Low pungency and phytochemicals relationship during bulb assessment in the sweet onion breeding program

Abstract

This work reports the results of a four-year Italian breeding program carried out over five locations, for the selection of low pungency onion genotypes. The performances of new Italian open-pollinated (OP) lines were compared to both pungent and non-pungent commercial varieties. Pungency level was evaluated on each single bulb as pyruvic acid concentration, together with other related quality traits, namely soluble sugars (SSR), total phenols (TPC) and flavonols (TFC). All OP lines were classified as low to medium pungent onions, and only the lines 09/12, 14/12 and 15/12 slightly exceeded the limit of 3 mmol/kg for the low pungency. In the first two years of selection, OP lines showed a general decrease in pyruvic acid concentration (from 16 to 67%) in the second year, while on average SSR did not significantly change and phenolics increased. SSR appeared positively correlated with pyruvic acid concentration, TPC and TFC. A marked effect of the environmental conditions was observed over the different years and locations of experiment. Overall, 13/12 OP line distinguished for the highest reduction of pyruvic concentration, which averaged 3.0 mmol/kg, while maintaining a high level of SSR (6.6 °Brix), TPC and TFC (1.78 and 0.49 mM gallic and rutin equivalents, respectively).