THE IMPACT OF DROUGHT STRESS ON MORPHOLOGICAL AND PHYSIOLOGICAL PARAMETERS OF THREE STRAWBERRY VARIETIES IN DIFFERENT GROWING CONDITIONS

摘要

This study was done to compare morphological and physiological responses of three strawberry varieties under water deficit conditions in controlled and natural environments. Plants of three strawberry varieties were grown in different soil moisture levels including 25% (severe stress), 50% (mild stress), and 75% (normal irrigation) and remained for 2 months as a duration of stress. It was observed that there were significant differences among varieties, drought stress regimes, environments, and duration of drought stress for different traits (P<0.05). Leaf area, total shoot length, leaf number, chlorophyll content, chlorophyll stability index, leaf expansion rate, and plant height were higher in natural condition compared to the protected environment under drought stress. These parameters were diminished significantly (P <= 0.05) under stress. Plants in natural condition produced thicker leaves than protected environment which indicated their higher resistance to drought condition. Severe stress (25%) reduced leaf thickness significantly compared toother drought treatments. Varieties cultivated in glasshouse condition produced higher leaf moisture under 25% of stress level. Leaf yield is one the most important traits which is related to fruit yield. Higher leaf yield leads to enhanced fruit yield. Plants showed higher performance in terms of leaf yield in natural environment compared to glasshouse. Leaf yield was higher under optimal soil moisture conditions, compared to 50% and 25% soil moisture levels in both environments. Fruit yield was higher in natural environment compared to glasshouse condition and plants showed lower fruit yield under stress conditions. Correlation analysis showed strong relationships among traits. In the two growing environments, leaf area and leaf thickness were significantly correlated (0.805**). A weak relationship was observed between chlorophyll stability index and chlorophyll content at significant level of 0.01 (0.297**). Relative leaf expansion rate had negative medium relationships with chlorophyll (-0.403**) and chlorophyll stability index (-0.291*). Significant relationships were seen between leaf yield and chlorophyll content (-0.537**), leaf yield and chlorophyll stability index (-0.374**), and leaf yield and relative leaf expansion rate (0.433**). Finally, fruit yield was significantly correlated with total shoot length (0.713**), leaf area (0.891**), plant height (0.661**), leaf thickness (0.561**), leaf number (0.509**), chlorophyll (0.440**), and leaf yield (0.801**). It is concluded that drought stress and the duration of stress had negative effects on different growth parameters. Moreover, plants cultivated in natural conditions were more capable of coping with stress compared to the plants grown in controlled environment.