Crotolaria juncea L., a new legume crop for cultivation in Russia: characterization and prospects (review)

Sunn hemp ( Crotalaria juncea L.) is a multi-purpose annual legume plant. This is the oldest bast crop grown in tropical regions for fiber (H.R. Bhandari et al., 2016; 2022). In 1791, the plant was brought to Europe where it is cultivated as an alternative green manure crop. Crotalaria has been shown to produce sufficient dry matter to cover and protect the soil from potential erosion, as well as providing nitrogen in amounts useful for subsequent harvests of crops in a diversified crop rotation (D. Scott et al., 2022, A.P. Barros et al., 2022). In the United States, the plant occupies one of the leading places in the list of intermediate cover crops. Dry green biomass contains from 18 to 22 % protein, but can only be used in limited quantities for livestock feed (˂ 10 % of the silage produced), since sunn hemp during flowering accumulates the toxic alkaloid monocrotaline. The sunn hemp seeds are up to 35-40 % protein, and also contain a small amount (up to 0.1 %) of toxic dehydropyrrolizidine alkaloids (trichodesmine, junsein, apigenin-7-4'-0-diglucoside, apigenin-7-glucuronide, lectin, senecionine and seneciphylline) and amino acids (alpha-amino-beta-oxylaminopropionic, alpha-aminoxylaminobutyric and/or alpha,gamma-diaminobutyric) (V.B. Malashetty et al., 2015; F. Prada et al., 2020). Their use in animal feeding requires special attantion and is, if possible, undesirable. The main non-toxic variety currently used in the United States is Tropic Sun. In other varieties, the accumulation of toxic concentrations of alkaloids in the biomass occurs at flowering, so plant biomass for silage should be harvested 60 days after sowing (J.E. Garzon et al., 2021; J.B. Morris et al., 2015). It was noted that pruning shoots to 30 cm 60-100 days after sowing and re-growing for 70 days increases the nitrogen content in the biomass (A.S. Abdul-Baki et al., 2001). In Russia, crotalaria can be an unconventional cover crop in biological farming to reinforce the soil, improve fertility and for reclamation. The area for sunn hemp cultivation may be southern regions, in particular the Krasnodar Territory, the Republic of Adygea and Crimea. Polysaccharides (galactomannans) from the sunn hemp seeds are bioactive growth stimulant for other plants (R.P. Zakirova et al., 2020). These metabolites, obtained as a result of the refining (degumming) process of vegetable oil extracted from seeds, can be comparable in quality to seed extracts from guar ( Cyamopsis tetragonolaba (L.) Taub) - another currently in demand annual legume crop (E.A Dzyubenko et al., 2023). Secondary metabolites extracted from Crotalaria leaves are a rich source of carbohydrates, steroids, triterpenes, phenols, flavonoids, alkaloids, amino acids, saponins, glycosides, tannins and volatile oils (S.K. Dinakaran et al., 2011). Thus, C. juncea has hypolipidemic, antioxidant, antibacterial, antifungal, antidiarrheal, anti-inflammatory, hepatoprotective and many other pharmacological effects. Another practical application of C. juncea is the production of cost-effective biofuels (S. Sadhukhan et al., 2016).