Detoxification of oxalic acid by Pseudomonas fluorescens strain PfMDU2: Implications for the biological control of rice sheath blight caused by Rhizoctonia solani

Abstract

Rhizoctonia solani isolates varying in their virulence were tested for their ability to produce oxalic acid (OA) in vitro. The results indicated that the virulent isolates produced more OA than the less virulent isolates. In order to isolate OA-detoxifying strains of Pseudomonas fluorescens, rhizosphere soil of rice was drenched with 100 mM OA and fluorescent pseudomonads were isolated from the OA-amended soil by using King's medium B. These isolates were tested for their antagonistic effect towards growth of R. solani in vitro. Among them P. fluorescens PfMDU2 was the most effective in inhibiting the mycelial growth of R. solani. P. fluorescens PfMDU2 was capable of detoxifying OA and several proteins were detected in the culture filtrate of PfMDU2 when it was grown in medium containing OA. To investigate whether the gene(s) involved in OA-detoxification resides on the plasmids in P. fluorescens PfMDU2, a plasmid-deficient strain of P. fluorescens was generated by plasmid curing. The plasmid-deficient strain (PfMDU2P-) failed to grow in medium containing OA and did not inhibit the growth of R. solani. Both PfMDU2 and PfMDU2P- were tested for their efficacy in controlling sheath blight of rice under greenhouse conditions. Seed treatment followed by soil application of rice with P. fluorescens strain, PfMDU2, reduced the severity of sheath blight by 75% compared with the control, whereas PfMDU2P- failed to control sheath blight disease.

Chemical characterization of Agaricus bohusii, antioxidant potential and antifungal preserving properties when incorporated in cream cheese

“…This organic acid has been employed in food additives and in polymer and pharmaceutical industries. During a process of pathogenesis by some fungi, oxalic acid is produced while their mycelium is in advancement, in order to make the plant more susceptible (Nagarajkumar et al, 2005). Thus, the production of this organic acid by fungi could have toxicity effects.…”

A comparative study of chemical composition, antioxidant and antimicrobial properties of Morchella esculenta (L.) Pers. from Portugal and Serbia

“…The first mentioned organic acid might have toxicity effects (Nagarajkumar, Jayaraj, Muthukrishnan, Bhaskaran, & Velazhahan, 2005), while fumaric acid possesses interesting biological effects such as anti-inflammatory, neuroprotective, chemopreventive and antimicrobial activity (Baati, Horcajada, Gref, Couvreur, & Serre, 2011). Malic acid was also found in SP, while quinic and citric acids were only found in SS ( Table 2).…”

Oxalic acid-induced resistance toRhizoctonia solaniin rice is associated with induction of phenolics, peroxidase and pathogenesis-related proteins

“…Control of sheath blight disease through genetic resistance is not possible at present because no rice cultivars with high levels of resistance to R. solani are commercially available (Mew et al 2004). Control of this disease depends mostly on fungicides, although considerable efforts have been made in developing biocontrol methods (Mew and Rosales 1986;Vidhyasekaran and Muthamilan 1999;Nagarajkumar et al 2005;Someya et al 2005). Activation of the plant's own defense mechanisms with the aid of synthetic molecules is a new technology for plant disease management (Kogel and Langen 2005).…”