Study On The Mechanisms Of Internal Bark Necrosis Of Apple Trees

Pot experiments and field investigations in Yantai were conducted to investigate relationship between the Internal Bark Necrosis (IBN) of apple trees and the tolerance to manganese toxicity in Delicious apple trees and Qiaonajin apple trees. The research methods included element analysis,microscopic and Physiology methodologies. The main results were presented as follows:1,The apple IBN occurrence was highly positively correlated with soil pH and Mn concentration and negatively correlated with soil Fe concentration. Mn concentration in rhizophere and bulk soils was higher for Mn-sensitive cultivar (delicious apples) than that for Mn-resistant cultivar (Qiaonajin).2.,Apple IBN resulted from the heavy accumulation of Mn. Severity of apple IBN was positively correlated with Mn concentration in tree plant. Mn concentration of the heavy IBN is much higher than that of the light. Mn concentration in the various plant parts was greater significantly in Delicious apple trees than in Qiaonajin. Mn concentration of shoots in apple trees was higher than that roots, The leaves was higher than the stems, The Barks was more higher than the woods.3,Two cultivars of apple trees differed greatly in tolerating Mn stress. The result of pot experiments indicated that apple IBN was induced by using 330 mg/kg Mn, but have no effect when the apple trees were exposed to 33 mg/kg Mn. IBN of Mn-tolerant cultivar (Qiaonajm) was not induced by using 330 mg/kg of Mn application.4, Physiological parameters indicated that the apple IBN occurrence was related to oxidation stress Activity of peroxidase(POD) and H2O2 content was found to significantly increase and ascorbic acid (Vc) content decrease by using 330mg/kg Mn. So is apple IBN trees in the field. Cell membrane permeability were considerably increased with 330mg/kg Mn stress and IBN apple tree in the field. but significantly decreased when the plant was grown with 0,33mg/kg manganese and no IBN trees in the field. 5,Histochemical localization of Mn showed that accumulation of Mn was positively correlated with apple IBN. Compounds of IBN was oxygen-manganese Accumulation of Mn of IBN spot was identical to scatter of IBN spot. Scatter of Mn of Mn-resistant cultivar (Qiaonajin) was well-distributed in apple trees. Lesions were histologically identical to those occurring naturally in the field and pot experiment. The result of x-ray microanalysis showed that localized accumulation of excess Mn was directly cause for cell death and IBN of apple trees. The distribution of Fe,Ca and Si showed significant difference between Mn-sensitive cultivar and Mn-tolerant cultivar except that of Mn.