Identification of Phenotypic Characteristics in Three Chemotype Categories in the Genus Cannabis

• Published in: HortScience Vol. 56; no. 4; pp. 481 - 490
• Main Authors: Jin, Dan, Henry, Philippe, Shan, Jacqueline, Chen, Jie
• Format: Journal Article
• Language: English
• Published: American Society for Horticultural Science (ASHS) 01.04.2021
• Subjects: cannabis; cbd; chemotypes; phenotypic markers; thc
• ISSN: 0018-5345; 2327-9834
• DOI: 10.21273/HORTSCI15607-20

Modern Cannabis cultivars are morphologically distinguished by their leaflet shapes (wide for “Indica” and narrow for “Sativa”) by users and breeders. However, there are no scientific bases or references for determining the shape of these leaflets. In addition, these two categories contained mostly THC dominant (high THC) cultivars while excluded CBD dominant (high CBD) and intermediate (intermediate level of both THC and CBD) cultivars. This study investigated the phenotypic variation in 21 Cannabis cultivars covering three chemical phenotypes, referred to as chemotypes, grown in a commercial greenhouse. Thirty morphological traits were measured in the vegetative, flowering, and harvest stages on live plants and harvested inflorescences. The collected data were subjected to correlation analysis, hierarchical clustering, principal component analysis, and canonical correlation analysis with preassigned chemotypes. Canonical correlation analysis assigned individual plants to their chemotypes with 92.9% accuracy. Significant morphological differences were identified. Traits usable as phenotype markers for CBD dominant cultivars included light-green and narrow leaflets, a greater number of primary and secondary serrations, loose inflorescences, dense and resinous trichomes, and Botrytis cinerea resistance. Traits for intermediate cultivars included deep-green and medium-wide leaflets, more primary and secondary serrations, medium compact inflorescences, trichomes that are less dense and less resinous, and Botrytis cinerea resistance. Traits for THC dominant cultivars included deep-green and wide leaflets, large and compact inflorescences, dense and resinous trichomes, and Botrytis cinerea susceptibility. The results of this study provide a comprehensive profile of morphological traits of modern Cannabis cultivars and provides the first such profile for CBD dominant and intermediate cultivars. Additionally, this study included the traits of inflorescences, which have not been compared between three chemotypes in the literature. Phenotype markers identified in this study can facilitate preliminary cultivar identification and selection on live plants before or as a supplement to chemical and genetic analysis.