Incidence and harmfulness of potato late blight (Phytophthora infestans Mont. de Bary) on potato stems.

Józefa Kapsa

Abstract

Changes in the occurrence of the initial late blight symptoms have been noted in some regions of Poland. Observations of potato crops showed that occurrence of the primary infections and blight symptoms is sometimes on the stem rather than on the leaves. It was confirmed that in both cases, a cause of late blight was the same species Phytophthora infestans. Surveys of many potato crops done in 1997-1999, around Poland enabled assessment of the incidence of stem blight in Poland. In 1997 - 80.5%, 1998 - 65.2% and in 1999 – 72.4% of observed crops were primary affected with late blight on stems. Stem form of the disease appeared more often in the years with less rainfall in the period from June to July. The largest number of genotypes with initial blight symptoms on stems was observed among first early clones and cultivars. Glasshouse experiments confirmed the importance of stem lesions in decreasing yield and increasing tuber infection. Results confim that blighted tubers were the least probable source of the late blight appearing on stems.