6 Conclusions and perspectives
From research reviewed here, it is clear that some environmental stresses can enhance fruit colour: low temperature, high light (and UV) and a degree of water deficit can all be beneficial. Against this, the severity and timing of these stresses are critical in determining whether outcomes are positive or negative. Some of these stresses can be controlled horticulturally, such as limiting water supply, but climate change is outside grower control and thus likely to disrupt our current growing practices. Consumer desire for ever more healthy fruits is unlikely to dissipate — the pigments in fruits provide many of these health benefits, packaged with one of the strongest motivators for purchase — the attractiveness of colourful fruit. Of course, fruit cultivars, no matter how colourful, will also have to reach other key consumer expectations, such as texture, storability and flavour. As climate change creates less predictable temperatures across many fruit-growing regions, understanding how fruit pigmentation will be affected will become increasingly important if we are to maintain or improve fruit colour. For some fruit crops, indoor production may become a more attractive (and commercial) proposition to avoid crop losses due to damaging climatic events.
Various options are available to maintain fruit colour in this changing environment, including agronomic approaches (Poiroux-Gonord et al. 2010). Similarly, postharvest treatments can provide the potential to preserve and enhance fruit pigments (de Pascual-Teresa & Sanchez-Ballesta 2008). In the future, more substantive advances may be required to augment the incremental changes that can be made by in-field or postharvest management. In some circumstances, fruit breeding programmes have reduced the genetic and phenotypic diversity in breeding populations. To address production challenges associated with severe climate change, incorporating new genetic diversity is likely to become essential to maintain or improve fruit crops: the use of crop wild relatives that are better adapted to environmental stresses should be considered to introduce beneficial traits. Ideally, this would be in conjunction with deep bioinformatic resources (high quality genomes, transcriptomes and metabolomes), and an emphasis on mapping and molecular markers to help to target ‘resilience’ traits and rapidly incorporate these in new cultivars that are better adapted to our changing environment. Breeding varies markedly between species and varieties, and there will be an increasing need for developing crops suited to (and tested at) different geographic and environmental locations. The complexity of GxE interactions on fruit pigmentation is complex, and more research into this area is required to understand the plant response and potential breeding strategies for fruit colour improvement.
‘Traditional’ genetic engineering has provided many examples of successfully increasing plant pigments (Martin & Li 2017). Sophisticated molecular engineering of fruit can provide platforms for elevated amounts of specific phytochemicals, including pigments (Liet al. 2018). The new breeding technologies such as CRISPR provide untapped potential for modifying our fruit crops both to improve their nutritional benefit (colour) and to tackle changing growing conditions (Wang, Zhang & Zhu 2019). It is likely that adoption of new breeding approaches will be required to maintain and enhance fruit pigments as we navigate environmental changes to fruit-growing regions across the globe.