MICROBIAL-POPULATIONS AND CHEMICAL-PROPERTIES OF A CITRUS GROVE DIFFERENTIALLY AFFECTED BY BLIGHT

Microbial populations and soil chemical properties of blight-suppressi ve and blight-conducive soils were compared within a grove of 35-year- old 'Valencia' orange (Citrus sinensis [L.] Osb.) on rough lemon (C. j ambhiri Lush.) rootstock. The site is unique in that there is a I-ha a rea of Chobee muck soil located within the larger grove, consisting of Riviera fine sand. Most of the trees within the muck area remain heal thy, whereas the majority of trees (about 75%) in the surrounding sand y soil have been removed due to blight. Populations of seven functiona l microbial groups and 16 soil chemical properties were determined for soils sampled at the muck soil center-and outward in four directions into the surrounding sandy soil. Correlation and regression analyses w ere used to examine associations and relationships among variables. Si gnificant gradients were observed for nine of the soil chemical proper ties and for actinomycete, Fusarium spp., and Trichoderma spp. populat ions from the healthy to adjoining blighted areas of the site.