Morphological Difference In Leaves Of Various Apple (Malus Domestic) Cultivars And Its Correlation With Water-use Efficiency Under Drought Stress

Drought is a major environmental stress limiting plant growth, productivity, and survival worldwide, especially in the arid and semi-arid regions. Plants adapt to drought through morphological, physiological, and metabolic modifications in all organs. Leaf is the main tissue of plant photosynthesis and transpiration. And it has the larger surface area, which makes it have more contact with the environment and more sensitive to the changes of environmental factor. At the present experiment, young trees of 31 apple cultivars were used as materials to determine the influence of drought stress on leaf morphological and physiological parameters. Moreover, we evaluated water-use efficiency (WUE) and drought resistance of them and analyzed the correlation between some leaf morphological and physiological parameters and WUE and drought risistance.The main results are as follows:1. Significant differences in WUE and drought resistance of apple trees were observed among different apple cultivars and close relationship between them was found. Under well-watered condition,'Hanfu'and'Hirosakifuji'had the highest WUE, while'Hongro','Braeburn'and'Ryoka no Kisetsu'had the lowest value in WUE. Under drought-stressed condition,'Golden Delicious','Qinguan'and'Hanfu'had the highest value in WUE, while'Hongro'and'Modi'had the lowest value. In addition, drought resistance varied among the different cultivars.'Orin','Tsuqaru','Senshu','Naganofuji No.2','Jonagold'and'Hokudo'were high-drought resistant cultivars,'Hanfu','Hokkaido No.9','Jazz','Cinano Red'and'Hirosakifuji'were non-resistant cultivars.2. Drought stress greatly influenced leaf (e.g. total leaf area, leaf thickness, and wax thickness) and stoma (stoma size and density) morphological parameters, photosynthesis rate, transpiration rate, stomal conduction, and intercellular CO2 concentration. And significant differences in these parameters were observed among the different apple cultivars. Both WUE and Pn had significant and positive correlation with leaf thickness, wax thickness, stoma density, and stomal conduction.3. Two-way ANOVA was made to test the cultivar and drought treatment differences of the 12 morphological and physiological parameters. Cultivar had significant influence on most of the parameters except leaf thickness, leaf water-holding capacity, and transpiration rate. Watering significantly influenced most of the parameters except leaf water-holding capacity. All of the 12 parameters were significantly influenced by cultivar and watering interaction.4. Scanning electron microscope (SEM) was used in the present experiment to image the distribution and structure of leaf stoma, and to determine stoma density, leaf thickness, and wax thickness. Compared with optical microscope, SEM had higher image separation, third dimension, and veracity.