Physiological response to iron deficiency stress and evaluation of tolerance to iron deficiency of different ecotypes of Pyrus betulifolia

Abstract:【Objective】Pyrus betulifolia is widely distributed in China, and is often used as rootstock for pear. Previous study has showed that the tolerance to iron deficiency of different ecotypes of P. betulifolia are different. The aim of this study was to study the difference of physiological response to iron deficiency of different ecotypes of P. betulifolia, in order to provide theoretical basis for breeding ironefficient rootstocks for pear.【Methods】The seedlings of P. betulifolia from Shandong province, Gansu province and Henan province were used as experimental materials. The seed germination was accelerated under the condition of 4 ℃, and the seed sowing was carried out after blanching. The seedlings with same height and 10 true leaves were transplanted into the hole dish with high purity quartz sand as the matrix. Three iron supply concentrations, 0 μmol∙L^-1 , 20 μmol∙L-1 and 40 μmol∙L^-1 were set , and the seedlings were irrigated with the nutrient solutions every 5 days the during treatments.【Results】Under normal conditions, the growth vigors of different ecotypes of P. betulifolia were different, the strongest was P. betulifolia collected from Shandong (SD), followed by P. betulifolia collected from Gansu (GD)and the weakest is P. betulifolia collected from Henan (HD). The plant height and dry and fresh weight of Henan P. betulifolia were significantly higher than those of the other two ecotypes of P. betulifolia. The iron deficiency affected the growth of P. betulaefolia, SD was affected most seriously, followed by GD and HD. Plant height, dry weight and leaf yellowing index can reflect iron deficiency to a certain extent. During the test period, iron deficiency had no significant effect on stem diameter of the three different ecotypes of P. betulifolia. When the iron concentration was 20 μmol∙L^{- 1} , the chlorosis index of GD was significantly higher than that of HD and SD, and when the iron concentration was 0 μmol∙L^-1 , the chlorosis index of GD and SD was significantly higher than that of HD. The plant height of SD decreased most obviously, while that of HD decreased most lightly. The effect of iron deficiency on the aboveground part of P. betulifolia seedlings was greater than the underground part. The iron deficiency reduced the chlorophyll content and net photosynthetic rate of leaves of three different ecotypes of P. betulifolia. The net photosynthetic capacity of GD was most affected by iron deficiency, followed by SD and HD, which was consistent with the change of leaf chlorosis index. Under the iron deficiency stress, the root tip number and root surface area of the three ecotypes increased significantly. The increase range of root tip number and rhizosphere acidification ability of the seedlings of HD was significantly higher than those of the other two ecotypes. The results showed HD had the strongest root growth vigor, SD and GD had the weakest root growth vigor under the iron deficiency stress. The rhizosphere acidification capacity change trend was consistent with the increase of root Fe3+ reductase activity. The iron deficiency led to the unbalanced decline of iron content in the organs of the seedlings, and the decrease of active iron in the roots and new leaves was larger than that of the total iron. Among the three ecotypes, the decrease of active iron in GD was the largest, followed by SD and HD. The accumulation of the active iron and total iron in the roots was the lowest in GD. When the concentration of iron supply was 0 μmol∙L^-1 , the root total iron accumulation in SD was significantly higher than that in HD, but there was no significant difference in the root active iron accumulation. The effects of the iron deficiency on the contents and distribution of nitrogen, phosphorus and potassium elements in different organs of the three different ecotypes were different. The iron deficiency resulted in decreased absorption of nitrogen and phosphorus to a certain extent, but increased absorption of potassium. The contents of nitrogen, phosphorus and potassium in the organs of the three ecotypes also decreased due to the iron deficiency stress. GD was affected most obviously, HD was affected most lightly, and SD was in the middle.【Conclusion】The sensitivity of physiological response to the iron deficiency stress was different of three ecotypes of P. betulaefolia. The seedlings of P. betulifolia collected from Henan and Shandong had better iron deficiency tolerance than those of P. betulifolia collected from Gansu.