Lime-induced Iron Chlorosis Research Articles

Evaluation of Advanced F4 Groundnut Breeding Lines for Chlorosis Tolerance, Morphological and Yield Parameters under Lime-induced Iron Chlorosis Condition

Iron deficiency chlorosis, a major physiological disorder affecting the groundnut production worldwide and is prevalent in alkaline and calcareous soils with a pH of 7.5 to 8.5. Identifying and developing a chlorosis tolerant genotype is the best solution to overcome this major abiotic stress in calcareous soils. Therefore, a field experiment was conducted at University of Agricultural Sciences, Dharwad, in June, 2019 under rainfed conditions to evaluate a set of sixteen advanced breeding lines along with three parents of groundnut checks for chlorosis tolerance, morphological and yield parameters. Associated traits like SPAD chlorophyll meter reading (SCMR) and visual chlorotic rating (VCR) were assessed to evaluate the chlorosis tolerance. Among the parents, lime induced iron chlorosis (LIIC) tolerant parent, ICGV 86031 had recorded higher SCMR value and lower VCR (35.62 and 2.40, respectively) at 60 DAS with lower plant height, higher number of branches per plant, total dry matter production and pod yield (19.27cm, 5.20, 9.34g and 9.21g, respectively) at harvest compared to LIIC susceptible parents. However, among the derived breeding lines, TIP 16-5 recorded higher SCMR value and lower VCR (28.82 and 1.72, respectively) at 60 DAS with higher plant height, number of branches and total dry matter (26.29 cm, 5.33 and 12.80g, respectively) at harvest over the respective susceptible parent TMV 2. Further, TIP 16-5 and JIP 29-14 recorded about 50.47 and 31.46 per cent increased pod yield over their susceptible parents. These results indicate introgression of dry matter production, pod yield and chlorosis tolerance from the tolerant parent.

Physiological response of new citrus rootstocks under the effect of lime induced iron chlorosis stress conditions

ABSTRACT Citrus orchards are highly affected by iron chlorosis in Mediterranean Basin, which is the second-highest producing region worldwide. In addition, citrus orchards from the Mediterranean Basin are exposed to emerging diseases, such as Huanglongbing, the most devastating citrus disease worldwide. Consequently, citrus rootstock can serve as an interesting tool to reduce crop losses caused by these abiotic and biotic stresses. In our study, we evaluated the effect of four Fe-chlorosis stress treatments on six new citrus rootstocks under greenhouse conditions and compared with Carrizo citrange and Forner-Alcaide 5. Above-ground symptoms and chlorophyll index (SPAD) were recorded on a regular basis during the experiment. At the end of the assay, root, stem, and leaves biomass and Fe concentration in leaves were recorded. Plant symptoms were detected under Fe-chlorosis stress treatments, in which 2247 × 6070-02-2 and UFR-6 displayed lower incidence than other citrus rootstocks. These plant symptoms were in keeping with the SPAD response per citrus rootstock. Almost all citrus rootstock reported the highest biomass reduction under the treatment of 1 g CaCO3/l pH 9. Only two citrus rootstocks (Carrizo citrange and B11R5T49) achieved the highest Fe concentration on leaves under control conditions compared with the other treatments per citrus rootstock. Abbreviations: F: iron; FC-R: Ferric Chelate Reductase; HLB: Huanglongbing or citrus greening; Without Fe: nutritive solution without iron; SAUASPC: standardised area under the abiotic stress progress curve; D1: day 1; D10: day 10; D21: day 21; D32: day 32; D42: day 42; D52: day 52; D64: day 64; D84: day 84; FW: fresh weight per section plant; DW: dry weight per section plant; FWT: total fresh weight; DWT: total dry weight; PBR: percentage of biomass reduction; CW: weight (g) of control treatment plants averaged eight replicates; TW: weight (g) of treated plants at each concentration of Fe tested; ICP-OES: inductively coupled plasma optical emission spectroscopy

The Key Physiological and Biochemical Traits Underlying Common Bean (Phaseolus vulgaris L.) Response to Iron Deficiency, and Related Interrelationships

