Silicon‐mediated cell wall modifications of sorghum root exodermis and suppression of invasion by fungus Alternaria alternata

Abstract

Silicon (Si) is an element frequently associated with remedial properties in plant defence against various biotic stressors. Application of Si in plant–fungus interactions offers an intriguing research subject for its potential to reduce fungal disease‐related losses in agriculture. However, Si‐mediated changes in the plant metabolism must be first elucidated. The present microscopic study explores the effect of Si amendment on ultrastructural, cytological and anatomical aspects of the interaction between Sorghum bicolor ‘Gadambalia’ primary roots and the necrotrophic fungus Alternaria alternata. Bright‐field microscopy observations revealed that Si supplementation helped sorghum seedlings to restrict the growth of A. alternata, possibly by cell wall modifications of the root exodermis, limiting further fungal invasion. Ultrastructural analyses by transmission electron microscopy showed intense vesiculation in exodermal cells of inoculated roots. Fluorescence microscopy with suberin‐ and phenolic‐specific staining indicated a significant enhancement in the deposition of these substances in exodermal cell walls upon Si supplementation. The increased accumulation of phenolics in Si‐supplied plants was also confirmed by Raman spectroscopy. In conclusion, Si amendment seemed to alleviate the negative effect of A. alternata infection in sorghum roots, which is shown by restricted distribution of fungal hyphae in root tissues probably due to Si‐mediated deposition of suberin and phenolics in the exodermis.

Silicon mediates the changes in physiological performance, nutrient uptake, root colonization morphology and secondary metabolite activity in rubber rootstock seedlings (Hevea brasiliensis) inoculated with Rigidoporus microporus

“…This observation is consistent Bathoova et al (2018) where Si amendment reduced the harmful effect of Alternaria alternata infection in sorghum roots, as seen by the limited distribution of fungal hyphae in root tissues. This research could contribute towards rubber rootstock selection that is more resistant to WRD and produce high quality rubber clones.…”

“…As shown in tomato and wheat, Si supplementation leads to a significant increase in the concentration of phenolics (Araújo et al, 2019; Fan et al, 2018). The antifungal phenolic compounds are important in inhibiting various fungal pathogens (Bathoova et al, 2018). In the current study, the antifungal activity of phenolic compounds extracted from Si‐treated plants revealed an inhibitory effect against R .…”

Silicification of Root Tissues

“…These biotic stressors cause retardation of growth, yield production, and shortening of lifespan in hosts. According to the experimental studies, Si in plant roots can alleviate the stress after bacterial [140][141][142], fungal [143][144][145], insect [146,147], nematode [148,149], and plant [150,151] attack, but also stress from auto-toxicity of the same plant [152]. The level of its beneficial effect is Si concentration dependent.…”

“…There are many studies which prove that Si-amendment can significantly reduce disease incidence and severity in the roots of plants infected by fungi [143][144][145]158,[163][164][165][166][167]. Cucumber (Cucumis sativus) and banana (Musa acuminata) plants fertilized by Si and threatened by Pythium ultimum and Fusarium oxysporum, respectively, increased chitinase and beta-1,3-glucanase activity and were able to degrade the body of a pathogen [144,167].…”

“…Roots also play an important role in delaying the initial infection and movement of the fungal pathogen from roots to the aboveground part of plants [166]. The invasion and distribution of necrotrophic fungus Alternaria alternata through the root tissues of sorghum (Sorghum bicolor) was restricted at the level of the exodermis, probably due to silicon mediated modifications of cell walls via deposition of phenolics and suberin [145]. However, it needs to be noted that plants unable to take up silicon sufficiently, such as poinsettias, cannot inhibit the onset of symptoms and severity of fungal attack [168].…”