketable fruit produced per plant, the length of cucumber shelf life, and total fruit life.