Genetics of tolerance to iron chlorosis in rice

Genetics of tolerance to iron chlorosis was investigated in eight crosses involving parents distinctly different in their level of tolerance. The segregating populations with parents and F₁s were screened under actual stress conditions in the field. Also, selected crosses were studied for Fe³⁺ uptake capacity. Tolerance/moderate tolerance to Fe chlorosis was dominant over susceptibility and it was controlled by two sets of nonallelic genes with complementary interaction. Gene Ic ₁ has been found to be basic and in complementation with Ic ₃ it confers tolerance. Likewise, Ic ₂ with Ic ₄ confers tolerance. The basic genes Ic ₁ and Ic ₂ are nonallelic and, in the absence of their respective complementary genes Ic ₃ and ₄ , ineffective, which results in susceptibility. Of tolerant cultivars, ARC 10372 and Cauvery have been tentatively assigned the genotype of Ic ₁ , Ic ₂ , Ic ₃ , Ic ₄ , and moderately tolerant IET 7613, Prasanna and Akashi Ic ₁ , ₂ Ic ₃ Ic ₄ . The susceptible ARC 5723 has been assigned Ic ₁ , ₂ , Ic ₃ , Ic ₄ , and IET 9829, Ic ₁ , ₂ Ic ₃ Ic ₄ . IET 7614 is susceptible, due to the presence of inhibitory genes I-Ic ₁ , I-Ic ₂ together with ic ₁ pt>, ic ₂ , Ic ₃ , Ic ₄ . Further, the gene Pc for purple coleoptile shows linkage with one of the complementary genes with a crossover value of 15.26%, while the gene(s) for seedling height Ts with Ic ₁ with a crossover value of 1.7%. It is possible that the gene(s) for iron chlorosis tolerance might belong to the second linkage group, where genes for purple leaf were located.     

Long-term effectiveness of vivianite in reducing iron chlorosis in olive trees

Iron (Fe) chlorosis is common in olive (Olea europaea L.) trees growing on highly calcareous soils in Southern Spain, where generally causes reduction in yield, size and commercial value of the olives. The objective of this research was to study the effectiveness of synthetic vivianite (Fe₃(PO₄)₂H₂O) to reduce Fe chlorosis in olive. Experiments were established in three orchards with cultivars `Hojiblanco', `Manzanillo', and `Picual'. The design was a randomised block design with two or three treatments (control with no Fe fertiliser and vivianite at one or two rates). A vivianite suspension (0.05 kg dm<sup>–3</sup> water) was injected into the soil at 10–20 points around the tree at the depth of maximum root density (25–35 cm). The rates (and times of application) were 0.5 and 1 kg tree<sup>–1</sup> for `Hojiblanco' (March 1997), 1 kg tree^–1 for `Manzanillo' (March 1998), and 2 kg tree<sup>–1</sup> for `Picual' (March 1998). The leaf chlorophyll content index (CCI) was estimated on the youngest expanded leaves by means of a Minolta apparatus (SPAD units). The colour index of the olives was estimated by visual comparison with a scale ranging from 1 (pale yellow) to 8 (normal green). For the period studied (July 1997–November 1999), the CCI of fertilised trees was, in general, significantly higher than that of control trees, and so was the case with the olive colour index. Olive yield, measured in the experimental fields with `Hojiblanco' (in 1999) and `Manzanillo' (in 1998 and 1999), was higher for the fertilised than for the control trees but differences were only significant in 1999. These results suggest that vivianite is effective to reduce Fe chlorosis for more than two seasons. Such effectiveness is probably due to the poorly crystalline Fe(III) oxides (which are good sources of Fe to plants) that result from the slow oxidation and incongruent dissolution of vivianite.     

