Symptoms of sunflower black stem and characterization of P. macdonaldii. A. Natural infection of black stem on sunflower stem. B. Culture characteristics of P. macdonaldii on PDA. Cotton-like aerial mycelia with black pycnidia underneath the central area. C. Back of the colony. D. Dark, pear-like pycnidia were observed under the microscope. E. Conidia. F. Conidia germinating from one and both sides of conidia. Scale bar = 30 μm (D, E) or 20 μm (F).