Augmenting iron accumulation in cassava by the beneficial soil bacterium Bacillus subtilis (GBO3).

Mônica A Freitas,Samuel P Carvalho,Paul W Paré,Flavio H V Medeiros,Huiming Zhang,William D Teixeira,Luiz R G Guilherme

doi:10.3389/fpls.2015.00596

Mônica A Freitas, Samuel P Carvalho + Show 5 more

Open Access

https://doi.org/10.3389/fpls.2015.00596

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Abstract

Cassava (Manihot esculenta), a major staple food in the developing world, provides a basic carbohydrate diet for over half a billion people living in the tropics. Despite the iron abundance in most soils, cassava provides insufficient iron for humans as the edible roots contain 3–12 times less iron than other traditional food crops such as wheat, maize, and rice. With the recent identification that the beneficial soil bacterium Bacillus subtilis (strain GB03) activates iron acquisition machinery to increase metal ion assimilation in Arabidopsis, the question arises as to whether this plant-growth promoting rhizobacterium also augments iron assimilation to increase endogenous iron levels in cassava. Biochemical analyses reveal that shoot-propagated cassava with GB03-inoculation exhibit elevated iron accumulation after 140 days of plant growth as determined by X-ray microanalysis and total foliar iron analysis. Growth promotion and increased photosynthetic efficiency were also observed for greenhouse-grown plants with GB03-exposure. These results demonstrate the potential of microbes to increase iron accumulation in an important agricultural crop and is consistent with idea that microbial signaling can regulate plant photosynthesis.

Highlights

Manihot esculenta is a perennial shrub in the Euphorbiaceae family native to South America and cultivated primarily by small-scale farmers for its storage roots that are eaten as a vegetable (Meenakshi et al, 2010)
Since inducible iron uptake by B. subtilis (GB03) is associated with growth promotion in the model plant Arabidopsis, growth parameters including plant height and biomass were measured in cassava plants exposed to GB03
All plants were grown under the same environmental conditions in terms of light, soilnutrients, and water, GB03-treated plants exhibited significant growth promotion with respect to plant height and total aboveground dry biomass at 28 and 59% greater values, respectively, when compared with GBO3 untreated plants (Figure 1)

Summary

Introduction

Manihot esculenta (cassava) is a perennial shrub in the Euphorbiaceae family native to South America and cultivated primarily by small-scale farmers for its storage roots that are eaten as a vegetable (Meenakshi et al, 2010). The tuberous roots provide the third largest source of food carbohydrates in the tropics, after rice and maize. The semi-woody species thrives on nutrient deficient soils ranging from acidic to alkaline conditions and the presence of cyanide-rich defenses minimize damage due to insect herbivory (Blagbrough et al, 2010). As a drought-tolerant crop, it is capable of growing in marginal soils and due to its wide harvesting window serves as fall-back crop in times of famine (Montagnac et al, 2009). In terms of food calories, cassava is 25–125% more efficiency per unit area-time than other staple crops such as rice, wheat, or maize (Meenakshi et al, 2010)

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