Pathological Survey on Early Leaf Blight of Tomato and In Vitro Effect of Culture Media, Temperature and pH on Growth and Sporulation of Alternaria solani

Abstract

Alternaria solani causing early blight of tomato is a serious disease, causing 50% to 86% losses in fruit yield and 20% to 40% losses in seedling establishment. Pathological survey, etiology and physiological characterization of the causal organism are necessary to formulate effective management strategy. Therefore, present study was conducted to determine the incidence and severity of early leaf blight of tomato in some selected area of Bangladesh and to evaluate the effect of different culture media on radial mycelial growth and sporulation as well as the effect of pH and temperature on mycelial growth. Survey was conducted in five upazilas of Bogura district and typical early blight disease sample was collected from surveyed field and Germplasm Centre, Agrotechnology Discipline, Khulna University, Khulna. Seven different culture media were used namely Potato Dextrose Agar (PDA), Richard’s Agar (RA), Waskman Agar (WA), Corn meal Agar (CA), Asthana and Hawker’s Agar (AHA), Oat Meal Agar (OMA), V-8 Juice Agar Medium (VJAM) and seven different pH level such as 5.0, 5.5, 6.0, 6.5, 7.0, 7.5 and 8.0 were used and also exercised five distinct temperatures such as 20°C, 25°C, 30°C, 35°C and 40°C to appraise cultural characters, mycelial growth and sporulation of A. solani. Cultural characters such as colony color, colony diameter, growth margin, growth surface and margin topography showed distinguished variation in culture media. Among the seven different media V-8 Juice Agar Medium gave not only maximum mycelial growth (73.10 mm) but also highest sporulation (2000 spores ml?1). The optimum pH for maximum mycelial growth ranged to 5.5 - 6.5. But maximum mycelial growth (71.70 mm) was observed in pH 6. Whereas, the mycelial growth was favored by 20°C - 30°C temperature but 25°C temperature provided highest mycelial growth (72.20 mm). However, temperature above 40°C was found adverse for the growth of tested fungus.