Growth in microgravity increases susceptibility of soybean to a fungal pathogen

The influence of microgravity on the susceptibility of soybean roots to Phy tophthora sojae was studied during the Space Shuttle Mission STS-87. Seedli ngs of soybean cultivar Williams 82 grown in spaceflight or at unit gravity were untreated or inoculated with the soybean root rot pathogen E! sojae, At 3, 6 and 7d after launch while still in microgravity, seedlings were pho tographed and then fixed for subsequent microscopic analysis. Post-landing analysis of the seedlings revealed that at harvest day 7 the length of untr eated roots did not differ between flight and ground samples. However, the flight-grown roots infected with P. sojae showed more disease symptoms (per centage of brown and macerated areas) and the root tissues were more extens ively colonized relative to the ground controls exposed to the fungus, Ethy lene levels were higher in spaceflight when compared to ground samples. The se data suggest that soybean seedlings grown in microgravity are more susce ptible to colonization by a fungal pathogen relative to ground controls.