The Greek mountain tea (Sideritis L.) belongs to the genus Sideritis (Lamiaceae). Its scientific name is a derivative of the Greek word sideros that means iron. Sideritis is known in Greece from ancient time, when Dioskourides (A.D. first century) described it.

Today, it is widely used in Greece as a specific traditional tea endowed with a number of beneficial properties. In addition to its pleasant taste, it has a distinguished aroma and yellow or brown-yellow color.

Its important role as traditional Greek tea has imposed the need of its cultivation to meet the market increased requirements, as the production from wild selfsown plantations was insufficient to cover the demand of it. Nowadays, Sideritis is cultivated in low fertility hilly and mountainous area at over 1000 m altitude.

Because of its importance for Greek people, we were involved in Breeding of Sideritis species. So we produced interspecific hybrids by using indigenous species of Greek mountain tea. From the F₁ hybrids, 15 superior were selected on the basis of their yield and quality of their essential oil. The interspecific hybrids had higher fresh and dry weight, as well as essential oil yield than controls. Also, they exceeded their parents in yield and fresh and dry weight as well as the inferior parent in the essential oil content.

As a result, the interspecific superior hybrids has been introduced in the mountainous and semi-mountainous marginal areas of this country for cultivation significantly increasing grower's income.

The genus Sideritis includes about 140 known species. Ten of these species are annual and the remaining perennial (1,2,8,12). The annual species are indigenous to the area that extends from the Eastern Mediterranean coast as far as Armenia and Middle East. The perennial species are indigenous and self-sown to mountainous areas of Greece, Turkey, Lebanon, Syria, North Africa, Iberian Peninsula, Canary Islands and Madeira. The indigenous species to Greece are: (1) Sideritis athoa. Papanikolaou & Kokkini, (2) Sideritis clandestina Chaub. & Heldr., (3) Sideritis scardica Griseb, (4) Sideritis raeseri Boiss & Heldr.,(5) Sideritis syriaca L. (6) Sideritis euboea Heldr (8).

The Greek mountain tea (Sideritis L.) started being cultivated as a crop on low productivity soils in mountainous and semi-mountainous areas in Greece, because of its widespread use by Greek people (3). Lately the self-sown plantations on the mounts, those accessible to pickers, were inadequate to cover the consumption. All Greek species are cross-pollinated, so each plantation is a an open pollinated population (OPP). It is found that the species cross with each other rather readily and produce heterotic F₁ interspecific hybrids. The evolution of the species becomes faster through natural hybridization (11). The breeders are able to select the parents and apply artificial cross to produce new desirable characters, that were impossible to produce without human intervention (9,10). Particularly, for the Greek mountain tea, the breeders are able to direct the crossing of the species and select individual interspecific hybrid plants with higher yield and content in essential oil than the parents (5). Given that Sideritis is mainly asexually propagated, it is obvious that a highly productive F₁ individual plant could be utilized directly as a new clone for cultivation (5).

This work was undertaken to produce F₁ interspecific hybrids between various Sideritis species indigenous in Greece, and the evaluation of their performance with the aim to isolate superior F₁ interspecific hybrids (5).

The genetic material intended to produce hybrids was selected from the self-sown Greek mountain tea populations of different regions of Greece. The taxonomic determination of the selected plants was carried out according to Papanikolaou & Kokkini (8) and Baden (1). The following species were selected:

1. Sideritis scardica Griseb. (One population selected from mountain Vermio and another one from mountain Olympos),

2. S. clandestina Chaub. & Borry (selected from mountain Taygetos),

3. S. euboea Heldr. (selected from mountain Dirphi),

4. S. raeseri Boiss & Heldr (One self-sown population selected from mountain Orthris and another cultivated from mountain Parnassos,

5. S. athoa Papanikolaou & Kokkini (selected from mounatin Athos),

6. S. syriaca L. (selected from the area of Omalo in Crete).

The selected plants were planted in rows in the fields of the department of Aromatic and Medicinal Plants of Agricultural Research Centre of Macedonia-Thrace. Each of the species was crossed as female parent with all the other species according to the technique described by Goliaris and Koutsika (4).

The young F₁ produced interspecific hybrids had been described (5) before the establishment of the evaluation trial in the area of Zoodochos Pigi on the mountain of Vermion. The evaluation trial was established in R-7 honeycomb design (7) and the individual plant yield production in 1991 was used (5). Fifteen high yielding hybrid plants were selected after application of a selection procedure described by Fasoulas (6). According to this procedure the center of a moving grid including 13 plants was moved from plant to plant and a particular plant was selected if it outyielded the remaining plants within the grid (7.7% selection pressure). The dry inflorescence from each individual selected hybrid plant were cut in pieces and 100 g. used for the determination of the essential oil and its components.

The yield per plant of the parental species used for comparison purposes was the average yield of 12 plants per species grown in a trial located beside the hybrid trial and established in the same year with the hybrid plants.

The essential oil was extracted by distillation in a Clevenger apparatus. Distillation was made separately for each interspecific hybrid. For this 100g of dry inflorescence cut in pieces was put in a glass bottle (Quickfit) with 1 L. of water. Each distillation lasted 2.5 h.

The extracted oil (0.5 ml/sample) was analyzed by gas-liquid chromatography, in a Varian series 3.300 apparatus, with head-space analyzer, automatic integrator and hydrogen flame ionization detector.

After a large number of pollinations, seeds were obtained from all cross combinations applied. The number of plantlets that survived, however, varied within the cross and group. Thus, the number of plantlets that survived in the group Sideritis syriaca x Sideritis spp was 42. This is the reason why only 42 plants per group were evaluated.

