Anatomic Characteristics Associated with Head Splitting in Cabbage (Brassica oleracea var. capitata L.)

Cabbage belonging to Brassicaceae family is one of the most important vegetables cultivated worldwide. The economically important part of cabbage crop is head, formed by leaves which may be of splitting and non-splitting types. Cabbage varieties showing head splitting causes huge loss to the farmers and therefore finding the molecular and structural basis of splitting types would be helpful to breeders. To determine which anatomical characteristics were related to head-splitting in cabbage, we analyzed two contrasting cabbage lines and their offspring using a field emission scanning electron microscope. The inbred line 747 is an early head-splitting type, while the inbred line 748 is a head-splitting-resistant type. The petiole cells of 747 seems to be larger than those of 748 at maturity; however, there was no significant difference in petiole cell size at both pre-heading and maturity stages. The lower epidermis cells of 747 were larger than those of 748 at the pre-heading and maturity stages. 747 had thinner epidermis cell wall than 748 at maturity stage, however, there was no difference of the epidermis cell wall thickness in the two lines at the pre-heading stage. The head-splitting plants in the F-1 and F-2 population inherited the larger cell size and thinner cell walls of epidermis cells in the petiole. In the petiole cell walls of 747 and the F-1 and F-2 plants that formed splitting heads, the cellulose microfibrils were loose and had separated from each other. These findings verified that anomalous cellulose microfibrils, larger cell size and thinner-walled epidermis cells are important genetic factors that make cabbage heads prone to splitting.