| Maize is one of the most important cereal and feed crops worldwide.Both diseas es and insect pests are key factors causing yield decrease and quality decline for corn production.Utilization of pesticides for control of diseases and insect pests,and extens ive use of chemical fertilizers are considered as the main measures for ensuring stable and high yield in corn production.However,the overuse of pesticides and chemical f ertilizers might not only lead to the increase of production cost,but also result in pest icide residue in agro-products and soil structural damage as well as water pollution.T o reduce the amounts of pesticides and chemical fertilizers used in corn production,en dophytic bacteria were isolated and isolates with strong growth-promoting activity on maize plants were screened out.The enhancement of resistance of maize plants against southern corn rust and corn ear pests by endophytic bacterial isolates was tested.Prel iminary analyses on the mechanism of enhancement of resistance to the disease and p ests on maize plants by endophytic bacteria were carried out for technical support on development of environment-friendly corn production techniques.The results were sum marized as follows.1.In this thesis,the soil from 5 locations in Nanyang city was sampled and used for potted cultivation of maize plants.A total of 27 bacterial endophytes were isolate d from different organs of healthy maize plants.2.The efficacies of the bacterial endophytes in promoting growth of the maize pl ants were tested.Based on the comparison of four growth parameters(plant height,fre sh weight,dry weight and leaf numbers),five bacterial endophytes(G16,G6,J15,J8,G12)were screened out and used for field trials together with another bacterial endop hyte(L2)isolated from the leaf of a maize plant in a previous work.3.Six bacterial endophytes were separately identified as members of Bacillus meg agenes(G6,G12,G6,J8),B.cereus(L2)and Pseudomonas putida(J15)based on their 16 S rDNA sequence homology.Partial physiological and biochemical properties of t he bacteria were characterized.4.Field trials on the efficacies of the bacterial endophytes in enhancing the resist ance of three maize varieties against ear pests were carried out in 2017 and 2018.In t he trial of 2017,the reduced rates of total ear pests on the G16-treated Xianyu 335 an d G12-treated Jundan 20 were 52.6% and 73.08,respectively.In the trial of 2018 whe n ear pests seriously occurred,the reduced rates of total ear pests on the G12-treated Xianyu 335 and Zhengdan 958 were 43% and 37%,respectively.The reduced rate of total pests on the G16-treated Xianyu 335 was 37%.On the L2-and J8-treated Zheng dan 958,the reduced rates of total pests were 36% and 34%,respectively.5.Significant variation was observed on the efficacies of bacterial endophytes in controlling southern corn rust.Except isolate G6,the five isolates(G16,G12,J15,L2,J8)showed a control efficacy varied from 6% to 42.9% against the disease on Xiany u 335.The control efficacies of the three isolates(G12,G16 and J15)were greater th an 30%.6.The activities of peroxidase(POD)and catalase(CAT)in the leaves of maize plants treated with bacterial endophytes were overall higher than those of the control,while the content of malondialdehyde(MDA)was overall lower than that of the contr ol.The variation of resistance-related biochemical parameters basically agreed with en hanced disease/pest resistance on some of maize cultivars treated by the bacterial endo phyte(s).7.The noon temperatures on the leaves of three cultivars treated by the bacterial endophytes were investigated three times.The leaf temperatures of Zhengdan 958 treat ed with G16 and J15 were overall lower than that of their controls during the investig ation.In the 3th measurement,the leaf temperature of Xianyu 335 treated with G6 wa s significantly lower than its control. |
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