Occurrence of Soilborne Diseases and Root Knot Nematodes in Strawberry Plants Grown on Compacted Rice Straw Bales Compared with Naturally Infested Soils

Abstract

The present investigation deals with a possible use of rice straw bales as soilless cultiva- tion medium, thus escaping the problems inherent in the natural soils and avoiding a serious pollution when disposed about 5°C million tons of rice straw annually by burning. Strawberry fruits of good quality and quantity were harvested from plants cultivated on compacted rice straw bales in compari- son with the control plots under natural soil conditions. A higher temperature of 2 to 5 in comparison to natural soil conditions favours all physiological activities including the absorption of nutrients by roots and thus stimulating the vegetative and the generative growth of strawberry plants. The pH values around the roots in straw bales ranged from 5.5 to 6.5, while values obtained around the root system in natural soil ranged from 7.5 to 8.5. So, growing strawberry on rice straw bales helps avoid and overcome the problem of alkalinity and salinity in the rhizosphere. This is very important, as strawberries are very sensitive to salinity. Fruit rot diseases reached 0.8% on rice straw bales while on the control plots these were about 52% of fruits were infected with fungi. Cultivating strawberry on rice straw bales keeps the fruits away from contacting the soil and thus limits the possibility of injec- tion by soilborne fungi. The occurrence of damping-off, root rot, crown rot and root knot nematodes in strawberry plants grown on rice straw bales reached 4.0, 0.85, 0.35 and 0.0%, respectively. However, the corresponding figures for strawberry plants grown in natural soil under the same conditions were 27.0, 16.15, 11.70 and 13.20%, respectively, 135 days after planting. Isolation from strawberry plants grown in natural soil showing symptoms of crown rot and black root rot yielded several fungi identi- fied as Phytophthora cactorum, Colletotrichum fragariae, Pythium ultimum, Rhizoctonia solani and Fusarium oxysporum. The wilt symptoms observed on few strawberry plants on rice straw bales might be attrib-