The effects of NaCl priming on salt tolerance in melon seedlings grown under saline conditions

Seeds of melon cultivars Hasanbey and Kirkagac were primed (P) with 18 dS m(-1) NaCl solution for 3 days at 20 degreesC. After priming, non-primed (NP) and P seeds were sown in germination boxes containing sphagnum peat. The germination boxes were placed in an unheated greenhouse and watered with five different NaCl solutions (0.3 (control), 4.5, 9.0, 13.5 and 18.0 dS m(-1)), for a period of 4 weeks. Total emergence and dry weight were higher in melon seedlings derived from P seeds and they emerged earlier than NP seeds. Moreover, seeds from NP groups could tolerate up to 9.0 dS m(-1) NaCl salinity, while the total emergence values of P groups in cvs. Hasanbey and Kirkagac did not decrease below 50% at 13.5 and 18.0 dS m(-1), respectively. NaCl priming enhanced total sugar and proline accumulation and prevented toxic and nutrient deficiency effects of salinity because less Na but more K and especially Ca was accumulated in melon seedlings. As a matter of fact, Na:Ca balances of seedlings derived from P seeds were significantly lower than those of NP seeds under similar salinity levels. These results suggest that NaCl priming of melon seeds increased salt tolerance of seedlings by promoting K and Ca accumulation, besides inducing osmoregulation by the accumulation of organic solutes. (C) 2002 Elsevier Science B.V. All rights reserved.