Zn-efficient Genotypes Research Articles

Revisiting the role of organic acids in the bicarbonate tolerance of zinc-efficient rice genotypes

It has been hypothesised that enhanced organic acid release from the roots of zinc-efficient rice (Oryza sativa L.) genotypes plays a strong role in plant tolerance to both bicarbonate excess and Zn deficiency. To address several uncertainties in the literature surrounding the tolerance of rice to bicarbonate, we initially assessed the tolerance of six rice genotypes to bicarbonate stress under field conditions and in solution culture. The landrace Jalmagna and its recombinant inbred offspring, RIL46, consistently performed better in terms of maintenance of biomass and root length under high bicarbonate concentrations. In the hydroponic experiments, increased root malate (but not citrate) accumulation and efflux were responses to high solution bicarbonate in the short-term (12h) in all genotypes. Although both citrate and malate accumulation and efflux increased after long-term exposure (10 days) to high bicarbonate and Zn deficiency, it coincided with amino acid leakage from the roots. Partial least-squares regression showed that this leakage consistently ranked highly as an indicator of poor plant health under all stress conditions, whereas specific malate efflux (the ratio of malate to amino acid efflux) was an important predictor of good plant health. The root leakage of Zn-inefficient genotypes under bicarbonate and dual stress (bicarbonate with low Zn) was typically higher than in Zn-efficient genotypes, and coincided with higher peroxide concentrations, suggesting that bicarbonate tolerance is related to the ability of Zn-efficient genotypes to overcome oxidative stress, maintain root membrane integrity and minimise root leakage.

COMPARISON OF ZINC EFFICIENCY AMONG WINTER WHEAT GENOTYPES CULTURED HYDROPONICALLY IN CHELATOR-BUFFERED SOLUTIONS

Zinc (Zn) efficient genotypes grow and yield well in Zn deficient environments. The objective of this study was to compare Zn efficiency and seed Zn content among nine winter wheat (Triticum aestivum L.) genotypes grown in chelator-buffered nutrient solutions containing 0 μmol Zn L−1 (−Zn treatment) or 3 μmol Zn L−1 (+Zn treatment). The Zn efficiency of the genotypes ranged from 24% to 46%. Zinc efficiency was positively correlated with shoot dry weight, shoot Zn content, but there was no significant correlation between Zn efficiency and shoot Zn concentration, seed Zn concentration, or seed Zn content. The results suggested that variation in Zn efficiency among these nine wheat genotypes is genetically inherent. Differences in Zn efficiency among these wheat genotypes, which are widely grown in northern China, indicate the potential to breed for wheat genotypes with increased tolerance to soil Zn deficiency.

Influence of arbuscular mycorrhizal fungi on uptake of Zn and P by two contrasting rice genotypes

There is little experimental evidence about the functional significance of arbuscular mycorrhizal fungi (AMF) colonization in providing nutrients for lowland rice. This study was undertaken to examine whether growth and nutrient deficiencies may affect plants benefit from AMF inoculation. Two contrasting rice (<I>Oryza sativa</I> L.) genotypes and two AMF species (<I>Glomus mosseae</I> and <I>G. intraradices</I>) were used in this experiment. Under P starvation, P uptake in the genotype tolerant to P deficiency (Fajr), declined significantly up to 36% (<I>P</I> < 0.05) in response to AMF inoculation, while it enhanced by about 70% (<I>P</I> < 0.01) in susceptible genotype (Shafagh). Under Zn starvation, Zn uptake of Zn-efficient genotype (Shafagh) increased by about 2 fold (<I>P</I> < 0.01), but a reduction of 52% (<I>P</I> < 0.05) was observed in the Zn-inefficient genotype (Fajr) upon mycorrhization. Greater genotypic differences were observed for –P–Zn plants. Our results imply that genotypic difference in responsiveness to inoculation with AMF is attributable to different contribution of mechanisms for increased nutrient uptake in mycorrhizal plants depending on nutrient, nutritional status and nutrient efficiency of genotypes.

