Comparative Study of Nutrient Deficiencies on Growth and Photochemistry of Tobacco

Abstract

Element deficiencies, such as molybdenum (Mo), iron (Fe), calcium (Ca), lead to disturbances of morphological and physiological processes of tobacco (Nicotiana tabacum L.). On exposure to nutrient solution without Mo, leaf morphology was significantly affected, whereas photosynthetic processes conserved their normal activities. The decreased Mo, Fe, and Ca concentrations in tobacco were associated with loss of pigments and photosynthetic disturbances. In Ca‐deficient plants a reduction in the rate constant of energy trapping by PSII centers and a physical dissociation of LHC from PSII core, were observed. The poisonous action of Fe and Ca deficiencies focused mainly in the decreased proportion of active chlorophyll associated with the reaction center (RC) of PSII (decreased F _v /F ₀) and in the declined total number of electrons that have gone through the RCs (decreased Area/F _m  ? F ₀). In parallel, the non‐photochemical quenching coefficient was significantly enhanced in Fe and Ca‐deficient plants, but remained unchanged in Mo‐deficient plants. It is obvious that nutrient deficiency may trigger some protective mechanisms in order to PSII could maintain its activity under that type of stress.     

Differences in Response to Iron Deficiency Among Some Lines of Common Bean

Abstract

Five dry bean cultivars (Coco blanc, Striker, ARA14, SVM29‐21, and BAT477) were evaluated for their resistance to iron deficiency on the basis of chlorosis symptoms, plant growth, capacity to acidify the external medium and the root‐associated Fe³⁺‐reduction activity. Plants were grown in nutrient solution supplied or not with iron, 45 µM Fe(III)EDTA. For all cultivars, plants subjected to iron starvation exhibited Fe‐chlorosis. These symptoms were more severe and more precocious in BAT477 and Coco blanc than in the others cultivars. An important acidification of the culture medium was observed between the 4th and the 8th days of iron starvation in Striker, SVM29‐21 and, particularly, ARA14 plants. However, all Fe‐sufficient plants increased the nutrient solution pH. This capacity of acidification appeared more clearly when protons extrusion was measured in 10 mM KCl + 1 mM CaCl₂. The above genotypic differences were maintained: ARA14 showed the higher acidification followed by Coco blanc and BAT477. Iron deficiency led also to an increase of the root‐associated Fe(III)‐reductase activity in all lines. However, genotypic differences were observed: Striker shows the highest capacity of iron reduction under Fe deficiency condition.     

Organic Acid Metabolism in Roots of Various Grapevine (Vitis) Rootstocks Submitted to Iron Deficiency and Bicarbonate Nutrition

Abstract

The effects of Fe limitation and bicarbonate addition to the nutrient medium on the organic acid metabolism were investigated in the root tips of various grapevine genotypes. Cuttings of two limestone‐tolerant and two limestone‐susceptible Vitis genotypes were grown for four weeks in nutrient solutions containing 10 or 0.5 µM Fe. The effect of bicarbonate addition (5 mM) was studied for two of these genotypes. Compared to 10 µM, Fe limitation (0.5 µM) significantly increased citrate concentration in root tips after 2 weeks, and malate concentration after 4 weeks. When Fe limitation and bicarbonate addition were combined, citrate and malate concentrations were significantly increased after 2 weeks. Fe limitation or addition of 5 mM bicarbonate had a larger effect on citrate than on malate concentrations. Addition of 5 mM bicarbonate discriminated more clearly tolerant and susceptible genotypes than Fe limitation. High malate and citrate concentrations in the roots were associated to high PEPC activities. These results confirm that root organic acid metabolism is involved in grapevine response to Fe deficiency stress. If verified on a larger range of genotypes, a procedure using bicarbonate effect on root tip citrate concentration could be proposed to screen limestone‐tolerant Vitis rootstocks.     

Purple versus green‐leafed Ocimum basilicum: Which differences occur with regard to photosynthesis under boron toxicity?

