Effect of pH and Temperature on the Mycelial Growth of Alternaria lini Causing Alternaria Blight of Linseed under in vitro Conditions

Alternaria blight of linseed, caused by Alternaria lini, is associated with fungal development under environmental conditions that influence mycelial growth and sporulation. This study evaluated the effects of pH and temperature on the radial growth, colony characteristics and sporulation of A. lini under in vitro conditions. The fungus was cultured on potato dextrose agar, with five pH treatments (4, 5, 6, 7 and 8) and five incubation temperatures (15, 20, 25, 30 and 35°C). Three replicates were maintained per treatment, and colony growth was measured after seven days of incubation. Among the pH treatments, maximum radial growth occurred at pH 6 (36.33 mm), followed by pH 7 (34.00 mm), whereas minimum growth was observed at pH 4 (11.67 mm). Excellent sporulation was recorded at pH 6 and 7. Among the temperature treatments, radial growth was greatest at 25°C (39.67 mm), followed by 30°C (25.33 mm), 20°C (23.33 mm) and 15°C (20.67 mm), and was lowest at 35°C (13.00 mm). Sporulation was excellent at 25°C and 30°C but poor at 15°C and 35°C. Colony growth patterns and textures also varied across treatments. The findings indicate that pH 6 and 25°C favoured radial mycelial growth of the tested culture on this medium. These laboratory observations describe fungal growth responses and do not establish field disease-severity thresholds.