Flowering Time in Hemp

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Jacob Toth, George Stack, Caroline Dowling, Jiaqi Shi, Rainer Melzer, Susanne Schilling, and Larry Smart.

Hemp is usually photoperiodsensitive, but exceptions exist. Most cultivars grown for CBD or CBG will only terminally flower when the night is long enough.
However, “Autoflowering” cultivars will flower regardless of day/night length. Induction of flowering for grain and fiber cultivars is more complex.

There is genetic variability in critical photoperiod of photoperiod-sensitive hemp (Figure 1). We have identified three distinct genetic loci that contribute to differential flowering time, and are developing molecular markers and investigating interactions between these loci.

terminal flowering date table
Figure 1. Flowering date in cultivars grown for CBD in 2019. Adapted from Stack et al. 2021 GCB Bioenergy.

 

Mapping and Analysis of Flowering Time Loci

Autoflower1 locus: Several high cannabinoid hemp cultivars are “Autoflowering “ (photoperiodinsensitive), and others are heterozygous for the trait. Homozygous Autoflower1 hemp is photoperiod-insensitive and very early, and plants heterozygous for this locus terminally flower earlier than wildtype hemp (Figure 2). The Autoflower1 locus is on chromosome 1.

bar graph showing effect of autoflower locus on flowering time
Figure 2. Effect of Autoflower1locus on flowering time in a segregating population.

Early1 locus: The cultivar ‘Umpqua’ segregates 1:1 for a major effect locus,Early1 (Figure 3). The early group is heterozygous for this locus while the late group is homozygous wildtypefor this locus. Early1is on chromosome 1, but is distinct from Autoflower1.

graph of Flowering date in ‘Umpqua’.
Figure 3. Flowering date in ‘Umpqua’.

‘FINOLA’-type earliness locus: The grain cultivar ‘FINOLA’ is very early and will flower under long days. The causative locus is on chromosome 8 and heterozygotes have a range of flowering times (Figure 4)

Days to flower for ‘FINOLA’ (early), ‘Felina 32’ (late),
Figure 4. A) Days to flower for ‘FINOLA’ (early),
‘Felina 32’ (late), and their F1
.

Acknowledgements: We would like to thank the technical staff of the Smart lab for their assistance in the field, lab, and greenhouse. This work was sponsored in part by New York Ag and Markets, and a FFAR grant in cooperation with Scotts Corporation. Caroline Dowling is a Fulbright-EPA scholar at Cornell funded by Irish Research Council and the Environmental Protection Agency (Grant No: GOIPG/2019/1987)

Author: cdc25

Craig Cramer is a communications specialist, in the School of Integrative Plant Science, College of Agricultur and Life Sciences, Cornell University, Ithaca, N.Y.