Iron deficiency is a worldwide nutritional problem affecting crop production. In Tunisia, this mineral disorder hampers the growth and yield of the major crops due to the abundance of calcareous soils that limit iron availability. The common bean is one of these crops suffering from lime-induced iron chlorosis. The exploration of the variability of common bean responses to iron deficiency allows us to screen tolerant cultivars and identify useful traits and indicators for further screening programs. To this end, two common bean cultivars (coco blanc, CB, and coco nain, CN) were cultivated hydroponically in standard nutrient solution (control) or nutrient solution deprived of iron (stressed). Analyses were reported on plant growth, photosynthetic pigments, photosynthesis, iron distribution, H-ATPase, and Fe-chelate reductase (Fe-CR) activities; important indicators were calculated; and convenient correlations were established. Current results demonstrated that iron deficiency stimulated specific symptoms of iron chlorosis on young leaves that were more precocious and severe in CB than CN. Spad index and chlorophyll pigments measurement confirmed these morphological changes and cultivar differences. Net photosynthesis (Pn) showed the same scheme of variation, with a significant decrease in Pn while respecting the previous cultivar’s variability. Plant growth is no exception to this general trend. The biomass decrease was two times higher in CB than CN. Otherwise, this mineral disorder significantly decreased Fe concentration in all plant organs. However, CN accumulated 40% more Fe than CB, resulting from its higher Fe Fe-CR and H-ATPase activities. Our results also demonstrated the close dependence of these metabolic functions on Fe availability in shoots and the strict relationship between Fe-CR and H-ATPase, photosynthesis, and chlorophyll content. Otherwise, CN demonstrated higher efficiency of Fe’s use (FeUE) for the key metabolic functions (photosynthesis, chlorophyll biosynthesis, and plant growth). The relative tolerance of CN as compared to CB was explained by its ability to establish a functional system less vulnerable to iron deficiency that operates effectively under problematic conditions. This system involves metabolic functions in shoots (photosynthesis, chlorophyll biosynthesis, Fe repartition, etc.) and others in roots (H-ATPase, Fe-CR), which are strictly interdependent.

Functional Analysis of the Genotypic Differences in Response of Pea (Pisum sativum L.) to Calcareous-Induced Iron Deficiency

Lime-induced iron chlorosis is a major nutritional disorder causing severe plant growth and yield reduction in the calcareous soils of Tunisia. The understanding the behavior of key metabolic functions of peas on calcareous soils, the identification of useful traits of tolerance, and the exploration of the genotypic differences in response to this constraint remain the most efficient approaches due to their coast, environmental benefits, and sustainability. For this purpose, a greenhouse experiment was conducted on three pea genotypes (Alexandra: Alex, Douce de provence: DP, and Merveille de Kelvedon: MK) cultivated on calcareous soil (Fe-deficient) and fertile soil (control). Plant growth, SPAD index, iron nutrition and distribution, photosynthesis, and antioxidant enzymes were deeply analyzed to discriminate genotypic differences. Calcareous-induced iron deficiency reduced SPAD index, plant growth, net photosynthesis, and tissue Fe content against a significant stimulation of the oxidative stress indicators, H2O2 and Malondialdehyde (MDA). Moreover, we reported a significant induction of SOD and CAT activity in shoots and roots of the Alexandra genotype. Fe use efficiency increased on calcareous soil and clearly discriminated the studied genotypes. Alexandra genotype was found to be the most tolerant to lime-induced iron chlorosis. This genotype protects its tissues against oxidative stress by stimulating enzyme activities (SOD and CAT) and develops significant efficiency of Fe uptake, translocation to shoots and use when cultivated on calcareous soil.

Genotypic differences in response of durum wheat (Triticum durum Desf.) to lime-induced iron chlorosis.

