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

The Seagram Ctr. for Soil and Water Sciences

Y. Hadar

Dep. of Plant Pathology and Microbiology, The Hebrew Univ. of Jerusalem, Rehovot 76100, Israel

* Corresponding author.

ABSTRACT

A 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.

Received for publication July 17, 1987.

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