Tolerance of durum wheat lines to an acid,aluminum‐toxic subsoil

Durum wheat, Triticum durum Desf., is reportedly more sensitive to aluminum (Al) toxicity in acid soils than hexaploid wheat, Triticum aestivum L. em. Thell. Aluminum‐tolerant genotypes would permit more widespread use of this species where it is desired, but not grown, because of acid soil constraints. Durum wheat germplasm has not been adequately screened for acid soil (Al) tolerance. Fifteen lines of durum wheat were grown for 28 days in greenhouse pots of acid, Al‐toxic Tatum subsoil at pH 4.5, and non‐toxic soil at pH 6.0. Aluminum‐tolerant Atlas 66 and sensitive Scout 66 hexaploid wheats were also included as standards. Based on relative shoot and root dry weight (wt. at pH 4.5/wt. at pH 6.0 X 100), durum entries differed significantly in tolerance to the acid soil. Relative shoot dry weight alone was an acceptable indicator of acid soil tolerance. Relative dry weights ranged from 55.1 to 15.5% for shoots and from 107 to 15.8% for roots. Durum lines PI 195726 (Ethiopia) and PI 193922 (Brazil) were significantly more tolerant than all other entries, even the Al‐tolerant, hexaploid Atlas 66 standard. Hence, these two lines have potential for direct use on acid soils or as breeding materials for use in developing greater Al tolerance in durum wheat. Unexpectedly, the range of acid soil tolerance available in durum wheat appears comparable to that in the hexaploid species. Hence, additional screening of durum wheat germplasm for acid soil (Al) tolerance appears warranted. Durum lines showing least tolerance to the acid soil included PI 322716 (Mexico), PI 264991 (Greece), PI 478306 (Washington State, USA), and PI 345040 (Yugoslavia). The Al‐sensitive Scout 66 standard was as sensitive as the most sensitive durum lines. Concentrations of Al and phosphorus were significantly higher in shoots of acid soil sensitive than in those of tolerant lines, and these values exceeded those reported to cause Al and phosphorus (P) toxicities in wheat and barley.     

Acid soil tolerances of wheat lines selected for high grain protein content

Literature suggests that nitrogen (N) metabolism is involved in differential acid soil (Al) tolerances among wheat (Triticwn aestivum L. en Thell) genotypes. Atlas 66 wheat is characterized by acid soil and aluminum (Al) tolerance, nitrate (NO₃ ^‐) preference, pH increase of the rhizosphere, high nitrate reductase activity, and high protein in the grain. Atlas 66 has been used as a high protein gene donor in the development of new high protein wheat lines at Lincoln, NE. The objective of our study was to determine the acid soil tolerances of such lines and to relate such tolerances to their abilities to accumulate grain protein when grown on near‐neutral, non‐toxic soils. Twenty‐five experimental lines, nine cultivars not previously classified as Al‐tolerant or ‐sensitive and three cultivars previously classified according to acid soil tolerance, were grown for 28 days in greenhouse pots of acid, Al‐toxic Tatum subsoil. Relative shoot dry weight (pH 4.35/pH 5.41%) varied from 83.2% for Atlas 66 to 19.3% for Siouxland. Atlas 66 was significantly more tolerant to the acid soil than all other entries except Edwall. Yecorro Roja and Cardinal were intermediate in tolerance. None of the high protein lines approached Atlas 66 in tolerance, but two lines (N87U106 and N87U123) were comparable to Cardinal (relative shoot yield = 54%) which is used on acid soils in Ohio. At pH 4.35, the most acid soil tolerant entries contained significantly lower Al and significantly higher potassium (K) concentrations in their shoots than did sensitive entries. Shoots of acid soil sensitive entries, Scout 66, Siouxland, Plainsman V, and Anza contained deficient or near deficient concentrations of K when grown at pH 4.35. Acid soil tolerance was not closely related to calcium (Ca), magnesium (Mg), phosphorus (P), manganese (Mn), or iron (Fe) concentrations at pH 4.35. Liming the soil to pH 5.41 tended to equalize Al and K concentrations in shoots of tolerant and sensitive entries. Results indicated that acid soil tolerance and grain protein concentrations were not strongly linked in the wheat populations studied. Hence, the probability of increasing acid soil tolerance by crossing Atlas 66 with Nebraskan wheat germplasm is low. However, the moderate level of acid soil tolerance in N87U106 and N87U123 (comparable to that of Cardinal) may be useful in further studies.     

