
%0 Journal Article
%A Lisson, S. N. 
%A Mendham, N. J. 
%A Carberry, P. S. 
%T Development of a hemp (<emph type="2">Cannabis sativa</emph> L.) simulation model 2.The flowering response of two hemp cultivars to photoperiod
%J Australian Journal of Experimental Agriculture
%D 2000/07/04
%V 40
%N 3
%P 413-417
%K hemp, model, phenology, flowering, photoperiod response.
%R https://doi.org/10.1071/EA99059
%U https://www.publish.csiro.au/paper/EA99059 
%X 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, daylength 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, aflower 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&#8217;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&#x02DA;Cd and 390&#x02DA;Cd, MOP was 14 h and 13.8 h, PS was 266&#x02DA;Cd/h and 252&#x02DA;Cd/h, and FDP was 76.8&#x02DA;Cd and 80.2&#x02DA;Cd. 
