Estimation of Cardinal Temperatures for Tomato (Solanum lycopersicom) Seed Germination Using Nonlinear Regression Models

Seed germination is one of the most important factors which determine the success of failure of crop establishment. In the absence of other environmental limiting factors such as moisture, temperature would determine the rate and overall seed germination. This research was conducted to investigate the effect of temperature regimes on seed germination, quantify the response of germination rate to temperature and determine the cardinal temperatures for different germination percentiles in Solanum lycopersicom.

Two-way factorial experiment including seven constant temperatures (5, 10, 15, 20, 25, 30 and 35 oC) and two tomato varieties (Red cherry: var. Cerasiformi and Yellow pearl: var. Yellow Pear) was conducted based on a completely randomized design arranged with thee replications at the seed technology laboratory of Agricultural Sciences and Natural Resources University of Khuzestan in 2019. Beta, segmented and dent-like functions were used to determine the relationship between germination rate and temperature. Logistic model was used to describe the suitable pattern for the germination of these two cultivars in response to each temperature level.

Results of analysis of variance showed that the interaction effect of temperature and cultivar was significant on all studied traits. Results showed that respectively at temperatures of 15, 20, 25 and 30 oC, total seed germination for yellow pearl tomato was 93%, 96%, 95% and 86% and for red cherry tomato was 95, 98, 93 and 98 percent. There was no seed germination for both tomato varieties at 5, 10 and 35 oC. Based on the results of the fitted models, it was revealed that among the tested non-linear regression models, segmented model described the germination rate of the studied tomato cultivars against the temperature the best (AICc≤70, R2=0.93). Three parameters logistic functions exhibited a reasonable fit (R2=0.96) for germination time course under temperature range of 15 to 30 oC in both cultivars. Based on the segmented model, base, optimum and ceiling temperatures of Yellow pearl and Cherry tomato were estimated 11.25, 28.72, 35.00 oC and 10.97, 28.361 and 35 oC, respectively.

Both tomato cultivars exhibited sensitivity to changes in temperature. Seed germination rate and number of the germinated seeds increased at temperatures higher than base. This increase continued until the optimum temperature and then started to decline as the temperature exceeded from optimum range. Also, results obtained from the logistic function showed that Yellow pearl cultivar is more sensitive to supra-optimal temperatures compared with Cherry tomato, and germination percentage of the 97.79 to 85.09 percent as temperature reached from 25 to 30 oC.