The duration from sowing to flowering is an important determinant of fibre yield potential in hemp, since maximum stem yield occurs shortly after flowering. As a short-day plant, has a key influence on the timing of flowering in hemp. This paper reports on studies into the effect of photoperiod on the thermal time duration from sowing to flowering for 2 hemp cultivars, and develops parameters to enable simulation of post-emergent phenology in the hemp model described in the final paper of this series. The hemp model divides the post-emergent period into a vegetative phase that ends at floral initiation, a flower development phase (FDP) between flower initiation and appearance, and a short phase between first flower appearance and harvest maturity (male anthesis). The vegetative phase is further divided into a temperature-dependent basic vegetative phase (BVP) and a daylength-dependent photoperiod induced phase (PIP). For a short-day plant, the duration of PIP is assumed to be zero degree days at daylengths below a base or maximum optimum photoperiod (MOP). Daylengths in excess of the MOP lead to an increase in thermal time within PIP, the duration of which is determined by a genotype's photoperiod sensitivity (PS). Two hemp genotypes, Kompolti and Futura 77, were exposed to 6 different photoperiod regimes ranging from 8 to 16 h in a growth chamber. Thermal time durations from emergence to flower initiation and first flower formation (harvest) were calculated from thermograph plots. The flowering responses for the 2 cultivars were typical for a short-day plant, with flowering occurring rapidly in daylengths less than about 14 h and with increasing delay at longer photoperiods. With the exception of a longer thermal time duration from flower formation to harvest maturity in the case of Kompolti, the 2 cultivars had similar values for the key phenology parameters. Respectively, for Futura and Kompolti: BVP was 383°Cd and 390°Cd, MOP was 14 h and 13.8 h, PS was 266°Cd/h and 252°Cd/h, and FDP was 76.8°Cd and 80.2°Cd.
History
Publication title
Australian Journal of Experimental Agriculture
Volume
40
Pagination
413-417
ISSN
0816-1089
Department/School
Tasmanian Institute of Agriculture (TIA)
Publisher
CSIRO Publishing
Place of publication
Melbourne, Australia
Repository Status
Restricted
Socio-economic Objectives
Other animal production and animal primary products not elsewhere classified