Growth Responses to Varying Zinc Activities in Rice Genotypes Differing in Zn Efficiency and Zn Density

ABSTRACT The relationship between tolerance to Zn-deficiency and Zn-dense in grain was examined. The results showed that the plant height and leaf growth rate (number) decreased more in the Zn-dense genotype (Biyuzaonuo) than in the Zn-efficient genotype (IR8192) when grown at pZn2+ ≥ 11.0. Shoot dry matter yield decreased about 6 times for the dense CV whereas only around 3 times for the efficient CV at Zn activities pZn2+ 9.7–11.4. Zinc uptake by the whole plant was greater in the Zn-dense genotype than in the Zn-efficient genotype, and the lowest in the Zn-inefficient genotype grown at pZn2+ ≥ 11.0. However, both the efficient and the dense cultivars showed higher Zn translocation efficiency at low Zn activity. These results indicate that Zn uptake by rice seedling and translocation might be more suitable than growth parameters for identifying Zn-efficient and Zn-dense genotype at seedling stage.

Effect of heavy manuring of phosphorous and its toxicity on growth, photosynthesis and photosynthetic pigments in Zn-efficient genotype of spearmint MSS-5

Effect of heavy manuring of phosphorous and its toxicity on growth, photosynthesis and photosynthetic pigments in Zn-efficient genotype of spearmint MSS-5

Genetic Analysis on Agronomic Traits Related to Zinc Efficiency in Lowland Rice

The hereditary characteristics of plant traits related to zinc (Zn) efficiency in lowland rice (Oryza sativa L.) were analyzed in this study. The plant traits include the relative values of the total plant dry matter, shoot dry matter, root dry matter, leaf number, plant height, and root length of rice seedlings grown at low Zn2+ activity compared to those at sufficient Zn2+ activity. The F1 progeny was obtained by using a diallel cross between Zn-efficient and Zn-inefficient rice genotypes. The results revealed that the variances of dominant effect of all the traits studied were significant or very significant with the ratio being more than 65.4% of total variance. The additive effect variances of other traits except for the root length were also significant or very significant, with the average ratio being 21.85% of total variance. The variance of epistatic effect for root length was significant, with a ratio of 48% of total variance. The relative values of root length at low Zn2+ activity to sufficient Zn2+ activity was found to be governed by dominant and additive effects of hereditary genes. The relative values of leaf number, plant height and dry matter weight of rice seedlings were mainly governed by dominant effects of genes, secondarily by additive effects of genes. As the ability of rice tolerance to Zn deficiency was closely related to these agronomic traits, zinc efficiency in rice was mainly governed by dominant effects of genes, secondarily by additive effects of genes, and might be influenced by its epistatic effects of genes.

Effect of bicarbonate on elongation and distribution of organic acids in root and root zone of Zn-efficient and Zn-inefficient rice ( Oryza sativa L.) genotypes

Bicarbonate content in growth medium has been considered to be one of the major factors in inducing zinc (Zn) deficiency in lowland rice. In this study, the effects of bicarbonate on root elongation, distribution and exudation of organic acids were examined in the Zn-efficient and Zn-inefficient rice genotypes. Bicarbonate significantly increased the growth of fine roots in the Zn-efficient genotype but inhibited their growth in the Zn-inefficient genotype. In fine root zones of 2–8 mm from the tip, of plants grown with bicarbonate, malate, citrate, and fumarate accumulation was greater in the Zn-inefficient genotype, but not the Zn-efficient genotype, than the control. Enhanced exudation of malate at fine root zones of 1–2 cm from the tip by bicarbonate was noted in the Zn-efficient genotype, but not in the Zn-inefficient genotype. Bicarbonate induced greater exudation of citrate at fine root zones of 1–2 cm from the tip in the Zn-efficient than in the Zn-inefficient genotypes. The increase in the concentrations of malate and citrate in xylem sap by bicarbonate were found to be greater for the Zn-efficient genotype than that for the Zn-inefficient genotype. The results indicated that bicarbonate-mediated inhibition of fine root elongation in the Zn-inefficient genotype might result from excessive accumulation of organic acids, particularly malate, in root elongation zones. In the Zn-inefficient rice genotype the increased accumulation of malate and citrate in fine roots by bicarbonate appeared to result from less exudation of them to the rhizosphere and transport up to the shoots.

