| Epidemics of wheat powdery mildew (caused by Blumeria graminis f. sp. tritici (Bgt) ) have been highly destructive to winter wheat crops in China, where the far-reaching effects resulting from its pathogen are also extremely sensitive to climate change. We analyzed trends in the regions of China experiencing wheat powdery mildew epidemics from 1970 to 2012 and PA (percent area affected by wheat powdery mildew) in response to climate change. Using PA and temperature for pathogen oversummering and overwintering periods, a model was constructed and subsequently used to predict changes in PA for 15 Global Climate Models in the CMIP3 (B1: low, A1B: medium, and A2: high climate emission scenarios) and CMIP5 (RCP2.6: low, RCP4.5: medium, and RCP8.5: high climate emission scenarios) for the 2020s (2010-2039), 2050s (2040-2069), and 2080s (2070-2099) relative to the 1970-2009 period. We also analyzed relationships between temperature and parasitic fitness for the isolates of B. graminis f. sp. tritici with low, moderately and highly sensitive to temperature, and constructed the competition model among these three isolates with different (low, moderately and highly) sensitivity to temperature. We also analyzed the relationship between survival time of conidia of Bgt in vitro and temperature. The study will provide the basic data to the delineation of the over-summering and overwintering ranges, and analysis of the genetic structure and variation of Bgt with the changing weather conditions. The main conclusions were drew as follows:Our results showed significant increase in T (mean monthly air temperature) and anomaly of temperature (P < 0.001), while SH (sunshine hours), sunshine percentage and RH (relative humidity)decreased. Trend in P (precipitation) and percentage of precipitation anomaly were different in the epidemic stages of wheat powdery mildew. Climate changes were different among all the winter wheat powdery mildew regions in China.Using the original value method, there was a significant positive correlation between T and PA (P <0.05),and a negative relationship between SH and PA for all epidemic periods. Using the first-differences time-series value method, AT (first-differences in T) in oversummering and late spring periods were negative for ?PA (first-differences in PA) while positive relationships were recorded in the rest of the periods. First-differences in RH (ARH) were significantly correlated to APA in early spring (P< 0.001). The results using the first-differences time-series value method were more precise for disease epidemics. Model y = -0.039 x1+0.028 x2+0.006 with y as wheat powdery mildew epidemics, x, as AT in oversummering and x2 as ?T in overwintering was constructed. Combining the model and predicted temperature, our results indicate that the values for the percent area affected by powdery mildew will increase under all climate scenarios in future including CMIP3 and CMIP5. These findings will aid in decision making for adopting management strategies for mitigating wheat powdery mildew.Parasitic fitness of Bgt under 10, 12, 14, 16, 18, 19, 20, 21, 22, 23 ? temperature separately were calculated according to test latent period, lesion cumulative sporulation, lesion daily-expansion area and infection probability of Bgt by detached leaf segment method. Then, we constructed the models of the relationship between temperature x and parasitic fitness y of Bgt and found that y =1.607E-6x(x-6.8)3.212(23.7-x)2.937, y = 1.764E-6x(x-7.2)2.879(24.8-x)3.069 and y =2.199E-7x(x-8.0)2 341(28.4-x)3 989 were corresponded to the isolates of Bgt with low, moderately and highly sensitive to temperature, respectively. Then, the competition relationship among these isolates with different sensitivity to temperature was constructed.In order to determine the survival time of conidia of Bgt in vitro, conidia germination and disease severity of wheat leaves infected by Bgt conidia were studied after treatments with serial temperatures and time. The results showed that conidia germination rates and disease severities were decreased as temperatures increased. There was a significantly negative correlation between survival time of conidia of Bgt in vitro and temperature, the lifetime of conidia decreased along with temperature increased,Based on these results, a model of relationship between survival time of conidia of Bgt in vitro (y) and temperature (x) y = -0.3205x+9.3534 was constructed. These could provide the basis for modeling dispersal distance of wheat powdery mildew. |
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