## 4 Factors Influencing the Phytochemical Compounds of _Brassica_ Vegetables
### Environmental and Agricultural Factors
#### 4.2.4 Fertilization Practices
Applications of sodium selenate (Na\({}_{2}\)SeO\({}_{4}\)) produced an increase in GLS [144]. Similarly, microelements availability can influence the phytochemical concentration in _Brassica_, with salts stress increasing GLS content. In detail, selenium seems to increase the GLS content (in particular sulphurabane), when applied up to a certain dose; above this level, it decreases the GLS production [51]. Furthermore, some _Brassica_ species are used as metal hyperaccumulator, and the type and amount of metal in the soil affects the concentration of glucosinolates in plant tissues. In particular, it was reported that glucosinolate concentrations in roots and shoots of _Thlaspi caerulecens_ responded in different way to enhanced Zn accumulation: decreased glucosinolate levels were observed in leaves of plants accumulating high Zn concentrations, while increased levels were detected in roots, with Zn accumulation [146]. Similarly, the content of total glucosinolates, mostly due to indolic glucosinolates as glucobrassicin, was increased only in the roots of Chinese cabbage, when subjected to high soil copper stress [147]. In two _B. juncea_ cultivars subjected to high arsenic levels, the increased levels of thiol related proteins, sulphur content and phytochemicals (phenolics and ascorbic acid) in leaves allow us to better tolerate the oxidative stress induced in the plant; different response pattern of total and individual GSLs content was observed in both cultivars under arsenic stress [148]. Besides the classical fertilizers, in the last years, new proposed products that are beneficial on crops, such as improving safety, enhancing growth and production, improving the defence against weeds and pests and nutritional quality, were developed. Among these, signalling molecules, biocontrol agents, and biostimulants are now gaining high interest for improving plant resilience and quality. Leaves and cotyledons of _B. napus_, _B. napa_ and _B. juncea_ showed an up to 20-fold increase in glucobrassicin content after treatment with JA (Jasmonic Acid), or MeJA (Methyl Jasmonate) [149]. In contrast, treatment with ABA (Abscisic Acid) reduced the accumulation of indole GLS in _B. napus_[150]. In summary, the levels of hormones, such as JA, SA (Salicylic Acid) and ABA, seem to be related to the regulation of GLS and of other bioactive compound content [151]. Consequently, hormonal elicitation can be a useful tool to induce the synthesis of bioactive compounds interesting for human health. Concerning the application of biocontrol agents, [PERSON] et al. [152] affirmed that the use of _Trichoderma_ and its metabolites led to an increase in GLS in plants. This could probably be due to their capability of inducing resistance mechanisms, stimulating the synthesis of salicylic and jasmonic acids and the cascade of events leading to the production of various metabolites; only ascorbic acid was lower compared to control plants. Additionally, in _Brassica_ spp. cultivation is increasing the use of biocontrol agents, there is also the utilisation of seaweeds extract, mycorrhizae, nematodes [153], humic acids such as vermicompost foliar sprayed [154], and protein hydrolyses, all compounds now classified as \"biostimulants\", useful to increase plant yield and the accumulation of bioactive compounds [155]. _Brassica_ species can contrast the main soil-borne agents thanks to their secondary metabolites that act as biofumigants. A study reported the effectiveness of the flour of dry plants of _Brassica juncea_, _Eruca sativa_, _Raphanus sativus_ and _Brassica macrocarpa_ in nematodes control (_Meloidogyne_ spp.) on tomatoes. Minced flour was distributed before planting (60 and 90 g m\({}^{-2}\)) and was successful for the sinigrin presence [156].