3-Methylthiopropionic Acid of Rhizoctonia solani AG-3 and Its Role in the Pathogenicity of the Fungus

Abstract

Studies were conducted to determine the role of 3-methylthioproprionic acid (MTPA) in the pathogenicity of potato stem canker, Rhizoctonia solani, and the concentrations required to inhibit growth of R. solani under laboratory and plant house-based conditions. The experiments were laid out in a completely randomized design with five treatments and five replications. The treatments were 0, 1, 2, 4, and 8 mM concentrations of MTPA. The purified toxin exhibited maximal activity at pH 2.5 and 30°C. MTPA at 1, 2, 4, and 8 mM levels reduced plant height, chlorophyll content, haulm fresh weight, number of stolons, canopy development, and tuber weight of potato plants, as compared to the control. MTPA significantly affected mycelial growth with 8 mM causing the highest infection. The potato seedlings treated with MTPA concentrations of 1.0–8.0 mM induced necrosis of up to 80% of root system area. Cankers were resulted from the injection of potato seedling stems with 8.0 mM MTPA. The results showed the disappearance of cell membrane, rough mitochondrial and cell walls, change of the shape of chloroplasts, and swollen endoplasmic reticulum. Seventy-six (76) hours after toxin treatment, cell contents were completely broken, cytoplasm dissolved, and more chromatin were seen in the nucleus. The results suggested that high levels of the toxin concentration caused cell membrane and cytoplasm fracture. The integrity of cellular structure was destroyed by the phytotoxin. The concentrations of the phytotoxin were significantly correlated with pathogenicity and caused damage to the cell membrane of potato stem base tissue.

Integrative transcriptome analysis discloses the molecular basis of a heterogeneous fungal phytopathogen complex, Rhizoctonia solani AG-1 subgroups

“…The metabolite MTPA in AG-3 plays a phytotoxic role during sheath blight because of its effect on membrane integrity in host cells 48 . Possible enzyme-encoding genes for the biosynthetic pathway of MTPA were observed in the transcriptome contigs.…”

The Evolutionary and Molecular Features of Broad Host-Range Necrotrophy in Plant Pathogenic Fungi

“…The proficiency of S. sclerotiorum to acidify host tissue has long been known; an early study demonstrated a reduction in the pH of sunflower stems to as low as four during S. sclerotiorum infection ( Marciano et al, 1983 ). Other broad host range pathogens are capable of acidifying host tissue via production of various organic acids including phenylacetic acid (PAA) and 3-methylthioproprionic acid (MTPA), produced by R. solani , and tenuazonic acid, produced by A. alternata ( Meronuck et al, 1972 ; Bartz et al, 2012 ; Kankam et al, 2016 ).…”

“…As well as the aforementioned effects on fungal virulence, some acids secreted by fungal pathogens exhibit direct phytotoxicity, a function that benefits fungi with a necrotrophic lifestyle. For example, botcinic acid, MTPA, OA, and tenuazonic acid produced by B. cinerea , R. solani , S. sclerotiorum , and A. alternata respectively, all have phytotoxic activity ( Visconti et al, 1987 ; Cutler et al, 1996 ; Kim et al, 2008 ; Kankam et al, 2016 ).…”

Improving evaluation of potato resistance to Rhizoctonia solani infection by optimizing inoculum-based method combined with toxin-based assay

“…Rhizoctonia solani produces toxin (RS toxin). The toxin is a host-selective pathogenicity determinant, meaning it only induces characteristic symptoms of corresponding hosts [22,23]. We anticipated that RS toxin could correlate with inoculum for resistance evaluation, as shown in rice pathosystem, where toxin of R. solani is a signi cantly correlated with phototoxic sensitivity and disease susceptibility [24][25].…”

“…The latter can be used for primary screening on large collection of potato germplasms before eld evaluation, which would greatly reduce the amount of work load and time consuming, therefore improve the e ciency of resistance screen.Rhizoctonia solani produces toxin (RS toxin). The toxin is a host-selective pathogenicity determinant, meaning it only induces characteristic symptoms of corresponding hosts [22,23]. We anticipated that RS toxin could correlate with inoculum for resistance evaluation, as shown in rice pathosystem, where toxin of R. solani is a signi cantly correlated with phototoxic sensitivity and disease susceptibility [24][25].…”