Abstract
Experiments conducted under controlled environments and using nine quinoa (Chenopodium quinoaWilld.) cultivars, the origin of which ranged from Colombia to southern Chile, demonstrated that all cultivars have a facultative short day response for duration of emergence to flowering. Furthermore, duration of all phases of development (emergence to floral initiation, floral initiation to first anthesis, and first anthesis to physiological maturity) is sensitive to photoperiod in this species. In experiments where two quinoa cultivars were subjected to constant photoperiods or were transferred between photoperiods at different phenological stages, it was shown that duration of a given phenological phase depended not only on duration of the photoperiod experienced by the genotype during this phase (immediate response) but was also affected by the duration of the photoperiod experienced during a previous phase (delayed response). Duration of the emergence-floral initiation phase was longer under a long photoperiod (14 h) compared to a short photoperiod (10.25 h), and this caused plants to initiate more leaf primordia under long days. Furthermore, long photoperiods applied during the floral initiation-anthesis phase affected duration of this phase and the proportion of leaf primordia developing into leaves. Seed growth was affected by photoperiod experienced after anthesis and also by preanthesis photoperiods. Inhibition of seed growth was strongest when long days were experienced in combination with high temperatures during seed growth. Sensitivity to photoperiod (PPS, °Cd h−1) and duration of the Basic Vegetative Phase [BVP: operationally defined as minimal thermal time (°Cd) from emergence to flowering as measured under a 10.25 h photoperiod] varied among origins: cultivars from the Andean valleys of Perú, Colombia, and Ecuador were characterized by a comparatively higher PPS and longer BVP; whereas cultivars from the Bolivian and Peruvian Altiplano, and central Chile had the lowest PPS and BVP values. Quinoa cultivars exhibited a photoperiod-insensitive subphase after emergence (juvenile subphase), with a linear duration and a negative correlation with cultivar latitude of origin. Leaf appearance rate (LAR) was also affected by photoperiod and temperature. Sensitivity of leaf appearance rates to temperature (leaves °Cd−1) increased, while sensitivity to photoperiod (°Cd h−1) decreased, as latitude of origin of the cultivars changed from 1° 13′ N to 38° 46′ S. The shortest phyllochrons (thermal time between the appearance of two successive leaves on the main stem) associated with early flowering cultivars were observed in cultivars from dry or cold climates, and the longest were observed in cultivars from more humid and warm climates.