Wheat, durum wheat, is the first cereal cultivated and consumed in Tunisia. Because the dominance of calcareous soils in its agroecological systems, known by their low availability of iron (Fe) inducing Fe chlorosis and limiting crop production, its yield remains low. Therefore, the search for tolerant genotypes is always current. In this context, the physiological behavior of six Tunisian genotypes of durum wheat (salim, karim, razek, khiar, inrat100, and maali) cultivated on calcareous and fertile soils for 2 months in a pot experiment was investigated. A greenhouse was used to conduct experiments under natural light. Plant growth, SPAD index, Fe nutrition, Fe distribution, and photosynthesis were monitored and used to evaluate and discriminate their respective physiological responses. On calcareous soil, results revealed reduced plant growth, active Fe, SPAD index, and net photosynthesis. Genotypic differences in the response of wheat to calcareous‐induced Fe deficiency were observed and allowed to classify the genotypes Salim and Karim as relatively tolerant. These genotypes expressed Fe translocation capacity (FeT) up to 3 times, Fe use efficiency for photosynthesis (FeUEAn) up to 1.6 times, and chlorophyll use efficiency for photosynthesis (ChlUEAn) up to 3.5 times greater than that expressed by the other genotypes, particularly inrat100 and maali. Thus, the relative tolerance of Salim and Karim is the result of the high ability of Fe uptake and translocation to shoots to support chlorophyll biosynthesis, photosynthesis, and plant growth as well as an important Fe and chlorophyll use efficiency.

Effectiveness of Amaranthus retroflexus L. aqueous extract in preventing iron chlorosis of pear trees (Pyrus communis L.)

The aim of this study was to evaluate the effectiveness of soil-applied aqueous extract of Amaranthus retroflexus L. in preventing lime-induced iron (Fe) chlorosis of pear trees (Pyrus communis L.). Tree growth, nutritional status, yield and fruit quality were also assessed. The aqueous extract was obtained by soaking dried and ground canopy (epigeal part) of spontaneous A. retroflexus plants in tap water. A. retroflexus extract was chosen because of its ability to solubilize Fe from calcareous soil, which was found to be 100-fold higher than deionized water alone. Two experiments were carried out (controlled environment and commercial field conditions) where soil-applied aqueous extract of A. retroflexus alone or mixed with iron sulfate (FeSO4) was compared with synthetic Fe-chelate and an untreated control. Soil-applied aqueous extract of A. retroflexus increased shoot length, leaf SPAD and total plant biomass in controlled environment. In the commercial orchard control trees showed severe leaf Fe-chlorosis symptoms effectively prevented by Fe-chelate. The supply of A. retroflexus aqueous extract improved Fe nutrition of trees, particularly when enriched with FeSO4. Fe-chelate increased tree yield but decreased fruit weight, leaf potassium (K) and manganese (Mn) concentration. At harvest, all strategies raised fruit soluble solid concentration compared to the untreated control. Results showed that soil-applied A. retroflexus aqueous extract improved Fe nutritional status of pear trees, probably because of the natural Fe chelating capacity of the compounds released by its tissues.

Effectiveness of Vivianite to Prevent Lime-Induced Iron Deficiency in Lemon Trees Grown on Highly Calcareous Soil

The short-term effectiveness of three application rates of vivianite [(Fe3(PO4)2·8H2O)] in preventing lime-induced iron (Fe) chlorosis in Eureka lemon (Citrus lemon L.) cuttings grafted on sour orange (Citrus aurantium L.) was investigated and compared with the commonly applied iron ethylenediaminedi(o-hydroxyphenylacetic) acid (FeEDDHA). Treatments were suspension of vivianite injected into the soil at three rates (0.5, 1.0, and 2.0 g kg−1 soil), 417 mg FeEDDHA per plant, and untreated plants. Chlorophyll concentration index (CCI) of the youngest fully expanded leaves was estimated. Growth vigor and leaf Fe concentration were also measured. Vivianite, particularly at the greatest two rates, resulted in significantly greater growth vigor and leaf Fe concentration and exhibited greater CCI values compared to untreated plants similar to FeEDDHA. However, if excessive growth vigor is not favorable, the 0.5 g vivianite kg−1 soil is recommended for farmers. Vivianite is a potential environmentally safe alternative to the expensive FeEDDHA to prevent Fe chlorosis in lemon.

