See: Linum usitatissimum. Linum usitatissimum

Flax and linseed. This species is a self-pollinating annual. There are three categories of cultivar in this crop. Flax cultivars tend to be tall, with few branches and flowers. The stems are retted to produce linen. Linseed cultivars are relatively short, many-branched, and many-flowered, they produce seed used for the production of linseed oil. This oil was originally in great demand for the manufacture of paint, but it has now been almost totally supplanted by plastic latex paints. The dual cultivars can be used for both linen and oil production. A very new development comes from the discovery that newly ground flax seed is an excellent dietary source of Omega-3 polyunsaturated oils.

Flax is historically interesting in that H.H. Flor, in 1940, discovered the gene-for-gene relationship while working on flax rust (Melampsora lini) in Illinois, USA.

This crop is suitable for amateur breeders working with horizontal resistance and recurrent mass selection . Liquorice

See: Glycyrrhiza glabra. LISA

See: Low input sustainable agriculture. Litchi

See: Nephelium litchi. Local optimisation

A term from systems theory that concerns responses to variation within a system. In ecology, local optimisation is illustrated by the formation of ecotypes, which vary as a result of different selection pressures in various localities within the ecosystem. Each ecotype is locally optimised to its own locality. Similarly, genetically flexible landraces, or agro-ecotypes, are locally optimised to their own local agro-ecosystem, and they will invariably perform less well in a different agro-ecosystem. In plant breeding, the purpose of On-site selection is to achieve local optimisation of many quantitative variables such as horizontal resistances. Locking

The system of locking that functions in the vertical subsystem of a wild plant pathosystem, controlled by the gene-for-gene relationship, apparently in accordance with the n/2 model, depends on a heterogenous mixture of locks and keys. A system of locking is ruined by uniformity ("What happens when every door in the town has the same lock, and every householder has the same key, which fits every lock?"). However, our use of vertical resistance genes in agriculture is based on uniformity, and this is why vertical resistance is temporary resistance in our crops. Locks and keys

Every vertically resistant plant has one or more vertical resistance genes that collectively constitute a biochemical lock. And every vertically parasitic parasite has one or more vertical parasitism genes that collectively constitute a biochemical key. When a parasite is allo-infections a host, its key either does or does not fit the lock of the host. The allo-infection succeeds only if the key fits (i.e., a matching infection). Lodging

Long-stemmed cereal plants are liable to be blown over when they are wet and heavy in a storm. This is called lodging. The basis of the Green Revolution was the development of short-strawed (i.e., dwarf) varieties of wheat and rice. These could be given high applications of fertiliser without risk of lodging, and the yields were increased accordingly. Lolium spp.

Ryegrass. Two species are used in sown grass for fodder. Perennial ryegrass (L. perenne) and Italian ryegrass (L. multiflorum) are very important. They hybridise freely and offer scope for amateur breeders . Long-day

Many temperate plants are photoperiod-sensitive, and depend on a long day to initiate flower production. For this reason, crops such as olives and hops cannot be cultivated in the tropics. Equally many tropical plants depend on a short day to initiate flower production and, possibly, other processes, such as tuber formation. See also: potatoes.

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