Photoperiod induced changes in ABA and soluble sugar content of two differently adapted quinoa cultivars.

Quinoa (Chenopodium quinoa Willd.) is a highly nutritious Andean seed crop with high adaptability to adverse environmental conditions that normally inhibit agricultural production. Most of the existing cultivars are short day plants and sensitive to day length conditions outside the centre of origin. This area needs to be addressed if quinoa is to be used as a worldwide crop. To further elucidate the effects of photoperiod on developmental processes of quinoa and whether abscisic acid (ABA) and soluble sugar signalling is involved, we subjected a short-day cultivar (Achachino) and a day length neutral cultivar (Titicaca) to continuous long day (17.5 hr) and short day (10.5 hr) conditions as well as a shift between the two. Under both 10.5 hr and 17.5 hr conditions, Titicaca continued normal development towards maturity and halted stem elongation after senescence. In contrast Achachino only fully developed its inflorescence under 10.5 hr days, while under 17.5 hrs stem elongation continued and re-shooting occurred from the inflorescence stage until the end of the study. The shift from 10.5 to 17.5 hr triggered a more than triple increase of ABA in Titicaca as well as an increase in soluble sugars, and a concurrent chlorosis of the lower leaf levels not observed under continuous 10.5 hr photoperiod. For Achachino there was a doubling of ABA in response to the change in photoperiod and an increase in soluble sugars. However, the initial levels of ABA in Achachino compared to Titicaca were much lower whereas the soluble sugar concentrations were of comparable levels. Developmentally the change in photoperiod to long days caused Titicaca to focus on reproductive growth and Achachino to continue vegetative growth rather than completing its growth cycle. These findings may have implications for future quinoa cultivar improvement and management.