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Soil-borne disease

Soil-borne pathogens are cryptic killers causing pre- and post-emergence mortality of large numbers of plants. Their effects are most pronounced on seedlings but they may also cause saplings and even trees to die (e.g. Sudden Oak Disease caused by Phytophthora ramorum). Plants with damping-off appear wilted. Close examination reveals necrotic stem and root tissue. A soil-borne disease (Phytophthora infestans a close relative to Pythium) was also responsible for the Irish Potato Famine (1845-1849). These pathogens can spread vegetatively with mycellium (microscopic threads), lay dormant with various spores, or swim through solution with motile zoospores. To see movies of zoospores being released and swimming visit The American Phytopathological Society.

The movie clip above shows various seedlings and saplings of black cherry (Prunus serotina) dieing from damping-off disease. At 1:02, a time-lapse video is shown of black cherry seedlings growing in Petri plates and becoming diseased. The diseased seedlings were inoculated with an isolate of Pythium sp. from Mammoth Cave National Park, Kentucky. This isolate was previously determined to be highly virulent and caused root necrosis by 3 days. The sequence spans 10 days and the development of necrotic tissue was retarded relative to pathogenicity experiments. In this studio time-lapse project, the diseased plants remain alive but stunted and necrotic. Being alive is probably an artifact of their growing conditions. The plants were grown in a closed chamber with humidity near saturation. Even the slightest bit of water stress would likely cause them to die with characteristic damping-off symptoms illustrated earlier in this video.

This particular sequence was taken using a Canon Digital Rebel tethered to a laptop running the program RemoteCapture 2.7. The photo interval was 60 minutes and the footage was shot over 10 days.