Lettuce (Lactuca sativa L.) is one of the most important foliar crops in vegetable crop production and may be established by direct seeding or by transplanting. Seed germination is particularly sensitive to environmental temperature changes and high temperatures adversely affect germination and seedling establishment. The aim of this study was to identify differences in the germination of twenty lettuce cultivars under conditions of optimum (20 °C), intermediate (27.5 °C) and critical (35 ºC) temperatures. Commercial seed from different companies was used, as well as seeds of the same cultivars grown at the Embrapa Horticulture Institute under greenhouse conditions. Some thermotolerant genotypes, 'Vitória de Verão' and 'Camila', were identified, with more than 90% germination for the critical and optimum temperature conditions. These genotypes could be used as a source of genetic tolerance to germination at high temperatures. Most of the seed produced in a greenhouse did not germinate satisfactorily under high temperatures.
Lactuca sativa; stand establishment; thermo-inhibition; thermo-dormancy
