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

Abstract

Background: The benefts of leaf stay-green for maintaining grain flling in sorghum under drought was largely dem‐ onstrated. 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. Methods: Four accessions with similar phenology were studied in two consecutive years in the feld 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 flling 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 efects and their interactions on the studied traits. Results: Panicle dry weight (PDW) was not afected 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 infuenced by the PDW. The bigger the panicle the higher the carbohydrates remobilization from the stem to panicle for grain flling. 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. Conclusions: This ability to better maintain green leaf area and high hexoses in the stem under post-fowering 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.