The effect of water deficit on chlorophyll fluorescence, sugar content, and growth parameters of strawberry (Fragaria×ananassa Duch. cv. Elsanta) was studied. Drought stress caused significant reductions in leaf water potential, fresh and dry masses, leaf area, and leaf number. A gradual reduction of photochemical quenching (q P ) and quantum efficiency (Φ PS2 ) was observed under drought stress while non-photochemical quenching (q N ) increased. Maximum efficiency of photosystem 2 (F v /F m ) was not affected by drought stress.Additional key words: Fragaria×ananassa; maximum efficiency of photosystem 2; photochemical and non-photochemical quenching; photosynthesis; water deficit.--Water deficiency is a limiting factor for plant growth and development as well as for a wide range of physiological processes such as photosynthesis. Chlorophyll (Chl) fluorescence provides useful information about leaf photosynthetic performance of many plants under drought stress (Baker and Rosenqvist 2004). However, studies on strawberry under drought stress are still limited and focus mainly to research on irrigation scheduling (Kruger et al. 1999). In order to better understand the response of strawberry to the onset and progress of drought stress we studied Chl fluorescence parameters in parallel with plant growth performance.A greenhouse experiment was conducted from October 2006 till February 2007 with the short day cultivar Fragaria×ananassa Duch. cv. Elsanta. Plants were grown in 3 000 cm³ pots in 80 : 20 % peat and perlite mixture at 18/14 °C day/night temperature, a daily average vapour pressure deficit (VPD) of 0.5−0.9 kPa, and a 16-h photoperiod. Natural day length was extended with metal halide lamps giving 30−40 µmol(PAR) m −2 s −1 at canopy level and daily average value of PAR ranged from 20 till 150 µmol m −2 s −1 . Plants were weekly supplied with 100 cm 3 of a standard nutrient solution for strawberry (Lieten 1995) and with rain water on the other days maintaining the pots close to field capacity. After nine weeks pots were assigned to a control and a drought stress (irrigation stop) treatment in a completely randomized block design with three replicates and 25 plants for each experimental plot. Volumetric substrate moisture content θ v (Theta probe, ML2X, Delta T Devices, Cambridge, UK) was recorded at hourly intervals. During the experiment, measurements were performed at days 1, 16, 27, 40, 44, and 51. The leaf water potential (Ψ w ) of the upper leaflet of the youngest fully developed leaf (n = 6 per experimental plot) was measured with a thermocouple psychrometer operating in the psychrometric mode between 08:00 and 09:00. Chl fluorescence was measured on the youngest fully expanded triplet leaf (n = 4 per experimental plot) using a portable fluorometer (PAM-2000, Walz, Effeltrich, Germany). Leaves were allowed to dark adapt for 20 min (Genty et al. 1998). Sugars of fully expanded leaves (n = 6 per experimental plot) were extracted with 80 % ethanol and analyzed by HPLC with pulsed amperometric detection (Dione...

Drought stress is one of the most important environmental factors that limit plant growth and development, thus reducing yield. The objective of the present research was to correlate the genetic structure of different Fragaria genotypes, as assessed by Expressed Sequence Tag (EST) and Amplified Fragment Length Polymorphism (AFLP) markers, and plant responses to drought stress. Firstly, physiological parameters related to the plant response to drought stress such as leaf relative water content (RWC) and water losing rate (WLR) were measured. WLR and RWC were compared for 20 cultivars of the octaploid Fragaria 9 ananassa, two ecotypes of the diploid species F. vesca and one octaploid species F. chiloensis. These parameters could discriminate genotypes showing a contrasting response to water stress. Secondly, AFLP and ESTs were compared in terms of their information content and efficiency in the study of genetic diversity and relationships among these 23 Fragaria genotypes. To evaluate the genetic basis for the observed variation in the measured physiological parameter, the effect of specific AFLP/EST loci on WLR and RWC for the different Fragaria genotypes was quantified by Kruskal-Wallis analysis. By Mantel testing, the hierarchical clustering of the Fragaria genotypes based on associated EST or AFLP markers was compared to the observed eco-physiological relevant grouping. A better discriminating capacity for associated markers was noted, enabling a functional marker selection approach to screen the strawberry gene pool for drought tolerance. Correlation of EST markers to leaf RWC and WLR enforces them as potential candidate genes in control of plant responses to drought stress in Fragaria sp.

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