Pattern ofThietaviopsis basicolain tobacco field soil

Abstract

The pattern of Thielaviopsis basicola in two tobacco field soils was examined using systematic and random sampling methods. In three systematic samplings and one random sampling, the frequencies of observed population densities gave a good fit to the negative binomial distribution; a poor fit was found for one random sampling. For all samplings, the variance to mean ratios were greater than 1, and Lloyd's index of patchiness values ranged from 1.5 to 5.7. These results indicate T. basicola is clumped in tobacco field soil and has a low to moderate degree of aggregation. Population densities of T. basicola were typically less than 10³ propagules per g soil and decreased with depth in the soil profile.