Analysis of the spatial distribution of rust-infected leek plants with the Black-White join-count statistic

Abstract

Leek rust, caused byPuccinia allii Rudolphi, is an important disease of leek (Allium porrum L.) in the Netherlands. For the development of a practical sampling method for early detection of leek rust in commercial fields, information on the spatial distribution of the disease is necessary. In this study, the spatial distribution of diseased plants during three naturally occurring epidemics of leek rust was observed. The observations were analysed with the Black-White join-count statistic. The spatial distribution of rust-infected leek plants was different for each of the three epidemics, ranging from random to highly clustered. These results show, that in the development of a practical sampling method for detection of leek rust, it is necessary to take into consideration a possibly clustered distribution of diseased plants.