Potato Black Dot – The Elusive Pathogen, Disease Development and Management

Black dot caused by Colletotrichum coccodes was initially considered a mild disease of potato, mainly infecting weakened plants. In the past two decades the fungus has been reported to infect roots and stems relatively early in the growing season, be prevalent on potato and in field soil in major potato production regions of the world, cause early death of foliage by itself and in association with other pathogens, reduce plant and root growth, and to reduce potato yields. Furthermore, the tuber phase of the disease is recognized as a major problem in that unsightly blemishes reduce value of fresh market potatoes. C. coccodes has been dubbed an elusive pathogen because infections are latent, disease symptoms on foliage are often non-descript and can be confused with other potential causes, disease effects on potato yield have not been consistent, and the disease is not satisfactorily managed. Sources of variation on yield likely arise from genetic variation within the pathogen population; the host population such as potato cultivar, maturity class, and plant organs infected; environmental variables; cultural and management practices such as timing of fungicide application; crop duration; post-harvest conditions; and interactions of C. coccodes with other microbes and with potato cultivars. Considerable research has been done on potato black dot during the last two decades, the scope of this paper is to define our current understanding on the disease and summarize disease management strategies.