Variation of Cannabis for phenological development and stem elongation in relation to stem production

Abstract

The variation of Cannabis in phenological development and in stem elongation was studied in relation to stem production. In two field evaluations, one including 98 and the other 75 accessions, large variation was found for day of anthesis and day of seed maturity. A higher latitude of origin of accessions was associated with earlier anthesis and seed maturity. The phenological pattern proved to be stable over years. Stem elongation in the evaluation trial of 98 accessions was characterized by the slope coefficient, inflexion point, and upper asymptote of a sigmoid curve fitted to periodical measurements of stem length. Significant differences among accessions were found for each of these curve parameters. Stem elongation was less stable than the phenological pattern over years. The stem elongation parameters were significantly correlated with the day numbers of anthesis and seed maturity. Early-flowering accessions were shorter than late ones. The influence of phenological development on stem elongation was however only evident for relatively early-flowering accessions. Stem elongation of Cannabis continued generally after the onset of anthesis. The proportion of the stem formed in the generative stage was larger the earlier accessions started to flower. Very late-flowering accessions reached the ultimate length in the vegetative stage. In the evaluation trial consisting of 75 accessions, phenological development and final stem length were observed in relation to stem dry matter production. Day of anthesis and final stem length were strongly and positively related with stem yield. Some very late-flowering landraces of fibre hemp exceeded by far the standard fibre cultivars in stem yield. Late-flowering drug strains were less persistent than late fibre strains in a dense crop situation. It was concluded that in an efficient crop growth system, seed production and stem production should occur in separate geographic areas, i.e. seed production at lower latitude and stem production at higher latitude. Breeding can contribute to yield potential by improving the persistency of cultivars. There seem also possibilities to select for more efficient stem dry matter accumulation and dry matter partitioning.