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

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 mechanism 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 ?moles 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.

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