Potassium and sodium fertilization affects leaf nutrient content and growth of ‘Shawnee’ blackberry

Aluminum (Al) has many detrimental effects on plant growth, and shoots and roots are normally affected differently. A study was conducted to determine differences among sorghum [Sorghum bicolor (L.) Moench] genotypes with broad genetic backgrounds for growth traits of plants grown at 0,200,400,600, and 800 μM Al in nutrient solutions (pH 4.0). Genotypes were categorized into “Al‐sensitive”, “intermediate Al‐tolerant”, “Al‐tolerant”, and SC 283 (an Al‐tolerant standard). As Al increased, shoot and root dry matter (DM), net main axis root length (NMARL), and total root length (TRL) became lower than controls (0 Al). Aluminum toxicity and/or nutrient deficiency symptoms become more severe, and shoot to root DM ratios and specific RL (TRL/root DM) values also changed as Al in solution increased. Root DM had greater changes among genotypes than shoot DM, and NMARL at 400 μM Al, and TRL at 200 μM Al had greater differences among genotypes than root DM, ratings for toxicity and/or deficiency symptoms, and other DM and RL traits. The wide differences among genotypes for NMARL and TRL could be used more effectively to evaluate sorghum genotypes for tolerance to Al toxicity than the other growth traits.     

Amelioration of Aluminum Toxicity by Pretreatment with Phosphate in Aluminum‐Tolerant Rice Cultivar

Abstract

The phytotoxicity of aluminum (Al) in relation to preculture with phosphates was examined in the rice cultivar Arkansas fortuna. In plants precultured with phosphates, Al did not inhibit shoot growth, while Al retarded shoot growth in plants precultured without phosphates. In contrast, Al inhibited root elongation, irrespective of the presence of phosphates in the preculture solution. A large proportion of the Al in roots was in unknown, insoluble forms. In phosphate‐precultured plants, Al deposition was slightly increased, presumably due to the formation of aluminum phosphates in the roots, and phosphorus levels in shoots were markedly increased. Binding with phosphates may ameliorate the toxicity of Al when it enters the shoots and account for the uninhibited shoot growth in the presence of Al in plants precultured with phosphates.     

Aluminum,manganese, and iron tolerance improves performance of wheat genotypes in waterlogged acidic soils

Waterlogging results in high shoot concentrations of iron (Fe), aluminum (Al), and manganese (Mn) in wheat grown in acidic soil. The verification of this observation in several acidic soils, development of screening techniques, and identification of genotypes differing in tolerance made it possible to test whether tolerance of ion toxicities improves performance of wheat in waterlogged acid soils. Six wheat varieties selected for tolerance/intolerance of Al, Mn, and Fe were grown in three acidic soils (pH_CaCl2 4.1–4.3) with or without waterlogging for 40 d. In terms of relative shoot dry weight, Al‐, Mn‐, and Fe‐tolerant genotypes tolerated waterlogging better, outperforming intolerant genotypes by 35%, 53%, and 32%, respectively, across the soils. The Al‐tolerant genotype had up to 1.8‐fold better root growth than the intolerant genotype under waterlogging. Waterlogging increased DTPA‐extractable soil Mn (71%) and Fe (89%), and increased shoot Fe (up to 7.6‐fold) and Al (up to 5.9‐fold) for different genotypes and soils. The Al‐tolerant genotype maintained lower tissue concentrations of Al as compared to intolerant genotypes during waterlogging. Waterlogging delayed crop development but distinctly less so in the tolerant than in the intolerant genotypes, thus jeopardizing the capacity of intolerant genotypes to produce yield in Mediterranean climates with dry finish of the season. Pyramiding multiple ion tolerances into current wheat varieties with desirable agronomic and quality characteristics to enhance their performance under waterlogged acid soils should be considered.     

