Iron deficiency stress response of various c‐3 and c‐4 grain crop genotypes: Strategy II mechanism evaluated

The relative amount of phytosiderophore produced by various Strategy II plants has been categorized as follows: barley (Hordeum vulgare L.) > wheat (Triticum aestivum L.) > oat (Avena byzantina C. Koch.) > rye (Secale cereale L.) >> corn (Zea mays L.) >> sorghum (Sorghum bicolor (L.) Moench) > rice (Oryza sativa L.). With the exception of rice, these plants developed under oxidized soil conditions, and the C‐3 species produce more phytosiderophore than C‐4 species under Fe‐deficiency stress. Iron‐efficient Coker 227 oat produced phytosiderophore in response to Fe‐deficiency stress, while Fe‐inefficient TAM 0–312 oat did not. Although Fe‐efficient WF9 corn and Fe‐inefficient ys₁ corn differed in their ability to obtain Fe, neither produced sufficient quantities of phytosiderophore to explain these differences. The objectives of this research were to determine: (a) if phytosiderophore production of Fe‐deficiency stressed C‐4 species millet (Panicum miliaceum L.) and corn is low or absent compared to identically stressed C‐3 species oat and barley, and (b) if native, inbred and hybrid corn cultivars differ in ability to produce and utilize phytosiderophores.

Although release of phytosiderophore for Fe‐stressed corn and millet was generally lower than oat, quantity of release was not always related to obtaining Fe and maintaining green plants. Barley maintained high leaf Fe and low chlorosis with a minor release of phytosiderophore. Oat with increased release acted similarly to barley, whereas a relatively high release of phytosiderophore from White maize did not effect Fe uptake or greening. Likewise, small amounts of phytosiderophore were produced by all corn types, but corn was generally unable to obtain adequate Fe from the growth medium. Two of the native corns, Coneso and Tepecintle, maintained relatively low chlorosis, but they differed in phytosiderophore release. Thus, it appears that the C‐4 plants studied herein generally release a lower amount of phytosiderophore than do C‐3 species, but overcoming Fe‐deficiency chlorosis is not guaranteed by such release. The Strategy II mechanism of mere release of phytosiderophore and consequential Fe acquisition appears simplistic. There is a need for understanding what other factors are involved.     

IRON EFFICIENCY IN KENTUCKY BLUEGRASS NOT RELATED TO PHYTOSIDEROPHORE RELEASE

Some Kentucky bluegrass (KBG; Poa pratensis L.) is susceptible to iron (Fe)-deficiency chlorosis. Under Fe-deficiency stress, phytosiderophore is produced and released by the roots of many grasses to solubilize soil Fe and enhance uptake. In other species, quantifying phytosiderophore screens for Fe-deficiency resistant cultivars. A hydroponic study was conducted at 1 and 10 μM solution Fe to variously stress ‘Baron’, ‘Award’, ‘Limousine’, and ‘Rugby II’ KBG cultivars. One μM Fe solution produced more Fe-deficiency stress in all cultivars compared to 10 μM, resulting in greater chlorosis and phytosiderophore release but reduced shoot and root Fe concentrations and shoot weight. Of the four cultivars, Baron was the most susceptible to Fe deficiency and exhibited severe Fe chlorosis and low shoot Fe but, surprisingly, produced the most phytosiderophore. These results imply that Fe-deficiency susceptibility in KBG may be less related to phytosiderophore release and more related to inefficient uptake or utilization mechanisms.     

INHERITANCE OF RESISTANCE TO IRON DEFICIENCY CHLOROSIS IN CHICKPEA (CICER ARIETINUM L.)

Iron (Fe)-deficiency chlorosis causes considerable yield losses in chickpea (Cicer arietinum L.) when susceptible genotypes are grown in calcareous soils with high pH. The most feasible method for alleviating Fe deficiency is the selection of suitable cultivars resistant to Fe deficiency chlorosis. ICC 6119 (desi type), which is Fe-deficient chlorosis, was crossed with CA 2969 and Sierra (kabuli types), resistant to Fe deficiency chlorosis. Inheritance of resistance to Fe deficiency in chickpea revealed that the resistance was controlled by a single dominant gene in these genotypes crossed. A negative selection for resistance to Fe deficiency chlorosis will be effective after segregating generations.     

