The high amylase activity of Py. ultimum during early infection is expected to provide that species with access to more glucose than Ph. infestans. Consistent with this is our observation that genes encoding glucose-6-phosphate dehydrogenase (EC 1.1.1.49) and 6-phosphogluconate dehydrogenase (EC 1.1.1.44) were expressed at about four-fold higher levels in Py. ultimum compared to Ph. infestans during early tuber infection (Fig 4B). This evidence concerns the gene G6PD and infection.