Abstract
We investigated and compared the relationships between the earliness of head formation and developmental characteristics of cabbage cultivars grown in spring (sown in early spring, harvested in early summer) and autumn (sown in summer, harvested in late autumn). In both seasons, earliness of head formation, namely the duration of the period to attain the target head weight from transplanting, was highly correlated with the leaf position at which head formation started (LPH): the lower the LPH value, the earlier head formation. This result suggests that a low LPH value is necessary for early-head-forming cultivars. However, the LPH value in some cultivars varied with the growing season, showing a significant genotype (G) × environment (E) interaction. To determine whether this G × E interaction might influence the use of LPH as a selection criterion, we analyzed the developmental pattern of the leaf shape. In cultivars with LPH values that largely differed between the two seasons, the leaves were longer up to a higher leaf position and widened later in the spring than in autumn, mainly because of delayed shortening of the petiole. We thus characterized the complex nature of early head-forming in spring, and suggested that LPH was a useful selection criterion for the development of early head-forming spring cultivars.
