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Influence of ploidy level on the physiological response of apple to water deficit

Hias, N., De Dauw, K., Davey, M. W., Leus, L., Labeke, M. C. van, Huylenbroeck, J. van, Keulemans, J.
Acta horticulturae 2017 no.1177 pp. 333-338
Malus domestica, apples, biotic stress, colchicine, diploidy, drought, genotype, leaf area, leaves, photosynthesis, physiological response, stomatal conductance, tetraploidy, water content, water use efficiency
Polyploids are ubiquitous throughout the plant kingdom. Their prevalence suggests that polyploidy confers an adaptive advantage to these species. In the case of artificially mitotically-doubled polyploid plants however, studies are more ambiguous. Nonetheless there are reports that these synthetic polyploids have increased resistance to (a) biotic stresses compared to their diploid progenitors. In this study we describe the impact of artificial polyploidization of two apple genotypes on the response to a progressive moderate water deficit under controlled growth conditions. In vitro apple plants were artificially doubled from nodal segments using colchicine. Morphological characterization demonstrated that leaf mean stomatal density was significantly lower in the tetraploids (4x) compared to the corresponding diploid (2x) progenitors. However, the stomatal area of the 4x's was significantly larger, so that mean stomatal coverage (percentage stomatal area/unit leaf area) was statistically unchanged. Growth of the 2x plants was more vigorous than 4x. Stomatal conductance and photosynthetic rate of 4x control plants were slightly lower but the stressed plants were less affected by water deficit than their diploid progenitors. Intrinsic water use efficiency was slightly better in 2x stressed plants. Under conditions of water deficit, 4x plants were able to maintain a higher relative leaf water content (RWC), than 2x progenitors. These results suggest that 4x, due to a higher mean RWC and higher photosynthetic rate might be more tolerant to moderate drought.