Variation of Cannabis with reference to stem quality for paper pulp production

Abstract

Ca. 160 Cannabis accessions were evaluated for stem quality characteristics. Stems from field trials in two years were analysed. The mass fractions of woody core, bark and primary and secondary bark fibres in the stem dry weight, and the dimensions of the wood fibres were considered most relevant for the evaluation of Cannabis germplasm as a raw material for paper pulp. The accession means for the woody core fraction ranged from 50% in fibre cultivars to 78% in wild populations, drug strains and fibre landraces. Consequently, the bark tissue, being the complementary stem fraction, ranged from 50% down to 22%. The ranges of the accession means were 8 to 27% and 0 to 14% for the fractions of primary and secondary bark fibres, respectively. The total bark fibre fraction ranged from 9 to 34%. Fibre cultivars had strongly increased fractions of primary and secondary bark fibres in comparison to wild populations, drug strains and fibre landraces. The levels of the assessed stem fractions were stable over years. Significant differences in wood fibre length among accessions were only detected in one of the two trials. The accession means in this trial ranged from 433 to 613 μm. For wood fibre width the accession means ranged from 24 to 37 μm and from 25 to 41 μm in the two trials, respectively. The stability of wood fibre dimensions over years was low. Within accessions, the wood fibres of male plants were usually somewhat shorter and wider than those of females. Apart from this difference between sexes there was little variation for wood fibre dimensions among individual plants within accessions. Breeding for improved woody core quality is considered not very promising. The best way for genetic improvement of hemp pulping quality is continuous selection for increased bark fibre content, which implies a reduction of the woody core fraction.