Light Use Efficiency of broccoli (Brassica oleracea var. italica Plenck) and rocket (Eruca sativa L.) during the initial plant growth stages

Abstract

The solar radiation (SR) is one of the key factors for plant adaptation, and of its growth and development, and for several horticultural crops is important for reaching good yield and produce quality. The SR vary in Europe from 2189 to 517 kwh m−2 from Sicily to North cape. Sprouts, microgreens, and baby-leaves, recognized as novel foods due to their high nutraceutical value, have attracted significant attention in the market. The novel foods production could be affected by solar radiation especially when it is carried out in greenhouse in several countries and along their latitudes. Our study aimed to investigate how solar radiation affects the growth of these plants by conducting a thorough analysis of their morphometric characteristics and biochemical profiles. Two different genotypes of commercial rocket, namely Eruca sativa L. var. darkita and var. lobata, along with the Sicilian Black sprouting broccoli (Brassica oleracea var. italica Plenck, Broccolo nero), were examined at different initial plant growth stages, sprouts, microgreens, and baby-leaves. The experimental trial was carried out in Sicily (Italy) utilizing black shade nets with varying levels of solar radiation (SR100, SR60, SR40). The harvested plantlets were analysed for their main morphometric traits, as sprout weight, hypocotyl length, cotyledon dimensions, in addition to the dimensions of the first true leaf for microgreens, and stem length for baby-leaves. Several biochemical parameters, such as total phenolic content (TPC), total flavonoid content (TFC), and several antioxidant assays including DPPH (2,2-diphenyl-1-picrylhydrazyl), ORAC (oxygen radical absorbance capacity), and FRAP (ferric reducing antioxidant power) were determined. The total glucosinolate content, the sucrose, fructose, fructooligosaccharides (FOS), and total sugars amount were detected. We observed significant variations in the sugar content, particularly under reduced solar radiation and during the baby-leaves stage, characterized by decreased FOS levels and simultaneous increases in sucrose, glucose, and fructose. Moreover, antioxidant capacity showed a progressive enhancement from sprouts to baby-leaves. FRAP and DPPH capacity were significantly affected by the genotype. Interestingly, TFC was the most influenced by SR100, particularly in microgreens. This expanded knowledge base not only advances scientific understanding of these novel foods but also provides substantial adaptation to the different solar radiation conditions in different latitude of the world, permitting to individuate the genotypes more efficient in relation to the solar radiation available.