Study On Resistance Of Pear Germplasm To Pear Scab And Its Physiological Mechanism

Pear scab also know as scab disease, have been occurrenced generally in the north and south of Chinese pear production areas. Pear was damaged by the disease as the time prolonging from fading dates to fruit maturation period, and has strong epidemicity. The disease brings enormous economic losses to the pear production areas. Based on the Venturia nashicola from the disease leaf, the author identified predominant pear germplasms and combined with the results, analysised the content of total phenols, mineral elements and reducing sugar in the leaves. The evaluation of pear scab disease resistance system was established through multiple regression analysis and correlation analysis. By comparing the differences between resistant and susceptible varieties in leaf tissue structure, analysising relation between the defense enzymes and active oxygen metabolism of leaf that was infected by Venturia nashicola with resistance, and using electron microscopy to observe the process of venturia infection, to explore the pear scab resistance of physiological mechanism. the results showed that:Venturia nashicola grew well in the Y+G medium with sealing tape. The bacteria propagation faster when the dish in the dark conditions, the temperature of 21℃, humidity 97%. The colour of Venturia nashicola colony presents dark purple to the green black, regular edge and circular growing. Under a 40 times microscope the author observed the dark brown conidiophore, conidial scars more and obvious. Conidia are monosporous, light brown, fusiform 7.5～22.5 mu m x 5～7.5 microns.30 pear germplasm were identificated and evaluationed of scab resistance by using the method of field inoculation. Results show that 3 immune varieties 8 high resistance varieties, 4 moderate ones,7 moderate susceptibility varieties and 8 high sensitive ones. By measurmenting the content of 30 pear germplasm of total phenols, mineral elements and reducing sugar, from multiple regression analysis and correlation analysis showed pear scab resistance positively related to K content showed positive correlation, the author thought that increasing K content in the leaves to enhance disease resistance. As the resistance is dependent variable, with different period of different indicators in leaves as independent variables, under the different significant level, the multiple stepwise regression analysis. Results show that under 0.10 significant level, resistance and Mg content in May and September zinc content there is a linear relationship, its relationship is y (resistance)= 1.943-1.6287* x1 (5 Mg content)+0.1360* x2 (zinc content in September).Study of resistant and susceptible in pear leaf tissue structure showed that, stomatal density of susceptible variety is the largest. Different varieties of the back of the leaf epidermis cells, spongy tissue structure are not uniform and not neat features, with the leaf development, the tissue structure is compacted gradually, the resistant variety is minimal change, but three varieties of the cuticle thickness does not exist significant differences. Thus, sstomatal density and tissue structure change is closely related with the resistance, cuticle thickness of the leaf has no obvious relation with the resistance.Study the change of the defense enzymes and active oxygen metabolism after infecting Venturia nashicola found that:SOD, POD, CAT activity in the leaves were increased at different degrees, resistant varieties’activities are higher than susceptible variety. So SOD, POD, CAT activity can enhanced the pear of resistance, susceptible variety of the O2-· and MDA content are higher than resistant varieties. Thus the content of 02-· and MDA decreased the resistance of pear.Study the resistant and susceptible varieties that inoculating the pathogen of tissue structure. The results showed that 3 leaf lower epidermis are complete before inoculating the resistant variety Huanggua has two layers lower epidermis besides stomatal area, but susceptible pear Yali is a layer of cells. and 13 days after inoculation, lower epidermis of Huangguan and Suli are intact, but Yali pear leaf epidermal cells began to damage. As the extension of inoculation time, lower epidermis of Huangguan and Suli are unchanged, but Yali have degradation after 19 days. Under the scanning microscope, the leaf surface of Yali bacteria breeding fast, but Huangguan and Suli are restrained, show the characteristic of resistance. Ultrastructure observation, the author found out that pear leaves after inoculation venturia abnormal mitochondria structure lead to mitochondrial dysfunction, eventually cause disease spot blade and local cell death.