Assessment of the Zn status of chickpea by plant analysis

Chickpea (Cicer arietinum L.) is extensively grown in areas where soils are deficient in zinc (Zn). To determine the response of chickpea to Zn nutrition and to diagnose Zn status in plant tissue, two glasshouse experiments were conducted using Zn-deficient siliceous sandy soil. In Experiment 1, two genotypes of desi chickpea (Dooen and Tyson) were grown at five Zn levels (0, 0.04, 0.2, 1.0 and 5.0 mg kg^-1 of soil). After 4 weeks, no difference in growth and no visible symptoms of Zn deficiency were detected. After 6–8 weeks of growth, chlorosis of younger leaves and stipules occured in the Zn₀ treatment, with shoot dry weight being only 24% of that recorded at the highest Zn level. Root growth increased from 0.52 g/plant when no Zn was applied to 1.04 g/plant in the treatment with 0.2 mg Zn kg^-1 of soil; no response to further increase of Zn fertilization occurred. Zinc concentration in the whole shoot increased significantly with increased in Zn application. The critical Zn concentration in the shoot tissue, associated with 90% of maximum growth, was 20 mg kg^-1 for both genotypes at flowering stage.In the second experiment, two genotypes of desi chickpea (Tyson and T-1587) were grown at three Zn levels (0, 0.5 and 2.5 mg kg^-1 of soil) under two moisture regimes (field capacity 12% w/w, and water stress 4% w/w). Shoot growth was influenced by both Zn supply and water stress. The effect of water stress was severe in the 0.5 and 2.5 mg Zn treatments where shoot dry matter was reduced 52 and 46%, respectively. T-1587 was less sensitive to Zn deficiency and produced higher shoot dry weight than Tyson in the Zn₀ treatment. Zinc concentration in shoots increased from 5 mg kg^-1 when no Zn was applied to 40 mg kg^-1 at the highest Zn level. The critical Zn concentration in shoots was 21 mg kg^-1.The results of the two experiments showed that the critical concentration for Zn did not differ amongst the three cultivars used and was not affected by soil moisture. Similar studies should be undertaken with a wider number of genotypes to discover if a critical concentration of 20–21 mg kg^-1 in the shoot can be used to diagose the Zn status of chickpea genotypes.     

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%). This revised version was published online in June 2006 with corrections to the Cover Date.     

Seed zinc content influences early vegetative growth and zinc uptake in oilseed rape (Brassica napus and Brassica juncea) genotypes on zinc-deficient soil

Low-Zn seed (around 80 ng Zn per seed) and high-Zn seed (around 160 ng Zn per seed) of Zhongyou 821 (a traditional Brassica napus genotype from China found to be Zn-inefficient in our previous experiments), Narendra (Zn-efficient B. napus genotype from Australia) and CSIRO-1 (a Zn-efficient B. juncea genotype from Australia) oilseed rape genotypes were sown in pots containing Zn-deficient siliceous sand fertilized with low Zn supply (0.05 mg Zn kg^–1 soil) or high Zn supply (2.0 mg Zn kg^–1 soil) in a controlled environment. After six weeks, plants derived from the high-Zn seed had better seedling vigour, increased root and shoot growth, more leaf area and chlorophyll concentration in fresh leaf, and higher Zn uptake in shoot compared to those from low-Zn seed at low Zn supply; the impact of high-Zn seed was more marked in Zhongyou 821 compared with CSIRO-1 and Narendra. The influence of high-Zn seed was dissipated at high Zn supply. CSIRO-1 was superior in terms of shoot dry matter production and Zn uptake in shoots at low Zn supply. The results demonstrate that although oilseed rape has very small seeds (about 3 mg per seed weight) compared with wheat (30 mg per seed weight), Zn reserves present in this very small seed still have a strong impact on early vegetative growth as well as on Zn uptake of plants in Zn-deficient soils. The results suggest that sowing high-Zn seed coupled with growing Zn-efficient genotypes may help in sustaining the production of oilseed rape in Zn-deficient soils, and this has implications for improved seed technology.     