Phytosiderophore release does not relate well with zinc efficiency in different bread wheat genotypes

Using six bread wheat genotypes (Triticum aesttvum L. cvs. Dagdas‐94, Gerek‐79, BDME‐10, SBVD 1–21, SBVD 2–22 and Partizanka Niska) and one durum wheat genotype (Triticum durum L. cv. Kunduru‐1149) experiments were carried out to study the relationship between the rate of phytosiderophore release and susceptibility of genotypes to zinc (Zn) deficiency during 15 days of growth in nutrient solution with (1 μM Zn) and without Zn supply. Among the genotypes, Dagdas‐94 and Gerek‐79 are Zn efficient, while the others are highly susceptible to Zn deficiency, when grown on severely Zn deficient calcareous soils in Turkey. Similar to the field observations, visual Zn deficiency symptoms, such as whitish‐brown lesions on leaf blades occurred first and severely in durum wheat Kunduru‐1149 and bread wheats Partizanka Niska, BDME‐10, SBVD 1–21 and SBVD 2–22. Visual Zn deficiency symptoms were less severe in the bread wheats Gerek‐79 and particularly Dagdas‐94. These genotypic differences in susceptibility to Zn deficiency were not related to the concentrations of Zn in shoots or roots. All bread wheat genotypes contained similar Zn concentration in the dry matter. In all genotypes supplied adequately with Zn, the rate of phytosiderophore release was very low and did not exceed 0.5 μmol/48 plants/ 3 h. However, under Zn deficiency the release of phytosiderophores increased in all bread wheat genotypes, but not in the durum wheat genotype. The corresponding rates of phytosiderophore release in Zn deficient durum wheat genotype were 1.2 umol and in Zn deficient bread wheat genotypes ranged between 8.6 μmol for Partizanka Niska to 17.4 umol for SBVD 2–22. In Dagdas‐94, the most Zn efficient genotype, the highest rate of phytosiderophore release was 14.8 umol. The results indicate that the release rate of phytosiderophores does not relate well with the susceptibility of bread wheat genotypes to Zn deficiency. Root uptake and root‐to‐shoot transport of Zn and particularly internal utilization of Zn may be more important mechanisms involved in expression of Zn efficiency in bread wheat genotypes than release of phytosiderophores.     

Alien cytoplasm effects on phytosiderophore release in two spring wheats (Triticum aestivum L.)

Iron (Fe) deficiency is a difficult nutrient problem particularly in crop plants grown on calcareous soils. Recently, phytosiderophore (PS) release has been linked to the ability of graminaceous species and genotypes to withstand Fe-deficiency chlorosis. So enhancing PS release is a critical step to improve iron efficiency of plants grown on iron stressed soils. The effects of alien cytoplasm on PS release in spring wheat were studied by analyzing PS release from twenty wheat genotypes, including two spring wheat 881 and 352-35, and their 18 alloplasmic lines with the participation of cytoplasms from the Aegilops and Triticum species. Different genotypes were grown in iron sufficient and deficient nutrient solution under controlled environmental conditions. PS release rates were determined at two or three days intervals after onset of iron deficiency symptoms by the measurement of iron mobilizing capacity of root exudates from freshly precipitated Fe^III hydroxide. High amounts of phytosiderophores were released from roots of all wheat genotypes without iron supplied, and the amount progressively increased with the development of iron deficiency chlorosis. The results revealed that (1) the release rate of phytosiderophores from roots of common wheat could be considerably influenced by alien cytoplasms. Some alien cytoplasms exerted positive effects, some ones did negative effects, and the other ones had no significant effects. (2) the same alien cytoplasm could affect similarly or oppositely the phytosiderophores release from different wheat. (3) some alien cytoplasms, such as Chinese Spring, Ae. speltoides Tausch and Ae. cylindrica Host showed promising and potential in improving the rate of phytosiderophore release in common wheat. These cytoplasms which showed the desired effect should be given priority in interspecific and intergeneric hybridization to develop and reconstruct the needed wheat cultivars.     

