Differential genotypic tolerance response to manganese stress in triticale

Abstract

Manganese (Mn) tolerance response in two aluminum (Al)‐tolerant triticale (× Triticosecale Wittmack) varieties was characterized by measurements of growth and dry matter production of seedlings in nutrient solution culture containing 100 mg L^‐1 Mn. Root weight index (RWI) and total weight index (TWI) based on relative plant growth were two indicators of differentiating genotypic Mn tolerance; these two indices were used to make a comparative assessment of the degree of Mn tolerance in a group of eight Australian and South African genotypes which differ in apparent Al tolerance. The G4–95A was more Mn‐tolerant than its Al‐tolerant counterpart Tahara. A wide range of Mn tolerance was found in the eight genotypes, but few were tolerant of both Al and Mn stresses; measurements of RWI at 100 mg L^‐1 Mn stress differentiated them into three response types (i.e., Mn‐tolerant, moderately Mn‐tolerant/Mn‐sensitive, and Mn‐sensitive) at the two critical values of 0.30 and 0.60. Covariation analysis indicated no association between Mn tolerance and Al tolerance; selective breeding for acidic stress tolerance should focus on both stress tolerances.     

Differential tolerances of oat cultivars to aluminum in nutrient solutions and in acid soils of Poland

Aluminum tolerant oat cultivars are needed for use on acid soil sites where neutralization of soil acidity by liming is not economically feasible. Oat germplasm in Poland has not been examined for range of Al tolerance. Eleven Polish oat cultivars were screened for Al tolerance in nutrient solutions containing 0, 5 and 15 mg L^‐1 Al. Three of these cultivars showing high to moderate tolerance to Al in nutrient solutions were also grown in greenhouse pots of soil and in field plots of soil over a pH range of 3.8 to 5.5 as determined in 1 N KC1.

The eleven oat cultivars differed significantly in tolerance to Al in nutrient solutions. Based on relative root yield (15 mg L^‐1 Al/no A1%), the cultivars ‘Solidor’ and ‘Diadem’ were most tolerant and ‘Pegaz’ and ‘B‐20’ were least tolerant. For these three cultivars, the order of tolerance to acid soil agreed with the order of tolerance to Al in nutrient solution ‐ namely, Solidor > Diadem > Leanda. Hence, for these cultivars, the nutrient solution methods used appear adequate for selecting plants that are more tolerant to Al in strongly acid soils. Additional study is needed to assess the value of this method for screening a broad range of germplasm.

Superior tolerance of the Solidor cultivar to acid soil was associated with significantly higher concentrations of N in the grain. Hence, results suggest that selecting for acid soil or Al tolerance may increase N efficiency in oats.     

Screening Kentucky bluegrass for aluminum tolerance

Aluminum (Al) toxicity is a growth‐limiting factor in acid soils for many turfgrasses. The genetic diversity among turfgrass cultivars for Al tolerance is not well known. One hundred‐fifty Kentucky bluegrass (Poa pratensis L.) genotypes (cultivars, selections, and breeding lines) belonging to seven ecotypes were selected to screen for Al tolerance under greenhouse conditions using solution culture, sand culture, and an acid Tatum subsoil (Clayey, mixed, thermic, typic, Hapludult). This soil had 69% exchangeable Al and a pH of 4.4. An Al concentration of 320 μM and a pH of 4.0 in a modified 1/4 strength Hoagland nutrient solution was used in solution screening and sand screening. The grasses were seeded and grown four to five weeks before harvesting. Differences were identified among cultivars and the seven ecotypes by measuring relative growth. ‘Battan’, ‘Viva’, and ‘Nassau’ were the most Al‐tolerant cultivars based on the rank average of the three screening methods. Among the seven ecotypes, BVMG, which refers to cultivars such as ‘Baron’, ‘Victa’, ‘Merit’, and ‘Gnome’, were most Al tolerant while Midwest ecotypes, which are frequently referred to as common Kentucky bluegrasses, consistently exhibited the least Al tolerance. The results indicate that the Kentucky bluegrass cultivars vary genetically in Al tolerance and that there is potential to improve such tolerance with breeding and to refine cultivar‐specific management recommendations regarding soil pH.     

EFFECTS OF CALCIUM AND SALINITY STRESS ON QUALITY OF LETTUCE IN SOILLESS CULTURE

Abstract

Fine fescues (Festuca spp.) are generally considered acid tolerant compared to other cool‐season turfgrasses. However, there is little information on aluminum (Al) tolerance of fine fescues at both the species and cultivar levels. The objectives of this study were to identy cultivars of fine fescues with superior ability to tolerate Al, and compare the Al tolerance of endophyte infected and endophyte‐free cultivars in Al tolerance. A total of 58 cultrvars of fine fescues belonging to five species or subspecies [14 hard fescue (F. longifolia Thuill), 25 Chewings fescue (F. rubra L. ssp. commutata Gaud), 15 strong creeping red fescue (F. rubra L. ssp. rubra), two slender creeping red fescue (F. rubra L. ssp. trichophylla), and two sheep fescue (F. ovina L.)] were selected from the 1993 National Fineleaf Fescue Test and screened under greenhouse conditions using solution culture, sand culture, and acid Tatum soil (Clayey, mixed, thermic, typic, Hapludult). The acid Tatum soil had 69% exchangeable Al and a pH of 4.4. An Al concentration of 640 μM and a pH of 4.0 were used in solution culture and sand culture screening. The grasses were seeded and grown for three weeks before harvesting. Aluminum tolerance was assessed by measuring relative root length, shoot length, root weight, shoot weight, and total dry matter. Differences in Al tolerance were identified at both the species and cultivar level based on relative growth were as follows: i) hard fescue and Chewings fescue were more Al tolerant than strong creeping red fescue; ii) within species or subspecies, significant differences were found among cultvars of Chewings fescue, strong creeping red fescue, slender creeping red fescue, and sheep fescue; whereas no difference was observed among the hard fescue cultivars; and iii) the cultivars containing endophyte exhibited greater Al tolerance compared the eudophyte‐free cultivars. The results indicate that fine fescues vary in Al tolerance and there is potential to improve Al tolerance with breeding and to refine their management recommendations regarding soil pH.     

