Elevated CO₂ differentially affects the properties of grain from wild and domesticated rice

Interspecific germplasm from wild species of Oryza will be increasingly applied to breeding programs over the coming decades. However, the concurrent impact of rising atmospheric CO₂ concentrations (atm-CO₂) on grain properties is unknown. Wild accessions of Australian native rice species (Oryza australiensis and O. meridionalis) and the local cultivar (O. sativa cv. Doongara) were grown to maturity in glasshouses at ambient (400 ppm; aCO₂) and elevated (700 ppm; eCO₂) atm-CO₂ and physicochemical properties of the grains were compared. Seed length (Sl), seed width (Sw) and 1000-seed weight (TSW) were higher at eCO₂ than aCO₂, while nitrogen content (N) and apparent amylose content (AC) were not significantly changed, irrespective of genotype. Rapid viscosity analyser (RVA) profiles revealed increased peak viscosity (PV) for rice under eCO₂, indicating differences in starch gelatinization. However, final viscosity (FV) increased in the wild rices in eCO₂, whereas it decreased in Doongara. Increases in PV were accompanied by lower estimates of protein contents (PC) at eCO₂ in all species. When AgNO₃ was excluded from the RVA, it became apparent that its presence had enhanced the effects of eCO₂ on flour pasting properties through inhibition of α-amylase activity of the flour. Our results suggest that grain morphology and pasting properties are differently affected by eCO₂ in the wild rices compared with cultivated rice. These data will inform the breeding criteria for rice grain properties and inform the introgression of wild germplasm.