Tools to Produce Hemp (Cannabis sativa L.) for Sowing Seed: Optical Differentiation of Seed Ripening Stages Through a Portable Spectrometer

Obtaining high-quality seeds is important for two reasons: from a nutritional point of view, for species in which the seed is the edible part; and for producing quality seeds for reproduction, which is fundamental for successful cultivation. Producing seed for reproduction in hemp (Cannabis sativa L.), presents many challenges and requires specific precautions. The present study analyzed the ripeness of hemp fruits using a portable and low-cost VIS/NIR spectrometer that covered a spectral range of 740–1070 nm. This study proposed the first attempt to apply optical systems to the hemp seed sowing production chain. The aim is to facilitate the handling of seeds at harvest and the complex post-harvest seed management. Seeds from two monoecious European industrial hemp genotypes, Carmaleonte and Codimono, were collected at the three growth stages of fruit ripening according to the BBCH scale from 50% of ripe fruits (BBCH 85 stage) to fully ripe fruits (BBCH 89 stage). The reflectance spectra showed a decreasing order BBCH 89-87 > 85 with the most obvious difference between the curves observed at a wavelength of 955 nm. At this wavelength, the reflectance at the BBCH 85 stage was clearly lower than at the BBCH 87 and 89 stages. In terms of germination rate the seeds collected at BBCH-85 had a higher percentage respect the other growing stages. These results demonstrate that a simple, portable spectrophotometer can discriminate the different ripening stages of the hemp seeds, thus confirming the effectiveness of optical systems in improving the production of certified seeds.