Genotypic variation in common bean in response to zinc deficiency in calcareous soil

Greenhouse experiments have been carried out to study the genotypic variation among 35 bean (Phaseolus vulgaris L.) genotypes with regards to tolerance to zinc (Zn) deficiency (Zn efficiency). Plants were grown for 45 days in Zn deficient soil supplemented with 0 or 5 μg Zn g−1 soil) and analyzed for Zn efficiency, plant Zn concentration and content, and the distribution of Zn between old and young parts of the shoot. Zn efficiency (ZE) was defined as the ratio of dry matter production at low and high Zn supply and was calculated for the whole shoot as well as for young and old parts of the shoot. There were marked differences in ZE among the bean genotypes. Genotypes G4449 and G11360 were about 2-fold and 10-fold more Zn-efficient than G11229 and G3871 in whole shoot and young-part based ZE, respectively. Interestingly, the older portions of the shoot for most genotypes had higher dry matter production under Zn deficiency than under sufficient Zn supply, suggesting that there was a significant inhibition of new shoot growth and transport of photosynthates from source to sink organs under low-Zn conditions. Zinc concentrations of both old and young portions of the shoot did not correlate with ZE, but shoot Zn content was found to be significantly correlated with ZE. Furthermore, Zn-efficient genotypes distributed more Zn into young parts of the shoot under Zn-deficient conditions than did the inefficient lines. Variation in seed Zn content did not significantly influence the determination of ZE. We concluded that there is a substantial variation in Zn efficiency in the bean genome, and ZE based on analysis of the young shoot tissues represents a suitable screening technique for the evaluation of ZE in low-Zn soils.

The role of shoot-localized processes in the mechanism of Zn efficiency in common bean.

Zn efficiency (ZE) is the ability of plants to maintain high yield under Zn-deficiency stress in the soil. Two bean ( Phaseolus vulgaris L.) genotypes that differed in ZE, Voyager (Zn-efficient) and Avanti (Zn-inefficient), were used for this investigation. Plants were grown under controlled-environment conditions in chelate-buffered nutrient solution where Zn(2+) activities were controlled at low (0.1 pM) or sufficient (150 pM) levels. To investigate the relative contribution of the root versus the shoot to ZE, observations of Zn-deficiency symptoms in reciprocal grafts of the two genotypes were made. After growth under low-Zn conditions, plants of nongrafted Avanti, self-grafted Avanti and reciprocal grafts that had the Avanti shoot scion exhibited Zn-deficiency symptoms. However nongrafted and self-grafted Voyager, as well as reciprocal grafts with the Voyager shoot scion, were healthy with no visible Zn-deficiency symptoms under the same growth conditions. More detailed investigations into putative shoot-localized ZE mechanisms involved determinations of leaf biomass production and Zn accumulation, measurements of subcellular Zn compartmentation, activities of two Zn-requiring enzymes, carbonic anhydrase and Cu/Zn-dependent superoxide dismutase (Co/ZnSOD), as well as the non-Zn-requiring enzyme nitrate reductase. There were no differences in shoot tissue Zn concentrations between the Zn-inefficient and Zn-efficient genotypes grown under the low-Zn conditions where differences in ZE were exhibited. Shoot Zn compartmentation was investigated using radiotracer ((65)Zn) efflux analysis and suggested that the Zn-efficient genotype maintains higher cytoplasmic Zn concentrations and less Zn in the leaf-cell vacuole, compared to leaves from the Zn-inefficient genotype under Zn deficiency. Analysis of Zn-requiring enzymes in bean leaves revealed that the Zn-efficient genotype maintains significantly higher levels of carbonic anhydrase and Cu/ZnSOD activity under Zn deficiency. While these data are not sufficient to allow us to determine the specific mechanisms underlying ZE, they certainly point to the shoot as a key site where ZE mechanisms are functioning, and could involve processes associated with Zn compartmentation and biochemical Zn utilization.