Effect of Glomus etunicatum inoculation on aluminum,phosphorus, calcium,and magnesium uptake of two barley genotypes with different aluminum tolerance

Abstract

This study was conducted to evaluate the effect of vesicular‐arbuscular mycorrhizal (VAM) fungus Glomus etunicatum on growth, absorption, and distribution of calcium (Ca), magnesium (Mg), phosphorus (P), and aluminum (Al) in one Al‐tolerant and one Al‐sensitive barley cultivar. The plants were grown in sand daily irrigated with nutrient solution containing 0 or 600 μM Al at pH 4.8. Significant interaction (P=0.05) among variety, mycorrhiza, and aluminum (VxMxAl) were noted for both shoot and root dry matter (DM); shoot concentration and content of Al, P, Ca, and Mg; root concentration of Al, P, and Mg; and root content of Al, P, Ca, and Mg. With VAM inoculation: i) root colonization degree was about 50% in all treatment, ii) shoot DM yield increased between 30 and 70%, iii) Al concentration and content decrease down to a half both in shoots and roots of sensitive barley, iv) Ca concentration in shoots of sensitive barley showed a high increase at 600 μM Al, and v) P concentration and content in shoots of both varieties increased significantly.     

Tall fescue aluminum tolerance is affected by neotyphodium coenophialum endophyte

Roots of endophyte‐infected (E+) tall fescue (Festuca arundinacea Schreb.) exude more phenolic‐like reductants than roots of endophyte‐free (E‐) plants when mineral stressed. Phenolic compounds are efficient chelators of aluminum (Al) and may influence Al tolerance in many plant species. The objective of our study was to determine if enhanced release of phenolic compounds by roots of E+ plants contributes to Al tolerance in tall fescue. Two cloned genotypes (DN2 and DN11) of tall fescue infected with their naturally occurring fungal endophyte Neotyphodium coenophialum (Morgan‐Jones and Gams) Glenn, Bacon and Hanlin and their noninfected isolines were grown in nutrient solutions at 0 μM Al (Al‐) and at 640 μM Al (Al+) under controlled environment conditions. Root and shoot dry matter (DM) of endophyte‐infected tall fescue was greater in E+ than E‐ plants by 57% and 40%, respectively, when plants were grown without Al. Endophyte infection did not affect root and shoot DM of tall fescue grown with Al but relative (to Al‐treatment) reduction in root and shoot DM was greater in E+ than E‐ plants. In response to Al stress, more Al (47%) and P (49%) could be desorbed from root surfaces of E+ than E‐ plants. Aluminum concentrations in roots of E+ plants were 35% greater and P concentrations were 10% less than those determined in roots of E‐plants. No differences in mineral concentrations were observed in shoots, regardless of endophyte status, or Al level in nutrient solution. Roots of E+ plants increased pH of both Al‐ and Al+ nutrient solutions to a greater extent than roots of E‐ plants in a 48 h interval. Our results show that more Al can be sequestered on root surfaces and in root tissues of endophyte‐infected tall fescue than in plants devoid of endophyte. Aluminum sequestration was greater on root surfaces and in root tissues of E+ than E‐ plants of a given tall fescue genotype. Our results suggest that increased exudation of phenolic‐like compounds from roots of endophyte‐infected tall fescue may be directly involved in Al tolerance and serves as a mechanism for widespread adaptability and success of endophyte‐tall fescue associations.     

