Zinc Deficiency in Selected Cultivars of Wheat and Barley as Tested in Solution Culture

Abstract

The relative zinc (Zn) efficiencies of 33 wheat and 3 barley cultivars were determined by growing them in chelate‐buffered culture solutions. Zn efficiency, determined by growth in a Zn‐deficient solution relative to that in a medium containing an adequate concentration of Zn, was found to vary between 10% and 63% among the cultivars tested. Out of the 36 cultivars tested, 12 proved to be Zn efficient, 10 were Zn inefficient, and the remaining 14 varieties were classed as intermediate. The most Zn‐efficient cultivars included Bakhtawar, Gatcher S61, Wilgoyne, and Madrigal, and the most Zn inefficient included Durati, Songlen, Excalibur, and Chakwal‐86. Zn‐efficient cultivars accumulated greater amounts of Zn in their shoots than inefficient cultivars, but the correlation between shoot Zn and shoot dry matter production was poor. All the cultivars accumulated higher concentrations of iron (Fe), copper (Cu), manganese (Mn), and phosphorus (P) at deficient levels of Zn, compared with adequate Zn concentrations. The Zn‐inefficient cultivars accumulated higher concentrations of these other elements compared to efficient cultivars.     

Bicarbonate Had Greater Effects Than High pH on Inhibiting Root Growth of Zinc‐Inefficient Rice Genotype

Abstract

Effects of bicarbonate (10 mM as NaHCO₃) and high pH (pH 8 buffered with HEPES) separately on root growth and accumulation of organic acids in the roots of zinc (Zn)‐efficient (IR36) and Zn‐inefficient (IR26) rice genotypes (Oriza sativa L.) were investigated in this study. The results indicated that shoot dry matter yields were decreased more by bicarbonate than by high pH for the Zn‐inefficient genotype, but not affected for the Zn‐efficient genotype. Root dry weights, especially root length, was significantly decreased by bicarbonate and high pH treatments for the Zn‐inefficient genotype, whereas was considerably enhanced by only bicarbonate treatment for the Zn‐efficient rice genotype. The reduction in root growth of the Zn‐inefficient rice genotype and the enhancement of root length in the Zn‐efficient genotype were greater when plants grown with bicarbonate than with high pH treatment. Accumulation of malate, citrate, and fumarate in roots of the two genotypes increased considerably due to both high pH and bicarbonate treatments, but to a greater extent for the Zn‐inefficient than for the Zn‐efficient cultivars. After an 8‐day treatment, more organic acids accumulated in the roots of the Zn‐inefficient genotype (IR26) when plants grown with bicarbonate than at high pH, but this was not the case for the Zn‐efficient genotype. The influence of root growth by bicarbonate appeared to be one of the major factors for the sensitivity of rice genotypes to Zn deficiency in calcareous soils. The greater inhibitory effect of bicarbonate than high pH on root growth of the Zn‐inefficient genotype might result from an excessive accumulation and inefficient compartmentation of organic acids, particularly citrate and malate, in the root cells.     

Effect of root morphological traits on zinc efficiency in Iranian bread wheat genotypes

Zinc (Zn) has a vast number of functions in plant metabolism, the lack of which had dramatic effects on growth and yield of plants. Plants have morphological and biochemical responses to enhance mineral solubility in the soil and facilitate uptake, such as root plasticity, secretion processes and symbioses. Root architecture modification is an important plant response to nutrient availability. The aim of this study was to identify root morphological reactions to Zn efficiency in Iranian bread wheat genotypes. Soil and solution cultures were used to survey Zn efficiency. In soil culture, six and seven genotypes with high and low Zn contents were selected among 110 Iranian bread wheat genotypes, respectively. The solution culture experiments were set up in a completely randomized block design and plants fed with Johnson’s grass solution. All traits were assessed at 30 and 60 DAPs (days after planting). Our results showed a significant difference between two groups of efficient and inefficient genotypes only at 60 DAP, and Zn-efficient genotypes showed 1.63-, 1.50-, 1.69- and 1.92-fold increases in root diameter, surface area density, shoot and root dry weight, respectively, compared to inefficient genotypes. In contrast, Zn-inefficient genotypes had 1.20- and 2.62-fold more root length and fineness, respectively, than efficient genotypes. The positive significant correlations were observed between shoot and Zn uptake as well as root dry weight and Zn uptake at both stages. Furthermore, shoot and root dry weight showed a significant correlation with root fineness, diameter and surface area density at both stages. The path analysis showed indirect effects on Zn uptake through root traits. Our results showed that roots have a major role in Zn efficiency. Therefore, the better growth and greater Zn uptake in efficient genotypes, compared to inefficient ones, can be attributed to greater root diameter and surface area density, and lower root fineness in these genotypes.     