Differential expression of zinc efficiency during the growing season of barley

Considerable genetic variation exists in zinc (Zn) efficiency among cereal species and genotypes within the same species. Currently, the mechanisms of Zn efficiency are not understood well; however, the research so far suggests that overall Zn efficiency can be partitioned into uptake, utilisation and translocation or remobilisation efficiency, all or some of which collectively determine the level of Zn efficiency in a particular genotype. In a growth room study, using two barley genotypes differing in Zn efficiency (Zn-efficient Unicorn and Zn-inefficient Amagi Nijo), we attempted to determine which of these components of Zn efficiency contributed to greater Zn efficiency in Unicorn, by examining growth responses to Zn over a wide range of Zn fertilisation rates (0, 0.05, 0.2, 0.8, 3.2 and 12.8 mg Zn/kg soil) during the entire growth period. Zn-efficient Unicorn showed less severe Zn deficiency symptoms, produced more dry matter, and grain yield under Zn deficient conditions compared with Zn-inefficient Amagi Nijo. These responses also varied with the level of Zn deficiency stress and growth stage. Most importantly, the greater Zn efficiency (e.g., ability to grow well under Zn deficiency) at maturity of Unicorn was due to greater translocation of Zn from vegetative to reproductive organs or greater ability to produce higher grain yield with limited Zn rather than Zn uptake from soil which was similar in both genotypes. Zn-efficient Unicorn also had a lower critical deficiency concentration for grain (12 mg Zn/kg DW) than the Zn-inefficient Amagi Nijo (18 mg Zn/kg DW), suggesting a lower requirement for metabolic processes in Zn-efficient Unicorn. The critical deficiency concentration in the grain has the potential to diagnose Zn-deficient soils. The results also show that grain Zn concentration can be increased by Zn fertilisation, with significant increases occurring above the Zn fertilisation rate that is adequate for production of grain. However, genetic variation in grain Zn concentration should be explored and wild relatives of barley may offer potential for crop improvement for this trait.     

Zinc efficiency of oilseed rape (t Brassica napus and t B. juncea) genotypes

Twenty five genotypes of oilseed rape (canola and mustard) were tested under varied supply of Zn (+Zn: 2 mg kg^–1 soil, -Zn: no Zn added) in two pot experiments in soil culture to determine the genotypic variation in tolerance to the Zn-deficient conditions, that is, to identify the Zn-efficient genotypes. On the basis of performance of genotypes in pot experiments, ten genotypes were tested in 1995 for their performance under varied supply of Zn (+Zn: 3.5 kg ha^–1, -Zn: no Zn added) on a Zn-deficient field in South Australia.Zn efficiency (ratio of shoot dry matter in -Zn to shoot dry matter in +Zn treatment and expressed in percentage) in pot Experiment 1 varied from 35% for 92-13 to 74% for Siren. Narendra, Dunkeld, Barossa, Oscar and Xinza 2 performed well under -Zn treatment. Zn efficiency in Experiment 2 varied from 32% for Wuyou 1 to 62% for Pusa Bold. Pusa Bold and CSIRO-1(mustard genotypes) were the most efficient in terms of dry matter production among all the oilseed rape genotypes tested. Root dry matter accumulation was significantly higher in Zn-efficient genotypes. Zn efficiency (ratio of seed yield in -Zn to seed yield in +Zn and expressed in percentage) in field experiment varied from 62% for Huashang 2 to 76% for Dunkeld. With few exceptions, the ranking of genotypes in pot and field experiments indicates similarity in their response to Zn deficiency. There looks to be genetic control over Zn concentration in tissues. Zn-efficient genotypes had lower Zn concentration in roots and higher Zn concentration in youngest fully opened leaf blades, indicating a better transport of Zn. This, together with a higher Zn uptake, appears to be the basis of expression of Zn efficiency.     

Genotypic variation in zinc efficiency and resistance to crown rot disease (Fusarium graminearum Schw. Group 1) in wheat

