| Wheat powdery mildew, caused by Blumeria graminis f. sp. tritici, is a serious disease worldwide, and also a problem faced by wheat production in Sichuan Province. In this study, we clarified ways and areas of the over-summering of this fungus, and provided information for control of the disease in Sichuan Province. The latent infection of powdery mildew was studies through Real-time PCR. In order to identify whether the volunteer wheat could survive or infected with powdery mildew in hot summer day, the experiment was done under different temperatures. The population virulence of 109 isolates of B. graminis f.sp.tritici was tested by 30 varieties which contain the resistance gene to powdery mildew. The genetic diversity of 105 isolates was tested by both ISSR and SRAP analysis. In order to find out whether the gene diversity was related to different altitudes or varieties,30 isolates from different altitude areas or different varieties were tested by ISSR analysis, respectively. The temporal dynamics of wheat powdery mildew in Ya’an was studied on two different varieties from 2009 to 2012. Prediction equations were established base on the historical meteorological data and the occurrence of powdery mildew over the years. To see the effect on the control of wheat powdery mildew, the intercropping plant patterns were carried out in the study.(1) The survival rate of the cleistothecia of B. graminis f. sp. tritici under several storage conditions was as follows:in desiccator> under eaves> in straw heap> on soil surface> underground. The cleistothecia in the desiccator and under the eaves survived until October 30. The survival rate of cleistothecia in the desiccator was as high as 44%. Cleistothecia placed in a humid environment (outdoors) had completely died by mid-July. The storage experiment of cleistothecial under different temperatures showed that cleistothecial was able to over-summer in many areas in Sichuan. Field inoculation experiments using ascospores and conidia at different altitudes (400 m-600 m) demonstrated that B. graminis f. sp. tritici is able to over-summer at an altitude of 536 m and above in Sichuan Province. At the meantime, the latent infection of volunteer wheat in Real-time PCR analysis showed that the volunteer wheat in some areas was latent infected with powdery mildew. There are three ways concluded which B. graminis f. sp.tritici over-summered in Sichuan Province. First, cleistothecia can survive until the fall seedling stage, and release ascospores to infect fall sown wheat at that time. Second, cleistothecia release ascospores to infect volunteer wheat to produce conidia, and then the conidia continue to spread until autumn. Third, conidia are carried by air currents to infect volunteer wheat plants in the same and different regions generation after generation to infect volunteer wheat plants and eventually infect fall seedlings. Reduction of the primary infection is one of the most effective control strategies for wheat powdery mildew. The diseased residues must be cleaned out after wheat harvest and/or before fall sowing. And volunteer wheat plants must be eradicated, especially in fungal over-summering areas.(2) Virulence frequency of Blumeria graminis f.sp.tritici in Sichuan Province was analyzed by 30 cultivars with known resistance genes. The result showed that the virulence structure of Blumeria graminis f.sp.tritici in Sichuan Province was very complex. The virulence frequency of Pm6, Pm5, Pm3b, Pm3a, Pm3d was up to 70%, Pm3f, Pm7f, Pm4a, Pm4b, Pml7, Pm3e, Pm3c was about 43.12-57.80%, Pm2, Pm8, Pml+2+9,Pm4+8, Pm4b+5b, Pm2+MLD was about 21.10%-35.78%, and Pm5+6, PmXBD, Pml3, Pm5b, Pm2+6, PmEra was about 0%-17.43%. There had no isolate was virulence to Pm21 in this studies. Pm21 are still the top candicate genes for wheat breeding program. Although Pm5+6, PmXBD, Pml3, Pm5b, Pm2+6, PmEra are still the main veraities in today’s wheat production, potential risks exsited in large-scale production.105 isolates were tested using ISSR and SRAP analysis, and the result showed that there was high level of genetic diversity in Sichuan province. The genetic diversity had no correlation with the geographical source. And the strains transmited between some regions. The study of 30 isolates from different altitudes using ISSR analysis revealed high levels of genetic diversity in Sichuan Province. The results of clustering analysis showed that there were no obvious differences between the stains from different altitudes. It was due to the transition among strains in different areas, where the strains transmited ftom high altitude regions to low altitude regions in preliminary estimate. The analysis result of the unrooted tree which was built by Tree View and PHYLIP-1 software was similar to the result of NTsys-2.10e.30 isolates from different varieties using ISSR analysis, and showed that there was high level of genetic diversity between strains. It was showed that some strains from different varieties could not cluster together. It can be seen that there were no obvious differences among stains from different varieties. The analysis result of the unrooted tree which was built by Tree View and PHYLIP-1 software was same as the result of NTsys-2.10e.