Chloride and sodium excluding capacities of citrus rootstock germplasm introduced to Australia from the People's Republic of China

The responses to root zone salinity (0, 25 and 50 mM NaCl) by 40 citrus rootstock genotypes introduced from the People's Republic of China, measured as shoot chloride (Cl−) and sodium (Na+) ion accumulation, growth and dry matter accumulation, were investigated under glasshouse conditions. Two experiments, one using aerated nutrient solutions and the other irrigated sand cultures, were conducted with plants grown from rooted cuttings taken from representative trees of different mandarin (Citrus reticulata Blanco and C. erythrosa Hort. ex Tan.), yuzu (C. junos Sieb. ex Tan.), Ichang papeda (C. ichangensis Swing.), sour orange (C. aurantium L.) and trifoliate orange (Poncirus trifoliata (L.) Raf.) genotypes. Two standard genotypes, viz. Rangpur lime (Citrus x limonia Osbeck.) and William's trifoliate orange were included in the experiments as reference controls.After 56 days, plant growth and shoot Cl− and Na+ concentrations varied significantly between genotypes within salt treatments in both experiments. There were significant differences between genotypes for relative tolerance indices, expressed as ratios of growth at 25 and 50 mM NaCl to growth at 0 mM, but the relative rankings did not change between root zone salt concentrations. Although there were some correlations between plant growth and tolerance indices with shoot ion concentrations, these were generally poor.As the plant material was clonal, estimates of broad sense heritability from intra-class correlation coefficients indicated that the genotypes investigated could prove to be valuable parents in breeding for new salt excluding rootstocks. Of particular interest were strains of trifoliate orange that accumulated low concentrations of Cl− and Na+ in shoot tissues. Since P. trifoliata is normally a poor Cl− excluder, but a major source of disease resistance, these results suggested that progeny testing should be conducted to investigate the value of these strains for future rootstock breeding.

► Clonal plants grown from cuttings of a range of citrus rootstock genotypes from China were screened for chloride and sodium exclusion in glasshouse-based experiments.
► The experiments identified salt excluding rootstock germplasm new to Australia and, thus, provided additional resources to help overcome the negative effects of root zone salinity on citrus production.
► Shoot Cl− and Na+ concentrations varied significantly between genotypes within salt treatments.
► Estimates of broad sense heritability from intra-class correlation coefficients indicated that the genotypes investigated could prove to be valuable parents in breeding for new salt excluding rootstocks. Of particular interest were strains of Poncirus trifoliata that accumulated low concentrations of Cl− in shoot tissues.