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An extensive survey of early blight of tomato was conducted in Peshawar and Hazara divisions of Khyber Pakhtunkhwa province, during the fruit bearing period of 2014 of the crop. Comparatively more disease incidence and severity was observed in Peshawar than Hazara Division. Data also revealed that more disease was prevalent in district Haripur than Abbottabad and Mansehra. The isolates of Alternaria solani collected during the survey were different in terms of their cultural characteristics and aggressiveness. Isolates from Peshawar division showed rapid growth on Potato Dextrose Agar medium and produced higher number of spores ml−1 as compared to isolates collected from Hazara Division. Moreover these also produced the largest size lesion (20.6mm) when compared with those collected from Hazara Division. A positive linear trend was observed when lesion size was regressed over colony diameter and spores concentration indicating that isolates showing aggressiveness also showed more radial growth and produced more spores mlˉ1. The studies also confirmed the existence of cultivar specific aggressiveness amongst the isolates of A. solani in screen house experiment. Isolates adapted on respective cultivars caused high disease severity, number of lesions per plant and lesion size with concurrent reduction in yield. Isolate AsRJ previously adapted on variety Red Jambo when inoculated on the same variety produced high disease severity (64.02%) and lesion size (8.2mm), with the lowest yield (436.71g). A similar trend was observed for other isolate and cultivar combinations which could have serious implications for cultivation of a particular variety on vast acreages over time.