Zinc efficiency is correlated with enhanced expression and activity of zinc-requiring enzymes in wheat.

Zinc (Zn) is an essential micronutrient for plants. The ability of plants to maintain significant yields under low Zn is termed Zn efficiency (ZE) and its genetic and mechanistic basis is still not well understood. Previously, we showed that root Zn uptake did not play a role in ZE. In the current study, Zn-efficient and -inefficient wheat (Triticum aestivum) genotypes were grown for 13 d in chelate buffer nutrient solutions at low (0.1 pM), sufficient (150 pM), and high (1 microM) Zn(2+) activities and analyzed for root-to-shoot translocation of Zn, subcellular leaf Zn distribution, and activity and expression of the Zn-requiring enzymes in leaves. No correlation between ZE and Zn translocation to the shoot was found. Furthermore, total and water-soluble concentrations of leaf Zn were not associated with ZE, and no differences in subcellular Zn compartmentation were found between Zn-efficient and -inefficient genotypes. However, the expression and activity of the Zn-requiring enzymes copper (Cu)/Zn superoxide dismutase (SOD) and carbonic anhydrase did correlate with differences in ZE. Northern analysis suggested that Cu/ZnSOD gene expression was up-regulated in the Zn-efficient genotype, Kirgiz, but not in inefficient BDME. Under Zn deficiency stress, the very Zn-efficient genotype Kirgiz and moderately Zn-efficient Dagdas exhibited an increased activity of Cu/ZnSOD and carbonic anhydrase when compared with Zn-inefficient BDME. These results suggest that Zn-efficient genotypes may be able to maintain the functioning of Zn-requiring enzymes under low Zn conditions; thus, biochemical Zn utilization may be an important component of ZE in wheat.

Effects of bicarbonate and high pH on growth of Zn-efficient and Zn-inefficient genotypes of rice, wheat and rye

A range of Zn efficient and inefficient genotypes of rice (Oryza sativa L.), wheat (Triticum aestivum L. and Triticum durum L.) and rye (Secale cereale L.) were investigated to examine shoot and root growth response to bicarbonate and high pH at different Zn levels. The treatment of bicarbonate was 10 mM as NaHCO3, high pH was 8.0 buffered with HEPES, and three Zn levels included without addition of Zn (deficient Zn), with 0.5 and 1.0 μM Zn (moderate Zn), and 1.5 and 3.5 μM (high Zn) for rice and wheat or rye, respectively. For rice, shoot and root growth of Zn-inefficient genotypes was strongly inhibited, whereas root length of Zn-efficient genotypes was considerably enhanced by bicarbonate. High pH had much less effect on reduced root growth of the Zn-inefficient rice genotypes and enhanced root length of the Zn-efficient genotypes, as compared with bicarbonate. Responses of plants to bicarbonate at different Zn levels showed that under deficient or moderate Zn supply conditions, root dry weight and length were significantly increased for the Zn-efficient rice genotypes, but were decreased for the Zn-inefficient rice genotypes grown with bicarbonate. At high Zn supply, however, root elongation of the Zn-efficient rice genotypes and of the Zn-inefficient genotypes was enhanced. In contrast to rice, either bicarbonate or high pH had little effects on shoot and root growth for all the Zn-efficient and Zn-inefficient wheat genotypes except for Dagdas (Zn-efficient) at moderate Zn levels. Decreased root growth due to bicarbonate treatment was observed only in the Zn-efficient rye. Root lengths of all the wheat and rye genotypes except for Kunduru (Zn-inefficient) were reduced by high pH but not affected by bicarbonate. At deficient Zn levels, shoot growth was reduced by bicarbonate for both Zn-efficient rye and inefficient wheat genotypes. Root lengths was reduced due to bicarbonate for the Zn-inefficient wheat genotype at deficient and high Zn, but not at moderate Zn levels. The results imply that Zn efficiency in rice is closely associated with plant tolerance to bicarbonate relative to root growth, and bicarbonate tolerance and Zn efficiency might be developed simultaneously in lowland rice.