Relationship between iron chlorosis and alkalinity in Zea mays

Mengel, K. and Geurtzen, G. 1988. Relationship between iron chlorosis and alkalinity in Zea mays . - Physiol. Plant. 72: 460–465.
Maize ( Zea mays L. cv. Anjou 21) grown in nutrient solution with Fe-EDTA and with nitrate as the sole nitrogen source showed typical Fe-chlorosis symptoms after a growth period of 14–21 days. Alkalinity in roots, stems and leaves of the chlorotic plants was high. Transferring the chlorotic plants from the nitrate-containing nutrient solution to a solution of (NH₄)₂SO₄ resulted in a regreening of leaves within 2–3 days which was associated with a decrease in solution pH, a decrease in alkalinity of plant parts, a translocation of Fe from roots to tops and a release of Fe into the outer solution. Similar effects were obtained when Fe chlorotic plants were transferred to a dilute HO solution with pH 3.5.
Spraying chlorotic leaves with indoleacetic acid or with fusicoccin led also to a regreening of leaves without having a major effect on leaf alkalinity.
Interpretation of the experimental results is based on the assumption that nitrate as sole N source leads to a high pH level in the apoplast resulting in the precipitation of Fe compounds, probably Fe oxide hydrate. Ammonium nutrition has the reverse effect since it lowers the apoplast pH and this can result in the dissolution of Fe compounds. Application of indoleacetic acid as well as fusicoccin supposedly stimulates the proton pumps in the plasmalemma of the leaf tissue. The resulting decrease in apoplast leaf pH in the microenvironment also leads to a dissolution of Fe compounds in the apoplast and thus promotes the uptake of Fe by the symplasm.     

Foliar fertilization to control iron chlorosis in pear (Pyrus communis L.) trees

The effectiveness of foliar fertilization to re-green chlorotic leaves in iron-deficient pear trees has been studied. Trials were made to assess the influence of (i) the level of Fe deficiency, (ii) the leaf surface treated (adaxial or abaxial), and (iii) two different surfactants, L-77 and Mistol. Treatments were ferrous sulphate alone, ascorbic, citric and sulphuric acids, applied either alone or in combination with ferrous sulphate, Fe-DTPA and water as a control. Solutions were applied with a brush and leaves were treated twice each year. None of the treatments caused a full recovery from Fe deficiency chlorosis. Treatments containing Fe caused the largest re-greening effects, and FeSO₄ had a similar re-greening effect to Fe(III)-DTPA. Increases in leaf Chl were more pronounced with abaxial leaf surface applications and in severely deficient leaves. Using Fe(III)-DTPA in foliar sprays does not seem to be justified, since their effects are not better than those of FeSO₄. The joint use of Fe(III)-DTPA and L-77 and that of FeSO₄ and citric acid do not seem to be suitable. With a single foliar application, FeSO₄ combined with acids gave slightly better results than FeSO₄ alone. Acidic solution applications without Fe may be effective in alleviating chlorosis in some cases, especially in the case of citric acid. In the current state of knowledge, foliar fertilization cannot offer yet a good alternative for full control of Fe chlorosis, although its low environmental impact and cost make this technique a good complementary measure to soil Fe-chelate applications and other chlorosis alleviation management techniques. Abbreviations: Chl – chlorophyll; EDDCHA – ethylenediamine di(5-carboxy-2-hydroxyphenylacetic) acid; EDDHA – ethylenediamine di(o-hydroxyphenylacetic) acid; EDDHMA – ethylenediamine di(o-hydroxy-p-methylphenylacetic) acid; EDDHSA – ethylenediamine di(2-hydroxy-5-sulfophenylacetic) acid     

Changes in DTPA-iron and management of iron chlorosis in rice nurseries

Summary On a Typic Ustochrept soil incorporation of 10 tons/ha of a green manure plus submergence for 10 days followed by raising upland nursery checked iron chlorosis. In contrast, presubmergence with and without FYM and iron sulfate or pyrite were a failure. Nor weekly sprays with 3.0% iron sulfate were found very effective. The success of green manure plus submergence was associated with the mobilization of soil iron as a result of intense reduction and its subsequent retention in available form at a sufficient high level during the growth of upland nursery.     

Evaluation of early generations for iron chlorosis in relation to productivity in groundnut (Arachis hypogaea L.)

Five popular but iron-inefficient cultivars were crossed with three efficient genotypes and both parents and F₁s were evaluated for iron-efficiency in potted calcareous and noncalcareous soil. The iron-efficient genotypes were dark green or green in both noncalcareous and calcareous soils whereas inefficient types were light green to yellow in calcareous soil. The chlorophyll and active iron (Fe²⁺) concentration of leaves was less in iron-efficient genotypes compared to efficient types in calcareous soil and reduction of both the parameters from noncalcareous to calcareous soil was considerably high in iron-inefficient lines. There was significant correlation between visual scores, chlorophyll and active iron content. There were no differences among F₁s for iron chlorosis and they were all iron-inefficient. The frequency of iron-inefficient plants was higher than the efficient plants in all F₂ populations. But most of the productive plants came from iron-efficient segregants indicating strong association between iron-efficiency and productivity. Based on the results selection for iron-efficiency in early generations and extensive evaluation for productivity in advanced generations is suggested for developing varieties for cultivation in calcareous soils.     

