SPATIAL DISTRIBUTION AND SPREAD DYNAMICS OF PAPAYA RINGSPOT DISEASE

Analysis of the spatial distribution of Papaya ringspot disease showed that thedistribution pattem of the diseased plants in the field changed with time. At the be-ginning of the disease development,a random pattern was observed,then a clusteringtype of distribution,and an even pattern at the last stage. Based on Fuzzy clusteringmethod, the characteristics of disease spread dynamics in different time were studied.Atthe early epidemic stage when virus-carried alate aphids immigrated into the papayafield,the disease began to develop. In this period,the development of the disease wasmainly the increase of the diseased spots.Later on,after a great amount of vectorsimmigrating into the field,a rapid increase of diseased spots was found to spread allover the field,a rapid increase of diseased spots was found to spread all over thefield.Meanwhile there was a rapid increase in number of the diseased plants.At thelast epidemic stage,the diseased plants increased in number slowly,and a hundredpercent of plants in the field was infected by the disease.