Response of sorghum stalk pathogens to brown midrib plants and soluble phenolic extracts from near isogenic lines

Abstract

Sorghum [Sorghum bicolor (L.) Moench] has drawn attention as potential feedstock for lignocellulosic biofuels production, and reducing lignin is one way to increase conversion efficiency. Little research has been previously conducted to assess the response of reduced lignin sorghum lines to the Fusarium stalk rot pathogens Fusarium verticillioides and Fusarium proliferatum and the charcoal rot pathogen, Macrophomina phaseolina. Loss of function mutations in either the Brown midrib (Bmr) 6 or 12 gene that both encode a monolignol biosynthetic enzyme in the pathway that produces subunits of the lignin polymer, results in reduced lignin content. Near-isogenic bmr6, bmr12, and bmr6 bmr12 lines had previously been developed, which were shown to have significantly reduced lignin content and increased levels of soluble phenolics. In the current study, these lines in two backgrounds were shown to not be more susceptible to F. verticillioides, F. proliferatum and M. phaseolina inoculations, and some bmr lines exhibited increased resistance to F. proliferatum and M. phaseolina, compared to wild-type lines. When the Fusarium stalk rot pathogen, Fusarium thapsinum, was grown on methanol soluble stalk extracts from bmr6 and wild-type plants, it grew significantly faster on medium with bmr6 extract than on wild-type extract or controls. This result suggested that factors other than soluble phenolics from the extract, such as cell wall bound phenolics or inducible defense compounds, contributed to increased resistance observed in bmr6 plants.

Low Lignin Mutants and Reduction of Lignin Content in Grasses for Increased Utilisation of Lignocellulose

“…However, negative impacts on agronomical traits have also been reported, such as reduced yield in grain sorghum [148] and biomass in forage sorghum [147], and thus do not affect susceptibility to disease [18]. However, a recent study concludes that weather conditions have a greater impact and in some cases free phenolic compounds even act as a defence mechanism, depending on the diseases reviewed [152].…”

Large scale genome-wide association study reveals that drought induced lodging in grain sorghum is associated with plant height and traits linked to carbon remobilisation

“…Twelve of the 21 genes involved in lignin biosynthesis (Bout and Vermerris, 2003; Jun et al , 2017, 2018, Saballos et al , 2012, 2009, Sattler et al , 2009, 2017, Walker et al , 2013, 2016; Wang et al , 2017) were located within genomic regions associated with lodging in this study (Figure 2), representing a significant enrichment (χ 2 test, p value = 0.008). Lodging resistant sorghum generally have more lignification, both in the number of cells with lignified walls and in the degree of lignification in the epidermis, sub-epidermis, and vascular bundles (Schertz and Rosenow, 1977).…”

“…bmr lines) can provide the same level of or higher resistance to Fusarium spp. and Macrophomina phaseolina than sorghum lines with normal lignin content (Funnell-harris et al , 2010, 2014, 2017, 2018, 2019). This might be due to the inhibition the infection of stalk rotting pathogens by cell-wall-bound phenolic compounds from monolignol biosynthesis that can induce defensible pathways (Funnell-harris et al , 2017).…”

“…and Macrophomina phaseolina than sorghum lines with normal lignin content (Funnell-harris et al , 2010, 2014, 2017, 2018, 2019). This might be due to the inhibition the infection of stalk rotting pathogens by cell-wall-bound phenolic compounds from monolignol biosynthesis that can induce defensible pathways (Funnell-harris et al , 2017). Therefore, the role of lignin in lodging resistance may act in two ways, either by providing mechanical support to the stem (Bashford et al , 1976) or by restricting the infection of stalk rotting pathogens.…”

“…Brown vertical bars to the right of each chromosome marked as “LDG” represent the locations of QTL previously detected for lodging (Kebede et al , 2001; Murray et al , 2008; Srinivasa Reddy et al , 2008); the black bars indicate the location of a QTL previously reported for charcoal rot and/or Fusarium stalk rot (Srinivasa Reddy et al 2008; Adeyanju et al 2015). The location of genes in the lignin biosynthesis pathways that co-located with lodging QTL detected in this study are highlighted in green to the right of each chromosome, and those that did not co-locate with lodging QTL are highlighted in blue (Bout and Vermerris 2003; Saballos et al 2009, 2012, Sattler et al 2009, 2017, Walker et al 2013, 2016, Jun et al 2017, 2018; Wang et al 2017). The location of the recently cloned Dry gene is highlighted in red (Zhang et al 2018).…”