Material and Methods
Plant MaterialIn 1995 cuttings of 16 L. alba populations from all over Guatemala (Table 1) were transplanted in an experimental field at ICTA (Instituto de Ciencia y Tecnologia Agricola), Cuyuta, Guatemala. The term 'collection source' in Table 1 specifies the origin of plant material, which was collected from house gardens ('cultivated') or from the wild. Cuttings were planted at distances of 75 × 50 cm in a randomized block design with three replications, 16 plants per replication.The decision to collect cuttings instead of seeds from wild populations derived from the extremely low germination rates found for L. alba of only 1-2%. Herbarium specimens of each population were deposited at the Universidad del Valle, Guatemala City, Guatemala. 90 days after transplantation, leaves and flowers were harvested and dried in a greenhouse at an average temperature of 32°C for 4 days. The temperature in the greenhouse was regulated by a ventilator.
Morphological CharactersThree out of several morphological characters were especially interesting in the context of essential oil composition: leaf shape, width of the leaf, and length of the flower stem. The length of the flower stem, measured at the 4th node from the top, is defined as the distance between the axilla and the node of the involucre.
Successful crossing experiments between the tetraploids Achillea ceretanica-4x, A. collina, A. distans subsp. styriaca, A. pratensis, and the octoploid A. monticola, all from the A. millefolium agg. (Compositae), are reported. Chromosomeswere studied ih 514 out of 883 hybrid plants obtained from 13 crossings. F,-offspring from tetraploid parents was generally tetraploid, but some combinations produced up to 30% of aneuploid, near-pentaploid, and even hexaploid F,-individuals. A backcross and a F2-progeny consisted of normal tetraploids. A reciprocal F,-combination involving a tetraploid parent with one B-chromosome showed an increase of B-chromosomes in the F,, when the male transmitted the B (69.2%), and a decrease, when the female had the B (33.3%). Mainly hexaploid offspring resulted from a reciprocal F,-cross between tetraploid and octoploid parents.
Successful crossing experiments between tetraploid individuals of Achillea ceretanica, A. collina, A. distans ssp. styriaca, and A. pratensis {A. millefolium complex, Compositae) were carried out. Sesquiterpenes of 1013 hybrid plants obtained from 13 crossings were studied by quahtative thin layer chromatography (TLC). F,-progenies from parent plants with guaianolides (GU-type), as well as the ofl"spring of a backcross, uniformly contained proazulenes. Diallel crosses between plants exclusively with eudesmanohdes (EU-type) resulted in a 7:1 segregationratio of EU-and GU-plants. Two reciprocal crossing experiments between EU-and GU-parents resulted in 28.6% and 89.3% EU-individuals, as well as GU-offspring. According to these findings, the quahtative marker 'proazulene' (GU-type) is thought to be a recessive character of the tetraploid Achillea species studied.
Three selfing and 13 crossing experiments between tetraploid individuals of Achillea ceretanica, Achillea collina, Achillea distans ssp.‘styriaca’ Saukel (ined.), and Achillea pratensis (Achillea millefolium complex, Compositae), five F1 crosses, three backcrosses and one further selfing experiment were carried out in order to study the inheritance of longipinenone (1) and its hydroxyl derivative (2). From these crossings, 1294 plants were studied by qualitative thin layer chromatography. Progenies from parent and F1 plants without longipinenones (0‐type, ll) uniformly contained none of these two sesquiterpenes. All other crossing experiments showed typical segregation patterns of 0‐type, L‐type (longipinenone (1) without hydroxylongipinenone, L.hh) and H‐type (hydroxy‐longipinenone (2) and occasionally longipinenone, L.H.) in the ratio of 1 : 1 and 1 : 3. According to these results both derivatives are under dominant genetic control regulated by genes L and H, whereby hydroxylation takes place after synthesis of longipinenone (1).
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