Iron availability in plant tissues-iron chlorosis on calcareous soils

The article describes factors and processes which lead to Fe chlorosis (lime chlorosis) in plants grown on calcareous soils. Such soils may contain high HCO₃ ^- concentrations in their soil solution, they are characterized by a high pH, and they rather tend to accumulate nitrate than ammonium because due to the high pH level ammonium nitrogen is rapidly nitrified and/or even may escape in form of volatile NH₃. Hence in these soils plant roots may be exposed to high nitrate and high bicarbonate concentrations. Both anion species are involved in the induction of Fe chlorosis.Physiological processes involved in Fe chlorosis occur in the roots and in the leaves. Even on calcareous soils and even in plants with chlorosis the Fe concentration in the roots is several times higher than the Fe concentration in the leaves. This shows that the Fe availability in the soil is not the critical process leading to chlorosis but rather the Fe uptake from the root apoplast into the cytosol of root cells. This situation applies to dicots as well as to monocots. Iron transport across the plasmamembrane is initiated by Fe^III reduction brought about by a plasmalemma located Fe^III reductase. Its activity is pH dependent and at alkaline pH supposed to be much depressed. Bicarbonate present in the root apoplast will neutralize the protons pumped out of the cytosol and together with nitrate which is taken up by a H⁺/nitrate cotransport high pH levels are provided which hamper or even block the Fe^III reduction.Frequently chlorotic leaves have higher Fe concentrations than green ones which phenomenon shows that chlorosis on calcareous soils is not only related to Fe uptake by roots and Fe translocation from the roots to the upper plant parts but also dependent on the efficiency of Fe in the leaves. It is hypothesized that also in the leaves Fe^III reduction and Fe uptake from the apoplast into the cytosol is affected by nitrate and bicarbonate in an analogous way as this is the case in the roots. This assumption was confirmed by the highly significant negative correlation between the leaf apoplast pH and the degree of iron chlorosis measured as leaf chlorophyll concentration. Depressing leaf apoplast pH by simply spraying chlorotic leaves with an acid led to a regreening of the leaves.     

A new technique of plant analysis to resolve iron chlorosis

Summary Iron though indispensable for the biosynthesis of chlorophyll, its total content in the plant was not associated with the occurrence of chlorosis. In order to overcome this inconsistency a new technique of plant iron analysis has been developed. It consists of the determination of Fe²⁺, the fraction of iron involved in the synthesis of chlorophyll.The choice of 1–10 o-phenanthroline (o-Ph) as an extractant for Fe²⁺ was based on its remarkably higher stability constant for Fe²⁺ than Fe³⁺. On this basis, it could preferentially chelate Fe²⁺. The highly specific organce colour of the Fe²⁺-phenanthroline complex made possible the determination of Fe²⁺ by reading the transmittancy at 510 nm.The procedure involves extraction of 2 g of thoroughly washed, chopped, fresh plant by 20 ml of o-phenanthroline extractant (pH 3.0, conc. 1.5%). The plant samples treated with the extractant are allowed to stand for 16 hours and Fe²⁺ is determined in the filtrate by reading the transmittancy at 510 nm.In sharp contrast to total iron the green plants always contained more Fe²⁺ than chlorotic plants. The technique has been developed for rice but is expected to be successful for other crops also.     

Physiological and biochemical adjustment of iron chlorosis affected low-chill peach cultivars supplied with different iron sources