A crown rot disease in wheat caused by the fungusFusarium graminearum Schw. Group 1 is a widespread problem in chronically Zn-deficient Australian soils. A link between crown rot and Zn deficiency was established by Sparrow and Graham (1988). This paper reports a test of a further hypothesis, that wheat genotypes more efficient at extracting zinc from low-zinc soils are more resistant to infection by this pathogen. Three wheat cultivars (Excalibur, Songlen and Durati) of differential Zn efficiency were tested at three zinc levels (0.05, 0.5 and 2.0 mg Zn kg⁻¹ of soil) and three levels ofF. graminearum S. Group 1 inoculum (0.1 g and 0.3 g kg⁻¹ live chaff-inoculum and control having 0.1 g kg⁻¹ dead chaff inoculum). Six weeks after sowing dry matter production of shoots and roots was decreased byFusarium inoculation at 0.05 mg and 0.5 mg kg⁻¹ applied Zn.Fusarium inoculum at 0.1 g was as effective as 0.3 g kg⁻¹ for infection and decreasing dry matter. The infection at the basal part of culm decreased significantly by increasing the rate of Zn application. Excalibur, a Zn-efficient cultivar (tolerant to Zn deficiency) produced significantly more shoot and root dry matter, and showed less disease infection compared with Zn-inefficient cultivars (Durati and Songlen) at low (0.05 mg Zn kg⁻¹ soil) and medium (0.5 mg Zn kg⁻¹ soil) Zn fertilization rates. Higher rate of Zn fertilization (2.0 mg Zn kg⁻¹ soil) reduced the disease level in Durati to the level of Excalibur but the disease level of Songlen was still high, indicating its high Zn requirement and or sensitivity to crown rot. The data on Zn uptake show that Excalibur, being Zn-efficient, was able to scavenge enough Zn from Zn-deficient soil, we suggest that besides sustaining growth Excalibur was able to build and maintain resistance to the pathogen; inefficient cultivars needed extra Zn fertilization to achieve performance comparable to that of Excalibur. The present study indicates that growing Zn-efficient cultivars of wheat along with judicious use of Zn fertilizer in Zn-deficient areas where crown rot is a problem may sustain wheat production by reducing the severity of the disease as well as by increasing the plant vigour through improved Zn nutrition. ei]Section editor: R Rodriques-Kalana     

Zinc fertilization and water stress affects plant water relations, stomatal conductance and osmotic adjustment in chickpea (Cicer arientinum L.)

Chickpea (Cicer arietinum) is an important dryland pulse crop in many parts of the world. Productivity is often limited by periods of water deficit and in a number of regions zinc deficiency occurs, but the interaction between zinc nutrition and water stress has not been studied extensively. This interaction was examined in two glasshouse experiments. Chickpea was grown under deficient (no applied Zn) or adequate (2.5 μg Zn/g soil) levels of zinc in pots for either 53 days (Experiment 1) or 40 days (Experiment 2) before being exposed to a single period of water stress that lasted for 12 days (Experiment 1) or 23 days (Experiment 2). In one experiment four genotypes (Tyson, ICC-4958, T-1587 and NIFA-88) differing in their sensitivity to zinc deficiency were compared during a single drying cycle, and in the second experiment a single cultivar (Tyson) was compared under well-watered and water stress conditions. Water stress was induced by allowing the soil to dry gradually and the responses in shoot biomass, water use, plant water relations and carbon isotope discrimination (Δ, ‰) were measured. Shoot biomass, water use and water use efficiency were reduced by zinc deficiency. Stomatal conductance was lower in zinc-deficient plants as well. Zinc deficiency reduced Δ by about 1‰ and there were significant differences in Δ between genotypes which were independent of the level of zinc nutrition. At an adequate level of zinc there was a significant negative correlation between Δ and shoot biomass and between Δ and water use efficiency among the four chickpea genotypes, but these correlations were not significant under zinc deficiency. Osmotic potential was lower and turgor higher in the leaves of zinc-deficient plants, but the ability to adjust osmotically was reduced by zinc deficiency as stress developed. In conclusion, zinc-deficiency reduced the efficiency with which the water was used for biomass production and compromised the plant’s capacity to respond to water stress by osmotic adjustment.     

Domesticated emmer wheat [T. turgidum L. subsp. dicoccon (Schrank) Thell.] as a source for improvement of zinc efficiency in durum wheat

Modern durum wheat (AABB) is more sensitive to zinc (Zn) deficiency than bread wheat (AABBDD). One strategy to increase productivity and expansion of durum wheat industry in Zn-deficient soils is to improve its ability to grow and yield in such soils. This ability is termed Zn efficiency. In a growth room experiment using soil culture, we assessed the potential of Triticum turgidum L. subsp. dicoccon (Shrank) Thell. (domesticated emmer wheat, AABB) as a genetic resource for further improvement of Zn efficiency in modern durum wheat. Twenty four accessions of domesticated emmer wheat, four durum landraces/cultivars, and two bread wheat cultivars/ advanced breeders lines of known Zn efficiency were tested under Zn deficiency and Zn sufficiency. Significant variation was observed among genotypes in Zn deficiency symptoms, dry matter production, shoot Zn concentration, shoot Zn content and Zn utilisation efficiency (physiological efficiency). We identified domesticated emmer wheat accessions with greater Zn efficiency than modern durum wheat and even bread wheat genotypes. These accessions could be used in breeding programs to improve Zn efficiency of durum wheat. The results suggest that Zn efficiency of durum or bread wheat is likely to be determined collectively by its progenitors.     

