The relationship of stem and seed yields to flowering phenology and sex expression in monoecious hemp (Cannabis sativa L.)

摘要

Flowering phenology and sexual dimorphism are two major features that affect stem and seed production in hemp (Cannabis sativa L), a short-day naturally dioecious plant. The sowing time is of primary importance because it affects flowering time and thereby influences stem yield. In spite of their unstable sexual phenotype, monoecious cultivars facilitate the harvest of both stems and seeds by reducing crop heterogeneity. The main objective of this paper was to determine the stem and seed yields for five monoecious hemp cultivars in relation to their flowering phenology and sex expression. Sowing was carried out on five distinct dates during 2007 and 2008 at two sites in Belgium. The duration from sowing to flowering in days, both stem and seed yields and the seed harvest index decreased when sowing was postponed from mid-April to the end of June. The stem and seed yields from the mid-April sowing (approximately 12.5 and 1.9 t ha(-1), respectively) were within the ranges that were reported for fibre and both fibre and seeds production, respectively, in monoecious hemp. No interaction was observed between the sowing date and cultivar for both yields. Sex expression varied among cultivars, indicating that it might be selected, and was partly linked to earliness. Stem yields were lowest in the earliest cultivar (Uso 31) and highest in the latest one (Epsilon 68) while seed yields were lowest in the most masculinized and earliest cultivar (Uso 31) and highest in the most feminized and early (Fedora 17) or mid-early (Felina 32) ones. Both stem and seed yields correlated best with the duration from sowing to full female flowering or from sowing to the end of male flowering. According to our results, harvesting the seeds in addition to the stems in monoecious hemp requires early sowing and the selection of feminized early or mid-early cultivars, earliness depending on the climatic conditions in the cultivation area. Therefore, it might be agriculturally valuable to take sex expression into account in addition to earliness during the selection of cultivars that are adapted to a dual purpose