Application of Taylor's Power Law to Sample Statistics of Tylenchulus semipenetrans in Florida Citrus

L. W. Duncan, J. J. Ferguson, R. A. Dunn, J. W. Noling


Taylor's Power Law was fit to Tylenchulus semipenetrans population data obtained from individual trees in a survey of 50 Florida citrus orchards (geographic survey) and to data from individual trees within a single orchard collected at regular intervals for 2 years (temporal survey). No significant differences were detected between slope or intercept values when log variance was regressed against log mean for the geographic and temporal data sets. The geographic survey was divided into two subsets of data according to the perceived size of patches of T. semipenetrans. Subsets consisted of orchards which appeared to have numerous small patches of trees infected by the nematode (small patch) and orchards in which most of the trees were infected (large patch). The slope value for the orchards with smaller patches of nematodes was different (P = 0.05) from that from large-patch orchards. Assuming mean nematode levels of 1,000 juveniles and males/100cm³ soil, sample sizes (predicted standard error to mean ratio = 0.20) estimated from the relationships of variances to means were 12 trees in the geographic survey and 11 trees in the temporal. Omission of the small-patch data from the geographic survey resulted in a 17% reduction in optimum sample size. Sample size in sporadically infested orchards was estimated to be 69 trees. A data transformation of x^[0.23] was calculated from parameters of Taylor's Power Law fit to the survey data. Key words: citrus, citrus nematode, population distribution, sampling, Taylor's Power Law, Tylenchulus semipenetrans.

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