Wheat genotypes differ in Zn efficiency when grown in chelate-buffered nutrient solution

Ten Triticum aestivum and two Triticum turgidum conv. durum genotypes were grown in chelate-buffered nutrient solution at Zn supplies ranging from deficient to sufficient (free Zn activities from 2 to 200 pM, pZn from 11.7 to 9.7). The critical level of Zn ion activity in solution for healthy growth of wheat plants was around 40 pM. Genotypes differed in the growth response: those classified as Zn-efficient suffered less reduction of shoot growth and did not change the rate of root growth at a Zn supply quite deficient for Zn-inefficient genotypes. Root growth of Zn-inefficient genotypes increased at deficient Zn supply. The shoot/root ratio was the most sensitive parameter of Zn efficiency; Zn-efficient genotypes showed less reduction in the ratio when grown at deficient compared to sufficient Zn supply. Classification of wheat genotypes into Zn-efficient and Zn-inefficient groups after screening in chelate-buffered nutrient solution corresponded well with classification obtained in field experiments on Zn-deficient soil.     

Phytosiderophore release by wheat genotypes differing in zinc deficiency tolerance grown with Zn-free nutrient solution as affected by salinity

There is limited information concerning the effect of salinity on phytosiderophores exudation from wheat roots. The aim of this hydroponic experiment was to investigate the effect of salinity on phytosiderophore release by roots of three bread wheat genotypes differing in Zn efficiency (Triticum aestivum L. cvs. Rushan, Kavir, and Cross) under Zn deficiency conditions. Wheat seedlings were transferred to Zn-free nutrient solutions and exposed to three salinity levels (0, 60, and 120 mM NaCl). The results indicated that Cross and Rushan genotypes exuded more phytosiderophore than did the Kavir genotype. Our findings suggest that the adaptive capacity of Zn-efficient ‘Cross’ and ‘Rushan’ wheat genotypes to Zn deficiency is due partly to the higher amounts of phytosiderophore release. Only 15 days of Zn deficiency stress was sufficient to distinguish between Zn-efficient (Rushan and Cross) and Zn-inefficient (Kavir) genotypes, with the former genotypes exuding more phytosiderophore than the latter. Higher phytosiderophore exudation under Zn deficiency conditions was accompanied by greater Fe transport from root to shoot. The maximum amount of phytosiderophore was exuded at the third week in ‘Cross’ and at the fourth week in ‘Kavir’ and ‘Rushan’. For all three wheat genotypes, salinity stress resulted in higher amounts of phytosiderophore exuded by the roots. In general, for ‘Kavir’, the largest amount of phytosiderophore was exuded from the roots at the highest salinity level (120 mM NaCl), while for ‘Cross’ and ‘Rushan’, no significant difference was found in phytosiderophore exudation between the 60 and 120 mM NaCl treatments. More investigation is needed to fully understand the physiology of elevated phytosiderophore release by Zn-deficient wheat plants under salinity conditions.     

Dry matter production and distribution of zinc in bread and durum wheat genotypes differing in zinc efficiency

