Plant growth-promoting rhizobacteria promote plant size inequality

Alan C Gange,Kiran R Gadhave

doi:10.1038/s41598-018-32111-z

Alan C Gange, Kiran R Gadhave

Open Access

https://doi.org/10.1038/s41598-018-32111-z

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Abstract

The uniformity of crop yield is extremely important for consumers and of as much relevance to the grower as overall yield. However, size inequality within a plant population is rarely measured and has never before been considered in relation to the use of beneficial microbes for yield enhancement. For the first time, we show that addition of soil bacteria to calabrese plants significantly increased size inequality. These effects were usually more apparent in above-ground biomass. This was caused by some (but not all) plants growing very large when inoculated with bacteria, while control plants were mostly small. We suggest that the main reason is the incompatibility of the inoculated bacteria with those already present in the rhizosphere. In some cases the inoculum matched the indigenous community, providing a benefit to plant growth, while often it did not and plants remained relatively small. We conclude that analyses of size inequality should be an integral part of experiments using microbial soil amendments. These analyses can help to inform the production of more effective microbial products and to ensure that the integration of beneficial microbes into sustainable production systems does not impair uniformity in yield.

Highlights

Conventional agriculture, through the use of selected varieties and inputs of fertilizers and pesticides, seeks to maximise total yield, and the uniformity of the crop
In a series of experiments in controlled and field conditions, with single and multiple Bacillus spp. additions, we showed that these plant growth-promoting rhizobacteria (PGPR) affected plant growth[12], altered endophytic bacterial community diversity, evenness and composition[13], and suppressed cabbage aphid growth[14] and field incidence[15] in a context specific manner
We hypothesized that addition of PGPR to the roots of calabrese plants would increase plant size inequality, due to the differential ability of bacterial species to establish in the rhizosphere[19]

Summary

Introduction

Conventional agriculture, through the use of selected varieties and inputs of fertilizers and pesticides, seeks to maximise total yield, and the uniformity of the crop. An important aspect of any agricultural system is the quality of the soil, with much recent interest focused on improving quality, and yield, through the addition of microbial inoculants[10]. Prominent amongst these inoculants are plant growth-promoting rhizobacteria (PGPR), including species in genera such as Azotobacter, Bacillus, and Pseudomonas[11]. We hypothesized that addition of PGPR to the roots of calabrese plants would increase plant size inequality, due to the differential ability of bacterial species to establish in the rhizosphere[19]. We hypothesized that plant size inequality would be further amplified in field conditions and with multispecies bacterial inoculants, because of nutrient heterogeneity and competitive interactions between the bacterial species[13,18]

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