ESTIMATING THE CONCENTRATION OF PROPAGULES OF A PLANT PATHOGEN FROM SOIL DILUTION PLATE COUNTS WHEN THE RESPONSE IS NONLINEAR

The estimation of micro-organism concentrations from dilution prate da ta is discussed for situations where expected counts are not proportio nal to the amount of sample per plate. Aspects of design and analysis are investigated in relation to an alternative non-linear model in whi ch the concentration is given by the slope at the origin. This exponen tial model generally provides a good fit to available experimental dat a. Simulations show that estimators based on the model perform well wh en the response is non-linear and remain reasonably efficient when the response is linear.