Fine roots for uptake and translocation of zinc into young leaves as important traits for zinc efficiency of maize genotypes

Suitable germplasm and breeding for zinc (Zn)-efficient genotypes has been prioritized to combat Zn deficiency problem. Six maize genotypes were grown in a nutrient solution with or without Zn to identify genotype tolerance to low Zn and its mechanism. Zhongnong 99 was found to be about 2-fold more Zn-efficient than L69 × 178. Young shoot Zn concentration and content was significantly correlated with Zn efficiency (ZE). Furthermore, Zn-efficient genotype as Zhongnong 99 distributed more Zn into young parts of shoot and also developed longer and thinner roots (≤ 0.2 mm) under -Zn conditions than inefficient genotypes. The close relationship (0.82***, 0.88***, 0.90***) between Zn content of young shoots and fine roots indicated that fine roots (≤ 0.2 mm) contributed more efficient Zn uptake into old parts which distributed to young parts. In conclusion, the analysis of young shoots and fine roots (≤ 0.2 mm) represent a suitable screening technique for ZE evaluation of under -Zn conditions.     

Zinc-Use Efficiency in Upland Rice Genotypes

Zinc (Zn) deficiency is very common in annual crops grown on Brazilian Oxisols. A greenhouse experiment was conducted to evaluate Zn-use efficiency of 20 upland rice genotypes. The Zn levels used were 0 mg kg^?1 (natural level of the soil) and 20 mg kg^?1 of soil applied with zinc sulfate (ZnSO₄). Zinc × genotype interactions were significant for grain yield, panicle number, panicle length, root dry weight, and specific root length, indicating different responses of genotypes with the variation of Zn levels and that selection for Zn-use efficiency is necessary at low as well as at high Zn rates. Based on Zn-use efficiency index, 11 genotypes were classified as efficient and nine were classified as moderately efficient. The most Zn-efficient genotypes were BRA 01596, BRA 042156, BRA 052053, BRA Primavera, and BRA 01506. The most inefficient genotypes in Zn-use efficiency were BRA 042094, BRA 052045, BRA 052034, and BRA 052023. Grain yield and most of the yield attributing characteristics have significant Zn × genotype interactions, which indicate that genotypes respond differently under different Zn levels. Thus, genotype selection is an important strategy for upland rice production in Brazilian Oxisols.     

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.     

Zinc uptake kinetics in the low and high‐affinity systems of two contrasting rice genotypes

