Studies On The Resistance Mechanism Of Dothiorella Canker Of Carya Tree And Some Factors

The Dothiorella(Botryosphaeria ribis) canker of carya is the major disease in Anhui Province, especially in Ningguo city and Jixi county. The flower and fruit, which infected often fall early and the growth and yield of the trees decreased seriously, even the whole tree died. In this thesis, the relationship between the stand conditions, soil fertility and physiological & biochemical characteristic and plants with different disease-resistance to Dothiorella gregaria were studied, and main factors affected the disease were found, which will give assist for control to this disease.Relationship between the tree age and disease was a parabola curve in the stand. That is to say, the disease seldom occurs in the young tree, the disease index increase with tree age increasing in 20-years, when tree age reach to 20 year, the disease decrease gradually with tree age increasing. The tree canopy was negatively related to the disease index and the correlation coefficient was 0.8686. The effect of soil depth on the disease index was obvious. There was close correlation between soil bulk density and disease index (R2=0.6830) while there was negatively correlation between humus content and disease index. There was significant negatively between the content of N, P, K in soil and the disease index.The thickness of periderm was negatively to the disease index. There was significant negatively correlation between the thickness of phloem and the disease index while there was close correlation between the width of the phloem and the disease index and the correlation between the phelloderm and disease index was not obvious; the thickness of phloem is the major factor to the resistance to disease. The cortex of bark was consist of 9-12 layer nutrient element parenchyma so its mechanical capability have influence on the resistance to the disease. The fiber proportion of bark about 30-50% and it was positive related to the tree age while negatively to the disease index. The more of the fiber proportion, the lighter of the disease in the same soil condition. The ratio of crystals fiber to phloem fiber is 50-55% and the variance is not significant in different age. The correlation between the number of the crystals cell and the resistance to disease was not obvious through the correlation analysis. There was negatively between sieve tube actively and the disease degree. The diameter of the sieve tube decreased by the disease degree. There was also negatively between ray proportion and the disease index. The more the moisture of the bark the lower the disease index based on the study of the physiological feature of carya tree. There were three ranks between bark moisture and disease. The disease incidence was very low or even no when the RT value was more than 82%, but the disease index was very high when the RT value below 67%. There was close correlation between the electrical resistance value at breast height and disease rank in the same forest stand, so it can be regarded as a feature of the resistance to the disease. Whether it was fit for different soil condition is not confirmed. There was an obvious change of the net photosynthesis efficiency of carya tree by the disease incidence in the same soil condition. The net photosynthesis increase by the disease, reach a maximum then decreases rapidly. On the contrary, the net photosynthesis was influenced by surroundings in different soil; as a result it was not a feature of disease.The correlation analysis of biochemical index of different disease rank in the same soil condition also was studied. The result showed that the phenol content of bark decrease as the disease index increases. It is easy to be infected in the tree, which has low content of N, P, K or high content of P and Fe. The POD activity differs from different disease rank. The POD activity decrease as the disease rank increase. There have same result in four plots that the POP content of tree resistance is higher than that infected one. The variation of PAL activity has the same result.