Spinach: Spinacea oleracea L

The common name ‘spinach’ is given to different species of leafy vegetables in different parts of the world. Seed production of the so-called European spinach (Spinacea oleracea) is discussed in this section. ‘African spinach’ (Amaranthus spp.) is dealt with in Chapter 16. The species that is commonly known as Indian or Malabar spinach is Basella alba L. and is in the botanical family Basellaceae.

Spinacea oleracea was introduced into Europe from south-west Asia prob- ably in the 14th century, and it later reached North America. It is now widely cultivated in all temperate regions. Cultivation in the tropics is not important except in the higher elevations.

The modern cultivars have been developed for their abundance of edible leaves. In the last four decades the crop has become important to processors, who market it as a canned purée and in frozen packs. It has also gained in popularity when produced as a small leaf salad crop.

Cultivar description of spinach

There are open-pollinated and hybrid cultivars and round or prickly seeded:

● Season: relative earliness, suitability for long-day sowing, resistance to early bolting.

● Leaf blade: approximate number of leaves before bolting, colour, shape, texture smooth or crinkled.

● Leaf petiole: length, pose, colour.

● Resistance to downy mildew and Cucumber mosaic virus.

(A detailed test guideline (055) is obtainable from UPOV; see Appendix 2.)

Soil pH and nutrition

The optimum soil pH is 6.0–6.8; if the pH is below 6.0, an appropriate dress- ing of a liming material is applied during soil preparations.

The general N:P:K recommendation is in the ratio of 1:2:2 applied during the final stages of seedbed preparation. Supplementary top dressings of nitrogen are given before and after bolting. Spinach plants are prone to lodging after flowering commences, and applications of nitrogen should therefore only be applied according to local experience and the amount of nitrogen lost by leaching.

Soils known to be infected with fusarium or verticillium wilt pathogens must not be used for seed production.

Sowing

In the USA, sowing is done either in the autumn or spring. Canadian produ cers sow only in the autumn. In Europe, sowing is done at either time according to location and hardiness of the cultivars.

Seed is sown at the rate of 6 kg/ha, in rows 45–60 cm apart. Seedlings are not normally thinned except for the production of basic seed.

Flowering and flower type

Spinach is a typical long-day plant. Flowering occurs in unvernalized plants, but is hastened by previous chilling.

Populations of spinach are composed of plants that are male, female or hermaphrodite. Male plants tend to flower before female plants. There also tends to be a correlation between the dioecious plants, leaf size and number;

male plants produce fewer and smaller leaves before flowering whereas female plants produce more and larger leaves before flowering.

Pollination and isolation

Spinach is mainly wind-pollinated. Recommended isolation distances are therefore up to 1000 m in some countries, although some authorities stipulate only 500 m for production of commercial seed of cultivars within the same type (e.g.

leaf type and seed type).

Roguing stages

1. Before main flowering (when the plant has formed a rosette), remove non- rosetting and early flowering male plants that are not true to type.

2. When flowering has commenced, as for stage 1.

Plants that are infected with specific seed-borne pathogens, e.g. mosaic (cucu- mis virus 1), are removed during roguing.

Hybrid seed production

The ratio of female-to-male rows depends on the potential pollen production of the male parent, and is usually 6:2 or 14:2.

Specific instructions for roguing and harvesting should be provided by the maintenance breeder. Roguing for hybrid seed production includes the removal of male plants from the female rows, this is usually done twice to ensure com- plete removal of the males from the female rows. Some hybrid lines are produced by crossing round-seeded and prickly seeded parents, and this enables the seed products of the parents to be harvested together and subsequently separated during processing (Sneep, 1958).

Harvesting

The ripening crop seed is subject to loss from shattering and birds. In the large- scale seed-producing areas with relatively calm and dry weather conditions, the crop is harvested with a combine when the plants are dry and the majority of the seeds are mature. Otherwise the crop is cut and placed in windrows to dry as soon as the plants start to dry out and the earliest seeds are mature. An approximate guide to this stage is when the later ripening plants start to become yellow. Material left to dry must be stacked on sheets to avoid loss from shattering.

Threshing

Spinach seed from cut and dried plants is threshed with a small-drum thresher or a cereal thresher. In the latter case the recommended drum speed is about 700 rpm, and the concaves are set relatively wide to minimize the amount of broken stalks. In addition to separating the seeds from the plant, the threshing operation breaks up the clusters of seeds.

Seed yield and 1000 grain weight

The generally accepted seed yield is approximately 800 kg/ha, although yields of up to 2000 kg are reported. The yield of hybrid cultivars per unit area is very similar to open-pollinated cultivars even allowing for discarding the male lines.

The 1000 grain weight of spinach is approximately 10 g.

Pathogens

The main seed-borne pathogens of spinach are listed in Table 7.2.

Table 7.2. The main seed-borne pathogens of spinach species; these pathogens may also be transmitted to the crop by other vectors.

Pathogens Common names

Cladosporium variabile Leaf spot Colletotrichum dematium f. spinaciae Anthracnose Colletotrichum spinaciicola

Fusarium oxysporum f. sp. spinaciae

Perenospora farinosa f. sp. spinaciae Downy mildew, blue mould Phyllosticta spinaciae Leaf spot

Rhizoctonia solani Damping off

Verticillium dahliae

Verticillium sp. Wilt

Spinach Latent Virus

Further Reading