The Potential Impact of Flower Characteristics and Pollen Viability of Four Industrial Hemp (Cannabis sativa L.) Grain Varieties on Cross-Pollination

Abstract

Industrial hemp (Cannabis sativa L.) is primarily a dioecious plant, and monoecious varieties have been developed for high yield. Production practices vary for each variety, prompting the need for the present study to describe the floral characteristics and evaluate pollen quantity and viability of monoecious and dioecious hemp varieties. All four hemp varieties, Henola, CFX-2, Canda, and Joey, have five lanceolate anthers, basifixed to a threadlike filament. Anther length was significantly different among varieties, but not anther width. The longest length (0.38 ± 0.046 cm) was recorded in Henola, and the shortest (0.34 ± 0.043 cm) in CFX-2. Anther width ranged from 0.088 ± 0.0024 to 0.095 ± 0.0021 cm. Pollen grains were triporate and spheroidal in shape and size and differed significantly, with the largest in Joey (27.83 ± 0.78 μm) and Henola (27.489 ± 0.99 μm), and smallest in Canda (22.04 ± 0.56 μm). The number of pollen grains per flower differed significantly among varieties, ranging from 29,183 in Henola to 104,548 in Joey. Even though Henola recorded the lowest pollen number, it had the highest percentage (69.3%) of viable pollen after 24 h of storage 4 °C and Canda had the lowest (54%). Three weeks after storage at the same temperature, pollen viability decreased for all the hemp varieties and ranged from 52% to 58%. There was a moderate, positive and significant relationship (r = 0.496) between anther length and the number of pollen grains in Joey. The relationship in Henola was moderate and non-significant (r = 0.356), and it was weak and non-significant in Canda (r = 0.188) and in CFX-2 (r = 0.037). The findings from this study provide information for growers and researchers on hemp breeding and cultivation practices that may contribute to the prevention of cross-pollination.