Six bread wheat (Triticum aestivum cvs. Kiraç-66, Gerek-79, Aroona, ES 91-12, ES-14 and Kirkpinar) and four durum wheat (Triticum durum cvs. BDMM-19, Kunduru-1149, Kiziltan-91 and Durati) genotypes were grown under controlled environmental conditions in nutrient solution for 20 days to study the effect of varied supply of Zn (0 to 1 µM) on Zn deficiency symptoms in shoots, root and shoot dry matter production, and distribution of Zn in roots and shoots.Visual Zn deficiency symptoms, such as whitish-brown lesions on leaves, appeared rapidly and severly in durum wheats, particularly in Kiziltan-91 and Durati. Among the durum wheats, BDMM-19 was less affected by Zn deficiency, and among the bread wheats Kiraç-66, ES 91-12, Aroona and Gerek-79 were less affected than ES-14 and Kirkpinar.Under Zn deficiency, shoot dry matter production was decreased in all genotypes, but more distinctly in durum wheat genotypes. Despite severe decreases in shoot growth, root growth of all genotypes was either not affected or even increased by Zn deficiency. Correspondingly, shoot/root dry weight ratios were lower in Zn-deficient than in Zn-sufficient plants, especially in durum wheat genotypes.The distinct differences among the genotypes in sensitivity to Zn deficiency were closely related with the Zn content (Zn accumulation) per shoot but not with the Zn concentration in the shoot dry matter. On average, genotypes with lesser deficiency symptoms contained about 42% more Zn per shoot than genotypes with severe deficiency symptoms. In contrast to shoots, the Zn content in roots did not differ between genotypes. Shoot/root ratios of total Zn content were therefore greater for genotypes with lesser deficiency symptoms than for genotypes with severe deficiency symptoms (i.e. all durum wheat genotypes).The results suggest that the enhanced capacity of genotypes for Zn uptake and translocation from roots to shoot meristems under deficient Zn supply might be the most important factor contributing to Zn efficiency in wheat genotypes. The results also demonstrate that under severe Zn deficiency, Zn concentration in the shoot dry matter is not a suitable parameter for distinguishing wheat genotypes in their sensitivity to Zn deficiency.     

Molecular marker linked to a chromosome region regulating seed Zn accumulation in barley

Zinc deficiency is a critical nutritional problem in soils, restricting yield and nutritional quality of barley (Hordeum vulgare L.). Some genotypes (Zn-efficient) can produce greater yield and accumulate more Zn in seed under Zn deficiency than standard (Zn-inefficient) genotypes. However, there is little information regarding the genetics of Zn uptake/accumulation and location of genes conferring Zn efficiency in barley. Selection through molecular markers for seed Zn accumulation might be an efficient complementary breeding tool in barley. With the aim of developing molecular markers for increased accumulation of Zn in seed, a population of 150 DH lines derived from a cross between Clipper (low-Zn-accumulator) and Sahara 3771 (high-Zn-accumulator) was screened in the field and glasshouse for seed Zn concentration and content. One dominant DNA polymorphism was detected using the microsatellite-anchored fragment length polymorphism (MFLP) technique. The candidate MFLP marker was isolated from the MFLP gel, re-amplified by PCR, cloned, sequenced, and converted into simple sequence-specific and PCR-based marker. This marker, located on the short arm of chromosome 2H, might be useful for the improvement of barley nutritional quality and productivity programs in Zn-deficient environments. However, high seed Zn alone can not replace the need for Zn fertilization.     

Expression of high zinc efficiency of Aegilops tauschii and Triticum monococcum in synthetic hexaploid wheats

The effect of varied zinc (Zn) supply on shoot and root dry matter production, severity of Zn deficiency symptoms and Zn tissue concentrations was studied in two Triticum turgidum (BBAA) genotypes and three synthetic hexaploid wheat genotypes by growing plants in a Zn-deficient calcareous soil under greenhouse conditions with (+Zn=5 mg kg^-1 soil) and without (−Zn) Zn supply. Two synthetic wheats (BBAADD) were derived from two different Aegilops tauschii (DD) accessions using same Triticum turgidum (BBAA), while one synthetic wheat (BBAAAA) was derived from Triticum turgidum (BBAA) and Triticum monococcum (AA). Visible symptoms of Zn deficiency, such as occurrence of necrotic patches on leaves and reduction in shoot elongation developed more rapidly and severely in tetraploid wheats than in synthetic hexaploid wheats. Correspondingly, decreases in shoot and root dry matter production due to Zn deficiency were higher in tetraploid wheats than in synthetic hexaploid wheats. Transfer of the DD genome from Aegilops tauschii or the AA genome from Triticum monococcum to tetraploid wheat greatly improved root and particularly shoot growth under Zn-deficient, but not under Zn-sufficient conditions. Better growth and lesser Zn deficiency symptoms in synthetic hexaploid wheats than in tetraploid wheats were not accompanied by increases in Zn concentration per unit dry weight, but related more to the total amount of Zn per shoot, especially in the case of synthetic wheats derived from Aegilops tauschii. This result indicates higher Zn uptake capacity of synthetic wheats. The results demonstrated that the genes for high Zn efficiency from Aegilops tauschii (DD) and Triticum monococcum (AA) are expressed in the synthetic hexaploid wheats. These wheat relatives can be used as valuable sources of genes for improvement of Zn efficiency in wheat. This revised version was published online in June 2006 with corrections to the Cover Date.     

