For millennia, humans have used plants and fungi, as foods, fuels, fibers, and medicines; and have developed techniques for improving their usefulness to our species, mostly through selection of desirable traits. With human populations forecast to rise, the availability of arable land likely to fall amid climate change and increasing urbanization, and modern communications technologies accelerating the dispersal of pathogens, further improvement is urgently needed. However, ensuring long-term resilience involves conservation of existing genetic diversity in addition to selection. New technologies, particularly those based on molecular biology, are increasingly driving conservation and improvement strategies. How to cite this article: Kersey PJ, Collemare J, Cockel C, et al. Selecting for useful properties of plants and fungi-Novel approaches, opportunities, and challenges. Plants, People,

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The term ‘rhizosphere’ has historically been vaguely defined. In particular, the extent of the rhizosphere: the zone of interaction between root and soil has been difficult to measure or has been measured differently by workers depending on their discipline. This is to be expected given the range of possible interactions that occur at the root–soil interface and the varying effects of rhizodeposits on soil flora and fauna. This article outlines challenges to defining the spatial extent of the rhizosphere and demonstrates that it may not be possible to generalise about the extent of the rhizosphere across a range of different plants and measured based on a range of interactions. The case is made that the rhizosphere is typically more extensive than the few millimetres often described in the literature. In the case of a plant–nematode relationship presented here as a case study, the effect of root exudates (i.e. the rhizosphere effect) can be measured, at least, in centimetres rather than millimetres from the plant. Given the interest in utilising the rhizosphere and the rhizobiome for sustainable crop production, this article will clarify the terminology used and propose basic principles on how the spatial extent of the rhizosphere should be considered.

Soil samples taken from the ridge of field-grown potato (cv. British Queen) as well as from bulk soil of the same field were incubated with sterile potato root leachate or water. Samples were filtered and filtrates used in anin vitrobioassay to determine their effect on hatch of potato cyst nematodes (PCN)Globodera rostochiensisandG. pallida. Concurrently, an experiment was established where the sterile potato root leachate or water was incubated with a sterile soil wash. Ridge soil was shown to induce significantly more hatching than bulk soil, indicating the presence of PCN hatching factors. When a soil wash of ridge soil was used it did not increase hatch, suggesting a role for soil microorganisms in the hatching process. Greater hatch ofG. rostochiensisin bulk soil compared toG. pallidasuggests a role for soil microorganisms in spontaneous hatch of PCNin vivo.

The effects of interspecific competition between the potato cyst nematodes (PCN), Globodera pallida and G. rostochiensis, under variable population conditions were examined. PCN-susceptible potato cultivars were inoculated with single- and mixed-species populations of PCN. There was a significant difference in species multiplication between single- and mixed-species populations. Globodera rostochiensis multiplication in mixed-species populations was significantly lower than single-species populations. Density-dependent trials showed a significantly greater increase in multiplication of G. pallida at low inoculation densities relative to G. rostochiensis. These results indicate that G. pallida has a negative effect on G. rostochiensis populations and is the more successful species when competing. A staggered inoculation trial showed that the greater competitiveness of G. pallida was not wholly attributed to its later hatch. Globodera pallida outcompeted G. rostochiensis regardless of the timing of inoculation; however, G. pallida multiplication was lowest when plants were simultaneously inoculated with both species.