Antimicrobial activity of phosphites against different potato pathogens

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 byPhytophthora infestans, Fusarium solaniandRhizoctonia solaniwhen 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 infestanswas the most inhibited pathogen by all phosphites, followed byStreptomyces scabies, whileRhizoctonia solaniandFusarium solaniwere 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 ofF. solanispores showed to be fungistatic rather than fungicidal.Phosphite besitzen eine geringe Umwelttoxizität sowie eine gute direkte und indirekte Wirkung gegenüber Oomyceten- Pathogenen von Pflanzen. Wir zeigen hier, dass sie ebenfalls die durchPhytophthora infestans,Fusarium solaniandRhizoctonia solaniverursachten Symptome an Kartoffeln nach einer Knollenbehandlung vermindern. Vier Kartoffelpathogene wurden mit dem Ziel untersucht, die direkte Wirkungsweise von Calcium-, Kalium- und Kupfer-Phosphiten (CaPhi, KPhi und CuPhi) auf die Erreger sowie die chemischen Determinanten ihrer direkten antimikrobiellen Aktivität zu ermitteln. Weiterhin wurde die Wirkung von Azidifizierung und Ionenstärke nach Zugabe von Phosphiten auf antimikrobielle, fungizide und fungistatische Aktivität untersucht. Die Phosphite beeinträchtigten das Wachstum aller untersuchten Erreger.Phytophthora infestanswurde durch alle verwendeten Phosphite am stärksten inhibiert, gefolgt vonStreptomyces scabies, während die Wirkung aufRhizoctonia solaniundFusarium solanigeringer war. CuPhi besaß die höchste antimikrobielle Aktivität gegenüber den vier untersuchten Pathogene, gefolgt von den ähnlich wirksamen CaPhi und KPhi. Die Wirkung von CuPhi und CaPhi kann zum Teil durch die Ansäuerung der verwendeten Medien erklärt werden. Die mit KPhi erhaltenen Ergebnisse zeigen dagegen, dass das Phosphit-Anion selbst antimikrobiell wirksam ist. Die Zunahme der Ionenstärke nach Phosphit-Applikation war nicht für die antimikrobielle Wirkung verantwortlich. Die Beeinträchtigung der Sporenkeimung vonF. solanizeigte, dass die Wirkung der Phosphite eher fungistatisch als fungizid ist

Analysing the expression of genes associated with induced resistance in potato plants treated with phosphites

Phosphites (Phi) have the ability to protect plants against different pathogens, both through a direct effect in oomycete metabolism and by an indirect effect stimulating the plant´s natural defence responses. We have previously shown that KPhi foliar application to potato plants resulted in different protection levels against Phytophthora infestans depending on dose and plant age at application time. In order to identify genes that are involved in induced resistant in plants treated with KPhi, we analyzed by RT PCR, the time course of transcript levels of two genes which encode predicted transcription factors involved in pathogen perception and defence gene expression. Preliminary results showed that WRKY and NPR1 were differentially induced in plants both treated with Phi and infected with Phytophthora infestans, showing an earlier and highest induction than infected plants non treated with Phi. These results may allow us to hypothetize that Phi treatment might trigger a fast mechanism to protect potato plants to pathogen infections

(Super)Gelators derived from push-pull chromophores: Synthesis, gelling properties and second harmonic generation

The present work takes advantage of the self-assembly process occuring along organogelation, to organize Second Harmonic Generation (SHG) active chromophores. To do so, three push-pull chromophores endowed with a dodecyl urea chain were synthesized and characterized. Their organogelating properties were studied in a wide range of solvents. Despite similar architectures, these derivatives exhibit very different gelling properties, from supergelation to absence of gelling ability. The utilization of the Hansen solubility parameters allows for observing clear relationships between the gelled solvents and critical gelation concentrations. By evaporating the solvents from the organogels, xerogel materials were prepared and systematically studied by means of optical and electron microscopies as well as SHG microscopy. These studies demonstrate the critical role of the solvent over materials structuring and allow generalizing the approach exploiting organogelation as a structuring tool to spontaneously organize push-pull chromophores into SHG-active materials

Effect of foliar applications of phosphite on post-harvest potato tubers

The utilization of phosphites (Phi) could be considered as another strategy to be included in integrated disease management programmes to reduce the intensive use of fungicides and production costs. The aim of the present work was to analyze whether the beneficial effects of phosphite treatment previously observed in potato plants grown under greenhouse conditions, were reflected after harvest of field grown potatoes, both in disease protection and in yield. In addition, biochemical compounds possibly involved in induced defence responses by Phi, like phytoalexins, pathogenesis related proteins and oxidative stress enzymes were measured. Foliar applications of KPhi to field grown crops resulted in post-harvest tubers with a reduced susceptibility to Phytophthora infestans, Fusarium solani and Erwinia carotovora infections, suggesting that this compound induced a systemic defence response. An increase in phytoalexin content in P. infestans inoculated tubers obtained from Phi-treated plants suggests their participation in the defence response. Chitinase content increased 72h after wounding or inoculation with P. infestans in tubers from KPhi-treated plants compared to wounded or infected tubers from non-treated plants. Contrary to this, the isoforms of β-1,3-glucanases analyzed did not increase in the tubers of Phi-treated plants. The increment in peroxidase and polyphenol oxidase activities indicated that these enzymes could be part of the Phi defence mechanism. No negative effects were observed in potato yield at harvest, measured as total tuber weight and dry matter, after foliar KPhi treatment. This suggests that the energetic cost involved in the defence response activation would not be detrimental to plant growth

Promoting Spontaneous Second Harmonic Generation through Organogelation

An organogelator based on the Disperse Red NLO-phore was synthesized according to a simple and efficient three-step procedure. The supramolecular gel organization leads to xerogels which display a spontaneous second harmonic generation (SHG) response without any need for pre-processing and this SHG activity appears stable over several months. These findings, based on an intrinsic structural approach are supported by favorable intermolecular supramolecular interactions, which promote a locally non-centrosymmetric NLO-active organization. This is in sharp contrast with most materials designed for SHG purposes, which generally require the use of expensive or heavy-to-handle external techniques for managing the dipoles alignment

Differentially expressed genes in potato sprouts after potassium phosphite application

We are studying the role of phosphites in disease control management, yield and potato tuber quality. In brief, our previous results showed a number of promising properties associated with these compounds. When we applied potassium phosphites (KPhi) at 3 litre $latex ha^{-1}$ to seed tubers immediately after cutting, this promoted early emergence, an increased in stem number and diameter, early tuber initiation and an increased in the number of tubers per plant. In addition to these physiological effects, phosphite treatment also resulted in greater resistance in seed tubers to Phytophthora infestans, Fusarium solani and Rhizoctonia solani. In order to understand the mechanisms which regulate these responses, we analyzed the changes in gene expression in tubers seeds at early stage of sprouting after KPhi treatment. Preliminary results of microarray analysis from potato sprouts treated or not with KPhi, showed that 26 genes were upregulated in the treated ones. These genes were classified into 5 groups: plant defense, metabolism, abiotic stress, transcription factors and unknown genes. We performed semiquantitative RT-PCR assays of some of these genes to validate the results. Interestingly one of these genes was CULLIN 1, involved in jasmonic acid mediated signaling pathway. This result may support the hypothesis that phophites could be involved in triggering IR (induced resistant)