| Apple is the first fruit in China and very popular with consumers, of which Fuji is of high quality but susceptible to disease, especially Ring-rot Disease. With Fuji being the main cultivar, numerous rotten fruits because of Ring-rot Disease before and after harvest and weak trees became a serious problem in production. In this research, some apple cultivars and a large number of hybrid rootstocks were identified of stems'resistance to the infection of B.berengriana f.sp piricola. Rootstocks with the resistance to Ring-rot Disease were picked out after artificial inoculation on stems. At the same time, The factors related to resistance to Ring rot Disease were researched and lays the foundation for the preven- tion and control of Ring-rot Disease. The primary research as follows:1. The pathogen of inoculantion were B.berengriana f.sp piricola,through identify -cation of the hypha,Pycindium,spore horn,conidium,germination of conidium and re- inoculation to the young fruits,ripe fruits and the living stems.2. The rate of spore germination was up to 87.7% in 22.5 hours, which ensured the spore germination of artificial inoculation; Through the re-isolation of lenticels, the infection cycle of B.berengriana f.sp piricola was determined. May-July was the period of infection on apple stems, and June was the peak of infection.The infection valley began in August and lasted until April in the second year.3. There was very significant difference among the resistance to infection of B. berengriana f.sp piricola. According to the incidence of disease by lenticel re-isolation, the materials of Infection-resistant was twenty-five and the rate of it was 44.64%,including 2-6-33-3, 99, 135, 2-4-18-1 and so on;the materisls of Middle infection-resistance was twenty-one and the rate of it was 37.50%, including 1-5-24-7,2-2-8-6, 2-2-16-8,2-2-8-1 and so on;the materials of Middle infection-susceptible was six and the rate of it was 10.71%,including 2-6-30-3,2-6-29-2,216,1-5-33-3 and so on; the materials of Infection -susptible was four and the rate of it was 7.15%, including 2-2-1-2, 2-2-6-5,2-4-21-4, Liquan spur.4. There was very significant difference among the resistance to Ring rot Disease. According to the disease index of field investigation, the materials of High resistance to Ring rot Disease was nineteen and the rate of it was 35.91%, including2-6-33-3,2-4-20-4, 136,2-4-18-1 and so on;the materials of Middle resistance to Ring rot Disease was eleven and the rate of it was 20.37%, including236, 2-6-31-3, 2-6-30-3, 2-6-29-2 and so on;the materials of Middle susptible was fourteen and the rate of it was 25.93 %,including 2-4-19 -6,1-5-33-3,149,1-5-23-8 and so on; the materials of High susptible was ten and the rate of it was 18.52%,including1-5-24-7, 135, 2-6-28-4,184 and so on.5. There was very significant difference among the resistance to Ring rot Disease and the resistance to infection of B.berengriana f.sp piricola.According the results of identif- ication,there were three kinds materials: the resistance to Ring rot Disease close to the resistance to infection; the resistance to Ring rot Disease worse than the resistance to infection; the resistance to Ring rot Disease better than the resistance to infection.The proportion of the three was 77.78%, 1.85%, and 20.37% respectively.6. The charceteristic of lenticels is closely related to the resistance to infection of B.berengriana f.sp piricola. The density and area of hybrid offspring's lenticels were different whether in the same combination or among different combinations. It showed three characteristics: patroclinal inheritance, matroclinal inheritance, and transgressive inheritance. There was remarkable negative correlation between the product of lenticel density and area of annual branches and the resistance to infection of B.berengriana f.sp piricola, but it had nothing to do with the resistance to Ring-rot Disease; Lenticels with resistance cracked so late that it could avoid Ring-rot Disease infection peak of B.berengriana f.sp piricola,of which complementary tissue were closely-arranged and of which phellen were complete and suberized below the lenticels.On the other hand, susptible lenticels cracked before or during infection period of B.berengriana f.sp piricola , the complementary tissue were loosely-arranged and phellen were poorly suberized and incomplete.7. Some physiological indexes such as the activities of protective enzyme of different resistant materials'stems were determianted.The results showed that the SOD activity had very significant difference between the middle resistant cultivar Dounan and the high susptible cultivar Fuji, and so did POD activity,but the CAT activity had no significant difference between them. The SOD activity of high resistant rootstock 2-4-18-1 was significantly higher than high suspitible rootstock 99,and there was no significant difference between them in POD activity. The PPO activity before and after inoculation of the middle resistant cultivar Dounan were very significantly higher than the high susptible cultivar Fuji,and so didn't Total phenollc content.8. NO could be used as an didex for evaluating the resistance to Ring rot Disease. The NO content before and after inoculation of the middle resistant cultivar Dounan and the high resistant rootstock 136 were very significantly higher respectively than the high susptible cultivar Fuji and the high susptible rootstock 216.
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