INFLUENCE OF WATERING FREQUENCY AND ELECTRICAL-CONDUCTIVITY OF THE NUTRIENT SOLUTION ON PHYTOPHTHORA ROOT-ROT IN POT PLANTS OF GERBERA

Recirculation of nutrient solutions in nurseries with ebb-and-flow ben ches will reduce discharges to the environment, but a prerequisite is that the quality and health of the plants are satisfactory. An experim ent investigating the possibility of reducing attacks of Phytophthora cryptogea through changes in watering frequency (WF) and values of ele ctrical conductivities (EC) was carried out in pot plants of Gerbera j amesonii grown on ebb-and-flow benches with recirculating nutrient sol ution. Nutrient concentrations EC 1.5 and 2.2 mS cm(-1), respectively, were combined with WF 0.5 and 1.5 times per day, respectively, with o r without inoculation with P. cryptogea in a factorial design. Symptom s of root rot were absent from plants on noninoculated benches. Raisin g EC and lowering WF both inhibited the attack, alone or in combinatio n. Percent plant death caused by P. cryptogea was 73.6% at WF 1.5 time s per day/EC 1.5 mS cm(-1) By contrast, only 4.7% plant death was obse rved at WF 0.5 per day/EC 2.2 mS cm(-1). Also, the treatments with WF 1.5 per day/EC 2.2 mS cm(-1) and WF 0.5 per day/EC 1.5 mS cm(-1) reduc ed the attacks (13.4 and 13.5%, respectively). Percent diseased plants was highest near the inoculation points in all four combinations, and there was no difference in the pattern of spreading, only in the seve rity of attack. The results show that Phytophthora zoospores in the nu trient solution in an ebb-and-flow system with recirculation could cau se an epidemic under certain conditions. The findings also demonstrate that it is possible to reduce attacks of Phytophthora considerably wi thout the use of fungicides by adjusting the WF and EC values appropri ately. This is possible without effects on the growth and flowering of the plants, even when the nutrient solutions are recirculated.