Temperature rise and water stress effects on two buckwheat species (Fagopyrum esculentum and Fagopyrum tataricum)

Aubert, Lauranne [UCL] Quinet, Muriel [UCL]

Buckwheat is a pseudocereal with high nutritional and nutraceutical properties. Although common buckwheat (Fagopyrum esculentum) is the main cultivated species, Tartary buckwheat (Fagopyrum tataricum) is gaining interest. In most western European countries, buckwheat production has declined during the 20th century with the development of more productive crops, but it is currently receiving renewed attention for its nutritional and environmentally friendly qualities. Both species were cultivated under field conditions in Belgium and showed good yield (2037 kg/ha - 3667 kg/ha) and good seed quality (Aubert et al., 2021). Fagopyrum esculentum flowered earlier, produced less nodes, less branches, less inflorescences, but more flowers per inflorescence than F. tataricum. The yield was higher in F. tataricum, while the thousand-grain weight was higher in F. esculentum. Both species differed by their reproduction: F. esculentum is a heterostylous and self-incompatible species mainly pollinated by insects while F. tataricum produces one type of flower that can self-fertilize. However, we observed that insects visited both species: F. esculentum was twice as visited and attracted a greater diversity of insects than F. tataricum, which generally attracted smaller insects. In the context of ongoing climate change, expected temperature rise and increase of drought periods may significantly limit plant growth and productivity of crop species. We investigated the effects of a sub-optimal temperature (27°C vs. 21°C) and of water stress (<20% vs. 40-50% soil water content) on F. esculentum and F. tataricum under controlled conditions (Aubert et al., 2020a, b). High temperature increased leaf production mainly in F. tataricum but decreased leaf area in both species. Water and photosynthesis-related parameters were affected by high temperature but our results suggested that although transpiration rate was increased, adaptive mechanisms were developed to limit the negative impact on photosynthesis. High temperature mainly affected the reproductive stage. It delayed flowering time but boosted inflorescence and flower production. Nevertheless, flower and seed abortions were observed in both species at 27 °C. Regarding flower fertility, heat affected more the female stage than the male stage and reduced the stigma receptivity. Pollen production increased with temperature in F. esculentum while it decreased in F. tataricum. Both species increased their antioxidant production under high temperature to limit oxidative stress. Total flavonoid content was particularly increased in the leaves of F. esculentum and in the inflorescences of F. tataricum. Regarding water stress, our results suggested that F. tataricum was more resistant to water stress than F. esculentum and that F. esculentum had characteristics of drought avoidance, while F. tataricum exhibited traits of drought tolerance. The vegetative growth was affected in F. esculentum but not in F. tataricum as water stress decreased leaf production, leaf fresh, and dry weight, stomatal conductance, transpiration rate, and photosynthesis rate in the former but not in the latter. However, chlorophyll fluorescence parameters were not affected by water stress, whatever the species, and the chlorophyll content increased in water-stressed plants in both species. Oxidative stress was observed in both species in response to water stress, and antioxidant content was increased in F. tataricum. The reproductive phase was affected by water stress in both species: the number of inflorescences and pollen production decreased, mainly in F. esculentum. Altogether, our results showed that abiotic stress response differed between buckwheat species and that reproductive stage was more affected than vegetative stage in both species but antioxidant production was boosted by abiotic stress, which could be interesting from a nutraceutical point of view.