Identification of an aluminum tolerant tropical cowpea cultivar by growth and biomass accumulation parameters

Ten‐day‐old seedlings of four cowpea (Vigna unguiculata Walp) genotypes were subjected to six levels of aluminum (Al) (0, 74, 148, 222, 296, and 370 μM/L) to test their tolerance to Al toxicity in a nutrient solution at pH 4.0±0.1. Seedlings were grown in the presence of Al under controlled environmental conditions in a growth chamber. The nutrient solutions were replenished once a week. After 20 days, treatments were terminated and the differences in their growth patterns were compared. Standard growth parameters, such as plant growth, dry matter production, relative growth reduction in roots (RGRS) and shoots (RGRS), and root and shoot tolerance indices (RTI and STI) have been used as markers of Al toxicity. The cowpea genotypes studied exhibited a wide range of responses in their tolerance to Al. Though the genotypes were subjected to six levels of Al, a good degree of separation in their responses was observed only at the 222 μM Al/L treatment level. Therefore, this concentration was chosen to treat and compare the performances of the genotypes. The genotype Co 3 showed an increase in growth, while Paiyur 1 and other genotypes showed severe inhibitions in the presence of Al. Furthermore, for RTI and STI, Co 3 also registered its tolerance to Al by showing increased ratios in the presence of Al. Whereas, Paiyur 1 recorded severe reductions. The RGRR and RGRS data also substantiates this finding. Based on the growth parameters, the four cowpea genotypes were ranked based on their tolerance to Al: Co 3 > Co 4 > KM > Paiyur 1. Co 3 was the most Al‐tolerant genotype which performed extremely well in the presence of Al, while Paiyur 1was the most Al‐susceptible genotype. Therefore, the Al‐tolerant genotype can be used for future breeding programmes to produce Al‐tolerant genotypes, subsequently, can be recommended for acidic infertile soils in the tropics.     

Tolerances of wheat germplasm to acid subsoil

Aluminum toxicity is a major growth limiting factor for plants in many acid soils of the world. Correcting the problem by conventional liming is not always economically feasible, particularly in subsoils. Aluminum tolerant plants provide an alternative and long‐term supplemental solution to the problem. The genetic approach requires the identification of Al tolerance sources that can be transferred to cultivars already having desirable traits. Thirty‐five cultivars and experimental lines of wheat (Triticum aestivum L. em. Thell) were screened for Al tolerance on acid Tatum soil (clayey, mixed thermic, typic Hapludult) receiving either 0 or 3500 mg CaCO₃/kg (pH 4.1 vs. pH 7.1). Entries showed a wide range of tolerance to the acid soil. On unlimed soil at pH 4.3, absolute shoot dry weights differed by 5‐fold, absolute root dry weights by 6.5‐fold, relative shoot weights (wt. at pH 4.3/wt. at pH 7.1 %) by 4.7‐fold and relative root dry weights by 7‐fold. Superior acid soil (Al) tolerance of ‘BH‐1146’ from Brazil and extreme sensitivities of cultivars ‘Redcoat’ (Indiana, USA) and ‘Sonora 63’ (Mexico) were confirmed. Seven experimental (CNT) lines from Brazil showed a range of acid soil tolerance but were generally more tolerant than germplasm from Mexico and the USA. One line, ‘CNT‐1’, was equal to BH‐1146 in tolerance and may be useful in transferring Al tolerance to existing or new cultivars. Five durum cultivars (Triticum, durum, Desf.) were extremely sensitive to the acid Tatum subsoil at pH 4.3 compared with pH 7.1.     

Differential responses of red clover germplasms to aluminum stress

Toxic levels of aluminum can cause severe yield reduction in red clover (Trifolium pratense L.), especially in the presence of drought stress. Aluminum tolerances of 17 red clover cultivars and germplasms representing a broad genetic base were evaluated in a Monmouth soil [26.2% Al saturation (pH 4.8) vs. 2.8% Al saturation (pH 5.7)] and in nutrient solutions (0 vs 111 μM Al; pH 4.5). The soil and nutrient culture studies were harvested 29 and 27 d after seeding, respectively.

Aluminum stress reduced shoot and root growth significantly in soil but not in nutrient culture. Entries differed significantly in shoot vigor in both media and in root vigor in nutrient culture; responses to the two media were positively correlated. Relative weights (dry weight stressed/dry weight unstressed) in soil and nutrient culture were not correlated.

