Adaptation Of Ageratina Adenophora Under The Influence Of Bacillus Cereus And Aphids

Ageratina Adenophora is one of the most serious invasive plants in China with the characteristic of selective accumulation of beneficial microorganisms to itself.Bacillus cereus may play an important role in the invasion of Ageratina Adenophora.It has been confirmed that the content of Bacillus cereus in rhizosphere soil of Ageratina Adenophora as the invasion of Ageratina Adenophora increased.Our preliminary work revealed that the level of Bacillus cereus in rhizosphere soil of Ageratina Adenophor increased significantly after parasitization by the specialist natural enemy,Procecidochares utilis.Cotton aphid(Aphis gossypii)is a generalist natural enemy that can feed normally on Ageratina Adenophora.How does the rhizosphere environment of Ageratina Adenophora,such as Bacillus cereus,respond to the action of the generalist natural enemies and how does the adaptation of Ageratina Adenophora change under the intercropping treatment between the two is the scientific question of this thesis.In this paper,we examined the effects of aphid feeding on the content of Bacillus cereus in the rhizosphere/root,soil physicochemical properties,and rhizosphere bacterial community structure of Ageratina Adenophora,using Eupatorium lindleyanum,as a control;we determined the changes in the parameters of aphid population growth,insect-resistant Ageratina Adenophora,and soil physicochemical properties after the addition of Bacillus cereus to the soil.The main results of the study were as follows:(1)The content of Bacillus cereus was determined by qRT-PCR.The content of Bacillus cereus in the root and rhizosphere soil of Ageratina Adenophora(A-0,A-5,A10,A-15)and Eupatorium lindleyanum(L-0,L-5,L-10,L-15)were determined after aphid feeding at different densities,which showed that the content of Bacillus cereus in the root and rhizosphere soil was significantly increased after aphid feeding on Ageratina Adenophora.Among them,the content of Bacillus cereus in rhizosphere soil of A-10 and A-15 treatments increased by 72.6%and 37.3%,respectively,compared with the control(A-0)during the first generation of aphid;the content of Bacillus cereus in root of A-15 increased by 67.5%compared with the control(A-0).During the second generation of aphid,the content of Bacillus cereus in rhizosphere soil of A-5,A-10 and A-15 increased by 130.6%,73.1%and 139.0%,respectively,compared with A-0;the content of Bacillus in root of A-5 and A-15 increased by 108.6%and 125.8%,respectively,compared with A-0.In contrast,the changes of the local relatives of Eupatorium lindleyanum were not obvious.After aphid feeding,the soil physicochemical properties of both plants changed to different degrees,such as the rhizosphere soil AK content of Ageradenophora was significantly higher than that of Eupatorium lindleyanum.In addition,the bacterial community structure in the rhizosphere soil of Ageratina Adenophora and Eupatorium lindleyanum was compared by 16S rRNA sequencing,and it was found that the α-diversity and β-diversity of bacteria in rhizosphere soil of Ageratina Adenophora were significantly changed after aphid feeding.The diversity of A-10 and A-15 was significantly higher than that of A0,while the diversity of rhizosphere soil bacterial community of Eupatorium lindleyanum did not change significantly under aphid feeding.These indicate that the invasive plant Ageratina Adenophora has a stronger ability to change its own bacterial community under natural enemy feeding.(2)The effect of Bacillus cereus treatment on the growth of aphid population and resistance index on both plants was examined using the Bacillus cereus addition/exclusion method(adding Thiosen Copper).The results showed that Bacillus cereus treatment promoted aphid resistance in Ageratina Adenophora.The number of aphids per plant was significantly lower than that of the clear water control from 4 d after the addition of Bacillus cereus,while in Eupatorium lindleyanum,the number of aphids did not change significantly under the treatment with 5 and 10 aphids.The determination of plant insect-resistant substances showed that the addition of Bacillus cereus significantly reduced the tannin,flavonoids and silicon content in Ageratina Adenophora.Among them,tannins were reduced by 43.1%;flavonoids by 57.8%and silica by 12.3%,while the changes in Eupatorium lindleyanum were not significant.Meanwhile,the silicon content in Ageratina Adenophora increased significantly under different densities of aphid feeding.It can be speculated that Bacillus cereus may have played a facilitating role in promoting silicon uptake and silicified cell formation in Ageratina Adenophora,thus inhibiting the growth of aphid populations.