This paper deals with the results of experiments and investigations made on late blight of potatoes to decide its primary occurence and to make clear the relation between the susceptibility of potato plant to late blight and the change of their chemical components in the growing season.
1) On the primary occurence of the late blight of potatoes
(1) Very few conidia of Phytophthora infestans- on the diseased plants were observed by December.
2) When shoot cuttings of potato plants were dipped in the conidial suspension ot late-blight fungus, the mycelia were observed in the epidermis and pith of the stem 15 om up from the cutting place. In the eld, the writers recagnized the existence of mycelia within the plants affected with late blight in their whole bodies down to the ground. After sprouting from the infected tubers, the plants which sproutedfrom the infected tubers showed the symptoms of late blight disease.
3) The translocation of the mycelia from tubers to shoots was investigated. It seems likely that mycelia invade shoots from tubers through cortices and vasoular bundles.
(2) On the relation between the change of chemical components in the growing potato plants and the occurence of late blight.
The writers measured the area of late-blight lesion caused by inoculation of Phytophthora infestans and analysed the total nitrogen, and the reducing and non-reducing sugar in leaves.
The area of lesions were larger in the lower leaves, and in the later growing stages, and in the susceptible varieties. Negative correlation was shown between the total nitrogen content and the area of late blight lesion in leaves.