Effects of wheat and rape intercropping on phyllosphere microbial community structure

【Objective】The objective of this study was to analyze the structural characteristics of the phyllosphere microbial community and its effects on the occurrence of crop diseases under wheat and rape intercropping and monoculture, so as to provide theoretical basis for the control of wheat diseases under wheat and rape diversity planting. 【Method】Pot experiments were used to monitor and investigate the occurrence of diseases in the growth process of wheat and rape by setting up 3 treatments: wheat monoculture, rape monoculture and wheat/rape intercropping. Leaf samples of wheat and rape were collected on the 30^th and 40^th d after sowing respectively, and the bacterial 16S rDNA V4 region and fungal ITS1 region of the samples were sequenced and analyzed by Illumina high-throughput sequencing. The number and changes of phyllosphere microorganisms（fungi and bacteria） of crops under different planting patterns and different times at the genus classification level were analyzed by using operational taxonomic unit（OTU） cluster analysis and species annotation analysis. Alpha diversity index and MRPP analysis were used to explore the richness, diversity and structural differences of phyllosphere fungal and bacterial communities in wheat and rape. Based on the Spearman correlation matrix, the bacteria-fungi interaction network was constructed, and the complexity of the intercropping and monocropping crop phyllosphere microbial network and the interaction between bacteria and fungi were analyzed and compared. 【Result】Compared with monoculture, the number of phyllosphere bacteria in wheat and rape was higher than that of monoculture under the same time point in intercropping pattern, while the number of phyllosphere fungi was lower than that of monoculture. In the intercropping pattern, the number of shared phyllophyl bacterial genera in crops on the 30^th and 40^th d of planting was higher than that in the monoculture. The results of Alpha diversity analysis showed that the number of observable species, Chao1 and ACE indexes of the intercropping pattern were higher than those of the monoculture pattern, and intercropping increased the richness of the phyllosphere bacterial community. The results of MRPP analysis showed that the difference in the population structure of phyllosphere fungi between intercropping and monoculture on the 40^th d was the largest among all treatments, and the difference in the population structure of phyllosphere fungi in each treatment of wheat was smaller than that of rape phyllosphere fungi. The population structure difference of phyllosphere bacteria was the most largest between intercropping and monoculture rape on the 40^th d, followed by wheat under intercropping and monoculture on the 40^th d. The results of bacteria-fungi interaction network analysis showed that the intercropping had a higher complexity of the microbial network in the phyllosphere than that of monocropping, and the positive and negative interactions between fungi and bacteria in the phyllosphere of wheat were increased by intercropping, and the negative interactions increased in a greater range. Intercropping increased the positive interaction between fungi and fungi in the phyllosphere of rape, and increased the competition between fungi and bacteria phyllosphere of wheat, while intercropping rape increased the cooperative relationship between fungi and fungi and reduced the competition between fungi and bacteria. The survey results on number of powdery mildew pathogen and the incidence showed that the number of powdery mildew pathogen and the incidence of powdery mildew in intercropping wheat were significantly lower than those in monoculture wheat（P＜0.05）. 【Conclusion】Wheat and rape intercropping can improve the diversity and richness of crop phyllosphere bacteria, enhance the interaction of crop phyllosphere microorganisms, balance and stabilize the structure of phyllosphere microbial community, maintain the stability of plant phyllosphere microecological environment, and effectively control the occurrence of wheat powdery mildew.