Abstract
The present paper deals with the criticism on the diagnostic value of the “Jodine method” and the “Phenol method” for virus-infected potato tubers. The Jodine method formerly proposed by WARTENBERG and KLINKOWSKI was slightly modified by the writer. A test tube contains 0.5 cc. of potato juice, in which 0.5 cc. of diluted pasty starch solution (1.5 g. of starch in 100 cc. of dist. water) and 15 cc. of Jodine solution (2 g. of Jodine in 100 cc. of 30%ethyl alcohol) are added. These test tube series were kept under a room temperature (about 30°C.). The diseased tuber juice fades more quickly (within 50 minutes) than that of the healthy (more than 3 hours). The diagnostic value was about 70% when 74 tubers of Benimaru variety were tested immediately after harvest, and remarkably lower when the tubers sprouted. Furthermore the Jodine method is very dificult to determine the adequate dose of the juice and the reagents. In the case of the Phenol method, a series of test tubes which contain 1 cc. of potato juice and 0.2 cc. of 0.1% phenolic solution was kept under the room temperature. In 5 hours the healthy becomes dark brown in color, while the diseased whitish yellow. The slice of tuber dripped with Phenol shows the similar result. The diagnostic value of this method was yet very low.
