Vol. 72 No: 5

Title:
Variability in Chromosomes, Herb Yield, Essential Oil Content and Potentials of Horehound for North American Commercial Production

Authors:
W. LETCHAMO and S. MUKHOPADHYAY

pp: 741-748

Abstract:
The main objectives of this programme were to determine the variability in yield, morphological traits and the content of active substances in Marrubium vulgare populations and develop a superior cultivar for commercial production and extraction in Canada. Plants were grown in the fields of the Horticultural Research Station of Laval University, Quebec, Canada from 1992 to 1994. There was great variation within the plant population in terms of chromosome number and size, morphology, time of flowering and the shoot yield. The shape and size of somatic chromosomes of horehound showed significant variations. Although the chromosomes had numerical stability, we found aneuploidy and variations in the shape and size of the chromosomes. Such variations might have contributed to the differences in certain morphological features and developmental variations in the population leading to the evolution of different genotypes of this species. The dry shoot yield varied from 6.2 to 67.9 g per plant, while plants height varied from 15 to 56 cm. Leaf shape varied from round to oval, and the colour from deep dark green to light silver green. Some plants flowered as early as 3–4 weeks after planting, while others started flowering at mid-August, September or not at all. We also found that 3% of the plants which induced flowering had faster and uniform seed set and seed ripening, while others developed slowly and only few seeds ripened or none. We were able to select and maintain three separate lines from the population based on the differences. Further screening and tests in field and greenhouses resulted in the identification of three distinctly different cultivars (MAR-92, Late-1 and Late-2) of M. vulgare. The content of essential oil in the plants was low; leaves contained more essential oil (0.29%) than flowers or stems.

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