A greenhouse technique for screening Trifolium seedlings for iron‐deficiency chlorosis 1

Susceptible Trifolium plants often exhibit symptoms of iron (Fe)‐deficiency chlorosis when grown on high pH, calcareous soils. A greenhouse method was developed to screen seedlings for Fe‐deficiency chlorosis. ‘Yuchi’ arrowleaf (T. vesiculosum Savi.) and ‘Dixie’ crimson (I. incarnatum L.) clover seedlings were grown in “Super Cell”; Cone‐tainers in six calcareous Texas soils differing in Fe and selected other chemical characteristics. At the fourth trifoliolate leaf stage, chlorosis was induced by saturating the soil for a minimum of 2 weeks. The soils differed in their capacity to induce chlorosis in both clovers. Yuchi was more susceptible than Dixie, showing a higher percentage of chlorosis in five of the six soils. The results indicate that this screening method would be a useful tool for studying Fe‐deficiency chlorosis in Trifolium spp.     

Iron‐manganese interactions among clones of Nilegrass

Tetraploid clones of Nilegrass (Acroceras macrum, Stapf.) develop a chlorosis resembling iron (Fe) deficiency on acid (pH 5.0) soils in the Midlands of KwaZulu, Natal, South Africa. Hexaploid and pentaploid clones appear more resistant to the disorder. Iron deficiency would not be expected in such acid soils, but foliar sprays of Fe sulfate reduce the symptoms within 24 hours. Aluminum (Al) toxiciry has been ruled out as a cause of this chlorosis on the basis of soil tests. Manganese (Mn)‐induced Fe deficiency has been postulated. Six Nilegrass clones, differing in ploidy levels, were grown under low Fe or high Mn levels in nutrient solutions, in Mn‐toxic soil, in calcareous soil and in a standard potting soil at pH 7.0. Differential chlorosis symptoms, similar to those observed in the field, were reproduced in plants grown in low Fe or high Mn solutions, in neutral potting soil and in calcareous soil at pH 7.8. Based on plant symptoms and dry weights, the tetraploids were generally more sensitive to these conditions than hexaploid or pentaploid clones. However, in Mn‐toxic soil, plants had leaf tip necrosis rather than the chlorosis typical of Fe deficiency. When grown in a standard potting soil at pH 7.0, plants showing chlorosis accumulated higher concentrations of phosphorus (P), Al, copper (Cu), Mn, Fe, and zinc (Zn) than non‐chlorotic plants. Differential susceptibility to chlorosis is apparently associated with interference of such elements in Fe metabolism, and not with differential Fe concentrations in plant shoots. Additional studies are needed to determine the chemical states of Fe and Mn in root zones and within plant shoots of these clones. Resolution of the differential chlorosis phenomenon would contribute to fundamental knowledge in mineral nutrition and could be helpful in tailoring plant genotypes to fit problem soils.     

Factors related to iron uptake by dicotyledonous and monocotyledonous plants. I. pH and reductant

Some plants respond to Fe‐deficiency stress by inducing Fe‐solubilizing reactions at or near the root surface. In their ability to solubilize Fe, dicotyledonous plants are more effective than monocotyledonous plants. In this study we determined how representative plants differ in their response when subjected to Fe‐deficiency stress in a calcareous soil and in nutrient solutions. Iron‐inefficient genotypes of tomato, soybean, oats, and corn all developed Fe chlorosis when grown in soil, whereas Fe‐efficient genotypes of these same species remained green. The same genotypes were grown in complete nutrient solutions and then transferred to nutrient solutions containing N (as NO₃ ^‐) and no Fe.

The T3238 FER tomato (Lycopersican esculentum Mill.) Fe‐efficient) was the only genotype that released significant amounts of H from the roots (the pH was lowered to 3.9) and concomitantly released reductants. Under similar conditions, Hawkeye soyhean [Glycine max (L.) Merr.] released reductants but the solution pH was not lowered. Both Fe‐inefficient and Fe‐efficient genotypes of oats (Avena sativa L.) and corn (Zea mays L.) released insufficient H or reductant from their roots to solubilize Fe; as a result, each of these genotypes developed Fe‐deficiency (chlorosis).

The marked differences observed among these genotypes illustrate the genetic variability inherent within many plant species. A given species or genotype may accordingly not be adapted to a particular soil. Conversely, a given species or genotype may be found (or developed) that is precisely suited for a particular soil. In this event, the need for soil amendments may be reduced or eliminated.     