Zn fertilization improves water use efficiency, grain yield and seed Zn content in chickpea

In a number of the major chickpea-growing areas in the world, rainfed crops of chickpeas are often grown on soils with low available zinc (Zn). Consequently, chickpea crops can be challenged by soil water deficits and Zn deficiency coincidentally during the growing season. The interaction between these stresses was examined in two glasshouse experiments using genotypes differing in Zn efficiency. Water stress was imposed during podding. Increasing the level of Zn resulted in large and significant increases in vegetative growth up to podding. Applying Zn increased grain yields when the plants were well watered, but not under water stress, except for the Zn-efficient and drought-resistant genotype ICC-4958. Harvest indices were generally reduced as the supply of Zn and water increased. Applying Zn increased water use and water use efficiency of chickpea. Yields were reduced by water stress, largely due to fewer pods set per plant. Losses from water stress were greatest at the highest level of Zn, which was attributed to the limited soil volume afforded by the pots and the rapid development of stress in the larger plants grown at adequate levels of Zn. However, at each level of Zn, the loss in yield from water stress tended to be less in a Zn-efficient genotype. The major factor determining the distribution of Zn in the plant was the supply of Zn, while differences due to water stress and genotype were relatively small. Two-thirds of the Zn present in the plant at maturity was accumulated after the start of podding and this was little affected by water stress. The proportion of Zn in the roots of Zn-deficient plants was less than that in Zn-adequate plants. As the Zn supply increased, Zn accumulation was higher in leaves than in the stem and reproductive parts, due to combined effect of both higher Zn concentration and higher dry matter. At maturity, senesced leaves and pod walls had relatively lower concentrations of Zn compared to leaves and pods at the start of podding in all Zn treatments. In contrast, the Zn content in the stem either increased or remained unchanged. At maturity, Zn accumulation in plant organs generally increased with increasing Zn supply, but the largest proportion of Zn was found in the seeds, which is a beneficial nutritional trait for human nutrition.

A soil-based method to screen for zinc efficiency in seedlings and its ability to predict yield responses to zinc deficiency in mature plants

Nutrient efficiency measures the ability of a plant to grow and produce grain when the availability of a nutrient is low. Seedling tests for nutrient efficiency will be most useful if the results correlate well with grain yield responses. In two experiments, a diverse range of barley genotypes was screened for zinc (Zn) efficiency at the seedling stage and the relationship between vegetative and grain measures of Zn efficiency was examined. In Expt 1, 54 barley and 4 wheat genotypes were grown at 2 levels of Zn (0.02 and 0.8 mg/kg soil) for 21 days. Zinc efficiency ranged from 18% to 52%. The visual symptoms of Zn deficiency varied considerably between genotypes and was significantly correlated with Zn efficiency. Root:shoot ratio was increased by Zn deficiency and varied between genotypes, but these differences were not related to Zn efficiency. Zinc concentration and especially Zn content at 0.02 mg Zn/kg were significantly related to Zn efficiency. In Expt 2, 15 genotypes, selected on the basis of their response in Expt 1, were grown to maturity at either 0.1 mg Zn/kg or 2.4 mg Zn/kg. Zn efficiency, based on relative grain yield, ranged from 5% to 54%. High efficiency was associated with a large number of grains per plant and high kernel weight. Rankings of Zn efficiency in the experiment were significantly correlated with the rankings for visual scores in Expt 1. The 2 experiments suggested that deficiency symptoms at the seedling stage can identify efficient genotypes and could be useful for routine screening for Zn efficiency. Independent data from multisite comparisons over 8 years were used to examine the long-term performance of efficient and inefficient genotypes in the field. Hierarchical cluster was used to define efficient and inefficient groupings within the 56 genotypes examined in Expt 1, based on their responses to Zn. The Zn-efficient genotypes tended to yield more than the Zn-inefficient genotypes. The data provide prima facae evidence that high Zn efficiency may contribute to improved adaptation of barley in South Australia.