In soil, Al stress significantly reduced shoot growth of all entries except ‘Tristan’, whereas root growth was not affected significantly in ‘Atlas’, ‘Lakeland’, ‘Persist’, ‘Reddy’, ‘Redman’, or Tristan. Reddy, ‘Redland II’, Redman, and Tristan had the highest relative shoot and root weights whereas ‘Kenstar’ had the lowest. In nutrient culture, only the shoot growth of Atlas, Lakeland, Redman and ‘YKYC’ and the root growth of Redman were significantly reduced under Al stress. Atlas, ‘Kenland’, and Redman had among the lowest relative shoot and root weights and Kenstar among the highest. Some entries exhibited a positive growth response to Al.     

Assessing the relative effects of hydrogen and aluminum ions on primary root growth of white clover seedlings

White clover (Trifolium repens L., cultivar Huia), a dominant forage legume in Appalachia, usually grows poorly on acidic soils common to the region. The effects of bulk solution concentrations of calcium (Ca), hydrogen (H), and aluminum (Al) on the relative root growth (RRG) of white clover were determined using one‐ to three‐day‐old seedlings to assess the relative toxicity of H⁺ and Al. The RRG was affected by bulk solution concentrations of Ca, Al, and pH, in a manner indicative of significant interactions among these parameters. The RRG was directly related to the activities of Al³⁺ or H⁺ at the surface of the root as calculated by the Gouy‐Chapman‐Stern model. Fifty percent inhibition of RRG occurred at activities of 5 and 200 μM Al³⁺ and H⁺, respectively. A large part of the interaction between bulk solution concentrations of Ca, Al, and H could be explained by how these parameters affected the activities of these ions at the root surface.     

Variation of tolerance to manganese toxicity in Australian hexaploid wheat

High concentrations of manganese (Mn), iron (Fe), and aluminium (Al) induced in waterlogged acid soils are a potential constraint for growing sensitive wheat cultivars in waterlogged‐prone areas of Western Australian wheat‐belt. Tackling induced ion toxicities by a genetic approach requires a good understanding of the existing variability in ion toxicity tolerance of the current wheat germplasm. A bioassay for tolerance to high concentration of Mn in wheat was developed using Norquay (Mn‐tolerant), Columbus (Mn‐intolerant), and Cascades (moderately tolerant) as control genotypes and a range of MnCl₂ concentrations (2, 250, 500, 750, 1000, 2000, and 3000 μM Mn) at pH 4.8 in a nutrient solution. Increasing solution Mn concentration decreased shoot and root dry weight and intensified the development of toxicity symptoms more in the Mn‐intolerant cv. Columbus than in Norquay and Cascades. The genotypic discrimination based on relative shoot (54% to 79%) and root dry weight (17% to 76%), the development of toxicity symptoms (scores 2 to 4) and the shoot Mn concentration (1428 to 2960 mg kg^–1) was most pronounced at 750 μM Mn. Using this concentration to screen 60 Australian and 6 wheat genotypes from other sources, a wide variation in relative root dry weight (11% to 95%), relative shoot dry weight (31% to 91%), toxicity symptoms (1.5 to 4.5), and shoot Mn concentration (901 to 2695 mg kg^–1) were observed. Evidence suggests that Mn tolerance has been introduced into Australian wheat through CIMMYT germplasm having “LERMO‐ROJO” within their parentage, preserved either through a co‐tolerance to Mn deficiency or a process of passive selection for Mn tolerance. Cultivars Westonia and Krichauff expressed a high level of tolerance to both Mn toxicity and deficiency, whereas Trident and Janz (reputed to be tolerant to Mn deficiency) were intolerant to Mn toxicity, suggesting that tolerance to excess and shortage of Mn are different, but not mutually exclusive traits. The co‐tolerance for Mn and Al in ET8 (an Al‐tolerant near‐isogenic line) and the absence of Mn tolerance in BH1146 (an Al‐tolerant genotype from Brazil) limits the effectiveness of these indicator genotypes to environments where only one constraint is induced. Wide variation of Mn tolerance in Australian wheat cultivars will enable breeding genotypes for the genetic solution to the Mn toxicity problem.     

