Leaf spots — sugar beet

The causative agent of cercospora leaf spot manifests as necrotic, circular spots 2–5 mm in diameter with an ash-gray center and a characteristic dark brown, reddish-brown, or purple margin. In humid weather, a velvety, grayish-white fungal sporulation layer forms on the surface of the spots. Severe infection causes yellowing and death of the leaves, which forces the plant to consume sugars from the root crop to form a new rosette, thereby reducing yield and sugar content.

The pathogen Cercospora beticola exhibits high genetic variability, with numerous races and pathotypes adapted to specific cultivation zones. Varietal resistance is provided by the NBS-LRR gene family; however, the development of fully immune hybrids is difficult. Other leaf spots differ in their morphology: ramularia leaf spot is characterized by the absence of a distinct margin and the presence of a silvery-gray coating, phoma leaf spot by pronounced zonation with black pycnidia, and bacterial leaf spot by the oily, translucent appearance of the spots.