A pot experiment was carried out to investigate the effect of iron supplementation on physiological and biochemical status of the low-chill peach cultivars (Saharanpur Prabhat, Shan-e-Punjab and Pratap) suffered from iron chlorosis in artificially created calcareous soil. Three most commonly used iron sources viz. Fe-sulphate (1.0 % and 0.5 %), Fe-citrate (1.0 % and 0.5 %) and FeEDTA (0.1 % and 0.2 %) were sprayed on the 4th and 5th leaves from the apex of the twig. And after 1 week of spraying, observation on various physiological and biochemical parameters in leaves were recorded. Improvement in plant physiological parameters like chlorophyll content index (CCI), photosynthetic rate (P_n), stomatal conductance (g_s) and intercellular CO₂ conc. (C_i) were recorded best with the application of 1.0 % Fe-sulphate both in treated and untreated upper leaves. The maximum recovery in biochemical parameters such as total leaf chlorophyll content, superoxide dismutase (SOD) and peroxidase (POD) activity was also noted with the application of 1.0 % Fe-sulphate. However, application of 1.0 % Fe-sulphate and 0.5 % Fe-sulphate had similar effect for most of the parameters under study. The ability of iron sources to induce physiological and biochemical responses in iron deficient low-chill peach plants were in the following order Fe-sulphate>Fe-citrate>FeEDTA. Differential responses in plant physiological and biochemical parameters were also exhibited by the low-chill peach cultivars with regard to supplementation of various iron sources. Among the low-chill peach cultivars, Saharanpur Prabhat responded best with the application of iron sources followed by Shan-e-Punjab and Pratap.     

Some properties of ferric citrate relevant to the iron nutrition of plants

Ferric citrate, the form in which iron is transported in dicotyledonous plants, diffuses slowly through cotton cellulose dialysis membranes, used to serve as a model for plant cell walls. KCl at m M concentrations stimulates diffusion.Photoreduction of ferric citrate results in a rapid and nearly complete reduction of iron when the citrate concentration is low (50 M) as in the xylem sap of plants growing on non-calcareous soils. In 1 m M citrate, as in the xylem sap of plants that activate their Fe-efficiency reactions, fast reoxidation prevents the buildup of high ferrous levels until after citrate has been largely broken down by photodestruction.Photodestruction of citrate, catalyzed by iron, results in increase of pH in the solution and in the formation of a non-dialyzable form of iron, and thus can lead to deposition of inactive iron in leaves.     

Nitrate induced iron deficiency chlorosis in Juncus acutiflorus

Chlorosis caused by iron deficiency is commonly associated with high bicarbonate levels in the soil. However, in rare cases such chlorosis has been observed in soils with high nitrate levels. In a dutch rich-fen, chlorosis has been noted in stands of Juncus acutiflorus at locations where groundwater containing high levels of nitrate reached the surface. Experiments revealed that the chlorosis could be attributed to iron deficiency although iron levels in the shoots were well above the known physiological threshold values for iron deficiency. It is postulated that increased nitrate assimilation leads to an increased apoplastic pH and to a concomitant immobilisation of iron and/or lower iron (III) reduction. Moreover free amino acid levels were markedly higher in the iron deficient plants in the field. It was found, however, that the percentage of nitrogen present as free amino acids was not influenced directly by low iron levels but mainly by the C/N ratios in the shoots. Nowadays, nitrate concentrations in ground water as high 1000 µM are no longer an exception in the Netherlands. We propose that strongly increased nitrate inputs may cause iron stress in natural vegetations, especially in wet habitats.     

Characterization of the tolerance to iron chlorosis in different peach rootstocks grown in nutrient solution

Iron chlorosis is an important problem in peach trees, but differences exist between peach rootstocks in their tolerance to Fe chlorosis in calcareous soils. The purpose of this investigation was to characterize the tolerance of different rootstocks to Fe chlorosis induced by bicarbonate in nutrient solution. The rootstocks studied included peach (Nemaguard), plums (Brompton, San Julian A and Puebla de Soto 101) and almond × peach hybrids (Adafuel and GF677). Young plants obtained from rooted cuttings or from in vitro culture techniques were grown individually, under controlled conditions, in flasks with 700 mL of aerated nutrient solution low in iron and with or without 10 mM bicarbonate or 10 mM phosphate. Susceptiblity to bicarbonate-induced chlorosis was inversely correlated with both the Fe content in young leaves and the reducing capacity of roots, but not with the phosphorus content in young leaves. The plum Puebla de Soto 101 and the hybrid GF677 showed the lowest degree of chlorosis and the highest reducing capacity. Phosphate did not induce chlorosis.     

Effect of iron chlorosis on mineral nutrition and lipid composition of thylakoid biomembrane in Prunus persica (L.) Bastch.

