Fungicide effects on N2-fixing bacteria and N2-fixation in chickpea
Fungicide application in field crops have unexpected non-target effects on the agroecosystem. Molecular methods (polymerase chain reaction – denaturing gradient gel electrophoresis and cloning technology) were used to test the effects of four fungicide application programs targeting Ascochyta blight (Ascochyta rabiei) on the N2-fixing bacterial communities associated with two chickpea cultivars, and on chickpea nodulation. Treatments were replicated four times in complete blocks in the field, in 2008 and 2009. Results showed the richness of the N2-fixing bacterial communities did not change significantly (P > 0.05, data didn’t shown) with fungicide application, but different intensities of fungicide application selected different dominant N2-fixing taxa, as revealed by Correspondence Analysis (CA) of DNA sequences. Genotypes of chickpea cultivars significantly affected both the richness and composition of the N2-fixing bacterial communities, as revealed by results of CA. Both fungicide and crop genotype affected nodulation scores of chickpea based on ANOVA results (P < 0.001 for nodulation scores test and P = 0.04 for fixed N test), reflecting impacts on nitrogen fixation. Redundancy analysis (RDA) also revealed significant relationships (P = 0.014) among fixed nitrogen, nodulation scores and identified rhizosphere N2-fixing bacteria. Based on these results, we conclude that both the foliar fungicide applications and chickpea genotype can affect the composition and function of N2-fixing bacterial community in chickpea field.
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