(3) The spread distance was surveyed from the infection center to the place where only existed one conidia in one meter which is determined as the lowest infection of powdery mildew in the study. The results showed that the pathogen spread as far as 534 cm from the disease center in one infection cycle. The temporal dynamics of wheat powdery mildew from 2007 to 2012 showed that the time curve of general rate, disease index and the severity of wheat powdery mildew were "S" curve. Through 5 years study, it was seen that the initial stage of wheat powdery mildew was mainly in late-December and early-November, and the stage of logistic in 2010-2011 was the longest of all. The initial stage in 2009-2010 and 2011-2012 lasted for 10-15 days early than the other three years. The severity of disease in Chuannong26 was significantly higher than Chuanyu20 from the overall trend in these years. Understanding of the temporal dynamics of wheat powdery mildew provides a scientific basis for prediction of the disease. It can be seen from the multi-peak graph that the rapid growth period of the disease index was much later than the general rate, while rapid growth period of general rate was synchronization with the period of logistic. To make out the growth dynamic of the disease provides theoretical basis for the control of wheat powdery mildew. Using SPSS software conducted logistic curve and S-curve fitting of the general rate, the average severity and the disease index of wheat powdery mildew which occurred during 2007 and 2012, the results showed that the logistic curve was the best fitting curve.(4) A prediction model of wheat powdery mildew was built according to the inspection history of wheat powdery mildew from 1990 to 2007 in Ya’an district, which combined with the historical meteorological data. After stepwise regression analysis and verification, the prediction equation was obtained (Y= 13.968+1.363X9-1.064X46-0.213X25-0.331X22+0.166X30+0.011X37-0.692X26). The Y and X9 (Rate of diseased leaves on Feb 5th), X30 (The highest temperature on average in February) and X37 (Rainfall in February) were significantly positively correlation, while Y were significantly negative related with X46 (The average relative humidity in March), X25 (The extreme minimum temperature in January), X22 (The highest average temperature in January) and X26 (The average relative humidity in January). The prediction equation was used to forecast the occurrence of wheat powdery mildew in early April,2008. The prediction accuracy was 88.51%. The inspection history of wheat powdery mildew from 2007 to 2012 as well as the historical meteorological data was used to build the prediction model of wheat powdery mildew. The prediction equation was obtained (y=10.583+3.432x29-1.812x47+0.067X11+0.278x49). This prediction equation suggested that the disease index at the early March of Ya’an in Sichuan province (y) was significantly positively related with X29 (The extreme lowest temperature in late January), X11(The artificial rainfall in early January) and X49 (The extreme minimum temperature in mid-February), while was significantly positively related with X47 (The lowest average temperature in mid-February). The prediction equation was used to forecast wheat powdery mildew in March,2013.The model can be used for disease prediction with a prediction accuracy of 90%.(5) Intercropping system reduced the incidence rate of the powdery mildew, and increased the yield of wheat. Experimental results showed that the disease index of single wheat planting were greater than intercropping in every stages. It can be seen from the result that intercropping obviously reduced the occurrence of wheat powdery mildew. The results in 2011 and 2012 demonstrated that the wheat theoretical yield and thousand seed weight in intercropping system were significantly higher than those in wheat monocropping system in Ya’an district. Thousand seed weight of intercropping improved over 10% than wheat monocropping, and the theoretical yield in the intercropping system increased about 25%, whereas the experimental results in 2012 in Jianyang showed that the thousand seed weigh and the theoretical yield of wheat monocropping were all lower than wheat intercropping. Combined the results with the spread distance of one generation, we found that intercropping controlled the disease to a certain extent, and set a barrier for the fungus to spread. The intercropping system not only reduced the occurrence of plant diseases and insect pests, improved the yield of wheat, but also reduced the use of pesticide and to protect our environment. Nowadays, the intercropping system is an important role in the control of the plant disease and insect pests. |
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