Phytosiderophore release from manganese‐induced iron deficiency in barley

An experiment was conducted in the phytotron with barley (Hordeum vulgare L. cv. Minorimugi) grown in nutrient solution to compare iron (Fe) deficiency caused by the lack of Fe with manganese (Mn)‐induced Fe deficiency. Dark brown spots on older leaves and stems, and interveinal chlorosis on younger leaves were common symptoms of plants grown in either Mn‐toxic or Fe‐deficient treatments. Dry matter yield was affected similarly by Fe deficiency and Mn toxicity. The Mn toxicity significantly decreased the translocation of Fe from roots to shoots, caused root browning, and inhibited Fe absorption. The rate of Fe translocated from roots to shoots in the 25.0 μM Mn (toxic) treatment was similar to the Fe‐deficient treatment. Manganese toxicity, based on the release of phytosiderophore (PS) from roots, decreased from 25.0>250>2.50 uM Mn. The highest release of PS from roots occurred 7 and 14 days after transplanting (DAT) to Mn‐toxic and Fe‐deficient treatments, respectively; but was always higher in the Fe‐deficient treatment than the Mn‐toxic treatments. The release of PS from roots decreased gradually with plant age and with severity of the Mn toxicity symptoms. The PS content in roots followed the PS release pattern.     

Genetic Differences in Resistance to Iron Deficiency Chlorosis in Peanut

Iron (Fe) deficiency has been a widespread problem in peanut (Arachis hypogaea L.) grown on calcareous soils of northern China and has resulted in significant yield losses. Field observations showed considerable variability in visual chlorosis symptoms among peanut cultivars in the same soil. The objective of this study was to confirm the genetic differences in resistance to Fe-deficiency chlorosis in peanut and to identify feasible indicators for screening Fe-efficient genotypes. Resistance to Fe chlorosis of sixteen peanut cultivars grown on calcareous soil was evaluated in the field and physiological responses to Fe-deficiency stress were studied in nutrient solution. There were significant differences in resistance to Fe-deficiency chlorosis among the sixteen peanut cultivars tested, which was identified with SPAD readings, active Fe concentrations in young leaves in the early growth stages, and the pod yield. For Fe-resistant peanut cultivars, Fe-reduction capacity and quality of releasing hydrogen ions from roots increased under Fe-deficiency stress. Highly correlated relationships were observed between the summation of root Fe reduction and field chlorosis scores for sixteen cultivars (r² = 0.79). It was concluded that Fe-reduction capacity was a better physiological indicator for screening Fe-efficient peanut genotypes of the mechanisms measured.     

Responses of aerobically grown iron chlorosis tolerant and susceptible rice (Oryza sativa L.) genotypes to soil iron management in an Inceptisol

Iron deficiency is a serious nutritional disorder in aerobic rice, causing chlorosis, poor yields and reduced grain nutritional quality. The problem can be managed by complementing the use of Fe-efficient plant type with a suitable Fe management strategy. In the present paper, we report the effect of eight iron management practices to resolve the problem of iron (Fe) chlorosis through the use of an iron deficiency tolerant (IDTR) and iron deficiency susceptible (IDSR) rice genotype, i.e. Pusa 33 and ADT 39, respectively. Fe deficiency tolerance of these genotypes was related to the root release of PS which enabled a higher uptake of Fe in the IDTR than the IDSR under Fe deficiency. In general, IDTR performed better than the IDSR as evident from a significant increase in total iron, active iron, chlorophyll content and grain and straw yield. IDSR produced the highest grain and straw yield under slow iron release nano clay complex source. Grain Fe content of the IDTR and IDSR increased by 18.9 and 13.4%, respectively, under recommended dose of Fe. The results identified the most effective soil management strategies for the alleviating Fe deficiency chlorosis and improving Fe nutrition of both IDTR and IDSR genotypes.     

