The following is a summary of his findings. This happens when healthy seed pieces are physically mixed with blighted seed pieces with sporulating areas of Phytophthora . Therefore, it takes only 2 days for blighted seed pieces to become infectious. During the loading and planting operation, spores of the fungus are spread, contaminating healthy seed pieces. With an increase in exposure time, transmission rate increases.
Diseased sprouts are a source of spores for spread of late blight within the field.
The seed tuber is one source of inoculum for late blight in the field. The late blight pathogen can be transmitted from blighted seed pieces to healthy seed pieces during the seed handling operation. Two cycles of late blight increase may occur between cutting and emergence. If contaminated seed pieces are planted, the fungus can be transmitted to the sprout. Spores on emerging sprouts with symptoms of late blight are readily spread to healthy plants creating foci of disease within the field.