Determination of Cardinal Temperatures and Photoperiodic Response of Quinoa (Chenopodium quinoa L.) Lines using Linear and Nonlinear Models

The length of the growth period is the key to crop adaptation to new environments. It is strongly affected by the environment in such a way that it is possible to predict the length of the growing period based on some correlations with environmental factors. Simple models that quantify intraspecific variability in flowering responses to temperature and photoperiod can be useful for characterizing lines. Quinoa (Chenopodium quinoa) shows considerable resistance to a wide range of abiotic stresses. Cardinal temperatures and day length at each development stage are necessary to find an appropriate model for predicting plant growth and development.

Ten separate experiments (10 planting dates included: 29 March, 29 April, 28 May, 28 June, 26 July, 23 August, 6 September, 20 September, 29 January, and 29 February) were conducted as randomized complete block design with three replications. The experimental factor consisted of five quinoa lines plus one cultivar (Titikaka). Five promising lines were modified at Yazd Salinity Research Center. Four lines belong to the middle maturing group, one to the late maturing group, and the Titikaka cultivar belongs to early maturing group. The time of beginning and end of each developmental stage, including germination, pollination, and seed maturity, was recorded. The response of developmental stages to temperature and photoperiod was used to determine the cardinal temperature and day length of the main developmental stages (emergence, flowering, and seed maturity).

Based on the coefficient of determination (R2) it seems that the quadratic model is suitable for estimating the cardinal temperatures of germination, flowering, and ripening of quinoa seeds. Using both quadratic and segmented models to estimate the length of special days resulted to satisfactory robustness. The results showed that on days with a length of lesser than 12 hours and temperatures lesser than 30°C, the flowering rate increased with a simultaneous increase of temperature and day length. As the day length increased to 14 hours, the rate of flowering development changed more significantly when temperatures were between 19 and 25°C than at temperatures below 19°C. For all lines, increasing the day length or temperature resulting in an increased plant maturation rate (from flowering to seed maturity) at a constant temperature or day length. The optimal temperature range for all developmental stages of quinoa lines was between 20 and 25°C. There was a significant difference in the base temperatures of the developmental stages. The base temperature for germination of quinoa lines was above 0°C, the base temperature for flowering was between -2 and +2°C, and the base temperature for seed maturity was below 0°C. The maximum temperature of all quinoa developmental stages was above 40°C (42-51°C). At low temperatures, the flowering stage was more sensitive than the seed ripening stage. The critical day length for flowering and seed ripening of quinoa lines was between 11.5 to 12 hours.

The optimum temperature range for germination was obtained by 25-34°C, for flowering by 28-21°C, and for seed ripening by15-32°C. The optimum temperature of all developmental stages of quinoa lines was between 20 and 25°C. The optimum day length range for flowering is estimated at 11.37-34.12 hours and for seed ripening by 10.58-12.3 hours. Using the segmented and quadratic models to estimate quinoa cardinal temperature and photoperiod response resulted in the same estimations, although in most values, the quadratic model showed a higher coefficient of determination. In general, the results indicated that the temperature and day length have a compensatory effect on the flowering rate and seed ripening stages of the studied lines.