Physiological responses of grapevine callus cultures to iron deficiency

Grapevine is considered a ‘Strategy I’ plant because it performs some peculiar biochemical and physiological responses when grown under iron (Fe) deficiency stress conditions. Callus cultures were started from leaf and internode cuts of micropropagated plantlets of two grapevine genotypes well known for their Fe‐chlorosis characteristic: Vitis riparia a very susceptible genotype and Vitis berlandieri a resistant one. Modification of NADH: ferric (Fe³⁺) reductase activity was spectrophotometrically evaluated by following the formation of the complex ferrous (Fe²⁺)‐(BPDS)₃, while the malic and citric acid production were determined in callus cultures grown both in the presence (+Fe) and absence (‐Fe) of Fe. Moreover, a microsomal fraction was isolated from the calli to evaluate the H⁺‐ATPase and the Fe³⁺‐EDTA reductase activities. As expected, calli of the Fe‐efficient genotype (V. berlandieri) was able to enhance Fe³⁺‐EDTA reductase activity when growing under Fe deficiency while the Fe‐chlorosis susceptible V. riparia could not or did it with lower efficiency. Therefore, the H⁺‐ATPase assay showed a higher enzymatic activity in the microsomal fraction isolated from Vitis berlandieri grown without Fe with respect to its control (+Fe). Organic acid determination gave quite contradictory results, specially regarding malic acid which, under our study conditions, seemed not to be linked with the strategies of response to Fe deficiency.     

Phytosiderophore release by Sorghum,wheat, and corn under zinc deficiency 1

Zinc (Zn) deficiency is more common in corn (Zea mays L.) than in sorghum [Sorghum bicolor (L.) Moench] or wheat (Triticum sp.). The ability of wheat to withstand low soil Zn conditions is related to increased release of phytosiderophore from its roots. The reasons for sorghum's ability and corn's inability to utilize low levels of soil Zn have not been explored adequately. The objectives of this research were to 1) ascertain if Zn deficiency could be induced in sorghum, wheat, and corn grown in a chelator‐buffered nutrient solution and 2) determine relative releases of phytosiderophore from roots of sorghum, wheat, and/or corn under Zn‐deficiency conditions. Sorghum, wheat, and corn were grown hydroponically in the greenhouse with a chelator‐buffered nutrient solution designed to induce Zn deficiency, while supplying adequate amounts of other nutrients. Root exudates were collected over time to measure phytosiderophore release. Shoot Zn concentrations and shoot and root dry matter yields were determined also. The technique was effective for inducing Zn deficiency in sorghum, wheat, and corn, as evidenced by reduced shoot and root dry matter yields, shortened internodes, reduced shoot Zn concentrations, and plant Zn concentrations below the suggested critical values for these species. Sorghum and wheat plants increased the release of phytosiderophore in response to Zn deficiency, but com did not. The total amount of phytosiderophore released by the roots was in the order wheat>sorghum>corn. The absence of a “phytosiderophore”; response to Zn deficiency of corn, coupled with the evidence that this species requires, or at least accumulates, more Zn than wheat or sorghum, provides an explanation as to why Zn deficiencies are more prevalent for corn than wheat or sorghum under field conditions.     

Screening for resistance to iron deficiency chlorosis in dry bean using iron reduction capacity

Identifying cultivars resistant to iron (Fe) deficiency chlorosis so prevalent in calcareous soils is a more economical solution than fertilizer application in field crops. The current method of screening for resistance using chlorosis ratings in field trials is time consuming and highly variable. Root Fe reduction successfully separated cultivars or rootstocks, varying widely in resistance, of soybean (Glycine max L.), peach (Prunus persica L.), and grape (Vitis spp.), but was unsuccessful in sub‐clover (Trifolium subterraneum L.). Dry bean (Phaseolus vulgaris L.) exhibits Fe deficiency chlorosis in calcareous soils and initiates Fe reduction by the roots in response to such stress. The resistance of 24 dry bean cultivars to Fe deficiency chlorosis was assessed by measuring and summing daily Fe reduction by the roots. The cultivars were grown both hydroponically in an environmental chamber in low Fe solutions (0.05 mg‐L^‐1) and at three field sites in both 1995 and 1996. A significant relationship (P<0.01) between field chlorosis scores made 36 days after planting and root Fe reduction summations was observed for all sites in 1995 and 1996 (r = ‐0.42 to ‐0.71). The variability of chlorosis scores among sites, especially in 1996, points out the difficulty of using field chlorosis scores for screening. These results indicate that measurements of root Fe reduction can be used to predict resistance to Fe deficiency chlorosis in dry bean. Successful implementation of this technique should reduce if not eliminate field trials for screening resistance to Fe deficiency chlorosis.     

