164 – II.3. BRASSICA CROPS (BRASSICA SPP.)
the head splits open and the flowering stalk bolts to 1.5-2.0 metres tall with branches
bearing flowering racemes of self-incompatible flowers.Figure 3.12. Heads of B. oleracea var. capitata and Savoy cabbages
A. Head of cabbage, B. oleracea var. capitata
with its rosette leaves intactB. Heads of red, smooth green and Savoy cabbage
with lower leaves removedSource: Courtesy Floridata.Figure 3.13. Head of cauliflower and broccoli B. oleracea var. botrytis
Cauliflower is derived from broccoli, being selected for short stout stems with a
dense, terminal head or curd, made up of arrested inflorescence meristems, over topped
by leaves (Figure 3.13). About 10% of the meristem mass will eventually develop into
normal flowers and set seed (Sadik, 1962). Specific alleles of the BoCAL-a gene have
been shown to be associated with discrete inflorescence morphologies (Smith and King,
2000; Purugganan, Boyles and Suddith, 2000). Smith and King (2000) present evidence
suggesting that the cauliflower curd arose in southern Italy from a heading Calabrese
broccoli via an intermediate Sicilian crop type.Figure 3.13. Head of cauliflower (left) and broccoli (right) B. oleracea var. botrytis(^)
Source: Courtesy Cavaganaro, David/Sunset/Invision.
Broccoli differs from cauliflower in that broccoli flower heads tend to be smaller with
more slender floret-stalks and are made up of arrested green (or purple) flower buds
whereas the heads of cauliflower are formed by a condensed and thickened, malformed
white (also purple or lime green) flower cluster. Both crops are biennial and, provided the
plants have been vernalized, produce viable flowers and pods in the second year from the
stump or parts of the head that remain. Vernalization requires a prolonged cold period of
at least ten days with temperatures between 2°C and 10ºC. The larger the plant when
exposed to the cold treatment the greater the incidence of bolting. Plants of both crops are