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