Harnessing the genetic diversity of watercess (Rorippa nasturtium-aquaticum) for improved morphology and anticancer benefits: underpinning data for molecular breeding

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Description/Abstract

Watercress (Rorippa nasturtium-aquaticum) is a member of the Brassicaceae family.
Increasing interest in healthy diets has turned the focus to watercress since it is
known to contain one of the highest concentrations of the beneficial antioxidant
phenethyl isothiocyanate (PEITC). This has exciting possibilities to breed a higher
quality crop with increased concentrations of this key antioxidant providing a
meachanism to aid in the prevention of cancer. Dwarfism is another desirable
characteristic for many agricultural crops. A crop with a reduced stem length
produces a stable increased yield and is easier to harvest as well as package. Dwarf
mutants have been extensively characterized in many plant species and endogenous
phytochrome Gibberellin (GA) is one of the several genes associated with the dwarf
phenotype. The three candidate genes of particular interest are: GA2ox, GA3ox and
GA20ox. GA20ox and GA3ox are involved in GA biosynthesis whilst GA2ox is
involved in GA catabolism. The aim of my research was to establish a collection of watercress from around the world and breed watercress that not only has a reduced stem length but is also nutritionally beneficial therefore breed an ‘ideal’ watercress cultivar. Initial
screening of the germplasm shows significant variability in stem length (ranging
from 7-17cm), stem diameter (ranging from 1.58-3.18mm) and antioxidant
concentrations (ranging from 80-140 mmol Fe2+ equivalent per gram fresh weight).
The antioxidant concentrations were assessed using an adapted antioxidant assay
Ferric Reducing Ability of Plasma (FRAP) which revealed a ranking order for the
watercress lines. Two lines with high FRAP values, Wx_0033 (143.84 mmol Fe2+
equivalent per gram fresh weight) and Wx_0011 (126.44 mmol Fe2+ equivalent per
gram fresh weight), and one line with a low FRAP value, Wx_0038 (87.49 mmol
Fe2+ equivalent per gram fresh weight), and also a control line Wx_0001 (130.66
mmol Fe2+ equivalent per gram fresh weight) was taken forward for further
glucosinolate and isothiocyanate analysis.The lines did indeed vary in the
concentration of glucosinolate and isothiocyanate. Wx_0001 had both the highest
concentration of phenethyl glucosinolate, 19.35 μmoles per gram weight and
phenethyl isothiocyanate, 0.20mg/ml phenethyl isothiocyanate.
The genetic diversity of the watercress lines held within the collection were
assessed using the Amplified Fragment Length Polymorphism (AFLP) technique
revealing a higher level of variation within (76%) each line than between (24%).
Variation in gene expression was analysed using microarrays and verified using real
time PCR. From the various data collected and recorded from the watercress
germplasm collection this has lead to a breeding programme successfully being
initiated at the University of Southampton.