Tolerance of Ten Lettuce Cultivars to High Temperature Combined with NaCl during Germination

Abstract

Water that may contain salt often is used to cool soil to help overcome high-temperature inhibition of lettuce germination. This study was done to determine how lettuce cultivars differ in their germination response to high temperature and NaCl. Ten lettuce (Lactuca sativa L.) cultivars (Grand Rapids, Climax, Coolguard, Empire, Great Lakes 659-700, Mesa 659, Salinas, Vanguard 75, Red Coach 74, and Wintersupreme) were germinated at 20, 25, 30, or 35C with 0.0, - 0.3, - 0.6, - 0.9, - 1.2, or - 1.5 MPa NaCl. With no NaCl, germination percentages and rates decreased significantly at 35C for all cultivars except `Salinas', which decreased at 30C. With higher concentrations of NaCl, decreases in germination percentages and rates were observed at lower temperatures. Cultivar differences in response to temperature were present with no NaCl but became larger in the presence of NaCl. `Great Lakes 659-700' and `Mesa 659' were most sensitive to high temperature and salt. `Coolguard' and `Empire' were most tolerant to high temperature and salt, with some tolerance also present in `Grand Rapids' and `Vanguard 75'. Relative tolerance of cultivars to NaCl as shown by germination percentages and rates was consistent with growth of roots.