MORPHOLOGICAL, PATHOGENIC, CULTURAL AND PHYSIOLOGICAL VARIABILITY OF THE ISOLATES OF ALTERNARIA SOLANI CAUSING EARLY BLIGHT OF TOMATO.

Alternariasolani is an important and widely distributed pathogen that caused early blight of tomato. Isolates of the A. solani were isolated from naturally diseased tomato fields in Hada Al Sham region, Jamoom. Therefore, the present investigation was undertaken to demonstrate morphological, cultural and physiological variation among the isolates of the pathogen.A. solani was isolated and pure culture for each isolate was obtained by Hyphal Tip isolation method. Morphological characteristics of A. solani including conidia size, length of beak, hypha and septa were studied under light microscope. Cultural characters such as colony colour, colony diameter, pigmentation, type of margin were studied using different culture media. PDA medium was used to study the effect of pH, temperature and light regime on the radial growth of A. solani The results indicated that two isolates of the A. solani were identified and both of the test isolates showed a wide range of variability in respect of their mycelial and conidial dimentions and septation. On the culture media, maximum mycelial growth of AS1 was noted with Sabouraud’s Agar medium (9 cm) followed by host agar medium (8.7cm) and PDA (7.9cm). While, the maximum linear growth of AS2 was recorded with Richard’s Agar (9cm) followed by Czapeck’s Agar (8.6cm) and Sabouraud’s Agar (8.5cm).Isolates of A. solani showed highly variation in pigmentation, sporulation and feature of mycelial growth such as colony surface, growth margin and zonation.Temperature of 30°C was suitable for AS1 and AS2 and recorded the maximum mycelial growth of (7.05cm and 6.57cm, respectively). Optimum pH of PDA medium for the growth of AS1 and AS2 was 6.5. Alternative 12 h light and 12 h darkness recorded the maximum colony growth of AS1 (7.3cm), whereas, highest colony growth of 7.95cm was observed by AS2.