MAIZE HYBRIDS DIFFER IN THEIR 24-H PATTERNS OF PHYTOSIDEROPHORE RELEASE

Iron (Fe) chlorosis tolerant gramineous species respond to Fe-deficiency stress by releasing phytosiderophores. The objective of this study was to characterize the diurnal pattern of phytosiderophore release from Fe-chlorosis tolerant and susceptible maize (Zea mays L.) hybrids. Phytosiderophore was collected from individual, Fe-deficient maize plants in 10 mg L^?1 Micropur solution during 4-h collection periods. The diurnal pattern of phytosiderophore release differed among maize hybrids. Similar levels of phytosiderophore were released during light and dark conditions for three hybrids. Greater phytosiderophore release was measured from a fourth hybrid when the collection procedure began 2-h after the initiation of light compared to 2-h before the initiation of dark. When a single plant was used for six consecutive collection periods, phytosiderophore release declined during the final 8- to 12-h of collection. The decline in phytosiderophore release was attributed to dissolution of apoplastic Fe and deactivation of the Fe-stress response mechanism.     

根分泌物与禾本科植物对缺铁胁迫的适应机理

本文系统地总结了自然基金重点项目根分泌物在根际微生态系统中的营养机理的研究进展和部分主要成果。研究表明,养分专一性根分泌物是植物营养遗传特性控制基因的标记物,它受某一养分缺乏的诱导,是在植物体内合成并可通过主动分泌作用进入根际的代谢产物。它的合成和分泌只受该养分胁迫的专一诱导和控制,只要改善这一营养状况就能抑制或阻止其合成和分泌。当植物缺乏这一养分时,植物体可通过自身的调节能力,合成专一性物质并自根分泌到根际,促进该养分的活化并提高植物对其吸收利用效率,从而达到克服或缓解该营养胁迫的目的。用单基因突变材料进行的研究表明,植物铁载体的生物合成和吸收利用是受单基因控制的过程。这一发现不仅使人类有可能运用生物学研究技术来解决营养缺乏问题,而且也为有效地利用自然资源、降低生产成本、减少环境污染提供了可能性。麦根酸类(mugineic.acids)植物铁载体(phytosiderophores)在缺铁禾本科植物体内的生物合成,从植物根内向根际的分泌、在根际环境中对铁的活化及植物对F63+植物铁载体螯合体的吸收四个过程组成了禾本科植物对缺铁胁迫的适应机理。植物铁载体只在早晨日出后2～6h内大量分泌的节律性增加了它们在根际土壤中的相对浓度,减少了它们与土壤颗粒的接触和被吸附;分泌部位集中在微生物尚未侵染的根尖避开了微生物的破坏和分解,同时也增加了它们在土壤微区中的相对浓度。分泌作用和螯合作用不受介质pH值和Ca2+离子浓度影响的特性使该机理在经常出现缺铁现象的石灰性土壤上具有特殊意义。研究结果还表明,缺铁可以诱导激活根细胞原生质膜上可能存在的Fe3+植物铁载体复合体的专一性吸收和运载蛋白,高pH值和CaCO3对这一蛋白的载体功能只有很小的抑制作用,即使在pH值和CaCO3含量都较高的石灰性土壤上,也能有效地发挥作用。这一结论揭示了小麦等禾本科植物适应铁胁迫的实质及其生态学意义。     

Physiological basis of iron chlorosis tolerance in rice (Oryza sativa) in relation to the root exudation capacity

Micronutrient deficiency in cultivable soil, particularly that of iron (Fe) and zinc (Zn), is a major productivity constraint in the world. Low Fe availability due to the low solubility of the oxidized ferric forms is a challenge. An experiment was, thus, executed to assess the performance of eight genetically diverse rice genotypes on Fe-sufficient (100 µM) and Fe-deficient (1 µM) nutrient solution, and their ability to recover from Fe deficiency was measured. Fe efficiency under Fe deficiency in terms of biomass production showed a significant positive correlation with the root release of phytosiderophore (PS) (R² = 0.62*). This study shows that the Fe deficiency tolerance of Pusa 33 was related to both a high release of PS by the root and an efficient translocation of Fe from the root to the shoot as the Fe–PS complex, which could be useful for improving the Fe nutrition of rice particularly under aerobic conditions.     

