Changes in Apical Morphology during Floral Initiation and Reproductive Development in Quinoa (Chenopodium quinoaWilld.)

A numerical scale for identifying main apex morphological development stages from vegetative to open flower in quinoa ( Chenopodium quinoa Willd.) has been developed, using SEM photographs and stereomicroscope observations. The scale accounts for the different patterns of development found in the two inflorescence types known in the species (glomerulate and amaranthiform). Eight stages are described for the glomerulate inflorescence, and seven for the amaranthiform inflorescence. Development of the apical meristem ends with the formation of an apical flower in the glomerulate type, and is interrupted by the appearance of a cap-like structure in the amaranthiform type inflorescence. This structure has not been observed in other Chenopodium species. A terminal flower is formed in all flower-bearing second-order axes in the glomerulate inflorescence; and the formation of a cap is repeated for the apical meristems of second-order axes in the amaranthiform inflorescence. Differentiation of axillary meristems progresses basipetally at a constant rate of 0.21 nodes °Cd -1 (base temperature 6.4 °C) for the glomerulate inflorescence (variety Baer I) and in two stages for the amaranthiform inflorescence (variety Amarilla de Marangani): an initial faster period with a rate of 0.28 nodes °Cd -1 (base temperature 3.7 °C) in the upper nodes and a second, slower one, with a progression rate of 0.07 nodes °Cd -1 in lower nodes. A description of the distribution of the grain-bearing glomeruli on the mature inflorescence is given.