A comparative study was performed to elucidate changes in the water relations of Fragaria chiloensis (L.) Duch. `BSP14' (FC) and F. virginiana (L.) Duch. `NCC85-13V' (FV), grown in containers in a greenhouse, in response to imposed water deficit stress and subsequent recovery. At incipient wilting, a reduction in osmotic potential at full turgor (Ψπ100 of 0.42 MPa occurred in leaves of FC, while no change was found in FV. Leaf water potential (Ψ) isotherms revealed that as leaf Ψ and relative water content (RWC) declined, stressed FC plants maintained a higher turgor potential (ΨP) and lower osmotic potential (Ψπ) than nonstressed (control) plants, while there was no effect of drought stress on these relationships in the FV plants. From the isotherms, turgor loss was estimated to occur at a lower leaf Ψ and RWC in stressed FC plants than either in control FC plants or stressed and control FV plants. During a diurnal phase 36 hours after wilting, leaf Ψ, Ψπ and RWC of the FC selection were generally lower in stressed than in control plants, with differences ranging from 0.14 to 0.74 MPa, 0.28 to 0.47 MPa, and 1% to 8%, respectively. In the FV selection, Ψπ was 0.09 to 0.31 MPa lower in stressed than in control leaves, while the other characteristics were not affected. Leaf ΨP, of stressed FC plants was 0.09 to 0.27 MPa higher than controls during the dark period, but was similar during the day. When plants of both species were grown and stressed in the same container, FV plants wilted ≈4 days earlier than FC plants, and foliar Ψπ100 of FC was 0.35 MPa lower than that of FV at incipient wilting. The isothermal relationships between leaf Ψ and Ψπ100 indicated FC had a Ψπ100 ≈ 0.25 MPa lower than FV at a Ψ <1.5 MPa. This study provided evidence for greater osmotic adjustment in response to imposed water deficit stress in a selection of F. chiloensis than in one of F. virginiana.
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 wilting, followed by a recovery period. The length of each cycle for the FC selection was J-fold that for the FV selection. Wilting of FC plants occurred at a leaf water potential (ψ) 1.1 MPa lower, a leaf osmotic potential (ψπ) 0.45 MPa lower, and a relative water content (RWC) 14% lower than for FV plants. Leaf ψπ at full turgor (ψπ100) 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 ψπ100 in control plants, although the average contribution of these solutes to the measured leaf ψπ100 increased to 40% or more in stressed FC plants. However, the stress-induced increase in solute concentration fully accounted for the reduction of leaf ψπ100 in the FC selection plants.