ANALYSIS OF THE SPATIAL-DISTRIBUTION OF RUST-INFECTED LEEK PLANTS WITH THE BLACK-WHITE JOIN-COUNT STATISTIC

Leek rust, caused by Puccinia 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 commer cial 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 statis tic. The spatial distribution of rust-infected leek plants was differe nt for each of the three epidemics, ranging from random to highly clus tered. These results show, that in the development of a practical samp ling method for detection of leek rust, it is necessary to take into c onsideration a possibly clustered distribution of diseased plants.