Breeding Targets

Owing to the extremely large morphological and chemical variety encountered in Origanum sp. and taking into account the demand for homogenous raw material, wild collection accompanied with quality as well as species maintaining assurance systems (sustainability, GHP) and/or field production of reliable genotypes are the future methods of choice for quality products. As to the latter, selection and breeding represent an important part of the quality assurance system. The mentioned large variability represents at the same time a challenge for the breeder in search of homogeneity and an excellent basis for selection activities.

Generally, there are three major uses of oregano:

1 as ornamental in gardens, especially rockeries,

2 as kitchen herb responsible for the classical "pizza" oregano flavour,

3 for industrial purposes as source of antimicrobial essential oils and/or antioxidant extracts.

Ornamentals

Many oregano species and varieties offered as ornamentals are selected on their visual appearance only, and therefore without relevance for herb or essential oil production due to their low essential oil content and atypical composition. Some of them would still not be interesting for crude herb production even if containing much essential oil since the unusual leaf colour would result in an "off-colour" impression.

168 Chlodwig Franz and Johannes Novak Quality characteristics

Regarding the use of oregano as crude drug or as source of essential oils and extracts, the following parameters are of particular interest:

• Composition of essential oils (in oregano high carvacrol content, in marjoram high cis-sabinene hydrate content);

• Quantity of essential oils (in marjoram more than 2 per cent is desired);

• Colour of the dried herb (green is preferred over grey);

Essential oil composition

There is now a very clear quality profile for "oregano" to be observed: carvacrol is regarded as the valuable sensorial as well as important antimicrobial compound. Breeding will focus therefore mainly on the optimisation of the carvacrol content with as less other compounds present as possible to not interfere with sensorial/antimicrobial properties of the end product. Selecting the right chemotype means at first of course selecting for the presence of carvacrol, but on the second hand also selecting against other compounds like e.g. cis- and trans-sabinene hydrate, linalool or even thymol. A first rough selection can be based on simple organoleptical testings for the characteristic phenolic smell. It can easily be distinguished between the carvacrol and thymol taste, carvacrol being rather pungent than thymol.

Sampling for the determination of the carvacrol content is crucial due to the many changes in the essential oil profile during the ontogenesis. So it was observed that phenolic compounds were increasing during the vegetation period (Putievsky etal., 1985). But these compounds are also increasing from the top to the bottom of a plant, which has been proven for thymol by Werker etal. (1985), a fact that has to be considered in sampling, especially if using minor quantities of the herb for chemical analyses to not damage the plant before seed ripening if the selection is based on single plant evaluations. In addition, studies concerning the influence of environmental factors have shown the effect of temperature and daylength on the essential oil of oregano. As the day becomes longer, the essential oil content as well as the phenolic compounds increase, whereas at short day conditions (spring and autumn) the precur-sor^-cymene prevails (Dudai et al, 1992). Similar results have also been obtained with O. majorana (Circella etal, 1995).

Apart from the typical "oregano" profile correlated with the carvacrol content, the enormous inter- and infraspecific chemical polymorphism of Oregano sp. offers a wide range for selection towards the production of specific monoterpenes as fine chemicals, new odour and flavour profiles a.s.o. In O. syriacum, for instance, a certain geraniol and geranyl-esters as well as ethylcinnamate content is responsible for "a tender desert note" of the herb (Fleisher and Fleisher, 1991). And some of the minor compounds of O. vulgare ssp. hirtum have shown a very high antioxidant effect (Deans et al, 2000).

Essential oil content

Regarding the essential oil content, the breeding targets will differ significantly between genotypes to be selected for herb production or for essential oil production. Due to the enormous possible range of the essential oil content (see above) an optimisation has to be considered in the context of use. While oregano used as herb in cooking contains in average between 1 and 3 per cent essential oil, genotypes having more than 3 per cent oil would make it necessary to change recipes. But by using less herb on a pizza, for example, the visual impression of herbs would almost be absent. Therefore, the essential oil content should for that purpose not exceed approx. 3 per cent. For the production of the essential oil, on the other side, the situation is quite different, since by selecting for essential oil contents of more than 7 per cent the productivity is dramatically increasing.

It is very likely, that in the future there will be separate genotypes selected for herb and essential oil production, respectively. This will of course not exclude using herb genotypes for essential oil production in combined systems, where e.g. the first cut is sold as herb, the consecutive cuttings in a year may be used for essential oil production.

