EFFECTS OF INTERCROPPING AND SOIL AMENDMENT WITH UREA AND CALCIUM-OXIDE ON THE INCIDENCE OF BACTERIAL WILT OF TOMATO AND SURVIVAL OF SOIL-BORNE PSEUDOMONAS-SOLANACEARUM IN TAIWAN

Intercropping and soil amendment experiments were conducted to determi ne if they reduced populations of Pseudomonas solanacearum and bacteri al wilt of tomato at the Asian Vegetable Research and Development Cent er (AVRDC) and at three other locations in Taiwan. At AVRDC, intercrop ping tomato with cowpea planted within the row significantly reduced b acterial wilt (P < 0.05) compared to when tomato was cropped alone. Th e P. solanacearum population in soil was not affected by intercropping with cowpea, soybean, or Welsh onion. At the same site, however, a pr eplanting soil amendment consisting of urea (200 kg ha(-1) N) and CaO (5000 kg ha(-1)) significantly reduced the pathogen population and tom ato bacterial wilt (P < 0.001). The effect of the soil amendment was n ot consistent when applied to soil from three other sites in Taiwan; i n soil from two sites no reduction of the pathogen population occurred . At these sites, tomato bacterial wilt in the field was not reduced s ignificantly after amending. In comparison with a non-amended control, the addition of only CaO reduced the P. solanacearum population in AV RDC soil significantly (P < 0.05), but the reduction was significantly greater when the complete soil amendment was added. In contrast, urea alone did not affect the survival of P. solanacearum in the soil. In a greenhouse experiment with AVRDC soil, P. solanacearum was undetecta ble 2 weeks after soil amendment, but in the same treatment tomato yie ld was significantly reduced by 48% (P < 0.05) compared with non-amend ed treatments. The suppressive effect of the soil amendment on the P. solanacearum population was probably due to the generation of one or s everal toxic substances during the transformation of urea in the prese nce of CaO.