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Most phosphorus (P) in agricultural soils is found in the surface layers and topsoil foraging is often considered to be important for P recovery. The aim of this work was to examine how the amount and distribution of roots in the surface soil layer affects growth and response to P fertiliser in wheat and barley. Between 10 and 20 varieties of wheat and barley were grown at 0 kg P/ha and 30 kg P/ha at P responsive sites over two years. The amount of roots in the surface 10 cm of soil between and within sowing rows and their ratio were assessed using the concentration of root DNA in the soil at Zadok’s growth stage (ZGS) 30–31. Shoot biomass and P concentration were measured at the time of root sampling and plots were harvested for yield. Adding P increased root DNA density with the greater response observed in the seeding row. Significant differences in root DNA density were measured among varieties and these showed some consistency over sites. The degree of lateral spread of roots did not differ between barley and wheat, but within-row root growth of barley showed a greater response to P than that of wheat. Biomass production, yield and yield response to P were not related consistently to root DNA density nor to the ratio of root DNA between and within rows. Genetic differences in root growth in the top 10 cm can be identified but the root DNA density in the soil and the distribution of roots within and between rows were not consistently associated with P uptake, yield or yield response to P.

Aims: Root branching is a fundamental phenotypic property of a root system. In this paper we present a system for the fully automated detection and classification of root tips in root images obtained either by 2D flat bed scanning or by 3D digital camera imaging.With our system we aim to provide a robust, efficient and accurate means of phenotyping of roots. Methods: Structural information derived from image features such as root ends and root branches is utilised for the detection and classification processes. A statistical analysis based on training data sets of root tips and non-root tips is used to assign image features to one of three different classes: non-root tips, primary root tips and lateral root tips. The automated procedure is optimised to ensure as high true detection rate and low false detection rate as possible. Results: We apply the method to images of barley,rice, and corn roots taken either by 2D scanning of washed and cut roots or digital camera images of plant roots growing in a transparent medium. The results of our detection and classification procedure are validated by a comparison with manually labelled images for all three species. Our results are also compared to two established platforms, EZ-Rhizo and WinRHIZO. Finally, we demonstrate the utility of the statistical learning approach by quantifying root phenotypic properties of barley double haploid lines. Conclusions: The method of statistical learning of characteristic features is an accurate means of not only counting root numbers, but also discriminating between primary and lateral roots. The fully automated procedure presented in this paper can be used reliably in high throughput situations to characterise quantitative phenotypic variation. Refereed/Peer-reviewed

Mn efficiency is defined here as an ability of a genotype to grow and yield well in a soil which is limiting in available Mn for a standard genotype (Graham, 1984). Screening for Mn efficiency in soil-based pot testing had been producing inconsistent results, and thus improvement of pot screening became an objective. One possible factor, pot size was examined as the cause, using two sizes of pot. In large pots, the expectation of higher dry matter and shoot Mn concentration in a Mn-efficient genotype compared to a Mn-inefficient genotype was realised over a wide range of Mn supply, whereas in small pots, the genotypic differences were expressed at only one, low rate of Mn supply (10 mg kg soil-1). Plants in the small pots strongly responded to root restriction by decreasing yields and increasing root/shoot ratios and Mn concentrations of shoots. The critical value of Mn concentration for shoot growth was not affected by the small pots, but the Mn mobilization by plants might be affected in the small pots. The practical outcome of these results is that using an adequate size of pot and measuring the Mn concentration of shoots, soil-based pot screening for Mn efficiency can be improved.

The effects of toxic boron (B) concentrations on the growth of wheat genotypes at organ level and cellular level were investigated using excised root culture techniques. At the organ level, wheat genotypes differed for root elongation and lateral root development in response to toxic B concentrations. Genotypes classified as resistant from field studies had longer root axes and more lateral roots than sensitive or moderately sensitive genotypes, but there was no difference in axis elongation between sensitive and moderately sensitive genotypes. At the cellular level, callus production of root explants among genotypes still different at toxic B concentrations: resistant genotypes could produce more callus than sensitive or moderately sensitive genotypes. These results suggest that differences among genotypes in resistance to toxic B concentrations may be related to cell membrane permeability to B since they were also expressed in undifferentiated callus cells. The distinct and consistent differences among genotypes in response to B toxicity both at the organ level and at the cellular level could serve as a basis for selection in a breeding program. The methods were precise and efficient.