Linking diverse salinity responses of 14 almond rootstocks with physiological, biochemical, and genetic determinants

Authors: Sandhu, Devinder; KAUNDAL, AMITA - Utah State University; ACHARYA, BISWA - University Of California; FOREST, THOMAS - University Of California; Pudussery, Manju; Liu, Xuan; Ferreira, Jorge; Suarez, Donald

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/13/2020
Publication Date: 12/3/2020
Citation: Sandhu, D., Kaundal, A., Acharya, B.R., Forest, T., Pudussery, M.V., Liu, X., Ferreira, J.F.S., Suarez, D.L. 2020. Linking diverse salinity responses of 14 almond rootstocks with physiological, biochemical, and genetic determinants. Scientific Reports. 10. Article 21087. https://doi.org/10.1038/s41598-020-78036-4.
DOI: https://doi.org/10.1038/s41598-020-78036-4

Interpretive Summary: Almond is a valuable nut crop in the world. The United States is the top producer representing more than 80% of the global share. California farmers produce more than 99% of the almonds in the U.S. Water is the most restraining component of agriculture in the 21st century. This reduced availability of good-quality water, and the increased demand for water from different sectors, is making the use of alternative or degraded waters unavoidable. The most important consideration for the use of greywater is its salt concentration. Almonds are considered sensitive or moderately sensitive to salt; even a low level of salinity can lead to significant reductions in crop yield and quality. We have evaluated fourteen (non-grafted) rootstocks under mixed salt composition water treatments and showed that peach hybrids and peach-almond hybrids are more tolerant to salinity. Our data suggested that sodium, to a lesser extent, chloride concentration in irrigation waters are the most critical ion toxicities for almond rootstocks, and sodium and chloride exclusion is crucial for salinity tolerance. Photosynthetic rate and relative proline accumulation correlate well with the performance of a rootstock under salinity, suggesting that these can be used as markers for evaluating salinity tolerance in Prunus. Expression analysis allowed us to partition complex salt tolerance mechanism into individual component traits, which may provide better precision in the manipulation of salt tolerance in almond rootstocks. Combining different components of salt tolerance mechanism may lead to the development of superior salt-tolerant rootstocks. Outcomes of this study will be utilized by almond breeders and geneticists in developing salt-tolerant rootstocks, which will provide incentives to make augmented use of alternative/degraded waters for the almond cultivation.

Technical Abstract: Fourteen commercial almond rootstocks were tested under five types of irrigation waters to understand the genetic, physiological, and biochemical bases of salt-tolerance mechanisms. Treatments included control (T1) and four saline water treatments dominant in sodium-sulfate (T2), sodium-chloride (T3), sodium-chloride/sulfate (T4), and calcium/magnesium-chloride/sulfate (T5). T3 caused the highest reduction in survival rate and trunk diameter, followed by T4 and T2, indicating that Na and, to a lesser extent, Cl were the most toxic ions to almond rootstocks. Peach hybrid (Empyrean 1) and peach-almond hybrids (Cornerstone, Bright’s Hybrid 5, and BB 106) were the most tolerant to salinity. Rootstock’s performance under salinity correlated highly with its leaf Na and Cl concentrations, indicating that Na+ and Cl- exclusion is crucial for salinity tolerance in Prunus. Photosynthetic rate correlated with trunk diameter and proline leaf ratio (T3/T1) significantly correlated with the exclusion of Na+ and Cl-, which directly affected the survival rate. Expression analyses of 23 genes involved in salinity stress revealed that the expression differences among genotypes were closely associated with their performance under salinity. Our genetic, molecular, and biochemical analyses allowed us to characterize rootstocks based on component traits of the salt-tolerance mechanisms, which may facilitate the development of highly salt-tolerant rootstocks.