Investigating the genetic control of postharvest shelf life and vitamin C content in broccoli (Brassica oleracea var. italica)

Abstract

Broccoli (Brassica oleracea var. italica) is a popular vegetable, known for its nutritional benefits. However, the marketability of broccoli is limited by a short shelf life. Broccoli is susceptible to rapid postharvest senescence, which causes visible head yellowing and wilting from dehydration. Visible quality loss is also accompanied by a decline in nutrients, resulting in a product with reduced postharvest nutritional value. These factors combined cause broccoli to become unmarketable, leading to severe wastage in the retail chain. Postharvest yellowing in broccoli has been shown to be controlled by genotype, as a doubled haploid population (MGDH) created from an F1 cross between GD33, a poor performing DH line (yellow in 2 days) and Mar34, a good performing DH line (staying green > 4 days) exhibited natural variation for shelf life. Therefore, to investigate the genetic control of quality in broccoli, the fixed mapping population was assessed for shelf life, morphological traits and vitamin C content and stability in replicated field trials. Visual inspections identified head yellowing, stem turgor and bud compactness as the main traits affecting the marketability of broccoli. Two methods to quantify head yellowing were also evaluated. Spectrophotometer readings were found to be more sensitive than Image J in detecting colour change, but Image J data was more reproducible. Vitamin C quantification using HPLC, confirmed that natural variation was present in the MGDH population at harvest. Vitamin C content during postharvest storage, detected by plate assays, found vitamin C to be unstable, degrading quickly after harvest. A unique broccoli x broccoli linkage map, covering ~72.9% of the B.oleracea genome, was also constructed by genotyping the MGDH population with SSR and AFLP markers. QTL analysis of the trait data positioned 48 significant QTL in the linkage map for head yellowing (4), colour co-ordinates (17), morphological traits (17), bud quality (2) and postharvest vitamin C content (3) and stability (5). The identification of QTLs associated with the above traits has provided useful information for breeders to breed for improved nutritional and quality in broccoli using marker-assisted selection (MAS). The location of QTLs has also provided targets for fine-scale mapping and for the identification of candidate genes underlying traits