Standardized Fungal Growth Conditions

All strains used in this study were derived from Guy11 (Table S4). Strains were grown on complete medium (CM) containing 1% (W/V) glucose, 0.2% (W/V) peptone, 0.1% (W/V) yeast extract and 0.1% (W/V) casamino acids, or on minimal medium (MM) containing 1% glucose and 0.6% sodium nitrate, unless otherwise stated, as described in [21] (link). 55 mm petri dishes were used unless stated otherwise. Allyl alcohol (ACROS organics, USA), kanamycin (Fisher, USA), sorbose (Sigma, USA), 2-deoxyglucose (Sigma, USA) and ethionine (Sigma, USA) were added to CM or MM in the amounts indicated. Plate images were taken with a Sony Cyber-shot digital camera, 14.1 mega pixels. Nitrate reductase enzyme activity was measured as described previously [21] (link). For spore counts, 10 mm² blocks of mycelium were transferred to the centre of each plate, and the strains grown for 12 days at 26°C with 12 hr light/dark cycles. Spores harvested in sterile distilled water, vortexed vigorously and counted on a haemocytometer (Corning). Spores were counted independently at least four times. Rice plant infections were made using a susceptible dwarf Indica rice (Oryza sativa) cultivar, CO-39, as described previously [23] (link). Fungal spores were isolated from 12–14 day-old plate cultures and spray-inoculated onto rice plants of cultivar CO-39 in 0.2% gelatin at a concentration of 5×10⁴ spores/ml, unless otherwise stated, and disease symptoms were allowed to develop under conditions of high relative humidity for 96–144 hrs.