Rice (Oryza sativa L.) cultivars differ widely in their susceptibility to zinc (Zn) deficiency. The physiological basis of Zn efficiency (ZE) is not clearly understood. In this study, the effects of Zn‐sufficient and Zn‐deficient pretreatments on the time and concentration‐dependent uptake kinetics of Zn were examined at low (0–160 nM) and high Zn supply levels (0–80 μM) in two contrasting rice genotypes (Zn‐efficient IR36 and Zn‐inefficient IR26). The results show that ⁶⁵Zn²⁺ influx rate was over 10 times greater for the Zn‐deficient pretreatment plants than for the Zn‐sufficient pretreatment plants. At low Zn supply, significant higher ⁶⁵Zn²⁺ influx rates were found for the Zn‐efficient genotype than for the inefficient genotype, with a greater difference (over three‐fold) at Zn supply > 80 nM in the Zn‐deficient pretreatments. At high Zn supply levels, however, a difference (2.5‐fold) in ⁶⁵Zn²⁺ influx rate between the two genotypes was only noted in the Zn‐deficient pretreatments. Similarly, the ⁶⁵Zn²⁺ accumulation in the roots and shoots of Zn‐efficient IR36 pretreated with Zn‐deficiency were sharply increased with time and higher than that in the Zn‐inefficient IR26 with an over four‐fold difference at 2 h absorption time. However, with Zn‐deficient pretreatments, the Zn‐efficient genotype showed a higher shoot : root ⁶⁵Zn ratio at higher Zn supply. Remarkable differences in root and shoot ⁶⁵Zn²⁺ accumulation were noted between the two genotypes in the Zn‐deficiency pretreatment, especially at low Zn level (0.05 μM), with 2–3 times higher values for IR36 than for IR26 at an uptake time of 120 min. There appear to be two separate Zn transport systems mediating the low and high‐affinity Zn influx in the efficient genotype. The low‐affinity system showed apparent Michaelis–Menten rate constant (K_m) values ranging from 10 to 20 nM, while the high‐affinity uptake system showed apparent K_m values ranging from 6 to 20 μM. The V_max value was significantly elevated in IR36 and was 3–4‐fold greater for IR36 than for IR26 at low Zn levels, indicating that the number of root plasma membrane transporters in low‐affinity uptake systems play an important role for the Zn efficiency of rice.     

Genotypic variation of potato for phosphorus efficiency and quantification of phosphorus uptake with respect to root characteristics

Potato (Solanum tuberosum L.), an important food crop, generally requires a high amount of phosphate fertilizer for optimum growth and yield. One option to reduce the need of fertilizer is the use of P‐efficient genotypes. Two efficient and two inefficient genotypes were investigated for P‐efficiency mechanisms. The contribution of root traits to P uptake was quantified using a mechanistic simulation model. For all genotypes, high P supply increased the relative growth rate of shoot, shoot P concentration, and P‐uptake rate of roots but decreased root‐to‐shoot ratio, root‐hair length, and P‐utilization efficiency. Genotypes CGN 17903 and CIP 384321.3 were clearly superior to genotypes CGN 22367 and CGN 18233 in terms of shoot–dry matter yield and relative shoot‐growth rate at low P supply, and therefore can be considered as P‐efficient. Phosphorus efficiency of genotype CGN 17903 was related to higher P‐utilization efficiency and that of CIP 384321.3 to both higher P‐uptake efficiency in terms of root‐to‐shoot ratio and intermediate P‐utilization efficiency. Phosphorus‐efficient genotypes exhibited longer root hairs compared to inefficient genotypes at both P levels. However, this did not significantly affect the uptake rate and the extension of the depletion zone around roots. The P inefficiency of CGN 18233 was related to low P‐utilization efficiency and that of CGN 22367 to a combination of low P uptake and intermediate P‐utilization efficiency. Simulation of P uptake revealed that no other P‐mobilization mechanism was involved since predicted uptake approximated observed uptake indicating that the processes involved in P transport and morphological root characterstics affecting P uptake are well described.     

Dry Bean Genotypes Evaluation for Zinc-Use Efficiency

Dry bean is an important legume for human consumption worldwide. Low soil fertility, including zinc (Zn) deficiency, is one of the main factors limiting yield of this legume in South America, including Brazil. The objective of this study was to evaluate 30 dry bean genotypes for zinc (Zn)–use efficiency. The Zn rates used were 0 mg Zn kg^?1 (low) and 20 mg Zn kg^?1 (high) of soil. Grain yield, straw yield, number of pods, hundred-seed weight, number of seeds per pod, maximum root length, and rood dry weight were significantly affected by Zn and genotype treatments. The Zn × genotype interactions were also significant for growth, yield, and yield components, indicating that some genotypes were highly responsive to the Zn application while others were not. Based on seed yield efficiency index (SYEI), genotypes were classified as efficient, moderately efficient, and inefficient in Zn-use efficiency. Most efficient genotypes were CNFP 10104, BRS Agreste, BRS 7762 Supreme, CNFC 10429, BRS Estilo, CNFC 10467, BRS Esplendor, and BRS Pitamaba. The most inefficient genotype was BRS Executive. Remaining genotypes were moderately efficient in Zn-use efficiency.     