This study was undertaken to investigate how different cultivars of sweet basil (Ocimum basilicum) responded to boron (B) excess. Two purple‐leafed and eight green‐leafed cultivars were hydroponically grown for 20 d with 0.2 or 20 mg L^–1 B in the nutrient solution. Leaf B concentration, gas exchanges, chlorophyll a fluorescence, and oxidative stress were determined at the end of the treatment along with the severity of leaf necrosis. A range of tolerance to B toxicity was found: the green cultivars were more susceptible than the purple‐leafed ones characterized by a higher constitutive anthocyanin concentration. In all the genotypes B excess resulted in oxidative stress as determined by accumulation of malondialdehyde by‐products (MDA), reduced photosynthesis, and the occurrence of leaf burn. A close correlation was found between leaf B accumulation and oxidative stress, as well as between oxidative stress and the severity of leaf burn. Net photosynthesis (P_n) was reduced due to both stomatal and nonstomatal limitations in the green cultivars whereas the reduction of P_n in the purple leaves was only attributable to stomatal factors. Chlorophyll a fluorescence revealed a decrease in the maximum quantum yield of PSII (F_v/F_m) and in the electron transport rate (ETR) in plants grown with B excess although less reduction was observed in the purple genotypes. The quantum yield of PSII (Φ_PSII) decreased as a result of B toxicity only in the green cultivars. It is concluded that anthocyanins are involved in attenuation of the negative effects of B toxicity.     

Uptake and Translocation of Copper in Brassicaceae

Abstract

Ten cvs. of four Brassicaceae species were tested to evaluate their copper (Cu) uptake and translocation. Germination and root length tests indicated that Brassica juncea cv. Aurea and Raphanus sativus cvs. Rimbo and Saxa were the species with the highest germinability and longest roots at Cu concentrations ranging from 25 up to 200 µM. Raphanus sativus cv. Rimbo grown in hydroponic culture at increasing Cu concentrations (from 0.12 up to 40 µM) for 10 days produced a relatively high biomass (17.2 mg plant^?1) at the highest concentration and had a more efficient Cu translocation (17.8%) in comparison with cvs. Aurea and Saxa. The potential of cv. Rimbo for Cu uptake was then followed for 28 days at 5, 10, and 15 µM Cu. In comparison with the control, after 28 days of growth the 15 µM Cu‐treated plants showed a reduction in the tolerance index (?40%) and in the above‐ground dry biomass (?19%). On the contrary, an increase in the below‐ground dry weight was observed (+35%). Copper accumulated during the growth period both in the below‐ and above‐ground parts (about 14 and 4 µg plant^?1 at 10 and 15 µM Cu, respectively), but the translocation decreased from 50 to 30% in the last week at all the concentrations used. In addition, cv. Rimbo grown in a multiple element [cadmium (Cd), chromium (Cr), Cu, lead (Pb), and zinc (Zn)] naturally‐contaminated site accumulated all elements in the above‐ground part in a range from 5 to 62 µg plant^?1.     

Comparison of the effects of nano-iron fertilizer with iron-chelate on growth parameters and some biochemical properties of Catharanthus roseus

Nanofertilizers, which supply nutrients to the plant, are used to replace conventional fertilizers. Iron (Fe) is one of the essential elements for plant growth and plays an important role in the photosynthetic reactions. To study the effects of nano-iron fertilizer on Catharanthus roseus, plants were treated with different concentrations (0, 5 10 20, 30, and 40 mM) of iron oxide nanoparticles (Fe2O3) for 70 days. Fe₂O₃ nanoparticles increased growth parameters, photosynthetic pigments, and total protein contents in the treated plants significantly. The maximum amounts of growth parameters, photosynthetic pigments, and protein contents were obtained with 30 µM Fe₂O₃ and minimum values of these parameters were found with 0 µM Fe₂O₃. The highest value of total alkaloid content was obtained in 0 µM Fe₂O₃ and the lowest value was observed in control plants. Iron oxide nanoparticles increased potassium, phosphorus, and iron absorption but did not show a significant effect on sodium content.     

