Soybean seed sugars: A role in the mechanism of resistance to charcoal rot and potential use as biomarkers in selection

Authors: Bellaloui, Nacer; Mengistu, Alemu; Smith, James - Rusty; Abbas, Hamed; ACCINELLI, CESARE - University Of Bologna, Italy; SHIER, THOMAS - University Of Minneapolis

Submitted to: Plants
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/10/2023
Publication Date: 1/14/2023
Citation: Bellaloui, N., Mengistu, A., Smith, J.R., Abbas, H.K., Accinelli, C., Shier, W.T. 2023. Soybean seed sugars: A role in the mechanism of resistance to charcoal rot and potential use as biomarkers in selection. Plants. 12:1-14. https://doi.org/10.3390/plants12020392.
DOI: https://doi.org/10.3390/plants12020392

Interpretive Summary: Charcoal rot is a major disease of soybean that causes significant yield loss and poor seed quality. Currently, there are no resistant soybean cultivars in the market, and physiological and genetic defense mechanisms controlling this disease are not known. Therefore, the objective of this research was to investigate the role and responses of soybean seed sugars in moderately resistant (MR) and susceptible (S) soybean genotypes to charcoal rot. A two-year field experiment was conducted in 2012 and 2013 under irrigated (IR) and non-irrigated (NIR) in Jackson, TN, USA. The results showed that both MR and S genotypes showed a wide range of sugar levels. The MR genotypes had the ability to maintain higher levels of sucrose, glucose, and fructose (desirable sugars for taste and flavor) under NIR conditions where the disease was more severe. The S genotypes showed, generally, higher levels of stachyose (undesirable and considered anti-nutritional components, causing flatulence in monogastric animals), and lower levels of sucrose, glucose, and fructose under IR and NIR. The response of S genotypes with higher levels of stachyose and lower sucrose, glucose, and fructose under NIR conditions compared with those of MR genotypes may reflect the possible role of these sugars in the defense mechanism to charcoal rot in soybean. The ability to maintain higher levels of sucrose, glucose, fructose under IR and NIR conditions in MR genotypes reflects healthier xylem and phloem tissue conducting system and active sugar enzymes. This research provides new knowledge on seed sugars and further helps scientists understand the impact of charcoal rot and irrigation on seed sugars, using moderately resistant and susceptible genotypes.

Technical Abstract: Charcoal rot, caused by the pathogen Macrophomina phaseolina, is a major disease of soybean that results in a significant yield loss and poor seed quality. The use of agricultural practices of crop rotation, biological control, fungicide, irrigation, and seed treatment had no effects in controlling the disease. The disease is believed to infect plants from soil through the roots by unknown toxin-mediated mechanism. Currently, there is no resistant soybean cultivar in the market, and mechanisms of resistance of soybean to charcoal rot are still unknown. Therefore, the objective of this research was to further investigate the role of seed sugars (sucrose, raffinose, stachyose, glucose, and fructose) in the defense mechanism of soybean to charcoal rot using seven moderately resistant (MR) and six susceptible (S) genotypes grown under irrigated (IR) and non-irrigated (NIR) conditions. A two-year field experiment was conducted in 2012 and 2013. The results showed that both MR and S genotypes showed a wide range of sugar levels. The main findings in this research were that, generally, MR genotypes had the ability to maintain higher levels of sucrose, glucose, and fructose under NIR conditions where the disease was more severe. Susceptible genotypes showed higher level of stachyose, and lower levels of sucrose, glucose, and fructose under NIR. The response of S genotypes with higher levels of stachyose and lower sucrose, glucose, and fructose under NIR conditions compared with those of MR genotypes may reflect the possible role of these sugars, especially stachyose, in the defense mechanism to charcoal rot. This was observed in 7 out of 7 MR genotypes and 5 out of 6 S genotypes in 2012; and 5 out of 7 MR genotypes and 5 out of 6 S genotypes in 2013. The results also showed that under NIR consistent and significant (P=0.05) negative correlations between stachyose vs. sucrose, glucose, or fructose; significant (P=0.05) negative correlations between raffinose vs. sucrose, glucose, or fructose; and significant (P=0.05) positive correlations between sucrose vs. glucose or fructose. This research provides new knowledge on seed sugars and helps understand the impact of charcoal rot and irrigation on seed sugars in moderately resistant and susceptible genotypes.