Studies on the frequency distribution of Pythium-induced cavity spot of carrots

Data on Pythium-induced cavity spot from experimental plots and commercial fields were collated to study the frequency distribution of cavities on carrots. It was shown that cavities tended to occur in clusters with strong evidence that they followed a Polya-Aeppli distribution rather than the Negative Binomial distribution often associated with clustering. Possible biological interpretations of the Polya-Aeppli distribution are discussed, also their implications for estimation of inoculum potential and analysis of cavity spot field trials.