Transport of Foliar Applied Iron (59Fe) in Vicia faba

Abstract

Radioactively labeled iron (⁵⁹Fe) was used to study iron retranslocation from mature leaves of Broad bean (Vicia faba L. var. Scirocco). Our experiments offered the possibility to detect and quantify the translocation of foliar applied iron by imaging technique in combination with tissue analysis. ⁵⁹Fe labeled solution was placed as a droplet onto the leafs upper surface of intact plants. Distribution of ⁵⁹Fe was analyzed after 0.5 h up to 2 days. Iron was translocated acropetally (towards the tip of the treated leaf) as well as basipetally. Movement in the apical direction was predominant, amounting to about 65% of ⁵⁹Fe translocated from the application site. About 35% of ⁵⁹Fe were transported basipetally, corresponding to absolute amounts of 2.8–53.6 pmol h^?1. After 30 min, it was detectable in the petiole, which included a translocation of 20 mm basipetal from the application site. A mean of 15% of the iron retranslocated from a leaflet was detected in non‐treated leaflets of the same leaf. This iron was supposed to have been exchanged from the phloem into the xylem pathway, probably within the petiole. When the loading rate into the phloem was estimated on basis of the sum of retranslocated ⁵⁹Fe per time and per area of the leaf treated, a range of 0.031–2.21 pmol h^?1 mm^?2 (mean: 0.62 pmol h^?1 mm^?2) was obtained. This was not sufficient to meet an estimated demand for iron in the growing terminal bud, but could cover about 25% of it. In conclusion, average iron retranslocation from leaves of Fe‐sufficient plants was not large enough to meet the iron demand of the growing shoot. This was not due to a limitation in iron availability for transport, as an excess amount of iron was supplied which was not biologically bound, but a limitation due to transport facilities, probably in the phloem, seemed to be more likely in this case.     

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.     

IRON IS REQUIRED FOR THE INDUCTION OF ROOT FERRIC CHELATE REDUCTASE ACTIVITY IN IRON-DEFICIENT TOMATO

Two mutants of tomato and their corresponding wild-type genotypes, Tfer/TFER and chloronerva/Bonner Beste, were grown in nutrient solution under conditions leading to iron (Fe) deficiency. Iron deficiency caused decreases in growth, leaf chlorosis, and changes in the morphology of roots. Ferric chelate reductase activities of whole roots were generally lower in Fe-deficient plants than in control, Fe-sufficient plants. Plants grown for 7 days without Fe, however, had transient increases in whole root ferric chelate reductase activity after the addition of small amounts of Fe (2 μM) to the nutrient solution. Also, adding sequential 0.5 μM Fe pulses to the nutrient solution led to high whole root ferric chelate reductase activities. Similar results were obtained with a protocol using excised root tips instead of whole root systems to measure ferric chelate reductase activities. The protocol using root tips generally gave higher ferric chelate reductase rates than the method using whole roots, due to the localized expression of the enzyme in the distal root zones.     

Impact of Boron on Biomass Production and Nutrition of Aluminum‐Stressed Apple Rootstocks

Abstract

The aim of the experiment was to examine the effect of boron (B) on biomass production and nutrition of aluminum (Al)‐stressed apple (Malus sp.) rootstocks. The study was carried out under greenhouse conditions on Polish rootstock (P22) and Malling 26 (M.26) planted singly into 1‐L plastic pots filled with perlite and supplied with Hoagland's medium at pH 4.5 without or with Al (100 µM as AlCl₃). Boron was added into the Al‐containing medium at 20, 40, or 60 µM whereas into the medium without Al only at 20 µM as boric acid. The results showed that the presence of Al in the medium reduced biomass production of P22 and M.26 rootstocks by 22% and 41%, respectively. Rates of uptake and translocation of phosphorus (P), magnesium (Mg), and calcium (Ca) to aerial plant parts were decreased for Al‐treated rootstocks. Aluminum‐stressed P22 rootstocks grown in nutrient solution at 40 and 60 µM B had higher dry weight of leaves and roots, and also higher ability to take up P, Mg, and Ca and lower Al than those grown in the presence of Al at 20 µM B in the medium. Rates of absorption and transport of B to aerial plant parts corresponded with B level in the medium. These results suggest that on acid soils with high Al availability, supra‐optimal B concentrations in soil solution (40–60 µM) can prevent/alleviate Al toxicity in apple trees grafted on P22 rootstocks.     

Uptake and translocation of iron from ferrated rhodotorulic acid in tomato

Micro‐organisms may develop an iron‐deficiency stress when grown in an alkaline environment and secrete ferric‐specific chelators known as siderophores. Some of these siderophores may have stability constants which can exceed 30. This is comparable to the synethetic Fe chelate FeEDDHA. Our objective was to determine if the Fe‐efficient T3238 FER tomato and the Fe‐inefficient T3238 fer tomato could use iron supplied as the siderophore ferrated‐rhodotorulic acid. After these two tomato cultivars were grown with adequate nutrition to obtain plants large enough for experimental testing, they were grown without iron until Fe‐deficiency‐stress symptoms developed and then iron was supplied as ferrated‐rhodoturulic acid. Iron efficient T3238 FER tomato utilized iron supplied as the siderophore and greened whereas, the Fe‐inefficient T3238 fer tomato plants were chlorotic because they could not use the iron in the siderophore. This study demonstrated that some higher plants subjected to various degrees of iron‐deficiency stress in nutrient culture may derive their iron requirement from siderophores of microbial origin.     

