Seed growth and oil accumulation in two different varieties of industrial hemp (Cannabis sativa L.)

Nowadays, the main hemp foods products derive from hemp seed (seed, dehulled seed, meal and oil) and an uncertain economic sustainability of the hemp food supply chain remains to be resolved. The cause is often to be found in unsatisfactory quantitative-qualitative seed yield. Following the above, an experiment was conducted utilizing Futura and Zenit varieties with different crop cycle duration, cultivated in two locations (S. Osvaldo and Verzegnis), for two years (2019 and 2020) and with two sowing times (conventional and delayed). A total number of five-nine seed samples of ten seeds each, depending on location and variety, were collected from the middle of inflorescence of five plants for each of the three replications, starting from 50 Growing Degree Days (GDDs) after flowering until physiological maturity. The following characteristics were determined on each seed: whole seed weight, kernel weight, pericarp weight, whole seed oil content, oil weight, kernel oil content, kernel percentage, hull to kernel ratio and oil to kernel ratio. The achievement of seed with high oil content and high weight at maturity is mainly due to the accumulation rate intensity rather than length of the seed-filling period. The accumulation rate for seed growth and oil accumulation is mainly dependent on the genotype, but also affected by daily mean temperatures above 23◦C recorded during the first 20 days after flowering that resulted the sub-phase most susceptible to temperature. The use of the character oil weight per seed, instead of whole seed oil content commonly utilized in breeding activity with the aim of increasing the oil content in oil crops, could simultaneously improve the seed and kernel weight; both parameters highly appreciated in the hemp food chain.