REGULAR ARTICLE Crop root system traits cannot be seen as a silver bullet delivering drought resistance Jairo A. Palta & Neil C. Turner Received: 21 May 2018 /Accepted: 23 October 2018 # Springer Nature Switzerland AG 2018 Abstract Background The role of roots in determining the yield of a crop in water-limited environments (drought resis- tance) is controversial as individual root traits for water uptake do not necessarily guarantee a root system is efficient at capturing soil water. For increased drought resistance do we need deep or shallow root systems?, more or less roots?, high or low root resistance?, prolific root branching or restricted branching?, high sensitivity or low sensitivity to water deficits? Scope The root system characteristics to benefit yield under drought vary with the amount and distribution of precipitation; texture, depth and water-holding capacity of the soil; as well as root system characteristics. Our analysis shows that other drought-resistance traits such as early vigour, osmotic adjustment, and stay-green, increase drought resistance through increased root growth and water use. Conclusions The relationship between the root system and drought resistance is complex because the expres- sion of the root system traits that increase drought resis- tance depends on a number of factors and their interactions. Breeding for root systems that increase drought resistance cannot depend on identifying a silver bullet, single marker or single gene. Keywords Early vigour . Osmotic adjustment . Rainfall distribution . Root depth . Soil type . Stay green . Water capture Introduction The ability of a plant to survive or produce seeds in water-scarce environments has been termed its drought resistance which varies with species and genotypes with- in a species, but is not under single-gene control. Many mechanisms have been shown to increase the survival of plants in arid environments, but these are of little interest to agricultural scientists and crop breeders because sur- vival mechanisms are often the opposite of traits to maximise the economic yield of a crop in water-limited environments (Turner 1981). Historically these mecha- nisms of drought resistance were classified into drought escape, dehydration postponement and dehydration tol- erance (Kramer 1980; Turner 1986). In a paper simply titled ‘Roots and drought resistance,’ Passioura (1983) stated that ‘drought resistance is a nebulous term that appears to become more nebulous the more closely we look at it’. He argued that the understanding of drought resistance disappears as we attempt to extrapolate phys- iological and morphological traits associated with plant survival in arid regions to productive crops, and proposed that the ability of a crop to yield in water-limited Plant Soil https://doi.org/10.1007/s11104-018-3864-6 Responsible Editor: Rafael S. Oliveira. J. A. Palta (*) CSIRO Agriculture & Food, Private Bag No. 5, Wembley, WA 6913, Australia e-mail: jairo.palta@csiro.au J. A. Palta : N. C. Turner The UWA Institute of Agriculture and UWA School of Agriculture & Environment, The University of Western Australia M082, Locked Bag 5005, Perth, WA 6001, Australia