Temporal Patterns of Virus Spread

Abstract

There have been outstanding advances recently in work on the structure and replica­ tion of plant viruses, but studies on their spread and control have been relatively neglected, and progress has been limited. Nevertheless, there is an increasing aware­ ness of the prevalence of virus diseases in diverse crops of many countries. Cacao swollen shoot, cotton leaf curl, hop nettlehead, and many other virus diseases have long caused serious losses, and these continue. Other viruses including plum pox, citrus tristeza, and sugar cane mosaic have increased in importance because of spread into new areas or crops. As a result of detailed surveys or the introduction of new tests, newly detected and in some instances widespread and prevalent viruses have been discovered in maize, rice, apple, and many other hosts. The well characterized plant viruses are of several distinct morphological types and there is great diversity in their mode of spread. Recent reviews are available on transmission and spread of viruses by pollen and seed (64) and by vectors (20, 52, 56), especially aphids (73, 90), leafhoppers (7, 92), white flies (27), thrips (62), beetles (87), mites (55), nematodes (17, 75), and fungi (76). This paper emphasizes general features in the epidemiology of plant viruses that lead to characteristic curves of disease progress with time. 1 Spatial patterns of infection into and within crops will be considered in a subsequent review.