Germination, Mineral Composition, and Ion Uptake in Walnut Under Salinity Conditions

Walnut (J. regia L.) is one of the most sensitive plants to abiotic stresses for which finding salt-tolerant genetic resources is very important. Effects of salt stress on seed germination of seven walnut cultivars (Serr, Lara, Pedro, Chandler, Hartely, Vina, and Roun de Montignac) were studied. Salt stress treatments were applied using NaCl solutions ranging from 50 to 250 mM. The increase in salinity levels resulted in a substantial decrease in root relative water content. The percent of germination was also affected by salinity level and cultivar and their interactions. The mean germination time differed among treatment media and cultivars and a significant interaction was observed between these two factors. According to the cluster analysis, 'Chandler' was classified as the most tolerant cultivar. 'Hartley', 'Pedro', and 'Round de Montignac' ('RDM') were also classified in another group (semisensitive), whereas 'Vina', 'Serr', and 'Lara' were classified as sensitive cultivars. With the increase in salt stress, resistant cultivars accumulated more potassium (K) and calcium, especially in their shoots. However, in the semitolerant cultivars, accumulation of K in the root was more than in the shoot. Differences in magnesium accumulation in roots and shoots of all samples were significant at all stress levels and were dependent on genotypes. Sodium levels in roots were higher than in the shoots in most cultivars, especially in the semisensitive and tolerant ones. There was a low correlation (r(2) <= 0.15) between walnut seed traits (seed weight and kernel weight) and growth indices with respect to salinity tolerance.