Leaf colour and density of non-essential oil producing trichomes

Selection for favourable leaf colour and against non-essential oil producing trichomes are breeding targets for the sensorial impression of the herb. These are of course characters only to be observed for the herb use and not for essential oil production. The importance of leaf colour in herb production is not equal but depends on the requested quality features of the customer, on necessary post-harvest processes and selling as fresh, frozen or dried material. For marjoram, a green leaf colour is preferred, whilst greyish is more typical for oregano. Leaf colour has of course a higher impact on fresh and frozen than on dried material.

Agronomical Characters

Agronomical characters are of great importance for a higher productivity of the crop but in some cases also prerequisites for certain cultivation techniques (like e.g. seed weight). The most significant features are:

• Upright growth (to avoid soil contamination and spoilage of leaves);

• Ratio of leaves to stem (of special interest for herb-processing companies);

• Quick development of young plants (especially for marjoram which is a slowly established crop and is rather weak when facing weed problems);

• Resistance to pathogenes (for example, O. majorana is severely affected by Alternaria and Fusarium);

• Salt and drought tolerance (a much desired trait in Mediterranean areas);

• Winterhardiness (desired for biennial/perennial production in Central Europe).

The variability stated for the essential oil content and composition continues in the agronomical characters. Out of this group, yield is of course one of the most important parameters securing the necessary productivity for being competitive on the market. The yield can be expressed as weight per area unit in herb production or as essential oil yield per area unit. The variation between single plants can range between approx. 10 g dried leaf/flower-fraction per plant up to 250 g (Marn, 1999). Therefore also in yield high progress can be obtained within a relatively short time of breeding/selecting.

Of somewhat minor importance than yield are the leaf-stem ratio and machinability. However, having the opportunity to observe also these characters in breeding will result in better production techniques and qualities.

Oregano (Origanum sp.) belongs to the species with very small fruits (nutlets) weighing only approx. 60 pg per seed (thousand seed mass = 0.06 g) (Thanos, 1995). Also due to this reason direct sowing of oregano is difficult and until now plantlet production under protected conditions and planting is preferred. Selecting for higher seed weight will be a first step to enhance the production technique of direct sowing, since seed quality, germinability and vigour depend on it.

In a situation like oregano, where the selection starts from wild collected populations, non-resistant genotypes should of course be very strictly eliminated to avoid susceptibility in selected high-productive genotypes.

Breeding methods

Since breeding of oregano will start principally from wild populations, simple positive mass selection will still be the method of choice for a first progress. It has to be obeyed, that Origanum species are open-pollinated species. Therefore characters evaluated and selected before flowering will guarantee a by far better selection success than characters selected after flowering.

If valuable character expressions are scattered over several populations crossings are necessary to combine them in one genotype. Prerequisite of such breeding programmes is the knowledge of the floral and reproduction biology. Artificial pollination will be difficult due to the small flower size and the high number of flowers within an inflorescence. Here, the in Lamiaceae often occurring male sterility could be used to control crossings efficiently (Lewis and Crowe, 1952; Kheyr-Pour, 1980, 1981). Such a system of pollination control like male sterility could also be used to produce hybrids and to use advantages of hybrid systems like heterosis effects and uniformity as has been already established for marjoram (Origanum majorana) (Circella et al, 1995; Novak et al, 1999). Beyond "hybrids" in hybrid breeding also naturally occurring interspecific hybrids do exist in a vast number (Appl, 1928; Ietswaart, 1980) indicating the principal possibility to artificially create interspecific hybrids. In the case of the

Table 7.1 Ornamental Origanum cultivars used mainly in rockeries (Facciola, 1990)

Name

Description

White Anniversary

Golden Oregano (O. vulgare ssp. vulgare "Aureum"; Golden Creeping Oregano)

Silver (Silver Oregano)

Variegated Oregano

Bright green leaves, broadly margined in white. Spring growth in a white ground hugging mat, changing to a pale cream by fall.

Compact, creeping habit, to 6 inches high. Attractive golden coloured foliage. Good ground cover for rock gardens and edges of flower beds. Mild, thyme-like oregano flavour.

Ornamental silver leaves. Mild oregano flavour. Can be used in cooking. Tender perennial. Attractively streaked with golden variegation that contrasts prominently against the deep green background. Mildly flavoured. Excellent for edging or in the rock garden.

spontaneous Origanum X intercedens hybrid (Kokkini and Vokou, 1993), an interesting increase in the biomass yield has been detected, thus suggesting a particular economic significance of this plant. In some cases, however, the hybridisation is accompanied by complete sterility and therefore further genetic improvement of the material is not possible. On the other hand, if the hybrid is an exceptionally interesting plant, its

Table 7.2 Recently developed cultivars/varieties of Origanum sp. (1995—2000)

Species

Cultivar/ Variety

Reg.

Breeding method

Specific characters

O. dictamnus

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