INHERITANCE OF INTERNODE LENGTH AND ITS RELATION TO HEAD EXSERTION AND HEAD SIZE IN BROCCOLI

Broccoli (Brassica oleracea L. Italica Group) lines with heads borne a bove the foliage (exserted) favorably for mechanical harvest were cros sed with inbred lines with nonexserted heads. Length of the heads, def ined as the portion of the plant above the highest major leaf, was app roximate to 50% of the total plant height in short and tall parents an d all plants of the F-1, F-2, and backcross generations. The principal characteristic identified with good head exsertion was long internode s. Internode length was inherited mostly in an additive manner, with s ome effect of hybrid vigor apparent in the F-1, F-2, and backcross to the tall parent. Plant height was also inherited in an additive manner . Head weight in the high-exsertion parent was much lower than in the low-exsertion parent. Within each parent and the F-1, head weight was greater in plants with longer internodes and greater plant height. In the segregating generations (F-2 and backcross), head weight increased with decreasing internode length, indicating that selection for high head exsertion would result in smaller heads and reduced yield.