A soil sampling method to estimate the population density of Tylenchulus semipenetrans cobb, 1913 in infested citrus orchards of the Fars province in Southern Iran

Composite soil samples were taken to optimize sampling patterns used to estimate the soil population density of malse and second-stage juveniles (J2s) of the citrus nematode, Tylenchulus semipenetrans in four nematode-infested citrus orchards (1 ha each) in Fars province, southern Iran, during 2019. Samples were collected from the upper soil layer (20 to 30 cm depth) under the canopy of 13 selected trees in each orchard. The resulting data were used as the basis for further analysis. A negative binomial model was used to describe the nematode spatial distribution and to estimate sample size. Sampling patterns were evaluated using the coefficient of variation (CV) of the mean as a measure of precision. The cost of collecting, processing and counting the nematodes was calculated and used for the selection of the most suitable sampling pattern. Results indicated that sampling using a left zigzag pattern was the most cost-efficient method which provided a statistically acceptable level of reliability defined as the extent to which the same measurements obtained under different sampling patterns yield similar results. Furthermore, among the sampling patterns tested, sampling from a hypothetical large square of orchards could be recommended as an acceptable alternative for estimating the population density of the citrus nematode in soil.