Physiological and morphological diversity of cultivated strawberry (Fragaria×ananassa) in response to water deficit

A first step in breeding for improved water use efficiency is to determine the extent of adaptation to limited water availability already existing between cultivars. Cultivation of strawberry (Fragaria×ananassa Duch.) requires irrigation, but to date drought tolerance of different cultivars has not been explored; indeed there has been only limited research on between-cultivar variation for drought tolerance in any fruit crop. To address this issue, 10 cultivars were compared when irrigated to match 100% (control), or less than 70% (water deficit), of evapotranspiration. Transpiration rate, numbers and area of new leaves, dry mass of leaves and roots, and leaf water potential were significantly reduced under the water deficit treatment. Root to shoot dry mass ratio was significantly increased. Water use efficiency (WUE), measured as marketable yield per litre water transpired, increased under water deficit. There were significant cultivar differences for all these variables, and also for photosynthetic rate and for transpiration efficiency (TE), measured as biomass per litre water transpired. Of the two cultivars traditionally grown without irrigation (rain-fed only), one (‘Cambridge Favourite’) showed very high transpiration rates, while the other (‘Totem’) showed very low transpiration rates. Transpiration rates were low for ‘Elvira’, which has been previously considered as drought susceptible, but this was also true of ‘Idea’, which has been considered drought tolerant. Total transpiration was significantly correlated with final leaf area and total biomass. WUE of ‘Elvira’ was high but TE was low. On the other hand, WUE of ‘Hapil’ (for which there is anecdotal evidence of drought tolerance) and ‘Totem’ was low and TE high. ‘Idea’ showed intermediate WUE and TE. Since variation between cultivars in plant canopy and growth and transpiration efficiency was not strongly influenced by environment, genotypic variation in these variables could be utilised in a breeding programme for improved drought tolerance in strawberry. On the other hand, a significant interaction of cultivar and irrigation was found for stomatal conductance, midday osmotic potential at full turgor, marketable yield, and berry mass, suggesting that mechanisms of response to water deficits are not uniform across cultivars.