Abstract
Synthetic polyploids have been extensively studied for breeding in the last decade. However, the use of such genotypes at the agronomical level is still limited. Polyploidization is known to modify certain plant phenotypes, while leaving most of the fundamental characteristics apparently untouched. For this reason, polyploid breeding can be very useful for improving specific traits of crop varieties, such as quality, yield, or environmental adaptation. Nevertheless, the mechanisms that underlie polyploidy-induced novelty remain poorly understood. Ploidy-induced phenotypes might also include some undesired effects that need to be considered. In the case of grafted or composite crops, benefits can be provided both by the rootstock’s adaptation to the soil conditions and by the scion’s excellent yield and quality. Thus, grafted crops provide an extraordinary opportunity to exploit artificial polyploidy, as the effects can be independently applied and explored at the root and/or scion level, increasing the chances of finding successful combinations. The use of synthetic tetraploid (4x) rootstocks may enhance adaptation to biotic and abiotic stresses in perennial crops such as apple or citrus. However, their use in commercial production is still very limited. Here, we will review the current and prospective use of artificial polyploidy for rootstock and scion improvement and the implications of their combination. The aim is to provide insight into the methods used to generate and select artificial polyploids and their limitations, the effects of polyploidy on crop phenotype (anatomy, function, quality, yield, and adaptation to stresses) and their potential agronomic relevance as scions or rootstocks in the context of climate change.
Highlights
Triploidization can limit gametic fertility due to unbalanced meiosis. Associated with parthenocarpy, this reduced fertility allows the production of seedless fruit, which is a desirable trait for consumers
Much larger proportions of polyploid plants have been found in the Arctic (Brochmann et al, 2004) and at mountainous elevations (Schinkel et al, 2016), suggesting that these genotypes are better adapted to severe cold climatic constraints
We addressed (i) the methods to create artificial polyploids; (ii) the reproductive biology implications that using polyploid rootstocks and scions may have on crops; (iii) the importance of grafting in agriculture and the implications of using polyploid crops; (iv) the phenotypic variation induced by polyploidy and its effect biomass production and fruit; (v) the implications that polyploidy has in the regulation of genome expression with a focus on fruit quality and stress tolerance; and (vi) the role of polyploidy for enhancing stress tolerance
Summary
Polyploidy is one of the main factors driving evolution in higher plants (Grant, 1981; Soltis and Soltis, 1995, 2009; Wendel and Doyle, 2005; Cui et al, 2006; Chen, 2007, 2010; Husband et al, 2008; Hollister et al, 2012), conferring genotypic plasticity by increasing the number of copies of the genome (autopolyploidy) or adding different genomes (allopolyploidy), increasing their potential for adaptation (Leitch and Leitch, 2008) and promoting their selection (Feldman and Levy, 2012). Much larger proportions of polyploid plants have been found in the Arctic (Brochmann et al, 2004) and at mountainous elevations (Schinkel et al, 2016), suggesting that these genotypes are better adapted to severe cold climatic constraints These populations such as paleopolyploids may have experienced large genome changes leading to a loss of their polyploid status. We addressed (i) the methods to create artificial polyploids; (ii) the reproductive biology implications that using polyploid rootstocks and scions may have on crops; (iii) the importance of grafting in agriculture and the implications of using polyploid crops; (iv) the phenotypic variation induced by polyploidy and its effect biomass production and fruit; (v) the implications that polyploidy has in the regulation of genome expression with a focus on fruit quality and stress tolerance; and (vi) the role of polyploidy for enhancing stress tolerance
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