Abstract
A new leaf spot disease in the Egyptian clover (Trifolium alexandrinum L.) was observed in Kafr-Elsheikh Governorate, Egypt. Initial symptoms consisted of multiple, small, regular to oval leaf spots, which enlarge to produce brown to black lesions, sometimes surrounded by a bright yellow margin. As the disease progressed, lesions expanded and merged, resulting in withering of leaf tips. After isolation and pathogenicity test, the causal agent of clover leaf spot disease was identified as Stemphylium globuliferum (Vestergren) Simmons, according to its morphological characteristics and was confirmed by subsequent analysis of the internal transcribe spacer region of ribosomal DNA. When clover leaves were infected with S. globuliferum, leaf spot (necrotic) symptoms were appeared and associated with susceptibility (normosensitive necrosis). Consequently, the levels of reactive oxygen species (ROS), mainly hydrogen peroxide (H2O2) and superoxide (O-2), increased significantly compared with the control (non-infected leaves). It seems that ROS play a pivotal role in the necrotic symptoms of clover infected with S. globuliferum.