Effect of Light, Temperature, and Water Potential on Growth and Sporulation of Microdochium oryzae

Abstract

Radial growth or conidial production of Microdochium oryzae, the causal pathogen of rice (Oryza sativa) leaf scald, was higher on potato-sucrose-salt agar (PSSA) than malt extract agar, nutrient agar, potato-dextrose agar, potato-sucrose agar (PSA) or V8 juice agar. Radial growth on PSSA was 8.5 mm/d with production of 3 × 106 conidia/cm2/d at 21 C. The fungus grew appressed producing innumerable raised salmon-colored sporodochia. The sporodochia were cream colored on the reverse side of the PSA and PSSA plates. Radial growth or conidial production was greater in the dark at 25 or 30 C, than under 12-h cycle of light and dark at 21 C. The fungus grew faster when the water potential (ψ) was adjusted to —0.14 to —1.0 MPa with sucrose or KC1 than with NaC1. The radial growth in sucrose-, KC1- or NaC1-amended media increased as ψs decreased from -0.14 to -0.53 MPa and with increased incubation from 15 to 30 C; and declined with decreased ψs from -4.83 to -5.3 MPa in sucrose and -8.23 to -8.81 MPa in KC1 or NaC1. Conidial production on ψs -0.14 to -2.07 MPa in sucrose was two-fold higher than in KCl and four-fold higher than in NaCl. Conidial production increased steadily with decreased ψs from -1.0 to -1.2 MPa at 25 or 30 C in sucrose, however, decreased at ψs from -0.25 to -0.7 MPa and then increased at -1.8 MPa in KCl or NaCl.