EFFECT OF Fusarium solani f.sp. phaseoli INOCULUM DENSITY ON DRY ROOT ROT SEVERITY IN THE COMMON BEAN

Abstract

Four densities of Fusarium solani inoculum (1, 2, 4 and 8 g/L of soil) were tested for determining the minimum inoculum density for the occurrence of bean dry root rot, in two soil types. The response variables evaluated were the total number of microorganisms in the soil, the number of F. solani f. sp. phaseoli propagules, total soil microbial activity and seedling disease severity. The results indicated that the minimum inoculum density for disease occurrence varied with the soil type. For a non-cultivated soil, the minimum inoculum density was greater than 5,127 propagules per gram of soil, while for cultivated soil, the minimum inoculum density was 3,701 propagules per gram of soil. Disease severity in seedlings grown in cultivated soil was twice as great as for those grown in non-cultivated soil. Total soil microbial activity, as determined by dehydrogenase of fluorescein diacetate, did not correlate with the population of the pathogen, indicating that the mere presence of these organisms in the samesoils does not imply that they are active.

KEY-WORDS: Suppressive soil; conducive soil; Phaseolus vulgaris.