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.     

Differential response of rye,triticale, bread and durum wheats to zinc deficiency in calcareous soils

Field and greenhouse experiments were carried out to study the response of rye (Secale cereale L. cv. Aslim), triticale (× Triticosecale Wittmark. cv. Presto), two bread wheats (Triticum aestivum L, cvs. Bezostaja-1 and Atay-85) and two durum wheats (Triticum durum L. cvs. Kunduru-1149 and C-1252) to zinc (Zn) deficiency and Zn fertilization in severely Zn-deficient calcareus soils (DTPA-Zn=0.09 mg kg^-1 soil). The first visible symptom of Zn deficiency was a reduction in shoot elongation followed by the appearance of whitish-brown necrotic patches on the leaf blades. These symptoms were either absent or only slight in rye and triticale, but occurred more rapidly and severely in wheats, particularly in durum wheats. The same was true for the decrease in shoot dry matter production and grain yield. For example, in field experiments at the milk stage, decreases in shoot dry matter production due to Zn deficiency were absent in rye, and were on average 5% in triticale, 34% in bread wheats and 70%, in durum wheats. Zinc fertilization had no effect on grain yield in rye but enhanced grain yield of the other cereals. Zinc efficiency of cereals, expressed as the ratio of yield (shoot dry matter or grain) produced under Zn deficiency compared to Zn fertilization were, on average, 99% for rye, 74% for triticale, 59% for bread wheats and 25% for durum wheats.These distinct differences among and within the cereal species in susceptibility to Zn deficiency were closely related to the total amount (content) of Zn per shoot, but not with the Zn concentrations in shoot dry matter. For example, the most Zn-efficient rye and the Zn-inefficient durum wheat cultivar C-1252 did not differ in shoot Zn concentration under Zn deficiency, but the total amount of Zn per whole shoot was approximately 6-fold higher in rye than the durum wheat. When Zn was applied, rye and triticale accumulated markedly more Zn both per whole shoot and per unit shoot dry matter in comparison to wheats.The results demonstrate an exceptionally high Zn efficiency of rye and show that among the cereals studied Zn efficiency declines in the order rye>triticale>bread wheat>durum wheat. The differences in expression of Zn efficiency are possibly related to a greater capacity of efficient genotypes to acquire Zn from the soil compared to inefficient genotypes.     

Role of rye chromosomes in improvement of zinc efficiency in wheat and triticale

Using the disomic wheat-rye addition lines (Triticum aestivum L., cv. Holdfast-Secale cereale L., cv. King-II) and an octoploid triticale line (xTriticosecale Wittmark L. "PlutoxFakon") as well as the respective wheat and rye parents, greenhouse experiments were carried out to study the role of rye chromosomes on the severity of Zn deficiency symptoms, shoot dry matter production, Zn efficiency, shoot Zn concentration and Zn content. Plants were grown in a Zn-deficient calcareous soil with (10 mg Zn kg-1 soil) and without Zn supply. Zinc efficiency was calculated as the ratio of dry weight produced under Zn deficiency to the dry weight produced under Zn fertilization. In the experiments with addition lines, visual Zn deficiency symptoms were slight in the rye cultivar King-II, but were severe in the wheat cultivar Holdfast. The addition of rye chromosomes, particularly 1R, 2R and 7R, into Holdfast reduced the severity of deficiency symptoms. Holdfast showed higher decreases in shoot dry matter production by Zn deficiency and thus had a low Zn efficiency (53 %), while King-II was less affected by Zn deficiency and had a higher Zn efficiency (89 %). With the exception of the 3R line, all addition lines had higher Zn efficiency than their wheat parent: the 1R line had the highest Zn efficiency (80 %). In the experiment with the triticale cultivar and its parents, rye cv. Pluto and wheat cv. Fakon, Zn deficiency symptoms were absent in Pluto, slight in triticale and very severe in Fakon. Zinc efficiency was 88 % for Pluto, 73 % for triticale and 64% for Fakon. Such differences in Zn efficiency were better related to the total amount of Zn per shoot than to the amount of Zn per unit dry weight of shoot. Only in the rye cultivars, Zn efficiency was closely related with Zn concentration. Triticale was more similar to rye than wheat regarding Zn concentration and Zn accumulation per shoot under both Zn-deficient and Zn-sufficient conditions.The results presented in this study show that rye has an exceptionally high Zn efficiency, and the rye chromosomes, particularly 1R and 7R carry the genes controlling Zn efficiency. To our knowledge, the result with triticale and its rye parents is the first report showing that the genes controlling Zn efficiency in rye are transferable into wheat and can be used for development of new wheat varieties with high Zn efficiency for severely Zn-deficient conditions.     

