Breeding and screening persimmon rootstocks for saline stress tolerance

Soil and water salinity affect growth and cause physiological disorders in plants. Recently, the high level of salt accumulated in the soil has become a problem in the 'Ribera del Xuquer' area in Valencia. Diospyros lotus, the most common persimmon rootstock used in this area, is sensitive to salinity. Numerous studies have demonstrated that exclusion of Cl− and Na+ is under genetic control. Thus, selection of suitable genotypes would restrict the translocation of Cl− or Na+ to the grafted variety. To meet this goal, the 'Instituto Valenciano de Investigaciones Agrarias' (IVIA, Spain) started a persimmon rootstock breeding program focused on developing rootstock genotypes tolerant to salt stress. The rootstocks used for persimmon comprise three species: Diospyros kaki Thunb., D. lotus L. and D. virginiana L. The aim of our study was to test seedlings from these species for tolerance to salinity stress. The variables studied were chloride and sodium uptake, growth and leaf gas exchange parameters. Three-month-old plants were grown in a greenhouse and irrigated for 45 days with nutrient solutions differing in sodium chloride (NaCl) content (0, 30 and 50 mM). Plant water status was disrupted by salinity-induced osmotic stress. D. kaki and D. virginiana seedlings presented reduced leaf water content and stomatal conductance. After 60 days, the Cl− content was lowest in D. virginiana leaves and highest in D. lotus. Furthermore, the Na+ content was highly variable in D. lotus and D. kaki, but remained low in all D. virginiana genotypes. The leaf Ca2+ content was highly variable in all species. The Na+/Ca2+ ratio, an indicator of root selective permeability, showed high variability in D. kaki and D. lotus genotypes, but remained low in D. virginiana. Selection of D. lotus and D. kaki genotypes with low Cl− and Na+ contents could provide salt-tolerant persimmon rootstocks.