Determining morphological and physiological parameters for the selection of drought-tolerant geraniums (Pelargonium x hortorum L. H. Bailey)

Summary

Greenhouse experiments were carried out to study the effect of drought stress on morphological and physiological parameters of Pelargonium hortorum, to define the most sensitive indicators that could be used to evaluate genotypes for tolerance to water stress. Nine genotypes of P. hortorum and two genotypes of the parental species (P. inquinans L. and P. zonale L.) were examined. Drought stress was induced by withholding water until the soil water potential reached –80 kPa, followed by recovery and applying another drought stress cycle. Growth decreased with drought stress with regard to all parameters and all genotypes, compared to well-watered plants. Production and loss of leaves were sensitive indicators of drought stress to discriminate between genotypes. A classification of genotypes was obtained from these parameters. Changes in leaf area, the density of stomata (mm^–2 or per leaf), leaf water content and leaf cell osmolarity during the drought cycle and after recovery were also studied. Changes in stomata mm^–2, leaf surface and cell osmolarity were found to be sensitive indicators of drought stress. Correlations between different parameters made it possible to obtain a robust classification of genotypes using only a few parameters. Significant variation was found between genotypes of P. hortorum in their response to drought stress.The different mechanisms which can be used by tolerant genotypes to adapt to drought stress are discussed. The present study provides a simple method to evaluate and select for water stress-tolerance in P. hortorum genotypes.