Analysis of influencing factors on the pathogenesis and development of fire blight on Kuerlexiangli pear

【Objective】Fire blight (Erwinia amylovora), a highly destructive bacterial disease, has posed a serious threat to the yield and quality of Kuerlexiangli pears. This study aims to explore the influence patterns of external factors on the occurrence and development of fire blight in Kuerlexiangli pears, thereby providing an important theoretical basis for the comprehensive prevention and control of this disease.【Methods】An indoor simulation experiment was conducted to determine the disease incidence and disease index of detached leaves, branches, and young fruit after inoculation with E. amylovora. The experiment was designed from six perspectives: 1) infection routes (natural openings, friction wounds, incisions, and punctures); 2) Different isolated organs: flowers, leaves, branches, and young fruits.3) leaf ages (3, 7, 15, 30, and 40 d); 4) temperatures (15 ℃, 20 ℃, 25 ℃, 30 ℃, and 35 ℃); 5) relative humidity (RH) (25%-35%, 35%-45%, 55%-65%, 75%-85%, and 85%-100%); and 6) bacterial concentrations (OD600 = 0.4, 0.8, 1.0, 1.2, and 1.6). Each treatment was set with three replicates, each including 30 flowers and leaves, 10 branches, or 10 young fruit. After inoculation, the test materials were placed in trays lined with sterile gauze at the bottom; each tray was sealed with plastic film and then placed in an incubator with ambient temperature and humidity. The numbers of diseased leaves, branches, and young fruit were recorded at 24, 48, 72, 96, 120, 144, and 168 h post-inoculation. Meanwhile, the lesion diameter on leaves and young fruit, as well as the lesion length on branches, were measured. Finally, the disease incidence and disease index were calculated using standard formulas.【Results】The results showed that under the same environmental conditions, flowers and young fruit of Kuerlexiangli pears were more susceptible to E. amylovora infection than leaves and branches. For leaves, the younger leaf age, the faster the disease development: the 3-day-old leaves showed the fastest disease onset, while the 7-day-old leaves reached a disease incidence of 71.14%-100% at 72 h post-inoculation. Compared with natural openings (stomata), mechanical wounds (friction wounds, incisions, and punctures) significantly increased the disease incidence, with the disease incidence of mechanically wounded leaves being 3.2-4.5 times higher than that of leaves infected through natural openings. When the temperature was between 25 and 30 ℃, the humidity between 75% and 85%, and the inoculation concentration was OD600 = 1.2, the incidence of pear blight bacteria was the highest. Moreover, as the concentration of the bacterial solution increased, the disease progressed more rapidly.【Conclusion】 Among the organs of Kuerlexiangli pears, flowers are the most susceptible to fire blight, followed by young fruit, leaves, and branches. Infection routes, host organs, leaf age, temperature, humidity, and bacterial concentration all exert effects on the lesion expansion of fire blight, and their interactions determine the spread rate of the symptom in the host. In view of this, in the production of Kuerlexiangli pears, it is necessary to carry out prevention and control work in the early stages, especially during flowering and early fruiting stages, according to the changes in temperature and humidity.