Terminal drought effect on sugar partitioning and metabolism is modulated by leaf stay-green and panicle size in the stem of sweet sorghum (Sorghum bicolor L. Moench)

Thierry Klanvi Tovignan,Cyril Diatta,Delphine Luquet,Armelle Soutiras,Hubert Adoukonou-Sagbadja,Ndiaga Cisse,Anne Clément-Vidal

doi:10.1186/s43170-020-00003-w

Abstract

BackgroundThe benefits of leaf stay-green for maintaining grain filling in sorghum under drought was largely demonstrated. However, its role in the stability of a dual production (grain, stem sugar) in tall sweet sorghum remains to be elucidated. This study aimed to analyze the impact of a post-anthesis drought on sugar accumulation along stem internodes in sweet and tall West-African sorghum with variable leaf stay-green and grain yield abilities.MethodsFour accessions with similar phenology were studied in two consecutive years in the field at the National Agronomic Research Centre (CNRA) of Bambey (Senegal, West Africa) under two post-anthesis water treatments (irrigated, non-irrigated). Plant morphology, stem sugar related traits, grain production, and plant leaf area (PLA) variation were assessed. Carbohydrate contents (sucrose, hexoses, starch) were determined during grain filling in the whole stem juice and at three internode levels: bottom, median, top. Analysis of variance was performed to test post-anthesis water treatment, accession, organ, year effects and their interactions on the studied traits.ResultsPanicle dry weight (PDW) was not affected by drought, but strongly varied among years and accessions. The PDW/PLA ratio was negatively correlated with the variation of sucrose and hexoses at the three internodes levels. This carbohydrates reduction was mainly influenced by the PDW. The bigger the panicle the higher the carbohydrates remobilization from the stem to panicle for grain filling. This was mainly shown on accessions G3 and G11 which exhibited low stay green ability. However, G10 with low PDW/PLA ratio and showing higher stay green ability, exhibited a low reduction of total soluble sugars and sucrose and inversely higher increase of hexoses mainly at the median internode.ConclusionsThis ability to better maintain green leaf area and high hexoses in the stem under post-flowering drought could be an osmoregulation mechanism to adapt to drought. Therefore, stay-green is an important trait to consider for sweet sorghum breeding and particularly in the objective of developing dual purpose varieties in drought prone environments.

Highlights

Sweet sorghum is able to accumulate remarkable amount of soluble sugars in the stem while ensuring grain filling and for this reason can be used as a dual purpose crop (Rutto et al 2013)
By comparing two water treatments on twelve sweet, tall grain sorghum accessions, Tovignan et al (2016) pointed out that grain filling was not affected by a post-flowering drought, whereas stem sugar content was slightly reduced, to an extent positively correlated to the reduction rate of green leaf area between flowering and maturity. These results suggest that in sweet and tall sorghum types, drought impact can be buffered by the soluble sugars stored in the stem that, if associated to a stay-green aptitude, may ensure the maintenance of both grain and stem sugar productions, which might be of high agronomic value
Panicle production, plant height and post‐anthesis plant leaf area variation Figure 3 presents plant traits related to carbohydrates concentration in whole stem juice at dough grain stage, plant height, panicle dry weight measured at maturity and post-anthesis green leaf area variation

Summary

Introduction

Sweet sorghum is able to accumulate remarkable amount of soluble sugars in the stem while ensuring grain filling and for this reason can be used as a dual purpose crop (Rutto et al 2013). Stem non-structural carbohydrates are constituted of sucrose, glucose, fructose (Almodares et al 2007; Qazi et al 2012) and starch Their concentration in the stem depends on the genotype, the environment and plant phenological stage (Gutjahr et al 2013). Depending on crop cycle duration and internode rank, internode sucrose concentration can be almost completed at flowering or still increase until maturity At this stage, sucrose concentration is almost constant along the stem, with a slight decrease in top internodes (Gutjahr et al 2013). This study aimed to analyze the impact of a post-anthesis drought on sugar accumulation along stem internodes in sweet and tall West-African sorghum with variable leaf stay-green and grain yield abilities

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Conclusion