Sensitivity Of Wheat Powdery Mildew To Temperature And Fitness Of The Isolates With Different Sensitivity

The sensitivity of 113 isolates of wheat powdery mildew (Blumeria graminis f. sp. tritici) sampled from 6 provinces or cities in 2008 to temperature was tested by detached leaf segment method with setting up 5 different temperatures indoor. The 5 different temperatures were 22℃,23℃,24℃,25℃and 26℃, respectively. Pick out the isolates which stand for different sensitivity to temperature in accordance with the result of the sensitivity of the isolates tested. Then researched the parasitic fitness of the isolates by testing the latent period,infection probability,lesion daily-expanded area and lesion daily sporulation under 18℃and 22℃temperature condition, separately.The results of the 113 isolates'sensitivity to temperatures showed that under the 5 different temperature conditions, the higher the temperature was, the lower the disease severity was. The mean ET50 (which represents the temperature reaching to obtain 50% of the maximum effect) of all isolates tested was 23.02℃. The highest and the lowest ET50 of isolates were 25.22℃and 19.42℃, respectively. ET50 values of 17.70% isolates were more than 24℃. There were a certain difference for isolates sensitivity to temperature among different provinces or cites, which had a certain relations with the latitude of the provinces or cites. The results showed that the mean value of the termination threshold of 113 isolates tested was 26.24℃, and that the pathogenic colony in natural environment had been effected by the selection pressure of temperature.The results of researching the parasitic fitness of the isolates with different sensitivity showed that the mean latent periods of the isolates with low sensitivity were a little shorter than that of other style isolates in 18℃and 22℃conditions. The lower the sensitivity to temperature was, the higher the infection probability was, and the infection probability of the isolates with low sensitivity was obviously higher than other isolates in 22℃temperature condition. The difference of the total sporulation of single lesion between high-sensitive isolates and middle-sensitive isolates was not big in the two temperature conditions. But the sporulation of single lesion of low sensitive isolates was obviously bigger than the other two style isolates. The difference of the mean lesion daily-expanded areas between high sensitive isolates and middle sensitive isolates was not big in the two temperature conditions. In the two temperature conditions, the difference among the lesion daily-expanded areas of every low sensitivity isolate was big, but their single lesion daily-expanded areas were totally bigger than other isolates. The parasitic fitness of every tested isolates in 22℃condition was lower than which was in 18℃condition. The difference of the parasitic fitness between high sensitive isolates and middle sensitive isolates was not big in the 22℃temperature conditions. The lower the sensitivity to temperature of the isolate was, the higher the parasitic fitness was. Under 22℃temperature condition, the parasitic fitness of low sensitive isolates was obviously higher than middle and high sensitive isolates. These results showed that the parasitic fitness of the isolates with low sensitivity to temperature was totally stronger than that of middle sensitive and high sensitive isolates. These results will contribute to understanding the effection of the changing and evolution of the pathogenic colony to temperature, and providing a reference for the oversummering division of wheat powdery mildew, as well as the effection of climate to the disease.