Root morphology of wheat genotypes differing in zinc efficiency

The root morphology (root length, diameter) of the three wheat genotypes (Triticum aestivum L. cvs Excalibur and Gatcher, and T. turgidum conv. durum (Desf.) McKay cv Durati) grown in zinc (Zn)‐deficient, sandy soil under controlled conditions has been measured by a root scanner coupled to a computer. Wheat plants were supplied with 0, 0.025, 0.05, 0.1, 0.2, or 0.4 mg Zn/kg soil. Excalibur has previously been identified as the Zn‐efficient genotype which can take up more Zn and has higher yield in soils with low plant‐available Zn. Durati is Zn‐inefficient and Gatcher an intermediate genotype with respect to Zn efficiency. Root and shoot dry matter significantly increased at 0.1 mg Zn/kg soil compared to the 0 Zn level. Zinc content in shoots was lower in Durati than in Excalibur and Gatcher at sufficient supply of Zn. Zinc applications had no significant effect on root morphology at two weeks after sowing. At that time, however, the Zn‐efficient genotype Excalibur developed a longer and thinner roots (greater proportion of fine roots with diameter <0.2 mm) than the less efficient Gatcher and Zn‐inefficient Durati. Hence, growing longer and thinner roots and having a greater proportion of thinner roots in the total root biomass early in the growth period may be the two characters associated with the Zn‐efficient genotypes.     

Tolerance of barley cultivars to an acid,aluminum‐toxic subsoil related to mineral element concentrations in their shoots

Abstract

Barley, Hordeum vulgare L., is extremely sensitive to excess soluble or exchangeable aluminum (Al) in acid soils having pH values below about 5.5. Aluminum tolerant cultivars are needed for use in rotations with potatoes which require a soil pH below 5.5 for control of scab disease. They are also potentially useful in the currently popular “low input, sustainable agriculture (LISA)”; in which liming even the plow layer of soil is not always possible or cost effective, or in situations where surface soils are limed but subsoils are acidic and Al toxic to roots. Ten barley cultivars were screened for Al tolerance by growing them for 25 days in greenhouse pots of acid, Al‐toxic Tatum subsoil (clayey, mixed, thermic, typic Hapludult) treated with either 750 or 4000 μg?g^‐1 CaCO₃ to produce final soil pH values of 4.4 and 5.7, respectively. Based on relative shoot dry weight (weight at pH 4.4/weight at pH 5.7 X 100), Tennessee Winter 52, Volla (England), Dayton and Herta (Denmark) were significantly more tolerant to the acid soil than Herta (Hungary), Kearney, Nebar, Dicktoo, Kenbar and Dundy cultivars. Relative shoot dry weights averaged 28.6% for tolerant and 14.1% for sensitive cultivar groups. Comparable relative root dry weights were 41.7% and 13.7% for tolerant and sensitive cultivars, respectively. At pH 4.4, Al concentrations were nearly three times as high in shoots of sensitive cultivars as in those of the tolerant group (646 vs. 175 μg?g^‐1), but these differences were reduced or absent at pH 5.7. At pH 4.4, acid soil sensitive cultivars also accumulated phosphorus concentrations that were twice as high as those in tolerant cultivars (1.2% vs. 0.64%). At pH 5.7, these P differences were equalized at about 0.7% for both tolerant and sensitive groups. At pH 4.4, shoots of the Al‐sensitive cultivar Nebar contained 1067 μg?g^‐1 Al and 1.5% P. Concentrations of Al and P in the shoots of acid soil sensitive cultivars grown at pH 4.4 exceeded levels reported to produce toxicity in barley. The observed accumulation of such concentrations of Al and P in the shoots of plants grown under Al stress is unusual and deserves further study.     

