Antimicrobial activity of phosphites against different potato pathogens

Abstract

Phosphites have low-toxicity on the environment and show high efficacy in controlling oomycete diseases in plants, both by a direct and an indirect mechanism. We have shown that they are also effective in reducing disease symptoms produced by Phytophthora infestans, Fusarium solani and Rhizoctonia solani when applied to potato seed tubers. To gain better insight into the direct mode of action of phosphites on different potato pathogens, and to ascertain chemical determinants in their direct antimicrobial activity, four potato pathogens were assayed with respect to sensitivity toward calcium, potassium and copper phosphites (CaPhi, KPhi and CuPhi, respectively). The influence of acidification and ionic strength changes after Phi addition on the antimicrobial activity, and the fungicidal or fungistatic activity, were evaluated. Results showed that phosphites were able to inhibit growth of all pathogens. Phytophthora infestans was the most inhibited pathogen by all phosphites, followed by Streptomyces scabies, while Rhizoctonia solani and Fusarium solani were less inhibited. CuPhi had the highest antimicrobial activity against the four pathogens analysed, and CaPhi and KPhi showed similar antimicrobial activities. Inhibitions by CuPhi and CaPhi could be partially explained by acidification of the media. However, results obtained with KPhi demonstrated that the phosphite anion has antimicrobial activity itself. The increase in ionic strength after Phi addition was not important in the antimicrobial activity of Phi. The activity of phosphites on germination of F. solani spores showed to be fungistatic rather than fungicidal.

Dissecting Phosphite-Induced Priming in Arabidopsis Infected withHyaloperonospora arabidopsidis

“…Phi is extensively used to protect plants against diseases mainly caused by oomycetes (Lobato et al, 2010). The mode of action of Phi is unknown and remains controversial, given evidence for both direct and indirect modes of action (Guest and Grant, 1991).…”

Defense Activation In Soybean By The Action Of Amino Acids And Micronutrient Against Phakopsora pachyrhizi

“…Its effects against pathogens are characterized by the inhibition of the oxidative phosphorylation of the oomycetes, retarding their mycelial growth and suppressing their germination and sporulation (LOBATO, et al, 2010, SILVA, 2011DIANESE & BLUM, 2010;PERUCH ET AL., 2007). However, its use in relation to other groups of pathogens is not always observed strongly, especially in relation to the parasites classified as biotrophic as Phakopsora pachyrhizi.…”

Evaluation of in vitro inhibition of mycelial growth of Fusarium solani f. sp. piperis by different products in Brazil

“…Potassium phosphite was tested against Penicillium expansum, which causes postharvest blue mold infections on apple fruits; this compound completely inhibited the mycelial growth (Amiri and Bompeix, 2011). In a study made by Lobato et al (2010), phosphate exerted a fungicidal effect on pathogens of potatoes: F. solani, Rhizoctonia solani, and Streptomyces scabies. According to Guest and Grant (1991), phosphites inhibit the growth of pathogens in plants via a complex mechanism of action.…”