Normally at this time of year, we’re buried in tomatoes. Pyramids of them sit on our kitchen counter ¬– literal piles of tomatoes from our CSA share. We try to keep up by putting them into nearly every meal: sliced in salads and BLTs, pureed into gazpacho, or simply salted with oil and basil. But this year, there’s nothing but dead and dying vines in the fields. We’re living through the Great New England Tomato Famine.
OK, I’m being flip. But the parasite that’s attacking the tomatoes is a strain of the same fungus that caused the Irish potato famine 150 years ago. Phytophthora infestans, or “late blight” is native to central Mexico, where it infests many different members of the genus Solarium – a group that includes not just tomatoes and potatoes, but also nightshade and bittersweet. The fungus doesn’t survive well in our typical hot, dry summers, but this July was wet and cool, creating the perfect conditions for it to spread. When spores from mature P. infestans land in wet fields, they open and release zoospores. The zoospores are tiny, but their paired flagella help them swim over the moist leaves and drill into them. Once inside the plant, P. infestans acts like any other fungus, growing a network of threadlike structures called hyphae to digest the surrounding plant tissue. And as soon as the fungus is mature, it sends hyphae out of the leaves to release more spores into the wind.
Photo: P. infestans infects a leaf. (Cover image: Grenville-Briggs, L. J. et al. 2008. Cellulose Synthesis in Phytophthora infestans Is Required for Normal Appressorium Formation and Successful Infection of Potato. Plant Cell 20: 720-738.)