**3.11 Flavonoid content in lettuce breeding**

Lettuce (*Lactuca sativa*) is one of the world's most important vegetables. The GWAS identified 5311 expression quantitative trait loci (eQTL) that influence the expression of 4105 genes, including nine eQTLs that regulate flavonoid biosynthetic genes. GWAS has found six candidate loci for anthocyanin variation in lettuce leaves [112].

UV-A supplementation increased flavonoids, anthocyanin, and polyphenol levels and the 2,2-diphenyl-1-picryl-hydrazyl-hydrate (DPPH) free radical scavenging rate. UV-A can modify plant phenolic contents and flavonoid metabolism by increasing the expression of associated genes such as *CHS* and *MYB* in the flavonoid pathway and *PAL* in the propane metabolic pathway. Under additional UV-A and FR light, anthocyanin levels in lettuce seedlings were 11% higher and 40% lower, respectively [113] (**Table 3**).

Transformation of *L. sativa L*. with *rol C* gene inducing an increase in total flavonoid contents [114].

The gene expression of rol ABC genes was used to boost secondary metabolites in *L. sativa L.* (cv. Grand Rapids), particularly antioxidants such as phenolics and flavonoids. *A. tumefaciens* GV3101 and the *rol ABC* genes were used to transform *Lactuca sativa L.* (cv. Grand Rapids). The transformation increased the secondary metabolites in lettuce and also induced free radical inhibitor effect and lipid peroxidation scavenging properties [115].

Thereby, the three key categories that is used to group the goals of current lettuce breeding programmes include: (1) Improvement in horticultural traits such as quality and resistance to early bolting, (2) resilience to diseases and pests, and (3) to attain higher yield and uniformity [116].

#### **3.12 Flavonoid content in buckwheat**

Buckwheat (*Fagopyrum esculentum*) is an annual crop that is planted all over the world. Buckwheat seeds, leaves, and stems are high in flavonoids such as rutin and proanthocyanidins (PAs). The discovery of the ANR and LAR buckwheat genes could result in the development of buckwheat cultivars with different PA levels. In one investigation, one gene sequence (*AT1*, Fes sc0002933.1.g000003.aua.1) encoding ANR was found, along with three gene sequences encoding LARs (*LT1*, Fes sc0001063.1.g000007.aua.1; *LT2*, Fes sc0016501.1.g000002.aua.1; and *LT3*, Fes sc0010963.1.g000003.aua.1) [117].

The flavonoid contents in buckwheat sprouts were commonly in the following order: rutin > quercetin > isovitexin > vitexin > isoorientin > kaemferol [118]. Tartary buckwheat grain contains orientin, vitexin, rutin, and quercetin and is used to make drinks and biscuits. Because of its high content of flavonoids and other phenolic compounds, tartary buckwheat is resistant to pests, plant diseases, and UV-B radiation damage. As a result, Tartary buckwheat can be cultivated organically and without synthetic fertilizers or chemical treatments [119].


**Table 3.**

*Genes responsible for different flavonoid production in Lactuca sativa L.*
