The Influence Of Cultivar Mixtures On Wheat Powdery Mildew Disease

Wheat powdery mildew is caused by airborne pathogen Blumeria graminis (DC.) Speer. f.sp. tritici Marchal. The primary managements for the disease control are planting resistant cultivars and use of fungicide. Gnetic diversity among host cultivars provides a safer and more effective way to control the disease. In this study, we used five cultivars with different resistance, i.e. Jingshuang 16 (susceptible), Jing 411 (susceptible), Jingdong 8 (susceptible), Lunxuan 987 (resistant) and Baofeng104 (resisant). Mixtures with two, three, four or five cultivars and the pure stands were inoculated with mixed powdery mildew races in 2007-2008 and 2008-2009 seasons, respectively. The changes of AUDPC value, the yield, the weight of 1000 kernels and the crude protein content were investigated. The population dynamics of the pathogen in trial field were assayed with ISSR molecular marker.The main results are as follows:Proportion of combinations whose factual AUDPC is lower to theoretical AUDPC is 54.55%, and the control efficacy of the mixtures was 10.23% to 47.93% in 2008. Proportion of combinations whose factual AUDPC is lower to the theoretical value is 23.08%, and the efficay of mixtures was 1.85% to 18.96% in 2009. The results of the two years showed that cultivar mixtures can reduce the disease severity of wheat powdery mildew provided the mixtures are well consistituted. Mixtures with both resistant and susceptible cultivars showed better control to the disease and the higher the proportion of the resistant cultivar the higher the efficacy. The number of cultivars was not closely relatd to the disease efficay (2008:R2=0.0224;2009:R2=0.0789). The effect of mixtures was influenced by the diversification of the genetic background of the composed cultivars but the number of composition. So, we should select wheat cultivars with distant relationship as much as possible. The effect of cultivar mixture was decreased when there were exotic populations.Proportion of combinations whose factual yield is higher than the theoretical yield is 18.18%, and the range of increase was 1.09% to 7.9% in 2008. The proportion of combinations whose actual yield is higher than the theoretical yield is 61.54%, and the control effect of the mixtures was 0.52% to 18.14% in 2009. Comparison of the actual and the theoretical yield in different treatments shows that cultivar mixture can increase yield. The correlation between yield and the efficacy is not significant(2008å¹´:R2=0.0596;2009å¹´:R2=0.1006). The analysis of the weight of 1000 kernels indicates that the proportion of combinations whose actual weight of 1000 kernels is higher than the theoretical value is 27.27%, and range was 0.82% to 2.94% in 2008. Proportion of combinations whose factual weight of 1000 kernels is higher than theoretical value was 61.54%, and the range was 0.52% to 18.14% in 2009. The conclusion is that the mode of cultivar mixture did not influence the weight of 1000 kernels. The yield was compared with the weight of 1000 kernels and the result showes that the increase of the yield was not in accordance with the weight of 1000 kernels. The change of the yield was not influenced by the change of the weight of 1000 kernels in cultivar mixture. The crude protein content was analyzed in 2007-2008 and 2008-2009, respectively. The proportion of combinations whose factual protein content is higher than the theoretical one is 50%, and the range was 0.81% to 3.94% in 2008. Proportion of combinations whose factual crude protein content is higher than the theoretical one is 61.53% and the range was 0.29% to 3.14% in 2009. The result show that net value of all of the treatments was not significantly different from the theoretical value of all of the treatments. The protein content will not restrict the extension of the technique.The populations of B. graminis f.sp. tritici from pure-cropping and mix-cropping plots were studied with 8 pairs of ISSR primers. The result shows that proper cultivar combination can increase the genetic diversity of the populations. Simple increase of the number of components in mixtures can not neccerily increase the genetic diversity in the pathogen populations. The important factor that influence the population structure is the richness of the host genetic background. When the genetic background of host was more complicated, such as Lunxuan 987, the population genetic diversity of the pathogen was richer, the number of mildew lineage was more and the proportion of dominant lineage was relatively small. Mix-cropping should not merely be the increase of cultivar number in the combination in order to diversify the pathogen population. The exotic pathogen population minght affect the local population structure of the pathogen.