Nutrient Dynamics in Orange Trees: The Effect of Soil Fertility

Lime-induced iron (Fe) chlorosis is a nutritional disorder common in calcareous soils, which may result from a low level of Fe available or adverse factors that inhibit Fe mobilization and uptake by plants. Organic-matter amendments can prevent or correct Fe chlorosis in plants but the effect of endogenous soil organic matter (SOM) on this disorder is not known. The main subject of this work was to investigate the consequence of two contrasting levels of soil fertility on the nutritional status of an orange grove [Citrus sinensis (L.) Osb. cv. Valencia Late]. The field experiment was conducted in a commercial citrus grove using mature trees distributed in two plots with different values of SOM, phosphorus (P), and potassium (K), but with the same level of active lime. The concentration of nitrogen (N), P, K, magnesium (Mg), calcium (Ca), Fe, copper (Cu), zinc (Zn), and manganese (Mn) in young and mature leaves and flowers was evaluated. The level of Mg and the Mg/Zn ratio in flowers from both plots, although significantly different, only indicated moderate Fe chlorosis, as predicted by a previously developed model, and was consistent with the amount of chlorophyll present in the leaves. However, nutrient partitioning between leaves of contrasting age was very different. Mature leaves from trees grown in the high-fertility plot (HF) had larger concentrations of N, P, and K but lower concentrations of Ca, Fe, and Mn than did those from the low-fertility plot (LF). Young leaves from the LF had more N, P, Mg, Cu, and Mn and less Ca and Fe than did those from the HF. Flower analysis, although useful to predict Fe chlorosis, failed to detect differences in the nutritional status of plants resulting from contrasting levels of soil fertility. Furthermore, endogenous SOM had only a marginal effect on Fe chlorosis.

EVALUATION OF PEAR ROOTSTOCK SELECTIONS

European pear (Pyrus communis L.) is in Italy predominantly grown on clonal quince (Cydonia oblonga Mill.) rootstocks. However, this grafting combination shows several problems including poor graft compatibility, susceptibility to lime-induced iron chlorosis and pear decline, which are normally not observed when P. communis is used as rootstock. Since 1979, the University of Bologna (Italy) has undertaken a breeding programme to obtain new clonal pear rootstocks and in 1996 two clones (Fox 11 and Fox 16) were released. Recently, the programme focused on clones with a marked size-controlling aptitude and high yield efficiency. In 2002 and 2004 two experimental trials were arranged to evaluate the performances of cultivars ‘Abbe Fetel’, ‘Conference’ and ‘Bartlett’ grafted on eight pear clones of Bologna University (A74, C19, C91, D46, D50, E82, E105 and Fox 9), Farold® 40 Daygon and quinces BA29, MC and Sydo®. Fox 9 showed a slightly higher vigor and yield performance compared to quince BA29, and good fruit quality. In addition, Fox 9 showed high environmental adaptibility, good suitability to be micropropagated and high graft compatibility with the tested cultivars. Based on these findings, in 2008 Fox 9 was released as a new rootstock for P. communis and the application for community plant variety rights (EU patent) was lodged. Among the other pear selections tested, D46 and D50 induced good yield but also the highest vigour, while C91 was interesting for the moderate growth.

Tolerance to Lime-induced Iron Chlorosis of Asian Pear Rootstocks (Pyrus spp.)

Tolerance to Lime-induced Iron Chlorosis of Asian Pear Rootstocks (Pyrus spp.)

Floral analysis as a tool to diagnose iron chlorosis in orange trees

A three-year field experiment was conducted in a commercial orange grove [Citrus sinensis (L.) Osb. cv. `Valencia late' grafted on Citrange Troyer] established on a calcareous soil in the south of Portugal, to investigate if flower analysis could be used to diagnose lime-induced iron chlorosis. In April, during full bloom, flowers and leaves were collected from 20 trees. Leaf samples were again collected from the same trees in May, June, July and August. Total chlorophyll was estimated in all the leaves sampled for foliar analysis, using a SPAD-502 apparatus. Leaves and flowers were analysed for N, P, K, Ca, Mg, Fe, Zn, Mn and Cu. Principal Component Analysis was used to evaluate the variation of nutrient concentrations in flowers, and linear regressions were established between these and the chlorophyll content of leaves 90 days after full bloom. Evaluation of the best-fit equation was carried out using separate data obtained from other groves. Variation in the pattern of floral mineral composition in the flowers showed contrasts between the increase in N, P and K and that of Ca, Fe and Zn, while the concentration of Mg, Mn and Ca varied synchronously. The ratio of Mg:Zn in flowers explained about half of the variation of chlorophyll in leaves later in the season. A ratio below 100 indicated that trees would develop iron chlorosis, while with a ratio above 200 leaves would remain green. An early prognosis of iron chlorosis based on floral analysis can benefit growers, since it allows them to apply treatments in time to prevent loss of fruit yield and quality due to iron chlorosis.