Soybean genotype evaluation for iron deficiency chlorosis using sodium bicarbonate and tissue culture

The evaluation of soybean genotypes for resistance to iron deficiency through field experiments is complicated by variation in symptom expression. The objective of this study was to develop a tissue culture technique that could distinguish between Fe‐efficient and Fe‐inefficient genotypes. Ten soybean genotypes varying in sensitivity to iron deficiency were planted at 5 locations and rated based on chlorosis expression. For the lab evaluation, friable callus of the ten genotypes was placed on a 4MSII medium amended with 10 mM NaHCO₃. Callus growth reduction relative to a control medium without NaHCO₃ was recorded. Callus weight of all cultivars was affected by the addition of NaHCO₃ however, significant differences in growth reduction among genotypes was observed. The high correlation between callus growth reduction and field chlorosis ratings observed (r²=0.92) and the fact that the expiant source plant can be grown to produce seed indicates that this technique would be useful in a soybean breeding program.     

Activities of Iron‐Containing Enzymes in Leaves of Two Tomato Genotypes Differing in Their Resistance to Fe Chlorosis

Abstract

Two tomato (Lycopersicon esculentum Mill., cvs. Pakmor and Target) genotypes differing in resistance to iron (Fe) deficiency were grown in nutrient solution under controlled environmental conditions over 50 days to study the relationships between severity of leaf chlorosis, total concentration of Fe, and activities of Fe‐containing enzymes in leaves. The activities of Fe‐containing enzymes ascorbate peroxidase, catalase, and guaiacol peroxidase, and additionaly the activity of glutathione reductase, an enzyme that does not contain Fe, were measured. Plants were supplied with 2 × 10^?7 M (Fe deficient) and 10^?4 M (Fe sufficient) FeEDTA, respectively. Leaf chlorosis appeared more rapidly and severely in Target (Fe deficiency senstive genotype) than Pakmor (Fe deficiency resistant genotype). On day 50, Pakmor had 2‐fold more chlorophyll than Target under Fe deficiency, while at adequate supply of Fe the two genotypes were very similar in chlorophyll concentration. Despite distinct differences in development of leaf chlorosis and chlorophyll concentrations, Pakmor and Target were very similar in concentrations of total Fe under Fe deficiency. In contrast to Fe concentration, activities of Fe‐containing enzymes were closely related to the severity of leaf chlorosis. The Fe‐containing enzymes studied, especially catalase, showed a close relationship with the concentration of chlorophyll and thus differential sensitivity of tomato genotypes to Fe deficiency. Glutathione reductase did not show relationship between Fe deficiency chlorosis and enzyme activity. The results confirm that measurement of Fe‐containing enzymes in leaves is more reliable than the total concentration of Fe for characterization of Fe nutritional status of plants and for assessing genotypical differences in resistance to Fe deficiency. It appears that Fe deficiency‐resistant genotype contains more physiologically available Fe in tissues than the genotype with high sensitivity to Fe deficiency.     

Evaluation of world collection of kabuli chickpea for resistance to iron-deficiency chlorosis

Summary Iron-deficiency chlorosis is often seen in chickpea (Cicer arietinum L.) fields in the Mediterranean region and is particularly severe in fields where iron-deficiency susceptible cultivars are sown. Therefore, ICARDA's breeding programme field evaluated 6224 kabuli chickpea germplasm accessions for iron-deficiency chlorosis on a high pH Calcic Rhodoxeralf soil (pH 8.5, 20–25% calcium carbonate) at Tel Hadya, Syria during the winter and spring of 1987/88. Two resistant and 17 susceptible lines were grown during autumn, winter and spring of 1988/89 to examine the effect of sowing time on the appearance of the deficiency. About 99% of accessions showed no iron-deficiency symptoms. Evaluation of susceptible accessions during autumn, winter, and spring sowing revealed that iron-deficiency chlorosis was more pronounced during winter sowing. There were also significant genotype x season interactions, indicating differential responses of genotypes to time of sowing. Since the iron-deficiency chlorosis character is controlled by recessive genes, a negative selection to discard the susceptible lines from breeding material is recommended as an effective breeding strategy.Joint contribution from ICARDA and ICRISAT (International Crops Research Institute for Semi-Arid Tropics), Patancheru P.O., A. P. 502 324, India.