188 – II.3. BRASSICA CROPS (BRASSICA SPP.)
Hagley/Westbury and Devonport. Tasmania is climatically suited for “counter-season”
seed production for the northern hemisphere markets of Asia and Europe. Major seed
crops produced in 2001 were hybrid cabbage (150 ha) and cauliflower (97 ha)
(Government of Tasmania, 2003). Cabbage and cauliflower are high-value autumn
planted crops while the lower value mustard and Chinese vegetable types are spring
sown. Locations for hybrid seed production of cabbage and cauliflower are determined by
the need for an isolation zone of 1.5-3 km from other crops of the same botanical family.
Grower awareness and consultation between companies ensures adequate isolation
distances.
In New Zealand, the Canterbury Plains and other smaller areas of the South Island
(43º south) have become a major vegetable seed-production location, particularly for the
Asian Brassica vegetables. In this region, the seed merchants and growers have put in
place an isolation mapping system to avoid cross-pollination among different species and
varieties. The system is operated by a government-owned company called AgriQuality
that displays an Internet map of every farm field involved in seed production.
When a seed contract is arranged and a field is selected, the seed merchant logs the details
into the system and can see if there are any conflicts within the isolation distance
required. Normal minimum isolation distance for the Brassica crops is 1 000 m, but that
can be extended, particularly with hybrid seed production.
Not all seed-production regions are maritime based. In China, cauliflower and
broccoli seed production is concentrated in semi-desert regions around the cities of
Jiuquan and Jiayuguan in Gansu and in Yunnan provinces. In these high-elevation areas
precipitation is minimal, but irrigation is available and the temperatures remain within the
required range. Cabbage and Chinese cabbage seed production is located further south in
Hebei, Henan, Shandong and Shanxi provinces (X.-W. Wang, personal communication).
In these regions the normal isolation distances between production fields is 1 000 m.
On the Indian sub-continent, no concentrated areas for seed production were
identified. However, small individual fields occur scattered in the foothill valleys of the
Himalayas. For the production of certified cauliflower seed, the minimum isolation
distance is 1 000 m (Indian Minimum Certification Standards).
In Japan, no concentrated area exists for large-scale seed production. However,
various Brassica vegetables (B. rapa and B. juncea) are cultivated locally (Inomata,
2007) and seed production is practiced on a small scale. The minimum isolation distance
required for seed production is 600 m.
George (2009) notes that most authorities recommend having a greater distance (up to
1 500 m) between different types of B. oleracea (cabbage vs. kohlrabi) than between
varieties of the same type (two cabbage varieties, up to 1 000 m).
Vegetable seed cultivation and management
The optimum pH for cole crops is reported to be 6.0 to 6.5 with the generally
recommended ratio of N-P-K nutrients being 1:2:2 at soil preparation, but it varies
depending on the production region (George, 2009). The lower ratio of nitrogen is to
avoid “soft plants” that are less winter hardy. Extra nitrogen is normally topdressed in the
spring. It is important to ensure that adequate levels of sulphur as well as the
micronutrients boron, manganese and molybdenum are available. The development of
hybrids in Brussels sprouts has become very important (George, 2009) with
self-incompatible and cytoplasmic male sterility (CMS) hybrids becoming more frequent
