How the Pollen Grains of the Varieties of Cannabis sativa L. Respond to Biostimulant of Plant Growth and Development and Habitat Conditions?

The study aimed to determine the effect of habitat conditions and stimulating substances on Cannabis sativa L. pollen morphology, important for the quality of its generative reproduction. The research was conducted in 2024 at the Experimental Plant in Pętkowo (Poland, 52.21°N, 17.26°E) on 17 field-grown and two greenhouse-grown varieties (Henola, Białobrzeskie). In the greenhouse, eight combinations of choline 3-chlorosalicylate (biostimulant) with Nitron S fertilizer and/or honey were tested. A total of 990 pollen grains were analyzed under LM and SEM for six quantitative and several qualitative traits. Pollen was mainly small or medium (LA = 16.06–32.76 µm), with microgranulate exine and a pore complex (Pd) diameter of 2.39–12.43 µm. Field-grown Djumbo 20, Uso 31, Finola, Mona 16, and Rajan 714 were the most distinctive. Henola pollen differed markedly between field and greenhouse, while Białobrzeskie showed greater stability. The strongest pollen response occurred under Biostimulant+Nitron S+Honey, Biostimulant, and Nitron S treatments. The results confirm that environmental conditions and stimulating substances significantly affect pollen size, structure, and variability, which may influence C. sativa reproductive efficiency.