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.