Determinación del nivel de inóculo primario de Pseudomonas solanacearum en suelos con infestación natural

Abstract

Several methods were tested for detecting the residual inocuhnn of Pseudomonas solanacearum, Race 1, in inceptisols at Turrialba, Costa Rica, where lire bacterium is apparently endemic Planting healthy potato tubers in soil samples in the greenhouse, then using plant wilt as indicator of the pathogen's presence, was qualitatively the most efficient method; however, it was not possible to quantify precisely the level of primary inoculum in several soils A selective culture medium containing tetrazolium chloride plus antibiotics allowed detection of P. solanacearum at concentrations near 25 000 cells/gram of dry soil, even though a large number of antagonistic bacteria predominated in many samples, completely inhibiting P. solanaccarum Both methods were used to detect P. solanacearum in samples from soils subjected for nearly four years to three systems of minimum tillage or one of tradi-tional mechanical tillage, populations were consistent), larger in mechanically-tilled soil. This was confirmed by planting potato and tomato directly in the field, where significant contrasts in percentage of bacterial wilt resulted. The decrease of the bacterium in minimum-tilled soils was attributed to an increase in organic matter and thus an increase in antagonistic microorganisms.