Genotypic differences in morphological and physiological traits of genus Pyrus and clonal pear rootstocks under prolonged drought stress

The genetic potential of wild Pyrus species provided useful opportunities to breeders for identifying drought-tolerant pear rootstocks within the world fruit trees germplasm. This study aimed to explore the drought tolerance mechanisms of wild Pyrus species as seedling rootstocks and some clonal pear and quince rootstocks under well-irrigated and drought-stress conditions. The rootstocks used included 11 Pyrus species as seedlings, 'Pyrodwarf' (P. communis), and 2 cydone 'EMA', and 'BA29′ (Cydonia oblonga) as clonal rootstocks. Nine-month-old ungrafted seedlings and clonal rootstocks were divided randomly into two similar-sized groups with about 25 internodes. The control group was irrigated every 3 days (WI) while the drought-stressed group (DS) was subjected to 21 days of water stress and received no irrigation. Soil moisture was monitored during the experiment, and morphological and physiological parameters were recorded after 21 days of applying treatments. Results revealed significant genetic variation in drought tolerance across the rootstocks used in terms of the physiological and morphological criteria. Drought stress significantly (p ≤ 0.01) reduced plant height, internode length, leaf relative water content, and carotenoid content, although the amount of proline was increased in comparison to well-irrigated rootstocks. Drought stress also reduced the quantum yield of PSII (Fv/Fm), indicating impaired photosynthetic efficiency. Root length increased in most rootstocks under drought stress, but root dry weight decreased. In conclusion, growth and root parameters are highlighted as valuable indicators for identifying drought-tolerant pear rootstocks. Moreover, the substantial variation that exists among the collected species from different geographic origins represents a promising and valuable genetic resource for future pear breeding programs with specific pear breeding objectives for improving drought-resistant rootstock.