Solute accumulation in leaves of a Fragaria chiloensis and a F. virginiana selection responds to water deficit stress

The effect of water deficit stress on the foliar solute concentration of Fragaria chiloensis Duch. cv. 'BSP14' (FC) and F. virginiana Duch. cv. 'NCC85-13V' (FV) was studied to assess solute contribution to osmotic adjustment. Plants were stressed for three wilting cycles by withholding water until incipient witting, followed by a recovery period. The length of each cycle for the FC selection was 3-fold that for the FV selection. Wilting of FC plants occurred at a leaf water potential 1.1 MPa lower, a leaf osmotic potential 0.45 MPa lower, and a relative water content (RWC) 14% lower than for FV plants. Leaf water potential at osmotic potential at full turgor was reduced in the FC selection from 0.11 to 0.27 MPa but not in the FV selection. Water deficit stress increased the total foliar soluble carbohydrate (TSC) concentration from 1.4- to 2.4-fold for FC during each cycle. Glucose and fructose were the primary carbohydrates, comprising > 50% of the TSC. Leaf starch concentration decreased appreciably to 4% to 6% of nonstressed (control) levels for FC during each cycle. In the FC selection, the TSC: starch ratio was considerably higher, 30- to 50-fold, in stressed than in control plants. No consistent changes in solute or starch concentration were observed in the FV selection. Total free amino acid concentration increased from 1.8- to 2.7-fold in FC plants in response to stress. Proline accumulation was not detected. The solutes, TSC and amino acids, accounted for < 40% of the measured osmotic potential at full turgor in control plants, although the average contribution of these solutes to the measured leaf osmotic potential at full turgor increased to 40% or more in stressed FC plants. However, the stress-induced increase in solute concentration fully accounted for the reduction of leaf osmotic potential at full turgor in the FC selection plants.