Linking biochemistry and genetics in celery to taste and flavour perceived by consumers: developing a more acceptable product.

Celery characteristics
Celery Apium graveolens var. secalinum is popular as a fresh product due to its characteristic flavour and texture. It was originally adapted to marshy conditions, hence its tendency to produce hollow stems and petioles. Domestication of the crop has resulted in the selection of more edible varieties with reduced bitter and strong flavours. Celery is a good source of Vitamins C, K, sodium, and potassium in the diet (USDA, 2012) and has a strong protective effect against colorectal cancer (Jinfu et al., 1991). It is rich in flavonoids and phenolics (Lin et al., 2007); oxidation of the latter causes postharvest browning of cut surfaces. Key flavour compounds in celery are phthalides, and to a lesser degree the terpenes. Van Wassenhove et al (1990) found 33 compounds using GCMS that were present in all four varieties of blanching celery tested.

The aim of the project is to develop breeding lines and associated molecular markers that can give rise to a celery variety with improved postharvest performance and flavour attributes.

Project plan.
A L Tozer Ltd have 52 lines in total available to the project. We will select 30 lines that cover the diversity and grow them in controlled environment at Reading. We will determine flavour profiles of volatile compounds e.g. terpenes and phthalides using GCMS and non-volatile compounds such as phenolics and sugars using LCMS. From these data we will select 6 extreme lines = Milestone 1 (month 9).
We will conduct sensory panels to evaluate the selected extreme lines, thus validating the biochemistry against human perception = Milestone 2 (month 12).
We will start to generate mapping populations based on linked parents that represent the breadth of biochemistry and flavour perceptions. If the first crosses are made in year 1 we should be at F2 generation by year 3 = Milestone 3 (month 30).
The six extreme lines will be grown in Spain and the UK in year 2, thus testing the impact of different environments, soil types and seasons on the biochemical and sensory properties of the selections. This work will enable evaluation of the environmental impact on celery flavour = Milestone 3 (month 24).
In year three the project will examine changes in flavour and biochemistry at different plant development/field holding times, thus providing information on which lines are likely to impart seasonal and sensory stability = Milestone 4 (month 36). Consumer panels will be used to assess liking (or otherwise) of the parental celery lines.
Transcriptome sequencing of the parental generations will be used to assemble a celery genome. SNPs will be scored in the F2 population and a working map will be produced = Milestone 5 (month 40)
In year 4 the project will collaborate with G's to process celery from the parental lines and in the F2 generation of the mapping population through their commercial processing line. Postharvest quality (firmness, weight loss, browning, stem hollowing) and flavour biochemistry will be analysed and used as traits that can be mapped = Milestone 6 (month 45). These traits will give broad QTL, and possible association with transcriptome based markers that Tozer can refine and take forward beyond the life of this PhD. Even if transcriptome based markers cannot be found the project will still provide strong associations between biochemistry and desirable flavour profile, such that development of new lines based on metabolite profile will be possible.