Wheat genotypes differ in potassium accumulation and osmotic adjustment under drought stress

Potassium (K) is the principal mineral solute contributing to osmotic adjustment (OA) in many crop species, and the magnitude of OA under drought stress may be increased by application of K fertilisers. Genotypic differences in either the capacity for OA under drought stress or the efficiency of K uptake and utilisation by wheat have been separately documented. However, it is not known whether genotypic differences in K uptake and utilisation are linked to differences in OA under drought stress. In this study, we quantified changes in OA in response to variable K fertilisation among five wheat genotypes with contrasting efficiency of K uptake and utilisation. Fertilisation with K increased OA for most genotypes by increasing K+ uptake and translocation into shoots and its subsequent accumulation in young leaves when drought stress was imposed. Accumulation of K+ in young leaves accounted for 36-51% of OA among the genotypes. The magnitude of OA achieved by genotypes under K fertilisation was highly correlated with the net content of K accumulated in shoots. With K fertilisation, differences in shoot K+ content accounted for 84% of the difference in OA among wheat genotypes. By comparison, for plants without K fertilisation, K+ accumulation in young leaves contributed only 17-28% of OA. At low K supply, the magnitude of OA achieved by genotypes was independent of the content or concentration of K+ in shoots. Under K-fertilised conditions, genotype Nyabing achieved the highest OA under drought stress, accumulated the highest concentration of K+ in young leaves (-0.87 MPa, accounting for 51% of OA), and had the greatest net K+ content in shoots. Genotype Wyalkatchem accumulated the smallest content of K+ in shoots and the lowest K+ concentration in young leaves (-0.40 MPa, accounting for 38% of OA), and achieved the lowest OA under drought stress. The greatest OA was achieved where high genotypic capacity to take up K was paired with conditions of high soil K availability.