Mycorrhiza Effect on Maize P Uptake from Phosphate Rock and Superphosphate

Low available phosphorus (P) is a serious constraint for crop production in acidic tropical soils. Economical yields in these environments require application of large amounts of costly nitrogen (N) and P fertilizers. Although phosphate rock (PR) has been proposed as a less expensive P source, the slow P release to the soil limits its use for annual crops. The objective of this work was to examine the effect of inoculating a nonsterile acidic soil with vesicular arbuscular mycorrhizal (VAM) Gigaspora margarita on PR dissolution and P uptake by aluminum (Al)–tolerant maize inbreds. Three maize inbreds from CIMMYT, at Cali, Colombia, ranked as Al‐tolerant and one local breed ranked as Al‐susceptible were seeded in 4‐kg pots filled with a soil of pH 4.1 and 2.5 mg kg^?1 available P. Inoculants (Gigaspora margarita and indigenous VAM), P fertilizer (Riecito phosphate rock and triple superphosphate), and the four inbreds were arrainged in a factorial design (2 × 2 × 4) with four replications. Plants were harvested 35 days after seeding, and P was determined in shoots. Four 2.5‐cm‐diameter soil cores were obtained from each pot to determine root length (two cores), root colonization (one core), and available P (one core). The inoculation with Gigaspora margarita caused a reduction in root length but better root colonization, 55% increase in P uptake, and 27% increase in shoot growth. When PR was used as fertilizer, plant growth was reduced in both roots and shoots. However, when PR was used in the presence of Gigaspora margarita, inbreds had 13% longer roots and shoot growth was the same as shoots fertilized with triple superphosphate. Our data suggest that inbreds exhibit different abilities to acquire P from PR under the influence of Gigaspora margarita fungi.     

Differential response of cowpea lines to aluminum and phosphorus application

Two pot experiments were conducted, one to evaluate the levels of tolerance of fifteen cowpea [Vigna unguiculata (L.) Walp] lines to aluminum (Al) application, and the second to determine the effect of phosphorus (P) addition on the performance of Al‐tolerant lines (IT 91K‐93–10, IT 93K‐2046–1, and IT 90K‐2 77–2) and Al‐sensitive lines (IT 86D‐719, IT 90K‐284–2, and IT 89KD‐349) in an Alfisol with Al amendment. Fourteen of the fifteen lines tested showed decreased root biomass (between 19 to 81% reduction) with Al addition, but this effect was significant for eight of them. Fewer lines showed decreased shoot biomass and grain yield with Al application. Despite little change in nodule number following Al application, there was a significant decrease in nodule weight (between 24 and 53% reduction) for nearly all lines. Phosphorus fertilization increased shoot and root biomass, grain yield, nodule number, and weight, and nitrogen (N) and P content of nearly all lines. Al‐tolerant lines showed higher response in shoot and root biomass and nodulation to P fertilization than Al‐sensitive lines, with the highest response from IT 90K‐277–2. Increase in shoot dry weight as a result of P fertilization was from 64 to 107% for Al‐tolerant lines and from 44 to 48% for the Al‐sensitive lines, and increase in root dry weight was from 46 to 86% for the Al‐tolerant lines and from 7 to 42% for the Al‐sensitive lines. Results of these trials indicated that lines IT 91K‐93–10, IT 93K‐2046–1, and IT 90K‐277–2 have potential for good performance in soil with Al toxicity problems, and that cowpea lines with inherent genetic tolerance to Al will give higher response to P fertilization when grown in soil with Al toxicity problems.     

Waterlogging Induces High to Toxic Concentrations of Iron,Aluminum, and Manganese in Wheat Varieties on Acidic Soil

Six wheat varieties with different tolerance to waterlogging were studied in acidic soil (pH 4.5), neutral soil, and potting mix (pH 6.7–7.8) under controlled conditions. Waterlogging for 49 d reduced shoot dry weight by 48% to 85% compared with drained treatments. The ranking of varieties for waterlogging changed under different soils, and this change explains why waterlogging tolerance of these varieties may vary in different environments. In waterlogged acidic soil, shoot concentrations of aluminum (Al), manganese (Mn), and iron (Fe) increased by two- to 10-fold, and in some varieties they were above critical concentrations compared with plants in drained soil. These elements decreased or remained the same in shoots of plants grown in waterlogged neutral soil. Marginal nitrogen (N) deficiency was induced in most varieties in all soil types. The results support the importance of screening in soils from the target environment for accurate germplasm characterization for waterlogging tolerance.     

