Assessing Field Prunus Genotypes for Drought Responsive Potential by Carbon Isotope Discrimination and Promoter Analysis

In order to improve the effectiveness of breeding practices for Prunus rootstocks, it is essential to obtain new resistance resources, especially with regard to drought. In this study, a collection of field-grown Prunus genotypes, both wild-relative species and cultivated hybrid rootstocks, were subjected to leaf ash and carbon isotope discrimination (Delta C-13) analyses, which are strongly correlated to water use efficiency (WUE). Almond and peach wild relative species showed the lowest Delta C-13 ratios, and therefore, the highest WUE in comparison with hybrid genotypes. In addition, drought-related cis-regulatory elements (CREs) were identified in the promoter regions of the effector gene PpDhn2, and the transcription factor gene DREB2B, two genes involved in drought-response signaling pathways. The phylogenetic analysis of these regions revealed variability in the promoter region sequences of both genes. This finding provides evidence of genetic diversity between the peach- and almond-relative individuals. The results presented here can be used to select Prunus genotypes with the best drought resistance potential for breeding.