Zinc‐boron interaction effects in oilseed rape

The interaction effect of applied zinc (Zn) and boron (B) on early vegetative growth and uptake of Zn and B by two oilseed rape (canola) (Brassica napus L.) genotypes was investigated in a sand culture experiment under controlled environmental conditions. Two genotypes (Yickadee and Dunkeld) were grown at three Zn levels (0.05, 0.25, and 2.0 mg kg^‐1 soil) and two B levels (0.05 mg kg^‐1 soil and 0.5 mg kg^‐1 soil). Dunkeld produced significantly higher shoot and root dry matter than Yickadee at low Zn and low B supply indicating the superiority of Dunkeld over Yickadee for tolerance to both low Zn and low B supply. Chlorophyll content of fresh leaf tissue was increased significantly by an increase in Zn and B supply. Zinc deficiency enhanced B concentration in younger and older leaves. Boron concentration was higher in older leaves than in the younger leaves irrespective of B deficiency and sufficiency indicating immobility of B in two oilseed rape genotypes tested. Zinc concentration was higher in younger leaves than in the older leaves indicating mobility of Zn. An increased supply of Zn enhanced B uptake under high boron supply only. Zinc uptake in Dunkeld was enhanced significantly with an increased rate of B supply under high Zn supply, while the effect was not significant in Yickadee. Dunkeld proved to be more efficient in Zn and B uptake than Yickadee.     

Genotypic Divergence in Expression of Zinc-Deficiency Symptoms of Rice (Oryza sativa L.) in Sand Culture

Zinc (Zn) deficiency is a ubiquitous disorder constraining rice production worldwide. A sand culture experiment was conducted in factorial randomized block design with three replications to study the relative performance of 18 rice (Oryza sativa L.) genotypes experiencing Zn stress. Modified Hoagland’s solution was employed as the nutrient medium and the experiment was maintained for 60 days from sowing. The genotypes were categorized as efficient (Norungan, ASD 16, Pokkali, Pusa Vikas, TRY 1, and Triveni), moderately efficient (White Ponni, CO 47, ADT 36, IR 8, ASD 20, and TRY 2), and inefficient (ADT 38, PMK 3, CO 43, CSR 10, ADTRH 1, and MDU 5) to Zn stress based on the preliminary solution culture experiment (Sudhalakshmi 2007). Growth performance, dry-matter production, biochemical constituents, and enzymatic activity of rice were measured employing graded levels of Zn (at 0, 0.025, 0.05, 0.1, and 0.2 mg L^?1) and were statistically analyzed using the method of Panse and Sukhatme (1978). The efficient rice genotypes showed minimum reduction in dry-matter production in Zn stress conditions while the inefficient rice genotypes suffered severe reduction. Zinc-efficient rice genotypes were not responsive to fertilizer. Dry-matter production, chlorophyll a, chlorophyll b, total chlorophyll, soluble protein, and indole-3-acetic acid (IAA) oxidase activity can be employed as diagnostic tools to differentiate Zn-efficient and Zn-inefficient rice genotypes in sand culture.     

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

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

Iron deficiency studies of sugar beet using an improved sodium bicarbonate‐buffered hydroponic growth system

A sodium bicarbonate (NaHCO₃)‐buffered hydroponic growth system was developed that simulates alkaline soil growth conditions necessary to screen sugar beet genotypes for iron (Fe) efficiency character. Three genotypes (NB1, NB4, and F, hybrid, NB 1xNB4) with differing capacities for Strategy I Fe responses were phenotyped successfully using this system. Genotypes NB1 and NB1xNB4 are Fe efficient, while NB4 is Fe inefficient. It was demonstrated that 5 mM NaHCO₃ provided buffering within an optimal range (pH 7.3 ‐ pH 6.3) for the duration of ‐Fe treatments, promoted enhanced H⁺ extrusion, and increased the in vivo capacity for Fe³⁺‐chelate reduction (Fe³⁺‐chelate reductase [FCR] activity), especially in the roots of the Fe efficient genotypes. The same concentrations of NaHCO₃ did not interfere with Fe supply to +Fe control plants of any genotype. The in vivo capacity for Fe³⁺‐chelate reduction increased over fivefold in both Fe efficient genotypes (NB1 and NB 1xNB4), but just under twofold in the Fe inefficient genotype (NB4). Localization and duration of enhanced Fe³⁺‐chelate reduction capacity were dependent upon the Fe efficiency character of each genotype.     

