Characterisation of the germination responses to temperature of vegetable seeds. I. Tomatoes

Tests in incubators and on thermo-gradient bars were done with 13 cultivars of tomato (Lycopersicum esculentum Mill.) to establish the main features of their germination responses to temperature. Differences found between cultivars including F₁ hybrids, out-door strains, and plants with golden and red skinned fruits were small. Optimum temperatures occurred between 26 and 32°C; maxima for fifty percent rates of germination were between 35 and 38°C, and minima between 8 and 10°C. Seed of Lycopersicum pimpinellifolium and small fruited subspecies of L. esculentum germinated at lower temperatures, down to 6°C, and more rapidly at median temperatures. Results of experiments on thermo-gradient bars showed that statistically significant differences occurring between responses at particular temperatures in incubators may be of minor biological or economic significance when used to assess temperature tolerance of different cultivars, and demonstrated that tests over a range of temperatures are essential for such determinations. A method is proposed for using results obtained in the early part of an experiment to provide regressions which can be projected to indicate the course of germination over a long period.