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Background: Rice crop is known as very sensitive to water deficit, especially during the reproductive phase when growth of vegetative organs and formation of spikelets are concomitant. The present study questioned whether the maintenance of vegetative organ expansion during a water deficit at the reproductive phase affects the reproductive structure organogenesis, and if relevant traits for adaptation can be identified. To answer these queries, the response to a same reproductive water deficit of six contrasted japonica genotypes has been analyzed under two contrasted climates differing in incident radiation, air hygrometry and temperature (greenhouse in Brazil, Sitis, and growth chamber in France, GC).Results: Under irrigation, plant growth rate was reduced in GC while crop duration was extended: the trade-offs resulted in similar plant height and biomass. From a method able to determine a posteriori the date of panicle initiation (PI), elementary processes were positioned in time, allowing to evaluate how much each process was affected, despite the diversity in phenology across genotypes. Elongation rate decreased with water deficit and was highly associated with an increase in soluble sugars in stem and flag leaf in both experiments, while starch was reduced in Sitis and negligible in GC. This unique response, however, induced a different effect across experiments on branch and spikelet formation. In short, in both experiments, maintenance of spikelet number was highly associated with maintenance of flag leaf and internode width. All variables, including branch and spikelet number, were highly affected with IAC 25 in both experiments, while variations were non-significant with Cirad 409. In addition, some other genotypes expressed a differential response between Sitis and GC, conveying a specific sensitivity to low radiation or to high air temperature. Conclusions: This study highlighted the importance of finely mapping in time elementary growth processes, thanks to PI date determination, in order to detect key traits of adaptation to abiotic stress through phenotyping across genotypes of diverse phenology. The maintenance of flag leaf width or internode diameter under a mild water deficit was highlighted here as a trait associated with the maintenance of yield components.

Sweet and biomass sorghum are expected to contribute increasingly to bioenergy production. Better understanding the impacts of the genotypic and environmental variabilities on biomass component traits and their properties is essential to optimize energy yields. This study aimed to evaluate whether traits contributing to stem biomass growth and biochemical composition at different biological scales (co)vary with the genotype and the water status in sorghum. Height genotypes were studied over two years in field conditions in southern France under two water treatments (well watered vs. 25 days' dry down during stem elongation). Main stem internode number, size, (non)structural carbohydrate, and lignin contents were measured at the end of the stress period and/or at final harvest, together with biochemical and histological analyses of the youngest expanded internode. The tallest genotypes showed the highest stem dry weights and lignin contents. Stem (structural) biomass density was positively correlated with lignin content, particularly in internode parenchyma. Stem soluble sugar and lignin contents were inversely proportional across genotypes and water conditions. Genotypes contrasted for drought sensitivity and recovery capacity of stem growth and biochemical composition. The length and cell wall deposition of internodes expanding under water deficit were reduced and did not recover, these responses being weakly correlated. Genotypic variability was pointed out in the growth recovery of internodes expanding under re-watered conditions. According to the observed genotypic variability and the absence of antagonistic correlations between the responses of the different traits to water availability, it is suggested that biomass sorghum varieties optimizing their responses to water availability in terms of growth and cell wall deposition can be developed for different bioenergy targets.