Comparison of Winter Wheat Genotypes Differing in Zinc Efficiency and Origin: The Zinc Uptake and Enzyme Activity

Zinc (Zn)–efficient wheat genotypes yield well on Zn-deficient soil. In this study, two Chinese wheat genotypes, Kenong9204 and Han6172, and two reference genotypes, Bezostaja (Zn efficient) and BDME10 (Zn inefficient), from Turkey were conducted to measure their physiological responses to Zn deficiency in the greenhouse. Results showed obvious genetic variation among the genotypes with Zn efficiency from 76% to 105%. Bezostaja and Kenong9204 had greater shoot dry weight and accumulated more shoot Zn content than BDME10 and Han6172 without Zn application. In one aspect of enzyme activities, Bezostaja and Kenong9204 presented significantly greater activities of superoxide dismutase while maintaining similar activities of catalase, ascorbate peroxidase, and glutathione reductase compared with inefficient genotypes BDME10 and Han6172 under Zn-deficient condition. Zinc-efficient genotypes are recommended to satisfy the sustainable grain yield in China and other areas, where Zn deficiency in soil is spread and multiple stresses may happen at times.     

RESPONSE OF MAIZE GENOTYPES TO SEVERAL MYCORRHIZAL INOCULUMS IN TERMS OF PLANT GROWTH,NUTRIENT UPTAKE AND SPORE PRODUCTION

A greenhouse experiment was conducted at the University of Çukurova, Rhisosphere Lab, Adana, Turkey, on a growth medium to assess the impact of several selected mycorrhiza including indigenous AMF-maize hybrid combinations on spore production, plant growth and nutrient uptake. In the experiment, six maize (Zea mays L.) (Luce, Vero, Darva, Pegasso, P.3394, and P.32K61) genotypes were used. Control, Glomus mossea, G. caledonium, G. etunicatum, G. clarium, G. macrocarpum, G. fasciculatum, G. intraradices, Dr. Kinkon (Japanese species), indigenous mycorrhizae (Balcal? series) and cocktail mycorrhizae species spores were used. The growth of maize genotypes was found to depend on the mycorrhizal species. For shoot and root dry weight production G. intraradices is one of the most efficient mycorrhiza species on average on all maize genotypes. Genotypes P.3394 and P.32K61 produced the highest shoot and root dry weight as well. Pagasso and Darva genotypes compared to the other genotypes have high root colonization percentages. On average G. clarium inoculated plants also have high percentages of root colonization. It has been found that the P.32K61 genotype has a high phosphorus (P)% content and Pagasso genotypes have higher zinc (Zn) content uptake than other genotypes. G. clarium inoculated maize genotype plant tissues have high P% and Zn content. G. intraradices is also efficient for P and Zn uptake. Mycorrhizal dependent maize genotypes showed variability in P efficiency from inefficient to efficient genotypes.     

Influence of zinc on the growth,distribution of elements,and metabolism of one‐year old American ginseng plants

