Bioregenerative Life Support Systems (BLSS) are proposed for the production of food crops, water recycling, and air revitalization in future microgravity, Moon, and Mars habitats. The alternative hypothesis (Ha) for the current study was that simulated microgravity would increase phytopathogen growth rates potentially leading to increased levels of disease in space-based BLSS modules. Squash cotyledon leaf discs, and full canopies of Arabidopsis thaliana (At) plants, were dusted with conidia from 14-d-old colonies of Golovinomyces cichoracearum (Gc). Leaves were positioned into one of five gravity treatments including: (1) adaxial leaf surfaces pointed upward (1g-up control), (2) adaxial surface oriented 90° to Earth's 1g down vector (1g-90° control), (3) adaxial surfaces pointed down (1g-down control), (4) rotated on a 2D clinostat, or (5) randomly rotated on a 3D random positioning machine (RPM). Inoculated squash leaf discs and At canopies were incubated on agar media for 2- or 3-days post inoculation (dpi), fixed with 3% glutaraldehyde, and imaged with a SEM. The fastest growth rates on squash leaf discs were observed for germ tubes on squash leaf discs exposed to the 2D clinostat (mean = 94.2 µm at 3 dpi) and 3D RPM system (65.3 µm at 3 dpi); all three 1g controls were similar (~38-45 µm long). Growth rates of germ tubes on At leaves under similar gravity treatments were ~33% of the growth rates observed on squash leaves. Results suggest that Gc conidia may germinate more rapidly and grow faster in altered gravity conditions compared to 1g controls, supporting the Ha.
Keywords: Disease Resistance; Ecology; Etiology; Fungal Pathogens; Host Parasite Interactions; Pathogen Recognition by Plants.