ROOTSTOCKS FOR EUROPEAN PEAR: A REVIEW

European-pear cultivars are mainly propagated by means of Common Pear (Pyrus communis) or quince (Cydonia oblonga) rootstocks. The former are compatible with all scion cultivars, the latter only with a part of the pear-cultivar assortment. Common Pear rootstocks are considered more cold hardy and less susceptible to lime-induced iron chlorosis and quince rootstocks less vigorous, more precocious, better in fruit size, and less susceptible to pear decline. However, such generalisations are of little value, because within both species variations in the characteristics occur. The various rootstock qualities are discussed and it is shown that some progress has been made towards rectifying some of the short comings. It is stated that there is a shortage in suitable dwarfing rootstocks, hampering for pear the current world wide trend towards high-density plantings (HDP). For successful HDP with different cultivars under various growing conditions, rootstock vigour should range from that comparable to quince MA to that significantly less than quince MC. It is proposed to concentrate research to this vigour range and to do so in collaboration. Future efforts should encompass field trials and tests aimed at gaining early and quantitative information on sensitivities to certain environmental stresses and diseases and, in case of pear/quince combinations, on graft incompatibility.

In vivo growth and tolerance to lime-induced iron chlorosis of leaf-derived cvs. Tomuri and Hayward kiwifruit (Actinidia deliciosa) somaclones

SummaryThe present paper reports on somaclonal variation of leaf-derived ‘Tomuri’ and ‘Hayward’ somaclones regenerated at variable pH, and the effect of the in vitro selection pressure on their tolerance to lime-induced iron chlorosis as adult plants in pots and in the field. In most plants grown in pots, the above ground component length (AGL) and the node number (NN), and also root weight of ‘Hayward’, tended to increase with the regeneration pH (RpH). The higher vigour of ‘Hayward’ somaclones regenerated at high pH seemed to be confirmed in the field. In contrast, the pH selection pressure during regeneration had no clear effect on plant tolerance to lime. For ‘Hayward’, the group of somaclones obtained at pH 5.7 showed at high lime levels higher average AGL and NN than those of plants regenerated at pH 7; while clone 7.5-1, the only surviving somaclone among those obtained at the highest pH, was apparently the most tolerant to lime. The percentage of ‘Tomuri’ somaclones obtained at pH 7.5 that seemed less sensitive to lime was slightly higher than those of somaclones regenerated at pH 5.7 and 7. ‘Tomuri’ and ‘Hayward’ controls were both very sensitive to lime. Some somaclones which had been able to grow at high pH in vitro were also fairly tolerant to lime when cultured in pots and/or in the field, especially ‘Tomuri’ 5.7-5, -6; 7-6, -8, -14 and 7.5-6, and ‘Hayward’ 5.7-5; 7-2, -3, -5 and 7.5-1. The in vitro regeneration and selection methods here described therefore seem useful for creating and selecting new variability in kiwifruit and promising for obtaining plants tolerant to high pH and lime levels in the soil.

Screening of groundnut germplasm collection and selection of genotypes tolerant of lime-induced iron chlorosis

SUMMARYErect type groundnut germplasm belonging to the Valencia and Spanish botanical groups was examined in the field for five consecutive cropping seasons (wet 1988, 1989 and 1990 and dry 1989 and 1990) at Junagadh, India, in order to identify groundnut genotypes with the ability to grow in calcareous soil and tolerate iron deficiency (lime-induced iron chlorosis). On the basis of the visual chlorotic rating scores of their leaves, 17 and 19 genotypes of the Valencia and Spanish groups, respectively, which showed the least or no chlorosis were classified as tolerant (iron-efficient) to iron chlorosis. These genotypes may now be used as donor parents in groundnut breeding programmes for the development of iron chlorosis-tolerant varieties.Almost all the iron-efficient groundnut genotypes had higher pod and seed (kernel) yields and Harvest Index (HI) than the susceptible types. The seed yield of 12 iron-efficient groundnut genotypes was either equal to or higher than a commercial cultivar which showed tolerance to iron chlorosis and, hence, these genotypes could profitably be grown in those areas where chlorosis due to iron deficiency is a major problem.

