Incidence and severity of early blight of Tomato in Peshawar, Mardan and Malakand Divisions and variability amongst the isolates of Alternaria solani jones and mart

摘要

An extensive survey for incidence and severity of early blight of tomato was conducted in Peshawar, Mardan and Malakand Divisions of Khyber Pakhtunkhwa Province after flower formation and fruit setting during 2012. The survey points were 3-5 km apartfrom one another. At each location fields were assessed in “X” shaped pattern. A high incidence of the disease (40%) was recorded at Jahangira District Nowshera, whereas the lowest disease incidence 4.9% was recorded at Taru Jaba in Peshawar Division.In Mardan Division high incidence of the disease was recorded at Galadher 38.6% in District Mardan whereas the lowest at Jalbai 3.3% in Distrct Swabi. A similar disease incidence was found at Osaki and Nasafa locations in District Dir (L). Conversely, high incidence of the disease was recorded in Ghalegai (20%) in District Swat Malakand Division. In terms of the disease severity Jahangira (8.66%) in District Nowshera was the most severely infested area closely followed by Basher Mian Kaly (7.98%) and Shabqadar (7.66%). In general, isolates collected from Peshawar and Mardan Divisions were more virulent than those collected from Malakand Division by exhibiting rapid growth on PDA medium as well as producing high number of spore’s ml~(-1). Isolates collected from Shabqadar measured 33 mm in diameter with 28000 spore ml~(-1) and proved virulent by producing high disease severity (27.6%). Conversely, isolates collected from Talash (Malakand Division) showed minimum growth (22 mm) with least number of spores ml~(-1) and disease severity of 16.44% only. Regression analysis showed a simple linear relationship between growth parameters and virulence and as expected virulence increased with increase in colony diameter and spore concentration of the pathogen.Results are indicative of segregation in population structure of the pathogen and may correlate with the different environmental conditions prevalent in the central part of the province.