Hemp Inflorescence as a Sustainable Biostimulant Tool to Boost Growth and Antioxidant Capacity in Oilseed Pumpkin

The study investigates whether water extracts from industrial hemp inflorescences influence the germination and early growth of hull-less oilseed pumpkin (<i>Cucurbita pepo</i> L.), with the hypothesis that industrial hemp extracts may act as a biostimulant, enhancing growth, biomass, and bioactive compound accumulation in pumpkin seedlings. Fully developed and healthy inflorescences of industrial hemp were harvested, dried, ground into powder, filtered, and diluted to concentrations of control (water), 1.0%, 2.5%, and 5.0% for the seed germination bioassay. Morphological, growth parameters, and bioactive compounds of the hull-less oilseed pumpkin sprouts were determined. Total germination rate was not affected with industrial hemp inflorescent water extracts, while sprout vigor index and biomass increased at 2.5 and 5.0% of the extract applied. The average root length of hull-less oilseed pumpkin sprouts was 14.19 cm, the stem length was 5.45 cm, and the fresh mass of the sprouts was 14.10 g per plant. Water extracts of 2.5 and 5.0% significantly (<i>p</i> ≤ 0.001) increased stem length by more than double, and the sprouts' fresh mass by about 35% compared to the control. The average <i>Chl a</i> (chlorophyll), <i>Chl b</i>, <i>Chl a</i> + <i>b,</i> and <i>Car</i> (carotenoids) content was on average 0.161, 0.115, 0.268, and 0.136 mg g^-1 FW, respectively, and were significantly affected compared to the control. The highest total phenol (TPC) and flavonoid content (TFC) were determined for hull-less oilseed pumpkin sprouts at 1.0% of water extract (100.21 µg QC/1 g tissue and 0.02 µg GA/1 g tissue, respectively). Low absolute values are consistent with the early seedling stage, where secondary metabolism is underdeveloped. The antioxidant activity was determined with the FRAP (Ferric Reducing Antioxidant Power) method and a significant influence (<i>p</i> ≤ 0.05) of industrial hemp inflorescence water extracts on antioxidant activity of pumpkin sprouts was observed, which significantly (<i>p</i> ≤ 0.05) increased on all treatments compared to the control, by 36% on average, with no significant differences among different concentrations of water extracts. Overall, industrial hemp inflorescence water extracts have a positive influence on the observed parameters, supporting the potential use of industrial hemp inflorescence water extracts as a biostimulant for hull-less oilseed pumpkin.