Given that there are no data reported in the literature about yield performance of Sideritis as a crop and the number of years during which a Sideritis plantation could be maintained with a good yielding ability, the yield was measured in six consecutive years beginning with the year of establishment. It was observed that the yield during the year of establishment of the crop was relatively low and therefore, for a better evaluation, one should wait for the yield production of the following years. Nevertheless, all groups produced statistically higher yields than the control in both fresh and dry weight (Tables 1,2).

All hybrids produced higher yields during three years and their productivity started to decline after the fifth year. It is important to mention here that all of the interspecific hybrids produced higher yields than the control in all six years of the experiment (Tables 1,2).

Among the groups studied those with S. raeseri (cultivated clone) as the common female parent produced the highest yield across the years both in fresh and dry weight. This yield, however, was not always significantly different from the yield produced by the second in the rank family (S. clandestina x Sideritis spp). Third in the rank was the family S. euboea x Sideritis spp with a yield lower than that of the first two, but higher than that of the other hybrids and the control (Tables 1,2).

A significant yield reduction was observed in all groups and the control during the sixth year. The yield of the hybrids, however, was still higher than that of the control. This indicates that a Sideritis plantation should not be maintained for more than six years. It is clear therefore that the interspecific hybrids produced higher yields than the control in all of the six consecutive years studied.

A high correlation between fresh and dry weight yield was observed in all of the crosses studied (Table 3). In all cases the coefficient of correlation was higher than 0.99. It is obvious, therefore, that the breeder could use the fresh weight yield as a criterion of comparison in his selection schemes. This is very important since the breeder saves time and labor by keeping and drying only the yield of the selected plants.

The yield is not of course the only trait of interest, quality is also important. Mountain tea quality is determined by the essential oil included in the product. It is very interesting that the two groups of interspecific hybrids with the highest yield had also the highest yield in essential oil (Table 4). It is worth mentioning here that all the interspecific hybrids had higher yield in essential oil than the control species.

The essential oil content, however, in six hybrids (No.16, 41,248, 59,85 and 124), was higher than the high oil content parental species and in nine interspecific hybrids (No.103, 120, 240, 19, 45, 75, 173, 220 and 197), it was intermediate of the parental species or close to the content of the higher oil content parental species (Table 5). This is an indication that the essential oil content in Sideritis is controlled by genes with additive and dominance action.

The number of components of the essential oil of the parental species ranged from 25 in S. athoa to 49 (Table 5) in S. raeseri Boiss and heldr (Parnassos). Eight of the interspecific hybrids (No.16, 103, 248, 19, 45, 59, 75 and 85) had more components than the parental species with the highest number of components, two (No.173 and 124) had less than the parental species with the lower number of components, four (No. 120, 240, 41 and 220) had an intermediate number of components as compared with their parents and one (No. 197) had the same number observed in the parental species with the highest number of components. These results indicate that the number of components identified in the essential oil of the hybrids largely depends on whether the parental species carry the same or different components.

The content of the seven most important components of essential oil (a-, b-pinene, lemonene, p-cymene, menthone, a-, b-copaene, caryophyllene and valerianic ester) was calculated to compare the interspecific hybrids and their parental species. The better hybrid plants were selected from the family Sideritis euboea x S. athoa (Fig.1). Generally, the interspecific hybrids had a higher content in essential oil than the parental species. In addition, the essential oil of the hybrids contained components from both parents and different amounts than the parental species. A significant reduction, in some components with a simultaneous increase in others, was also observed in some hybrid plants (Fig.1). The amount of the components was influenced by the year, yet the general profile of the seven components remained the same from year to year in all of the hybrids studied.

Figure 1. Content of main essential oil components in Sideritis hybrid No 248.

CONCLUSIONS

The interspecific hybrids yielded more than the control species in both fresh and dry weight as well as in essential oil. Thus, the breeder could select individual interspecific hybrid plants having much better performance than the control species. Also, the interspecific hybrids, were superior than their parental species regarding the total content in essential oil and the content of some of the most important components. Thus, if yield superiority of the selected plants will be maintained from year to year, then the interspecific hybrids could be propagated asexually and cultivated on low productivity soils improving the farmers income.

1. Baden C. Sideritis L. In: Mountain flora of Greece. A. Strid and Kit Tan (eds). (1991): Edinburgh University press, Edinburgh, 2, 84-91.

2. Contandiopoulos J. (1978): Contribution a l'etude cytotaxonomique des Sideritis section Empedoclea (labiatae). Pl. Syst. Evol. 129, 177-289.

3. Goliaris A. (1984): Cultivation of the mountain tea, Ministry of Agriculture. Agrotica 16, 29-31.

4. Goliaris A.H. and Koutsika M. (1990): The Greek mountain tea (Sideritis L.) and its artificial cross technique. Agric. Research. Center North Greece Sc. Bulletin 5; 107-115.

5. Goliaris A.H. and Roupakias D.G. (1997): Yield performance of interspecific F1 hybrids of the Greek mountain tea (Sideritis spp. L.), Plant Breeding 116, 493-497.

6. Fasoulas A.C. (1993): Principles of plant breeding. Thessaloniki, Greece.

7. Fasoulas A.C. and Fasoulas V.A. (1995): Honeycomb selection design. Plant Breeding Rev. 13, 87-139.

8. Papanikolaou K. and Kokkini S. (1982): A taxonomic revision of Sideritis L. Section Empedoclea (Rafin) Bentham (Labiatae) in Greece. Aromatic Plants: Basic and Applied Aspects. Martins Nijhoff Publishers, Hague 101 pp.

9. Simmonds N. (1976): Evolution of crop plants. London.

10. Simmonds N. (1979): Principles of crop improvement. 408 pp.

11. Stebbins G.L. (1950): Variation and Evolution of plants. John Westand Sons, New York,

12. Tutin T.G. et al. (1972): Flora Europea 3. University press, Cambridge.