Using a water culture technique, 0.05 ppm zinc (Zn) was found to be the critical deficiency concentraction for one‐year American ginseng (Panax quinquefolium L) plants, 0.3 ppm was optimum, 0.5 ppm the critical Zn‐toxicity concentration, and 10 ppm the concentration when severe toxicity occurs. Therefore, the optimum Zn concentration for the growth of American ginseng plants was between 0.1 ppm ‐ 0.3 ppm. Zinc deficiency symptoms of one‐year old American ginseng plants were indicated by the inhabition of root growth, with little fibrous root development, and smaller leaves compared to normal leaves. The symptoms of toxicity were also indicated by the inhibition of root growth, and when seedlings were suffering from an acute toxicity, no fibrous roots appeared, and eventually the roots yellowed and leaves grew slowly or even entirely ceased to grow, the final result being very small leaves which are also chlorotic. Zinc maintained within the 0.1 ppm to 0.3 ppm sufficiency range promoted the synthesis and accumulation of ginsenosides by American ginseng plants, and both low and high Zn concentrations restrained the synthesis and accumulation of ginsenosides. Both Zn deficiency and the optimum Zn concentration (0.3ppm) are beneficial to the accumulation of amino acids in the roots of American ginseng plants. Close to the optimum Zn concentration, the ratios of P/Zn and Fe/Zn in the shoot of American ginseng plants were maintained at 77 and 9.4, respectively.     

Quantification of the confounding effect of seed manganese content in screening for manganese efficiency in durum wheat (triticum turgidum L. var. durum)

Whether due to the genotype or the environment of the mother plant, the nutrient content of seeds vary over a wide range; the amount of the nutrient contributes greatly to seedling vigor, especially on deficient soils and may result in major differences in grain yield. This effect has important implications for breeding programs. This paper examines the impact of seed manganese (Mn) on screening of durum wheats for tolerance to Mn‐deficient soils. Seed stocks with a range of Mn contents (0.4–2.4 μg seed^‐1) were produced, and the effect on expression of Mn efficiency measured as either relative yield or shoot Mn content for two durum wheat (Triticum turgidum L. var. durum) genotypes differing in Mn efficiency. Both genotypes responded to seed Mn content in terms of enhanced root and shoot growth; there was no genotype by seed Mn interaction, so Mn provided in seed was utilized additively by both Mn‐efficient and Mn‐inefficient genotypes. Manganese efficiency, measured as relative yield, was a function of seed Mn content and varied from 40 to 70% in Hazar and 58 to 90% in Stojocri 2, in the same assay using seed of variable Mn content. From the response curves of yield vs. soil Mn added, the Mn required for 90% relative yield was determined for each level of seed Mn content. Seed Mn was regressed against the soil added Mn needed to obtain 90% of maximal growth at each level of seed Mn content (a total of 8 levels) for each of two genotypes. There was an inverse linear relationship between the amount of soil Mn and seed Mn needed for each genotype. Using the Mn‐efficient genotype with high seed Mn content, the soil Mn needed to obtain 90% growth was nil, while inefficient genotypes with low Mn content required 75 mg Mn kg^‐1 soil to produce the same relative yield. This relationship can be used to adjust the levels of soil applied Mn to be used in a pot bioassay when seeds have a certain Mn content, so as to maintain the screening at an optimal overall level of Mn stress.     

Zinc nutrition effect on the tolerance of wheat genotypes to Fusarium root-rot disease in a solution culture experiment

Abstract

Zinc (Zn) nutrition and plant genotype are two factors that may affect the tolerance of wheat to root-rot diseases. The aim of the present study was to determine the effect of Zn on shoot yield, root permeability and infection by Fusarium solani in six wheat genotypes with different Zn efficiency. A greenhouse (solution culture) experiment was carried out in which five bread wheat genotypes (Triticum aestivum L. cvs Rushan, Kavir, Cross, Pishtaz and Falat) and one durum wheat genotype (Triticum durum L. cv. Yav79), which are common in Zn-deficient soils of Iran and were exposed to two levels of Zn (0 and 1?μmol?L^–1?Zn?kg^?1, as ZnSO₄.7H₂O) and two F. solani infection levels (0 and 10⁶?spore?mL^?1). Zinc deficiency significantly decreased shoot dry matter in five of the genotypes (Yav79, Kavir, Rushan, Cross and Falat), but had no effect on shoot growth in Pishtaz. Infection with F. solani significantly decreased the shoot dry matter in Yav79, but did not affect the shoot dry weight of the other wheat genotypes. Root membrane permeability was lower in the Zn treatments than in the Zn-free treatments. Zinc deficiency caused a decrease in root reactive sulfhydryl (SH) groups, particularly in the Cross genotype. Root sulfhydryl groups decreased with Fusarium infection. Zinc application sharply increased the Zn content and decreased the Mn content of the shoots. Application of Zn had a positive effect on the tolerance of wheat to F. solani root rot. The relationship between Zn nutrition and disease tolerance suggests that Zn deficiency should be treated before evaluating the cost-effectiveness of fungicides. No correlation was found between the Zn efficiency of the wheat genotypes and Fusarium root-rot disease severity in this solution culture experiment.     