Zinc deficiency-induced phytosiderophore release by the Triticaceae is not consistently expressed in solution culture

The effects of zinc (Zn) and iron (Fe) deficiencies on phytosiderophore (PS) exudation by three barley (Hordeum vulgare L.) cultivars differing in Zn efficiency were assessed using chelator-buffered nutrient solutions. A similar study was carried out with four wheat (Triticum aestivum L. and T. durum Desf.) cultivars, including the Zn-efficient Aroona and Zn-inefficient Durati. Despite severe Zn deficiency, none of the barley or wheat cultivars studied exhibited significantly elevated PS release rates, although there was significantly enhanced PS exudation under Fe deficiency. Aroona and Durati wheats were grown in a further study of the effects of phosphate (P) supply on PS release, using 100 μM KH₂PO₄ as high P, or solid hydroxyapatite as a supply of low-release P. Phytosiderophore exudation was not increased due to P treatment under control or Zn-deficient conditions, but was increased by Fe deficiency. Accumulation of P in shoots of Zn- and Fe-deficient plants was seen in both P treatments, somewhat more so under the KH₂PO₄ treatment. Zinc-efficient wheats and grasses have been previously shown to exude more PS under Zn deficiency than Zn-inefficient genotypes. We did not observe Zn-deficiency-induced PS release and were unable to replicate the results of previous researchers. The tendency for Zn deficiency to induce PS release seems to be method dependent, and we suggest that all reported instances may be explained by an induced physiological deficiency of Fe. Received: 25 October 1999 / Accepted: 3 December 1999     

Importance of seed Zn content for wheat growth on Zn-deficient soil

Seed nutrient reserves may be important for an early establishment of crops on low-fertility soils. This glasshouse pot study evaluated effects of seed Zn content on vegetative growth of two wheat (Triticum aestivum L.) genotypes differing in Zn efficiency. Low-Zn (around 250 ng Zn per seed) and high-Zn seed (around 700 ng Zn per seed on average) of Excalibur (Zn efficient) and Gatcher (Zn inefficient) wheats were sown in a Zn-deficient siliceous sand fertilised with 0, 0.05, 0.2, 0.8 or 3.2 mg Zn kg^-1 soil. After 3 weeks, plants derived from the high-Zn seed had better root and shoot growth; the cv. Excalibur accumulated more shoot dry matter than the cv. Gatcher. After 6 weeks, greater root and shoot growth of plants grown from the high-Zn seed compared to those from the low-Zn seed was obvious only at nil Zn fertilisation. A fertilisation rate of 0.2 mg Zn kg^-1 soil was required for achieving 90% of the maximum yield for plants grown from the high-Zn seed compared to 0.8 mg Zn kg^-1 soil for plants derived from the low Zn seed. The critical Zn level in youngest expanded leaves for 90% maximum yield was 16 mg Zn kg^-1 dry matter for both genotypes. Zn-efficient Excalibur had greater net Zn uptake rates compared to Zn-inefficient Gatcher after 3 weeks but they were not different at the 6-week harvest. Zinc-deficient plants had greater net uptake rates of Cu, Mn, B, P, and K but a reduced uptake rate of Fe. It is concluded that higher seed Zn content acted similar to a starter-fertiliser effect by improving vegetative growth and dissipating differences in Zn efficiency of wheat genotypes.     

