| Wheat powdery mildew is a worldwide disease caused by Blumeria graminis f. sp. tritici (Bgt). To further figure out the disease cycle of Sichuan wheat powdery mildew, this research discusses the survival situation of cleistothecia were studied, which is preserved under different conditions, through setting different temperature gradients and relative humidity gradients in the laboratory; through placing cleistothecia and sowing wheat seeding under different natural conditions to study the oversummering of Bgt in low-altitude areas. In addition, the dynamic development of cleistothecia in wheat growing period and field wild hosts also were observed in the study.The survival rate and the sporulation rate of the preserved cleistothecia were surveyed through setting different temperature gradients and relative humidity gradients in laboratory. Result showed thatthe cleistotheciapreserved under 20℃ had a survival rate over 50% and a sporulation rate about 50% after 6 months preservation;the cleistothecia preserved between 20℃-25℃ had a survival rate only about 40% and a sporulation rate only about 30%; the cleistothecia preserved at 30℃ and above had a survival rate only about 30% and a sporulation rate about 20%, but they could hardly produce ascospore. And after 6 months preservation under different relative humidity gradients, the cleistothecia preserved under 40% relative humidity had a survival rate up to about 90% and a sporulation rate over 80%; when the cleistothecium is preserved from 40% to 70% relative humidity, its survival rate and sporulation rate would fall as the humidity rises, and they would be lowest respectively as 22% and 14% at the 70% relative humidity; when the cleistothecia is preserved above 80% relative humidity, its survival rate would fall to 0% after 1.5 months at slowest speed and its sporulation rate would fall to 0% after 1 month. The results preliminarily indicates that the humidity sensitivity of cleistothecia is higher than the temperature sensitivity.Through placing cleistothecia under different natural environments and planting wheat seedling to surveyed the survive of cleistothecia in the field in low altitude areas. Result showed that the survival rate of cleistothecia which were placed in field dropped to 0% after three months, while the planted wheat seedlings were able to survive up to 2 months. The cleistothecia， which were placed under eave or in warehouse and other places with ventilated, shady, rain-proof and other good conditions, were able to survive for a longer time and release ascospores to infect autumn seedling at the time of sowing the autumn wheat. It means that the cleistothecia, which is placed under eave and in other places in the low altitude areas of Sichuan Province, may be one of the infection sources which cause the wheat powdery mildew in autumn.Taking the conidium inoculation on the wheat with different resistances in the field, and investigating the produced time and occupied percentage of conidia and the production situation of cleistothecia, and taking cleistothecia back to measure its activity. Result showed that would infect the disease and produce cleistothecia would be observed in its later period on susceptible variety; the development and maturation time of cleistothecia were preliminarily speculated as 2 to 3 weeks by measuring the cleistothecia activity; almost all cleistothecia were completely matured and able to release ascospore for secondary infection when harvesting the wheat.Investigating and taking back the weed blades with powdery mildew from the field, and disinfect the collected weed seed for breed together with wheat, and respectively inoculate weed powdery mildew and BGT on the breeding plant for comparison, is the results showed that BGT was able to infect wild oat blade and not infect the blade of Roegneria kamoji while the powdery mildew of wild oat and Roegneria kamoji not infect the wheat blade.Therefore, it is preliminarily speculated that the wild oat may be one of the field wild hosts of BGT. |
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