Growth and mineral nutrition of pear rootstocks in lime soils

Little information is available on the tolerance of pear rootstocks to lime-induced iron chlorosis. In a 2-year study, micropropagated plants of the pear rootstocks OH × F 51, OH × F 333, B 21, C 106 and D 50, and Adams quince were grown in low calcareous soil (LC, 1.6% lime) and high calcareous soil (HC, 72.9% lime) as well as in a mixture of HC:LC (50:50, w:w) (M1) at 33.8% lime content and a mixture of HC:LC (75:25, w:w) (M2) at 48.3% lime content. By the end of Year 2, OH × F 51, B 21 and C 106 had reduced dry matter accumulation in stem and roots in HC soil only; the other rootstocks were adversely affected by lower soil-lime contents. Only Adams decreased the shoot-to-root dry weight ratio in relation to increased soil lime. Leaf chlorotic symptoms of plants grown under increasing lime were most severe in OH × F 333, D 50 and Adams. Root Ca concentration increased linearly and root iron and manganese decreased linearly at increasing soil lime rates. Root Cu concentration increased linearly with soil Cu content, the latter being ten-fold higher in HC than LC soil. These findings indicate varying susceptibility of pear rootstocks to lime-induced iron chlorosis. Rootstock tolerance is a necessary condition in order to overcome lime-induced iron chlorosis in pear cultivars. In grafted trees it is, however, possible that mechanisms other than iron uptake are involved in leaf chlorosis.

Iron deficiency depresses growth of furrow irrigated soybean and pigeon pea on vertisols of northern N.S.W

Crops under furrow irrigation or after heavy rainfall on the alkaline, calcareous Vertisols of northern N.S.W. frequently exhibit chlorosis of young leaves after the soil is wetted, but the specific cause has not been identified previously. The quantitative effects of the syndrome on growth, physiological activity and yield are also unknown. Experiments on soybean and pigeon pea grown on a Vertisol at Breeza, N.S.W., Australia, examined the influence of applying Fe to the leaves, and Fe, Zn, N+P and lime to the soil before sowing, on leaf colour, leaf photosynthesis, crop dry matter, and yield of grain of soybean and dry matter and yield of pigeon pea. In soybean, chelated Fe applied to the soil before sowing increased the levels of active Fe (Fe2+) in leaves by up to 42% and dry matter of shoots by up to 46% early in the season. Active Fe and dry matter of shoots were linearly correlated (r2 = 0.76). Soil Fe treatments did not affect leaf photosynthesis, although addition of chelated Fe to the soil resulted in greener leaves than in the control. Foliar Fe had no significant effect on active Fe, leaf colour, or leaf photosynthesis. The 9% increase in grain yield in response to application of 20 kg Fe ha-1 to the soil was not significant. In pigeon pea, application of 20 kg Fe ha-1 to the soil increased dry matter by 140% and grain yield by 414%. Effects of lime and zinc were not significant, but N+P increased yield by 112%. The study showed that Fe deficiency is limiting the growth and/or yield of irrigated soybean and pigeon pea on the clay soils of northern N.S.W., and pointed to lime-induced iron chlorosis as a possible mechanism of damage.

SCREENING FOR ALKALINITY TOLERANCE IN PRUNUS WITH A HIGH CARBONATE SOLUTION

Peach trees when grown in calcareous soils frequently exhibit lime-induced iron chlorosis. There have been numerous reports of rootstock tolerant to soil alkalinity but given the wide range of field conditions under which the comparison were made, it is difficult to quantify the relative tolerance of the different rootstock. A greenhouse screening procedure using a 0.5g/liter potassium bicarbonate solution (pH 8.0-8.3) was employed to compare the tolerance levels of 50 peach, almond and hybrid lines. Most peach lines tested were very susceptible (Nemaguard) to susceptible (Nemared, Lovell). A few exhibited a low level of tolerance (Montclar, Rutger Red Leaf, Rancho Resistant). High levels of tolerance were found with in almond and almond-peach hybrid families.

