Sn. Lisson et al., Development of a hemp (Cannabis sativa L.) simulation model 2. The flowering response of two hemp cultivars to photoperiod, AUST J EX A, 40(3), 2000, pp. 413-417
The duration from sowing to flowering is an important determinant of fibre
yield potential in hemp, since maximum stem yield occurs shortly after flow
ering. 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 photop
eriod on the thermal time duration from sowing to flowering for 2 hemp cult
ivars, and develops parameters to enable simulation of post-emergent phenol
ogy in the hemp model described in the final paper of this series.
The hemp model divides the post-emergent period into a vegetative phase tha
t ends at floral initiation, a flower development phase (FDP) between flowe
r initiation and appearance, and a short phase between first flower appeara
nce and harvest maturity (male anthesis). The vegetative phase is further d
ivided into a temperature-dependent basic vegetative phase (BVP) and a dayl
ength-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 ba
se or maximum optimum photoperiod (MOP). Daylengths in excess of the MOP le
ad to an increase in thermal time within PIP, the duration of which is dete
rmined by a genotype's photoperiod sensitivity (PS).
Two hemp genotypes, Kompolti and Futura 77, were exposed to 6 different pho
toperiod regimes ranging from 8 to 16 h in a growth chamber. Thermal time d
urations from emergence to flower initiation and first flower formation (ha
rvest) were calculated from thermograph plots.
The flowering responses for the 2 cultivars were typical for a short-day pl
ant, with flowering occurring rapidly in daylengths less than about 14 h an
d with increasing delay at longer photoperiods. With the exception of a lon
ger 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 degrees Cd a
nd 390 degrees Cd, MOP was 14 h and 13.8 h, PS was 266 degrees Cd/h and 252
degrees Cd/h, and FDP was 76.8 degrees Cd and 80.2 degrees Cd.