Differences in Zinc Efficiency among and within Diploid, Tetraploid and Hexaploid Wheats

Greenhouse experiments were carried out with six diploid, ninetetraploid and seven hexaploid wheats, including wild and primitivegenotypes, to study the influence of varied zinc (Zn) supplyon the severity of Zn deficiency symptoms, shoot dry matterproduction and shoot Zn concentrations. In addition to wildand primitive genotypes, one modern tetraploid cultivar withhigh sensitivity to Zn deficiency and two modern hexaploid cultivars,one highly sensitive to and one resistant to Zn deficiency,were included for comparison. Plants were grown for 44 d ina severely Zn-deficient calcareous soil, with (+Zn; 5 mg Znkg^-1soil) and without (-Zn) Zn fertilization. Visible Zn deficiencysymptoms, including whitish-brown necrotic patches on leaf blades,appeared very rapidly and severely in all tetraploid wheat genotypes.Compared with tetraploid wheats, diploid and hexaploid wheatswere less sensitive to Zn deficiency. With additional Zn, shootdry matter production was higher in tetraploid than diploidand hexaploid wheats. However, under Zn-deficient conditionstetraploid wheats had the lowest shoot dry matter production,indicating the very high sensitivity of tetraploid wheats toZn deficiency. Consequently, Zn efficiency expressed as theratio of shoot dry matter produced under Zn deficiency to Znfertilization, was much lower in tetraploid wheats than in diploidand hexaploid wheats. On average, Zn efficiency ratios were36% for tetraploid, 60% for diploid and 64% for hexaploid wheats.Differences in Zn efficiency among and within diploid, tetraploidand hexaploid wheats were positively related to the amount ofZn per shoot of the genotypes, but not to the amount of Zn perunit dry weight of shoots or seeds used in the experiments.The seeds of the accessions of tetraploid wild wheats containedup to 120 mg Zn kg^-1, but the resulting plants showed very highsensitivity to Zn deficiency. By contrast, hexaploid wheatsand primitive diploid wheats with much lower Zn concentrationsin seeds had higher Zn efficiencies. It is suggested that notonly enhanced Zn uptake capacity but also enhanced internalZn utilization capacity of genotypes play important roles indifferential expression of Zn efficiency. The results of thisstudy also suggest the importance of the A and D genomes asthe possible source of genes determining Zn efficiency in wheat.Copyright 1999 Annals of Botany Company Seeds, Triticum aestivum, Triticum monococcum, Triticum turgidum, zinc concentrations, zinc deficiency, zinc efficiency.     

Phytosiderophore release in bread and durum wheat genotypes differing in zinc efficiency

The effect of the zinc (Zn) nutritional status on the rate of phytosiderophore release was studied in nutrient solution over 20 days in four bread wheat (Triticum aestivum cvs. Kiraç-66, Gerek-79, Aroona and Kirkpinar) and four durum wheat (Triticum durum cvs. BDMM-19, Kunduru-1149, Kiziltan-91 and Durati) genotypes differing in Zn efficiency.Visual Zn deficiency symptoms, such as whitish-brown necrosis on leaves and reduction in plant height appeared first and more severe in Zn-inefficient durum wheat genotypes Kiziltan-91, Durati and Kunduru-1149. Compared to the bread wheat genotypes, all durum wheat genotypes were more sensitive to Zn deficiency. BDMM-19 was the least affected durum wheat genotype. Among the bread wheat genotypes, Kirkpinar was the most sensitive genotype. In all genotypes well supplied with Zn, the rate of phytosiderophore release was very low and did not exceed 1 mol 32 plants^-1 3h^-1, or 0.5 mol g^-1 root dry wt 3h^-1. However, under Zn deficiency, with the onset of visual Zn deficiency symptoms, the release of phytosiderophores was enhanced in bread wheat genotypes up to 7.5 mol 32 plants^-1 3h^-1, or 9 mol g^-1 root dry wt 3h^-1, particularly in Zn-efficient Kiraç-66, Gerek-79 and Aroona. In contrast to bread wheat genotypes, phytosiderophore release in Zn-deficient durum wheat genotypes remained at a very low rate. Among the durum wheat genotypes BDMM-19 had highest rate of phytosiderophore release. HPLC analysis of root exudates showed that 2-deoxymugineic acid (DMA) is the dominating phytosiderophore released from roots of Zn-efficient genotypes. In root extracts concentration of DMA was also much higher in Zn-efficient than in inefficient genotypes. The results demonstrate that enhanced synthesis and release of phytosiderophores at deficient Zn supply is involved in Zn efficiency in wheat genotypes. It is suggested that the expression of Zn efficiency mechanism is causally related to phytosiderophore-mediated enhanced mobilization of Zn from sparingly soluble Zn pools and from adsorption sites, both in the rhizosphere and plants.