Impact of drought stress memory and variations in type and degree on root characteristic, yield stability and drought tolerance in Orchardgrass.

Background: As climate change intensifies, perennial plants face more frequent drought periods throughout their lifespan. Drought stress memory in certain plants significantly enhances their adaptability to challenging environmental circumstances. However, in open-pollinated crops, this process is influenced by population plasticity due to the type and degree of genetic diversity, and inbreeding depression. To understand how pre-exposure to moderate drought enhances the plants' response to subsequent severe stresses, four synthetic poly-crossed populations were constructed using parents with contrasting molecular and morphological genetic variation (i.e. narrow and wide genetic distance). The first and second generations were subsequently assessed in an outdoor pot experiment at Isfahan University of Technology over two years, 2018 and 2019, under three different moisture conditions: Control with normal irrigation, DIDII underwent mild drought stress during the stem elongation phase followed, by severe drought stress during flowering, and DII subjected only to severe drought stress during flowering.

Results: Genotypes pre-exposed to DIDII treatment exhibited enhanced tolerance to subsequent severe drought compared to those exposed to DII treatment, indicating the importance of drought stress memory. However, trait-specific response observed for stress memory. The DIDII treatment improves dry matter yield, root volume, and root weight at different soil depths. Populations derived from parents with higher molecular and phenotypic variation were better suited for accurately predicting the performance of their progenies in terms of drought tolerance while not necessarily for stress memory. Inbreeding depression for root volume, root area, and root dry weight was affected by moisture conditions and the diversity level among the parental genotypes.

Conclusion: Our research may pave the way for understanding the mechanisms behind drought stress memory in grasses, which can be exploited in future studies to develop synthetic varieties with improved drought tolerance through selective breeding using populations with diverse genetic backgrounds.