Methods for evaluating human impact on soil microorganisms based on their activity,biomass, and diversity in agricultural soils

The present review is focused on microbiological methods used in agricultural soils accustomed to human disturbance. Recent developments in soil biology are analyzed with the aim of highlighting gaps in knowledge, unsolved research questions, and controversial results. Activity rates (basal respiration, N mineralization) and biomass are used as overall indices for assessing microbial functions in soil and can be supplemented by biomass ratios (C : N, C : P, and C : S) and eco‐physiological ratios (soil organic C : microbial‐biomass C, qCO₂, qN_min). The community structure can be characterized by functional groups of the soil microbial biomass such as fungi and bacteria, Gram‐negative and Gram‐positive bacteria, or by biotic diversity. Methodological aspects of soil microbial indices are assessed, such as sampling, pretreatment of samples, and conversion factors of data into biomass values. Microbial‐biomass C (µg (g soil)^–1) can be estimated by multiplying total PLFA (nmol (g soil)^–1) by the F_PLFA‐factor of 5.8 and DNA (µg (g soil)^–1) by the F_DNA‐factor of 6.0. In addition, the turnover of the soil microbial biomass is appreciated as a key process for maintaining nutrient cycles in soil. Examples are briefly presented that show the direction of human impact on soil microorganisms by the methods evaluated. These examples are taken from research on organic farming, reduced tillage, de‐intensification of land‐use management, degradation of peatland, slurry application, salinization, heavy‐metal contamination, lignite deposition, pesticide application, antibiotics, TNT, and genetically modified plants.     

Iron stress response in tomato affected by potassium and renewing nutrient solutions

Iron‐efficient T3238FER tomatoes (Lycopersicon esculentum Mill.) did not respond to Fe‐deficiency stress by releasing hydrogen ions and reductants from their roots when the plants were grown in a K‐deficient nutrient solution with or without sodium. When increments of K were added to the nutrient solution, the plants responded proportionally to Fe‐deficiency stress, Fe was transported to plant tops and the chlorophyll concentration in plant tops increased. As the leaf Fe concentration was increasing, root K concentration was increasing and root Mn concentration was decreasing. The K and Mn in tops did not show the marked differences observed in roots.

In the presence of adequate K, renewing the solutions each time the pH was lowered to near 4 (days 7 and 11) caused an increased concentration of most elements in the plant, especially Mn in both tops and roots. These plants had the same Fe concentration as plants grown in unchanged solutions but they contained much less chlorophyll. Balance of nutrient elements to some degree seems required in order for iron to be made available to function properly in the plant.     

Does the Sulfur Assimilation Pathway Play a Role in the Response to Fe Deficiency in Maize (Zea mays L.) Plants?

Abstract

The finding that the methionine is the sole precursor of the mugineic acid family phytosiderophores induced us to evaluate whether sulfur assimilation pathway has a role in plant response to Fe deficiency. Maize plants were grown for 10 days in nutrient solution (NS) containing 80 µM Fe in the presence (+S) or absence (?S) of sulfate. After removing the root extraplasmatic iron pool, half of the plants of each treatment (+S and ?S) were transferred to a new Fe deficient NS (0.1 µM final Fe concentration) (?Fe). The remaining plants of each pre‐culture condition (+S and ?S) were transferred to a new NS containing 80 µM Fe (+Fe). Leaves were collected 4 and 24 hours from the beginning of Fe deprivation period and used for chemical analysis and enzyme assays. Results showed that iron content in the leaves was lower in plants grown in S‐deficiency than in those grown in the presence of the macro‐nutrient. Iron deprivation produced an increase in the level of SH compounds in both nutritive conditions (+S and ?S). These observations are suggestive of some relationship between S nutrition and Fe uptake. For this reason, we next investigated the influence of Fe availability on S metabolism through the evaluation of changes in ATPs and OASs activity, the first and the last enzyme of S assimilation pathway respectively. Results showed that S‐starvation increased the activity of both enzymes, but this effect disappeared in plants upon Fe deficiency suggesting that S metabolism is sensitive to Fe availability. Taken together these evidences suggest that S metabolism is sensitive to soil Fe‐availability for plant nutrition and support the hypothesis of S involvement in plant response to Fe deprivation.     