ROOT GROWTH OF UPLAND RICE GENOTYPES AS INFLUENCED BY NITROGEN FERTILIZATION

The plant root system is an important organ which supplies water and nutrients to growing plants. Information is limited on influence of nitrogen fertilization on upland rice root growth. A greenhouse experiment was conducted to evaluate influence of nitrogen (N) fertilization on growth of root system of 20 upland rice genotypes. The N rate used was 0 mg kg^?1(low) and 300 mg kg^?1(high) of soil. Nitrogen X genotype interactions for root length and root dry weight were highly significant (P < 0.01), indicating that differences among genotypes were not consistent at two N rates. Overall, greater root length, root dry weight and tops-roots ration were obtained at an N fertilization rate of 300 mg kg^?1compared with the 0 mg N kg^?1soil. However, genotypes differ significantly in root length, root dry weight and top-root ratio. Nitrogen fertilization produced fine roots and more root hairs compared with absence of N fertilizer treatment. Based on root dry weight efficiency index (RDWEI) for N use efficiency, 70% genotypes were classified as efficient, 15% were classified as moderately efficient and 15% were classified as inefficient. Root dry weight efficiency index trait can be incorporated in upland rice for improving water and nutrient efficiency in favor of higher yields.     

Differences in shoot growth and zinc concentration of 164 bread wheat genotypes in a zinc‐deficient calcareous soil

Abstract

A greenhouse experiment was carried out to study severity of the zinc (Zn) deficiency symptoms on leaves, shoot dry weight and shoot content and concentration of Zn in 164 winter type bread wheat genotypes (Triticunt aestivum L.) grown in a Zn‐deficient calcareous soil with (+Zn=10 mg Zn kg^?1 soil) and without (‐Zn) Zn supply for 45 days. Tolerance of the genotypes to Zn deficiency was ranked based on the relative shoot growth (Zn efficiency ratio), calculated as the ratio of the shoot dry weight produced under Zn deficiency to that produced under adequate Zn supply. There was a substantial difference in genotypic tolerance to Zn deficiency. Among the 164 genotypes, 108 genotypes had severe visible symptoms of Zn deficiency (whitish‐brown necrotic patches) on leaves, while in 25 genotypes Zn deficiency symptoms were slight or absent, and the remaining genotypes (e.g., 31 genotypes) showed mild deficiency symptoms. Generally, the genotypes with higher tolerance to Zn deficiency originated from Balkan countries and Turkey, while genotypes originating from the breeding programs in the Great Plains of the United States were mostly sensitive to Zn deficiency. Among the 164 wheat genotypes, Zn efficiency ratio varied from 0.33 to 0.77. The differences in tolerance to Zn deficiency were totally independent of shoot Zn concentrations, but showed a close relationship to the total amount (content) of Zn per shoot. The absolute shoot growth of the genotypes under Zn deficiency corresponded very well with the differences in tolerance to Zn deficiency. Under adequate Zn supply, the 10 most Zn‐ inefficient genotypes and the 10 most Zn‐efficient genotypes were very similar in their shoot dry weight. However, under Zn deficiency, shoot dry weight of the Zn‐efficient genotypes was, on average, 1.6‐fold higher compared to the Zn‐inefficient genotypes. The results of this study show large, exploitable genotypic variation for tolerance to Zn deficiency in bread wheat. Based on this data, total amount of Zn per shoot, absolute shoot growth under Zn deficiency, and relative shoot growth can be used as reliable plant parameters for assessing genotypic variation in tolerance to Zn deficiency in bread wheat.