Lime-induced iron chlorosis in sugarcane

Lime-induced chlorosis is a potential problem on most calcareous soils particularly in arid and semi-arid climates affecting most of the plants grown on them. Bicarbonates, phosphates, calcium, iron inactivation in plant tissue and organic anions have been held responsible as the mechanism leading to the disorder which is still not fully understood, and there is a lack of agreement as to the primary factor responsible for lime-induced chlorosis. To date, no hypothesis has adequately explained why chlorosis occurs on some high lime soils and not on others. Likewise, the nutrient ratios, K/Ca, P/Fe and Fe/Mn considered as diagnostic criteria for lime-induced chlorosis, have shown inconsistency. The presence of calcium carbonate, bicarbonate, calcium and imbalance of nutrient cations in the growth medium, injudicious addition of phosphates, quality of irrigation water, and other soil and plant factors have been held responsible for the disorder. Amelioration of lime-induced chlorosis by (i) acidification of calcareous soils, (ii) use of iron salts, (iii) use of synthetic iron chelates, and (iv) by management practices including the selection and development of varieties resistant to lime-induced iron chlorosis, is discussed. Suggestions for future research work are made.

Reaction of Genotypes of Rice (Oryza sativa) to Iron Chlorosis in a Calcareous Soil

SUMMARYNine rice genotypes were classed as tolerant, moderately tolerant, susceptible and highly susceptible, depending on their growth retardation and the intensity of lime-induced iron chlorosis. All except genotypes IET 7972 and IET 7973 showed varying degreees of chlorosis and corresponding decreases in shoot dry matter production. Chlorosis was negatively correlated with the orthophenanthroline reactive Fe2+ iron content of the leaves, the concentration of which accounted for 82% of the variability in chlorosis. However, total iron concentration in the leaves and the Fe/Mn, Fe/Cu and K/Fe ratios were not significantly correlated with dry matter accumulation in the plants.

MINERAL COMPOSITION OF CHLOROTIC ORANGE LEAVES AND SOME OBSERVATIONS ON THE RELATION OF SAMPLE PREPARATION TECHNIQUE TO THE INTERPRETATION OF RESULTS

sential mineral elements. Agreement does not always exist, however, as to whether a specific type of leaf-symptom pattern is related to total content of the deficient element or only to a specific fraction of it. This is particularly true of the presumed deficiencies of iron and zinc where sample selection, contamination, and poor precision of analytical procedures are all complicating factors. An extensive review of all previous work is beyond the scope of this report. Jacobson (8) and Lindner and H arle ? (10) point out some of the more pertinent discrepancies with respect to iron content and iron chlorosis. More recently McGeorge (11) reports the lack of any apparent relationship between total Fe or Zn and the appearance of the specific deficiency symptoms for these elements in citrus, pear, and several other plants. Other studies have occasionally shown this same result in the case of Fe; but Jacobson (8) found that surface contamination was a factor of major importance in producing discrepant results. When pear leaves from trees grown in calcareous soil were carefully washed in dilute HC1, a c'orrelation was found between the low total Fe values found and the iron chlorosis shown. Bennett (1) confirmed this observation with further studies, although he found a stronger relationship of chlorosis to an acid-soluble, or active'' Fe fraction than to the total. In Florida (?), New Zealand (7), and elsewhere citrus trees showing typical zinc deficiency symptoms have been found to contain less total zinc in their leaves than leaves from healthy trees. In Florida when the acidity of the topsoil of the Lakeland and related series drops below pH 5.0 (between 4.5 and 5.0) for a considerable length of time, citrus trees may become unthrifty in appearance, sparsely foliated, and show typical iron-chlorosis leaf patterns. This interveinal chlorosis condition strongly resembles the lime-induced iron chlorosis pattern (2) and that associated with poor drainage. Exploratory tests in small containers showed that reducing the acidity by treatment with the carbonates of Ca, Na, or ? (or extracting the soil with NH4-acetate) all resulted in the disappearance of this symptom in young citrus seedlings. In connection with this general problem, some analyses were made to determine the mineral composition of leaves from trees affected with this type of chloro-