Responses of photosynthesis,chlorophyll fluorescence,and grain yield of maize to controlled‐release urea and irrigation after anthesis

Controlled‐release urea (CRU) is a new type of urea, which may increase crop nitrogen (N)‐use efficiency compared with conventional urea (CU), but the conditions where it outperforms urea are not well defined. A field experiment assessing responses of plant growth and grain yield of maize to CRU and irrigation was conducted on a typical agricultural farm in Shandong, China. Five treatments of the two types of urea (75, 150 kg N ha^–1, 0 kg N ha^–1) were applied as basal fertilizer when sowing maize, and two water treatments (W₀ and W₁) were used 23 d after anthesis. Net photosynthetic rate (P_N) and chlorophyll concentration as well as leaf‐area index (LAI) increased significantly by both CRU and CU application, with the increases being larger in CRU‐treated plants than in CU‐treated plants at grain filling and maturing stages. CRU significantly enhanced the maximum photochemical efficiency (F_v / F_m), PSII coefficient of photochemical fluorescence quenching (q_P), and actual quantum yield of PSII electron transformation (Φ_PSII) but decreased the nonphotochemical quenching (NPQ). Cob‐leaf N concentration of CRU‐treated plants was significantly higher than that of CU‐treated plants under no irrigation, but not in the irrigation treatment 30 d after anthesis. Significant positive correlations were found between cob‐leaf N concentration and P_N both with and without irrigation. Grain yield of maize was significantly higher in the CRU treatment than in the CU treatment under both irrigation conditions. In conclusion, CRU as a basal application appeared to increase the N‐use efficiency for maize relative to CU especially by maintaining N supply after anthesis.     

Methodology to Screen New Iron Chelates: Prediction of Their Behavior in Nutrient Solution and Soil Conditions

Abstract

Iron chelates analogous to ethylenediamino‐di(o‐hydroxyphenyl)acetic acid (EDDHA) are the fertilizers chosen to treat iron chlorosis of crops grown on calcareous soils. Characterization of these synthetic ligands should be made to establish their chemical behavior and efficiency as chlorosis correctors. The aim of this research was to develop an appropriate methodology to screen new iron chelates using analytical determinations and chemical equilibrium concepts. Fe‐EDDHA, Fe‐EDDH4MA, Fe‐EDDH5MA, and Fe‐PDDHA chelates, were compared to check the proposed methodology. Titrimetric purity, protonation and Ca, Mg, and Fe(III) stability constants, pFe and species distribution in nutrient solution and soil conditions were determined. The iron chelate stability constants were in order EDDHA > EDDH4MA > EDDH5MA > PDDHA. When pFe was calculated, the larger value corresponds to Fe‐EDDHA chelate at pH below 8; but at pH above 8 the Fe‐EDDH4MA shows the larger pFe values. When the species was plotted against pH, the dominant species was FeL^? at the physiological pH range in all cases. The pH at a FeL/L_T ratio of 80% in both Fe(OH)_3amorp and Fe_soil systems was considered as an iron chelate stability index. This index was EDDH4MA > EDDH5MA > EDDHA > PDDHA in both systems, but shows that all of the chelates tested were sufficiently stable in most soil and nutrient solution conditions. In conclusion, the proposed procedure is adequate for the preliminary evaluation of the synthetic chelating agents, using important parameters such as analytical and speciation properties to predict their chelating behavior and efficiency in nutrient solution and soil conditions.     

Mobility of Iron and Manganese within Two Citrus Genotypes after Foliar Applications of Iron Sulfate and Manganese Sulfate

Seedlings of sour orange (Citrus aurantium L.) and Carrizo citrange (C. sinensis L. cv. Washington navel x Poncirus trifoliata)] were grown in plastic pots containing a sand: perlite mixture and watered with a modified Hoagland No 2 nutrient solution throughout the experiment. Three-months-old plants were divided in three groups and sprayed with 0.018 M iron sulfate (FeSO₄ ^.7H₂O), 0.018 M manganese sulfate (MnSO₄ ^.H₂O), or deionized water. Two months later, plants were harvested and divided into top leaves that grown after the treatments, basal leaves that existed prior to the treatments, stems that partially came in contact with the spray, and roots. The manganese (Mn) spray resulted in a significant increase of Mn concentrations in top leaves, basal leaves, stems and roots of sour orange, and in top leaves, basal leaves, and stems of Carrizo citrange. The iron (Fe) spray significantly increased the concentrations of Fe in the stems and basal leaves of both genotypes. For both genotypes, transport of Mn from basal (sprayed) leaves to top (unsprayed) ones was found. However, the results of this experiment did not give any evidence neither for Mn translocation from sprayed tissues to roots nor for Fe transport from sprayed tissues to unsprayed ones (top leaves, roots). Mn and Fe were found to be relatively mobile and strictly immobile nutrients, respectively, within citrus plants after their foliar application as sulfate salts.     