The effect of iron chlorosis on mineral, thylakoid lipids and fatty acids composition of field grown peach tree leaves was studied. Significant differences were found in iron extracted by using , -dipyridyl (active iron), total iron, P, K, Cu and the P/Fe and Fe/Mn ratios. The levels of total chlorophyll, total glycolipids and phospholipids were reduced under iron chlorosis. A slight iron deficiency does not modify the fatty acid composition of thylakoid membranes, while a strong deficiency changes the proportion of some fatty acids.Abbreviations Chl chlorophyll - DGDG digalactosyldiglycerol - MGDG mono-galactosyldiglycerol - PC phosphatidycholine - PE phophatidylethanolamine - PG phophatidylglycerol - TLC thin layer chromatography - 16:0 palmitic acid - 16:1 palmitoleic acid - 16:lt trans-hexadecenoic - 18:0 steric acid - 18:1 oleic acid - 18:2 linoleic acid - 18:3 linolenic acid     

Growth promoting influence of siderophore-producing Pseudomonas strains GRP3A and PRS9 in maize (Zea mays L.) under iron limiting conditions

Maize seeds were bacterized with siderophore-producing pseudomonads with the goal to develop a system suitable for better iron uptake under iron-stressed conditions. Siderophore production was compared in fluorescent Pseudomonas spp. GRP3A, PRS9 and P. chlororaphis ATCC 9446 in standard succinate (SSM) and citrate (SCM) media. Succinate was better suited for siderophore production, however, deferration of media resulted in increased siderophore production in all the strains. Maximum siderophore level (216.23 microg/ml) was observed in strain PRS9 in deferrated SSM after 72 h of incubation. Strains GRP3A and PRS9 were used for plant growth promotion experiments. Strains GRP3A and PRS9 were also antagonistic against the phytopathogens, Colletotrichum dematium, Rhizoctonia solani and Sclerotium rolfsii. Bacterization of maize seeds with strains GRP3A and PRS9 showed significant increase in germination percentage and plant growth. Maximum shoot and root length and dry weight were observed with 10 microM Fe3+ along with bacterial inoculants suggesting application of siderophore producing plant growth promoting rhizobacterial strains in crop productivity in calcareous soil system.     

Correcting iron deficiencies in annual and perennial plants: Present technologies and future prospects

Correction of Fe chlorosis is done mainly by foliar sprays because soil applications generally are ineffective, especially for annual crops. Inorganic Fe sources applied to soils react rapidly to forms which are not as available to plants; ferrous Fe is oxidized to the ferric form in well-aerated soils, especially as soil pH increases. Several synthetic chelates and organic complexes have been used with varying success, depending upon Fe source and rate, application method, plant species, and weather and soil conditions. Use of Fe-efficient cultivars is one method of counteracting Fe deficiencies in some species. Future prospects for improving control of Fe chlorosis lie more with development of Fe-efficient cultivars of Fe-sensitive species than with development of improved Fe fertilizers and methods of application. The techniques of molecular biology should be applicable to help solve this important plant nutrition problem, but priority has not been given to conduct this research at this time.     

Genotypical differences in responses to iron deficiency between sensitive and resistant cultivars of chickpea (Cicer arietinum)

Differences in responses to iron deficiency between two chickpea cultivars, NP-62 and K-850, were examined. The apical leaves of NP-62 quickly showed symptoms of iron-deficiency chlorosis when grown on an iron-free medium. By contrast, K-850 showed no visible symptoms on the same medium. Iron contents of the apical leaves of these two cultivars were similar during the first 7 days after they were transferred to the iron-free medium in spite of a marked difference in root-associated Fe³⁺-reduction activity. The susceptibility to iron-deficiency chlorosis observed in NP-62 was not attributable to the poor Fe³⁺-reduction activity of roots but to the inefficient utilization of iron within leaves under conditions when the supply of iron was limited.     

Distribution of the genes causing F2 chlorosis in rice cultivars of the Indica and Japonica types

Summary Chlorotic plants were segregated in F₂ populations in varietal crosses of common rice. The genetic basis and distribution of the genes causing F₂ chlorosis in native cultivars were studied to examine the role of the F₂ chlorosis in varietal differentiation of rice. It was proven that this F₂ chlorosis was controlled by a set of duplicate genes, hca-1 and hca-2. The hca-2 gene was widely distributed in native cultivars of the Japonica type, while many Indica types carried its dominant allele hca-2⁺. Japanese cultivar J-147 carried hca-2. The hca-1 gene was frequently distributed in cultivars containing the Hwc-2 gene for F₁ weakness. We concluded that F₂ chlorosis does not cause or promote varietal differentiation in rice.