Alternaria alternata and Alternaria sonchi: Two new records of fungal pathogens on Sonchus asper (annual sow thistle) in Pakistan

Abstract

Sonchus asper (annual sow thistle) is an annual or winter annual herbaceous plant native to Europe. It has become a very aggressive invader in many regions of the world. In February 2013, S. asper plants grown in and around the chickpea and tomato fields at Nuclear Institute for Agriculture and Biology (NIAB), Faisalabad, Pakistan were found to be severely affected by a leaf blight disease. Initially the disease symptoms began as small, circular, dark, necrotic lesions usually on the older leaves. At later stage, these lesions enlarged rapidly up to 4-12 mm in diameter and when spotting was abundant the entire leaf turned yellow. However, in April 2013, S. asper plants grown in and around the tomato and wheat fields at NIAB, Faisalabad, Pakistan were found with different leaf blight symptoms. The leaf spots were initially small, epiphyllous, irregular, scattered to marginal and dark-brown. Later on these spots enlarged, became orbicular to irregular but often angular, with brown to cinereous necrotic centers and usually with a narrow dark margin. On the basis of symptoms, morphological and cultural characteristics of the isolated pathogen, the causal agent was identified as Alternaria alternata from February infected plants while it was identified as Alternaria sonchi from April infected plants and Koch’s postulates were fulfilled. This is the first report of Alternaria alternata and Alternaria sonchi from S. asper plants in Pakistan