Involvement of Bacterial Siderophores in the Remedy of Lime‐induced Chlorosis in Peanut

Abstract

AbstractA Pseudomonas putida strain isolated from peanut (Arachis hypogaea L.) roots excreted yellow‐green fluorescent siderophores (pigments) when grown under Fe‐deficient conditions. The pigments were purified in their Fe complex form. Chromatography yielded eight peaks, the first two representing >90% of the total. Physico‐chemical characteristics of the materials exhibiting these two peaks were similar to those of the pseudobactin‐pyoverdine class of siderophores. In two growth chamber experiments peanut plants grown on a highly calcareous soil were able to use the Fe from unpurified Fe‐siderophore produced by P. putida cultures. When supplied with 11 mg Fe kg−1 soil as Fe‐siderophore the chlorophyll concentration in the leaves was 75% of that of FeEDDHA (ethylenediamine di‐o‐hydroxyphenylacetic acid)‐treated plants. Control plants that were not fertilized with Fe contained only 35% chlorophyll of that of FeEDDHA‐treated plants. Nonferrated siderophores were ineffective in correcting Fe deficiency. Relative chlorophyll concentration in the leaves of the treatment supplemented with Fe‐siderophore and bacterial cells was similar to that of applications that did not contain bacterial cells. In a second experiment, 100% remedy of the deficiency was achieved when 19 mg Fe kg−1 soil as Fe‐siderophores was applied in comparison to 1.2 mg Fe kg−1 soil as FeEDDHA. The degree of remedy of chlorosis was independent on the frequency of application (two or four times a month). In these treatments total bacterial and fluorescent pseudomonad counts [colony‐forming units (cfu) g−1 dry roots] were significantly higher than in the unfertilized and FeEDDHA treatments. The level of DTPA (diethylenetriam‐inepentaacetic acid) extractable Fe at the end of the growth period in both experiments was significantly higher in Fe‐siderophore amended soils than in FeEDDHA‐treated soils. In a third experiment, the siderophore Ferrioxamine B (FOB) was used as a source of Fe. Iron applications of 22.5 and 45 mg Fe kg−1 soil as FOB were required to reach 70 and 97%, of the chlorophyll concentration of the FeEDDHA‐treated plants, respectively. It was concluded that bacterial siderophores may serve as a remedy to lime‐induced chlorosis in plants grown in calcareous soils.