TOLERANCE OF 65 DURUM WHEAT GENOTYPES TO ZINC DEFICIENCY IN A CALCAREOUS SOIL

Sixty-five durum wheat (Triticum turgidum ssp. durum) genotypes were grown in a zinc (Zn)-deficient calcareous soil in a greenhouse for 32 days with (+Zn=5 mg Zn kg−1 soil) and without (−Zn) Zn supply to study genotypic variation in tolerance to Zn deficiency. Genotypes were ranked for their tolerance to Zn deficiency based on the relative shoot growth (Zn efficiency ratio) defined as the ratio of shoot dry weight under Zn deficiency to the shoot dry weight under adequate Zn supply. Zinc deficiency resulted in marked decreases in shoot dry matter production of the genotypes following 32 days of growth. Shoot dry weight of most genotypes was similar under adequate Zn supply, but differed greatly under Zn deficiency. Consequently, the Zn efficiency ratio showed a large variability and ranged between 20% to 51%. Generally, the genotypes showing lower tolerance to Zn deficiency had lower absolute shoot dry weight under Zn deficiency than the genotypes having greater tolerance to Zn deficiency. Differences in tolerance to Zn deficiency were related very significantly to the total amount (content) of Zn per shoot of the genotypes, but poorly to the concentration of Zn in shoot. As the shoot Zn concentration did not vary much between the genotypes under Zn deficiency, the higher amount of Zn per shoot of the Zn-efficient genotypes was a reflection of their greater shoot dry weight. Seed Zn concentration of the genotypes was quite similar and ranged from 18 to 25 mg kg−1 DW for almost all genotypes. Therefore, the genotypic variation in tolerance to Zn deficiency was most likely inherent and not related to the seed Zn content. The results of the present study show existence of a large variation in tolerance to Zn deficiency in durum wheat, and suggest that the absolute shoot growth like the relative shoot growth (Zn efficiency ratio) can be used as a reliable plant parameter for screening the durum wheat genotypes for their tolerance to Zn deficiency, provided that genotypes have a similar growth rate under adequate Zn supply.

Screening method of lowland rice genotypes for zinc uptake efficiency

Zinc deficiency in crop plants has been recognized as a worldwide nutritional constraint. A greenhouse experiment was conducted with the objective of developing a screening technique to evaluate lowland rice genotypes for zinc use efficiency. Ten lowland (Oryza sativa L.) genotypes were tested at low (0 mg Zn kg-1) and high (10 mg Zn kg-1) zinc levels applied to an Inceptisol. Genotypes differed significantly in grain yield and its components. Based on the grain yield efficiency index, genotypes were classified as efficient and inefficient. The most Zn efficient genotypes were: Metica 1, Epagri 108, CNA 7550, and CNA 8619. The most inefficient genotype was CNA 8319. The moderately efficient genotypes were: Javae, Rio Formoso, CNA 7556, and CNA 7857. The screening method used for Zn use efficiency is simple and does not require plant analysis. This methodology can be used for crop genotype evaluation of mineral stresses, which have direct bearings in genetic studies and breeding programes

GENOTYPIC DIFFERENCES IN MICRONUTRIENT USE EFFICIENCY IN CROPS

When grown on soils with low micronutrient availability due to either chemical or biological fixation, or spatial or temporal unavailability, micronutrient-efficient genotypes have a greater yield in comparison to inefficient ones, even when fertilized with smaller amounts of fertilizers or less frequently. This review summarizes published information on genotypic differences in Zn, Fe and Mn efficiency. Generally, micronutrient-efficient genotypes are capable of increasing available soil micronutrient pools through changing chemical and microbiological properties of the rhizosphere as well as by growing thinner and longer roots and having more efficient uptake and transport systems. For Zn-efficient genotypes, more efficient utilization of Zn in tissue also contributes to overall Zn efficiency. Understanding micronutrient efficiency mechanisms is important for designing suitable screening techniques for breeding micronutrient-efficient genotypes. Growing micronutrient-efficient genotypes contributes to environmentally-benign agriculture by lowering the input of chemicals and energy. These genotypes also offer a potential for producing grain for human consumption with higher concentration of Fe, Zn and Cu, the three micronutrients that about a third of the world population is deficient in.

