Abstract
A field study was conducted to compare the formationand bacterial communities of rhizosheaths of wheat grown under wheat-cotton and wheat-rice rotation and to study the effects of bacterial inoculation on plant growth. Inoculation of Azospirillum sp. WS-1 and Bacillus sp. T-34 to wheat plants increased root length, root and shoot dry weight and dry weight of rhizosheathsoil when compared to non-inoculated control plants, and under both crop rotations. Comparing both crop rotations, root length, root and shoot dry weight and dry weight of soil attached with roots were higher under wheat-cotton rotation. Organic acids (citric acid, malic acid, acetic acid and oxalic acid) were detected in rhizosheaths from both rotations, with malic acid being most abundant with 24.8±2 and 21.3±1.5 μg g-1 dry soil in wheat-cotton and wheat-rice rotation, respectively. Two sugars (sucrose, glucose) were detected in wheat rhizosheath under both rotations, with highest concentrations of sucrose (4.08±0.5 μg g-1and 7.36±1.0 μg g-1) and glucose (3.12±0.5 μg g-1 and 3.01± μg g-1) being detected in rhizosheaths of non-inoculated control plants under both rotations. Diversity of rhizosheath-associated bacteria was evaluated by cultivation, as well as by 454-pyrosequencing of PCR-tagged 16S rRNA gene amplicons. A total of 14 and 12 bacterial isolates predominantly belonging to the genera Arthrobacter, Azospirillum, Bacillus, Enterobacter and Pseudomonaswere obtained from the rhizosheath of wheat grown under wheat-cotton and wheat-rice rotation, respectively. Analysis of pyrosequencing data revealed Proteobacteria, Bacteriodetes and Verrucomicrobia as the most abundant phyla in wheat-rice rotation, whereas Actinobacteria, Firmicutes, Chloroflexi, Acidobacteria, Planctomycetes and Cyanobacteria were predominant in wheat-cotton rotation. From a total of 46,971 sequences, 10.9% showed ≥97% similarity with 16S rRNA genes of 32 genera previously shown to include isolates with plant growth promoting activity (nitrogen fixation, phosphate-solubilization, IAA production). Among these, the most predominant genera were Arthrobacter, Azoarcus, Azospirillum, Bacillus, Cyanobacterium, Paenibacillus, Pseudomonas and Rhizobium.
Highlights
Crop rotation is a sequence of crops grown in a specific area over a specific period of time and is practiced to control pests, diseases and to maintain soil fertility by recharging the soil with nutrients
A field experiment was conducted on experimental area of National Institute of Biotechnology and Genetic Engineering (NIBGE), Faisalabad to study the effect of crop rotation and plant growth promoting rhizobacteria (PGPR) inoculation on plant growth, rhizosheath formation, and the composition of bacterial communities associated with the rhizosheath of wheat grown under wheat-cotton and wheat-rice crop rotation
We set out to assess the effect of different wheat-containing crop rotation systems as well as inoculation with previously isolated plant growth promoting rhizosphere bacteria on plant growth and physical-chemical and microbial characteristics of wheat-associated rhizosheaths
Summary
Crop rotation is a sequence of crops grown in a specific area over a specific period of time and is practiced to control pests, diseases and to maintain soil fertility by recharging the soil with nutrients. Crop rotations have great influence on composition, richness and diversity of soil microbial communities [1], [2]. During the growth period of rice, downward movement of various micronutrients takes place due to prolonged anoxic (reducing) conditions [3]. Deficiency of such elements is a common problem for cultivation of wheat when grown in rotation with rice [3]. The nutrient status of the soil and its microbial community may change, which might in turn influence the growth of wheat cultivated in rotation with rice [4]. Incorporation of cotton stubble into the soil increases the soil fertility, microbial diversity and growth of crop that follows cotton crop in rotation [5]
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