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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.
Abstract
Seed of 11 phenotypes of tomato (Lycopersicon esculentum Mill.) were germinated in petri dishes at a constant 25, 30, 35, or 40C or at 12-hr alternating temperatures of 40/25, 40/30, and 40/35C. At constant high temperatures, the greatest differences between phenotypes occurred at 35C, based on percentage germination, but at 30C, based on germination rates. Phenotypes that germinated best at a constant 40C were ‘Nema 1200’, P28693, and ‘UC-82-L’. Phenotypes that germinated best at 40/25C were P28693, P28793, and ‘UC-82-L’. Germination increased greatly when temperatures were lowered by 10 to 15C for 12 hr per 24 hr, compared to a constant 40C. Tetrazolium tests showed that a high percentage of seeds that had not germinated after 14 days of imbibition at 35 or 40C was still viable, whereas, at the lower temperatures, fewer nongerminated seeds were viable.