Responses of radish (Raphanus sativus) to drought stress

With this study the effects of water deficit on radish growth, dry mass production and partitioning, source–sink relations, physiological responses and accumulation of secondary metabolites in storage roots and leaves have been investigated. Three water stress treatments were applied: (Control) 100% of water holding capacity (WHC), (WS50) 50% of WHC, (WS30) 30% of WHC. Water stress was effectively acquired starting from 287 growing degree days (GDD) as demonstrated by the lower values of relative water content (RWC), higher leaf temperature and NIR-based water indices values in water stressed conditions. Water stress reduced storage root dry weight by 27% at WS50 and 53% at WS30 as well as leaf dry matter accumulation (by 23% and 31% in WS50 and WS30, respectively), expansion (by 28% and 45% in WS50 and WS30, respectively) and specific leaf area (by 7% and 20% in WS50 and WS30, respectively) at 403 GDD. The increasing of leaf-to-root mass (L/R) and leaf area-to-root mass (LA/R) ratios indicated less dry matter allocation into storage organs under water stress conditions. Besides, water shortage increased leaf greenness as estimated by the higher soil–plant analysis development (SPAD) values (+14% and +20% on average for WS50 and WS30, respectively); other reflectance indices only partially confirmed SPAD readings. Substantially, water limitation did not significantly influence total anthocyanin content, ABTS-radical scavenging activity and total free phenolic compounds in storage roots, as well as the total free phenolic compounds in leaves. Radish showed a strong plasticity in its adaptation to drought thanks to avoidance mechanisms such as constrained leaf development, increased leaf thickness and adjusted source–sink relationships.