Effects of radiation on the phyllochron of nine quinoa ( Chenopodium quinoa Willd.) cultivars growing under field conditions were quantified. Rate of change of photoperiod had no effect on phyllochron. Radiation responses differed markedly between cultivars, ranging from insensitive in the most tropical cultivars (Nariño and Ecu-621) to 0.55 °Cd mol PPFD m −2 d −1 in the Peruvian cultivar Amarilla de Maranganí. Cultivars reported as having the highest photoperiod sensitivity and longest phyllochron were insensitive to radiation, while cultivars insensitive to photoperiod from the Bolivian and Peruvian altiplano (Kanckolla, Blanca de Julí and Sajama) or moderately sensitive to photoperiod from central Chile (Faro and Baer) were affected by radiation. It is suggested that variation in phyllochron sensitivity to radiation could be associated with differences in photoassimilate demand per unit time to sustain leaf growth. A model based on phyllochron responses to radiation and temperature produced an important improvement in the quality of predictions when compared with a model based on responses to photoperiod and temperature for seven of the nine cultivars evaluated. This is the first instance in which a quantitative relationship between incident radiation and the phyllochron in natural environments has been established, allowing the inclusion of this factor in predictions of the rate of leaf appearance in the field.
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Daniel Bertero (2001) studied this question.