Difference in response to aluminum stress among Tibetan wild barley genotypes

Wild barley (Hordeum sp.) germplasm is rich in genetic diversity and provides a treasure trove of useful genes for crop improvement. We carried out a comprehensive program combining short‐term hydroponic screening via hematoxylin‐staining of root‐regrowth procedure and filter paper–based evaluation of diverse germplasm in response to Al/acid stress using 105 annual Tibetan wild barley and 45 cultivated barley genotypes. Root elongation among the 105 Tibetan wild barley genotypes varied significantly after Al exposure, ranging from 62.9% to 80.0% in variation coefficients and 4.35 to 4.45 in diversity index. These genotypic differences in Al resistance were fairly consistent in both the hydroponic and filter paper–based evaluations: XZ16, XZ166, and XZ113 were selected as Al‐resistant genotypes, and XZ61, XZ45, and XZ98 as Al‐sensitive wild genotypes. Furthermore, significantly lower Al concentrations in roots and shoots were detected in the three selected Al‐resistant genotypes than in the three sensitive genotypes in the filter paper–based experiment. Meanwhile, XZ16 was the least affected by Al toxicity in regard to reduced SPAD value (chlorophyll meter readings), plant height, root length, dry biomass, tillers per plant, and chlorophyll fluorescence (Fv/Fm) in the long‐term hydroponic experiment compared with the Al‐resistant cultivated barley cv. Dayton, while XZ61 had the severest stress symptoms.     

Inverse Relationship Between Boron Toxicity Tolerance and Boron Contents of Barley Seed and Root

A filter-paper bioassay method was used to investigate the differential response of 23 barley (Hordeum vulgare L.) genotypes to boron (B) toxicity. Two-day-old seedlings with equal radicles were treated with 10 (B10) or 100 (B100) ppm B for 10 d. Root and shoot growth was not affected by B10, but root growth was significantly reduced by B100. The shoot growth at B100 was either unaffected or affected to a smaller extent than the root. A significant inverse correlation was found between B content of seed and seed germination, and between root growth and B contents of root and shoot under B100. The barley genotypes with lower B contents in seeds had a higher germination, longer root length, and accumulated less B in roots and shoots when treated with B100. The B-tolerant genotypes with longer roots had lower B contents in their seed, root, and shoot and vice versa. These results suggest that a great variation exists among barley genotypes in response to high B application. There was no difference between naked (uncovered) and covered varieties in response to B100. The B tolerance could be attributed to the lower B content of seed and lower uptake or accumulation of B in the root and shoot.     

Growth traits and mineral concentrations of maize hybrids grown on unlimed and limed acid soil

Growing crop plants tolerant to acid soils is an alternative for successful production on acid soils with limited inputs, especially lime. Acid soil‐ or aluminum (Al)‐tolerant plants offer considerable protection against soil acidity problems. Thirteen maize (Zea mays L.) hybrids developed for production under various environmental conditions were grown (greenhouse) on two acid soils (unlimed and limed) to determine differences among hybrids for growth traits, mineral acquisition, and relative tolerance to acid soil. Porters soil induced greater acid soil stress on maize than did Lily soil, although shoot/root dry matter (DM) ratios were affected more in plants grown on Lily than on Porters soil. Shoot and root DM and total root length (RL) over all hybrids followed sequences of Limed Lily ≥ Limed Porters > Unlimed Lily > Unlimed Porters, and the trait with the greatest variation among hybrids was total RL. Specific RL (total RL/root DM) over all hybrids followed a sequence of Limed Lily=Limed Porters=Unlimed Lily>Unlimed Porters, with relatively small variations among hybrids. Shoot DM/RL among hybrids followed a sequence of Unlimed Porters ≥ Unlimed Lily > Limed Lily = Limed Porters, and had the least variation among hybrids. Two Brazilian hybrids (HD 91102 and HD 9176) had highest DM and total RL to indicate relatively high tolerance to acid soil stresses, while other hybrids (ten from the United States and one from Brazil) had relatively small differences for growth traits to indicate moderate to low tolerance to acid soils. Although genotypes differed widely for mineral element concentrations, no significant differences in mineral elements between more and less tolerant genotypes were noted.