Alfalfa genotypes differ in their ability to tolerate zinc deficiency

Response of 13 alfalfa (Medicago sativa L.) genotypes to varied Zn supply (+Zn: 2 mg kg−1 soil, −Zn: no added Zn) was studied in a pot experiment under controlled environmental conditions. Plants were grown for four weeks in a Zn-deficient siliceous sandy soil. Plants grown at no added Zn showed typical Zn deficiency symptoms i.e. interveinal chlorosis of leaves, yellowish-white necrotic lesions on leaf blades, necrosis of leaf margins, smaller leaves and a marked reduction in growth. There was solute leakage from the leaves of Zn-deficient plants, while no solute leakage from Zn-sufficient plants. The ratios of P:Zn, Fe:Zn, Cu:Zn and Mn:Zn in Zn-deficient plants were extremely high compared with Zn-sufficient plants indicating disturbance of P:Zn, Fe:Zn, Cu:Zn and Mn:Zn balance within plant system by Zn deficiency. Genotypes differed markedly in Zn efficiency based on shoot dry matter production. Alfalfa genotypes also differed markedly in P:Zn ratio, Cu:Zn ratio and Fe:Zn ratio under —Zn treatment. The shoot dry weight, shoot:root ratio, chlorophyll content of fresh leaf tissue, solute leakage from the leaves, Zn uptake and distribution of Zn in shoots and roots were the most sensitive parameters of Zn efficiency. Zn-efficient genotypes had less solute leakage but higher shoot:root ratio and higher Zn uptake compared with Zn-inefficient genotypes. Under —Zn treatment, Zn-inefficient genotypes had less Zn partitioning to shoots (33–37%) and more Zn retained in roots (63–67%), while Zn-efficient genotypes had about equal proportions of Zn in roots (50%) and shoots (50%).

Chickpea genotypes differ in their sensitivity to Zn deficiency

Zinc (Zn) deficiency is common in most of the chickpea growing areas of the world and growing Zn-efficient genotypes on Zn-deficient soil is a benign approach of universal interest. Response of 13 chickpea genotypes (10 desi and 3 kabuli) to Zn nutrition was studied in a pot experiment under glasshouse conditions. Plants were grown in a Zn-deficient siliceous sand for 6 weeks and fertilized with 0 (Zn−) and 2.5 mg Zn per kg soil (Zn+). When grown with no added Zn, Zn deficiency symptoms (chlorosis of younger leaves and stipules followed by necrosis of leaf margins) appeared 3–4 weeks after planting and were more apparent in cultivars Tyson, Amethyst and Dooen than Kaniva and T-1587. Zn deficiency reduced shoot growth, but it was less affected in breeding lines T-1587 and CTS 11308 than cultivars Tyson, Dooen, Amethyst and Barwon. Among all genotypes, Tyson produced the lowest root dry weight in Zn– treatment. Zinc efficiency based on shoot dry weight showed marked differences among genotypes; breeding lines CTS-60543, CTS-11308 and T-1587 were 2-fold more Zn-efficient than cultivars Tyson and Dooen. A higher Zn accumulation per plant and higher Zn uptake per g. of root dry weight were recorded in T-1587 and CTS-11308 when compared with Tyson. Root:shoot ratio was increased and proportionally more Zn was transported to the shoot when the soil was deficient. Cultivars that were very sensitive to Zn deficiency tended to have their root:shoot ratio increased by Zn deficiency more than less sensitive cultivars. The insensitive lines T-1587 and CTS-11308 transported more than 70% of the total absorbed Zn to the shoot. It is concluded that chickpea genotypes vary in their sensitivity to Zn deficiency. Advanced breeding lines T-1587 and CTS-11308 are relatively more Zn-efficient compared with Australian chickpea cultivar Tyson. Zn efficiency in chickpea genotypes is probably related to an efficient Zn absorption coupled with a better root to shoot transport.