Effectiveness of Fe3+-citrate and Fe3+-edta in ameliorating arsenic-toxicity (chlorosis) in hydroponic rice

Effectiveness of iron (Fe³⁺)-citrate and Fe³⁺-EDTA (ethylenediaminetetraacetic acid) in reducing arsenic (As)-toxicity in rice was evaluated. The treatments: 1) 0 µM As + 10 µM Fe³⁺-citrate (control), 2) 13.4 µM As + 10 µM Fe³⁺-citrate (As-treated), 3) 13.4 µM As + 10 µM Fe³⁺-citrate + 40 µM Fe³⁺-citrate (additional Fe³⁺-citrate), and 4) 13.4 µM As + 10 µM Fe³⁺-citrate + 40 µM Fe³⁺-EDTA (additional Fe³⁺-EDTA) were studied for 14 days. Chlorosis was found in the young leaves of the As-treated plants. Additional Fe³⁺-citrate failed to remediate the chlorosis, however, additional Fe³⁺-EDTA removed the chlorosis almost completely, indicating that the effectiveness of Fe³⁺-EDTA was much higher than Fe³⁺-citrate. The Fe³⁺-EDTA treated plants were greener than the additional Fe³⁺-citrate treated plants. Iron concentration in the shoots of additional Fe³⁺-EDTA plants was much higher than that of additional Fe³⁺-citrate plants, indicating that Fe³⁺-EDTA might have been more readily available to the plants roots than Fe³⁺-citrate.     

Associating SSR Markers with Soybean Resistance to Iron Deficiency Chlorosis

Abstract

Iron deficiency chlorosis (IDC) causes soybean yield loss to growers when certain varieties are planted on calcareous soils. Planting IDC‐resistant varieties is the best management practice, although they may still exhibit chlorosis under certain environmental conditions. Environmental variation for chlorosis expression impedes progress in improving IDC resistance. Breeders could use molecular marker‐assisted selection (MAS), an environment‐independent tool, to improve soybeans' resistance to IDC. Our objective was to determine the efficiency of simple sequence repeat (SSR) markers in selecting for IDC resistance in soybean. A breeding population was developed using parents differing in IDC resistance and yield potential. The population was advanced to the F₂ and F_2:4 generations. Foliar chlorosis data were recorded for parents and F_2:4 lines in replicated field tests planted on calcareous soils at two Iowa locations in 2000 and 2001. Chlorosis scores between parents and F_2:4 lines varied according to location and year. Genotypic data were obtained on individual F₂ plants, and association between chlorosis scores and allele segregation was tested by single‐factor analysis of variance using 2001 data. Three SSR markers were associated (P ≤ 0.1) with chlorosis scores at each location; however, the identity of the markers associated with chlorosis scores was different at each location. In addition, two SSR markers associated with IDC resistance were examined for their efficacy in improving breeding efficiency. Preliminary data presented herein demonstrate the importance of environment on expression of this soil‐stress factor and the potential of using SSR markers as an environment‐independent selection tool for breeding IDC resistance in soybean.     

Diagnosis of Sulfur Status of Winged Bean [Psophocarpus Tetragonolobus (L.) Dc] by Plant Tissue Analysis

Winged bean [Psophocarpus tetragonolobus (L.) DC] plants, line UPS31, were grown in pots of sulfur (S)-deficient soil in a glasshouse without added S or with five levels of added S. The seed was inoculated with rhizobia (Bradyrhizobia sp. strain CB756) and plants were later given additional mineral nitrogen (N). Harvests of shoots were made at 39 and 78 days after sowing (DAS). Shoot dry matter yield, total S (S_T), S reducible by hydriodic acid (S_HI) – a measure of sulfate – and N were determined. At 78 DAS, the critical concentration (at 90% maximum yield) of S_T in shoots was 0.9 mg S g^?1 dry matter and in young leaves was 1.4 mg S g^?1 dry matter. Plants with these concentrations or below would be considered S-deficient. The usefulness of critical concentrations of S_HI or ratios of S_HI/S_T, and N/S_T as indicators of S status is discussed.