Variation of glucosinolates concentration and root growth of horseradish as affected by nitrogen and sulphur supply

The aim of the study was to evaluate total and individual glucosinolates concentration, root weight and diameters of horseradish accessions (Cor and Mon) grown by adding nitrogen (N) and sulphur (S) and harvested at the beginning (late autumn) and towards the end (early spring) of the harvest period. The concentration of the 9 glucosinolates (GLS) quantified in roots varied greatly between accessions (6-fold higher in Cor) and with fertilization (N alone led to an increase of 64% of GLS with an additional enhancement of 65% when S was added to N). Root GLS concentration was significantly higher in early spring compared to the previous harvest in late autumn (12.5 vs 8.9 µmol/g DW (dry weight)); a drastic decline of GLS (2.7 µmol/g DW) occurred in root harvested in the following autumn from plants left ad hoc in the field. The aliphatic sinigrin was the most abundant (80% of total GLS), followed by the aromatic gluconasturtiin and the indolic glucobrassicin (5.8% and 4.7%, respectively). Root diameter and weight increased in plants treated with fertilizers (19% and 61%, respectively) and throughout the harvests with Cor showing values double with respect to Mon (925 vs 476 g/plant). Relationships between GLS concentration and root weight (R2 = 0.61) and diameter (R2 = 0.69) were improved by excluding the roots harvested from plants left ad hoc in the field that showed the worst performances.