Residual effects of subsoil zinc and oilseed rape genotype on the grain yield and distribution of zinc in wheat

The residual effects of Zn supplied (+Zn: 1 mg kg−1 soil, -Zn: no Zn added) in subsoil to four oilseed rape genotypes (Zhongyou 821, Xinza 2 and Narendra: Brassica napus type, and CSIRO-1: Brassica juncea type) were studied on the following wheat in a glasshouse experiment in pots (100 cm long, 10.5 cm diameter). The topsoil (upper 20 cm soil in pots) was supplied with Zn (0.5 mg kg−1 soil) in all treatments whereas Zn (1 mg Zn kg−1 dry soil) was either supplied or omitted from the subsoil at time of sowing of oilseed rape genotypes. Oilseed rape plants were harvested at maturity and wheat (variety Songlen) was grown to evaluate the residual effects of subsoil Zn and oilseed rape genotypes. Subsoil residual Zn significantly improved the root growth, yield attributes, grain and straw yield of wheat. Wheat grain Zn concentration was 4 times higher in +Zn subsoil residual than under -Zn subsoil residual. Oilseed rape genotypes did not vary in their residual effect on grain and straw yield of wheat, but reflected a differential effect on Zn concentration and Zn content of wheat grain. Zinc uptake per wheat plant (grain + shoot + root Zn uptake) was about 4 times higher in +Zn subsoil residual than -Zn subsoil residual. Out of total Zn uptake per plant, 77%, 15% and 8% of Zn was loaded in wheat grains, shoots and roots respectively in +Zn subsoil residual. However in -Zn subsoil residual, distribution of Zn in grains, shoots and roots was 55%, 29% and 16% respectively. Zinc loading in grains of wheat was significantly higher in wheat grown after Narendra and Xinza 2 compared with wheat grown after Zhongyou 821 (Zn-inefficient genotype). These results indicate that subsoil residual Zn and Zn-efficient genotypes of oilseed rape have the potential to increase the Zn loading in wheat grains.

Herbicide chlorsulfuron decreases growth of fine roots and micronutrient uptake in wheat genotypes

Two Triticum aestivum (Excalibur and Gatcher) and one Triticum turgidum conv. durum (Durati) genotypes (differing in the ability to grow and yield well in environments with low Zn availability) were grown in chelate-buffered, complete nutrient solutions providing either deficient or sufficient Zn supply and supplemented with sulphonylurea herbicide chlorsulfuron [2-chloro-N-(((4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino)-carbonyl)-benzenesulphonamide] at 0 or 4 mg m -3 . Compared to Zn-sufficient roots, plants grown under Zn deficiency had thicker roots on average, with a shorter length of the fine roots (diameters <0.2 mm). Chlorsulfuron decreased growth of roots in the <0.2 mm diameter class during the first 4 d of exposure (14-18-d-old plants) and completely inhibited growth of these roots for the remaining 6 d of exposure. The Zn-efficient genotype Excalibur maintained a longer length of roots with diameters <0.2 mm and had a greater root surface area than the other two, non-efficient genotypes regardless of plant age or Zn nutrition. Chlorsulfuron tended to decrease net uptake of Cu and Mn in all three genotypes, and net uptake of Zn in Gatcher and Durati, regardless of the duration of exposure. In contrast, 6-10 d of exposure to chlorsulfuron were required for a reduction in net Zn uptake by Zn-efficient Excalibur. In conclusion, chlorsulfuron affects the growth of fine roots and interferes with micronutrient uptake per unit of wheat root. The inherent trait of having a longer length of the roots with diameters <0.2 mm lessens the deleterious impact of chlorsulfuron on root growth and micronutrient uptake in Zn-efficient Excalibur compared to the other two wheat genotypes.