Enhancement of sorghum grain yield and nutrition: A role for arbuscular mycorrhizal fungi regardless of soil phosphorus availability

Nathaniel Jewell,Emma Mace,Trevor Garnett,Christopher J. Brien,Bettina Berger,Binh T. T. Tran,Stephanie J. Watts‐Williams,David R. Jordan,Alison R. Gill,Timothy R. Cavagnaro,Alan W. Cruickshank

doi:10.1002/ppp3.10224

Abstract

Societal Impact StatementSorghum is an important cereal crop that provides calories and nutrients for much of the world's population, and it is often grown with low fertiliser input. Optimising the yield, nutritive content and bioavailability of sorghum grain with minimal input is of importance for human nutrition, and arbuscular mycorrhizal (AM) fungi have previously shown potential to assist in this. Across sorghum genetic diversity, AM fungi improved the yield, nutrition and zinc and iron bioavailability of grain in a low phosphorus soil. Thus, food production systems that effectively manage AM fungi may improve consumer outcomes.Summary Sorghum is a C4 cereal crop that is an important source of calories and nutrition across the world, predominantly cultivated and consumed in low‐ and middle‐income countries. Sorghum can be highly colonised by arbuscular mycorrhizal (AM) fungi, and the plant‐fungal association can lead to improvements in biomass and nutrient uptake. High‐throughput phenotyping allows us to non‐destructively interrogate the ‘hidden’ effects of AM fungi on sorghum growth and phenology. Eight genetically diverse sorghum genotypes were grown in a soil amended with 2 or 20 mg P kg−1 and inoculated with an AM fungal culture of Rhizophagus irregularis. High‐throughput phenotyping uncovered the ‘hidden’ effects of AM fungi on growth and phenology, while grain biomass, nutrition, Zn and Fe bioavailability and root AM colonisation was determined after destructive harvest. Sorghum plants colonised by AM fungi generally performed better than non‐AM control plants, with greater yield, harvest indices, and grain P, Zn and Fe contents. During the early growth stages, AM colonisation led to temporary growth depressions. There were also AM fungal and P fertilisation effects on sorghum time‐of‐flowering. The sorghum genotype with the highest AM colonisation could barely produce grain when non‐inoculated. The two genotypes that failed to mature had very low AM colonisation. Generally, the genetically diverse sorghum genotypes were highly responsive to AM colonisation and produced more grain of greater nutritive quality when colonised, without adverse consequences for micronutrient bioavailability.

Highlights

While cereals provide calories and micronutrients for human consumption, the absorption of some mineral nutrients in the gut are hindered by the anti-nutritional compound phytic acid/phytate
To explore the effects of arbuscular mycorrhizal (AM) colonisation on the growth and nutrition of sorghum, we used a subset of a panel of diverse grain S. bicolor genotypes (Tao et al, 2020) and investigated the effects of Rhizophagus irregularis inoculation and soil P fertilisation on plant growth, phenology, yield, and nutrition, with the focus on effects of AM fungi on sorghum grown at low P availability
The combination of high-throughput phenotyping and destructive endpoint harvesting allowed us to examine the effects of AM fungal inoculation over the life of the plant, and address the following questions: i

Summary

Introduction

While cereals provide calories and micronutrients for human consumption, the absorption of some mineral nutrients in the gut are hindered by the anti-nutritional compound phytic acid/phytate. Subsistence farming practices often rely on a low-input system due to the high cost and inaccessibility of inorganic fertilisers (Nziguheba et al, 2016) In these situations, effective agronomic management is important, management of the soil and choice of crop variety that best suits the environmental constraints (e.g., low nutrient, drought and salinity) (Chikowo et al, 2014; Whitbread et al, 2010). AM fungi can improve sorghum P, K, Zn and Fe nutrition (Caris et al, 1998; Ortas et al, 1996; Raju et al, 1990), and the tolerance of sorghum to drought and salinity stress (Cho et al, 2006) This is the case in many other cereal crops (maize, rice and wheat) which display positive growth responses to AM colonisation in both field and glasshouse experiments, except when intervention practices such as tillage or rotation with a non-host crop (e.g., canola) are taken into account (Zhang et al, 2019). Do genetically diverse genotypes of sorghum perform better in low soil P conditions when colonised by AM fungi?

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Conclusion