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.     

Evaluating landraces of bread wheat <Emphasis Type="Italic">Triticum aestivum</Emphasis> L. for tolerance to aluminium under low pH conditions

Bread wheat (Triticum aestivum L.) landraces held within ex situ collections offer a valuable and largely unexplored genetic resource for wheat improvement programs. To maximise full utilisation of such collections the evaluation of landrace accessions for traits of interest is required. In this study, 250 accessions from 21 countries were screened sequentially for tolerance to aluminium (Al) using haematoxylin staining of root tips and by root regrowth measurement. The staining test indicated tolerance in 35 accessions, with an intermediate response to Al exhibited in a further 21 accessions. Of the 35 accessions classified as tolerant, 33 also exhibited increased root length following exposure to Al. The tolerant genotypes originated from Bulgaria, Croatia, India, Italy, Nepal, Spain, Tunisia, and Turkey. AFLP analysis of the 35 tolerant accessions indicated that these represent diverse genetic backgrounds. These accessions form a valuable set of germplasm for the study of Al tolerance and may be of benefit to breeding programs for expanding the diversity of the gene pool from which tolerant cultivars are developed.     

Ozone tolerances of soybean cultivars and near‐isogenic lines in a fumigation chamber

Ozone (O₃) toxicity is a potential yield‐limiting factor for soybean (Glycine max L. Merr.) in the United States and worldwide. The most economical solution to the problem is to use O₃‐tolerant cultivars. Thirty‐four cultivars and 87 near‐isogenic lines (NILS) of soybean were screened for O₃ tolerance in a fumigation chamber (250 ppb for three hrs). Most tolerant cultivars tested were ‘Cloud’, ‘T‐276’, ‘T263’, and ‘Kindu’. Moderately tolerant cultivars included ‘Davis’, ‘T‐210’, and ‘Elton’. Most sensitive cultivars were ‘Corsoy 79’, ‘Noir’, and ‘Midwest’. The original ‘Clark’ cultivar was not tested, but ‘Clark 63’ tended to be more tolerant than ‘Harosoy’. The aluminum (Al)‐tolerant ‘Perry’ cultivar also tended toward greater O₃ tolerance than the Al‐sensitive ‘Chief’, as observed earlier. Our rankings of ‘Hark’ as moderately sensitive and ‘Davis’ as moderately tolerant are also in agreement with earlier reports. Among NILS, the order of O₃ tolerance was generally Williams>Clark>Harosoy, but differences were also observed within these parental groups. For example, L68–560 was more tolerant than some other NILS of ‘Harosoy’. ‘L76–1988’ appeared more tolerant to O₃ than other NILS of ‘Williams’, but all ‘Williams’ NILS were more tolerant than most NILS of ‘Harosoy’ and ‘Clark’. Ozone‐tolerant and ‐sensitive soybean cultivars or NILS identified in our study may be useful tools in studies on mechanisms of 03 tolerance and differential 03 tolerances in plants and in the development of ameliorative measures.     

Differential aluminum tolerance in some tropical rice cultivars: I. Growth performance

Ten‐day‐old seedlings of 22 rice (Oryza sativa.L) cultivars originated from various tropical countries were subjected to six levels of aluminum (Al) [0, 74, 148, 222, 296, and 370 μM] to test their tolerance to Al toxicity in nutrient solutions at pH 4.0±0.l. Seedlings were grown in the presence of Al under controlled environmental conditions in growth chambers. The nutrient solutions were replenished once a week. After 30 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), root tolerance index (RTI) and shoot tolerance index (STI) have been used as markers of Al toxicity.

Rice cultivars studied exhibited wide range of responses in their tolerance to Al. Though, the rice cultivars were subjected to six levels of Al, a good degree of separation in their responses was observed only at 222 μM Al. Therefore, this concentration was chosen to analyze and compare the performances of the cultivars. Further, only six cultivars showed significant changes in their expression in the presence of Al compared to control, and so data have been presented only for those cultivars for clarity. The cultivars BW 196, Bhura Rata, Basmati 370 and Co 37 recorded increases in growth, while Damodar and ADT 36 showed severe inhibitions in the presence of Al. Furthermore, in RTI and STI also Co 37 and Basmati 370 registered their tolerance to Al by showing increased growth in the presence of Al. Whereas, Damodar and ADT 36 recorded severe reductions. The RGRR and RGRS data also substantiates this finding. Based on the growth parameters, the six rice cultivars were ranked based on their tolerance to Al: Co 37 > Basmati 370 > BW 196 > Bhura Rata > Damodar > ADT 36. Co 37 and Basmati 370 are the two most tolerant cultivars which performed extremely well in the presence of Al, and Damodar and ADT 36 are the most susceptible cultivars. Therefore, the Al‐tolerant cultivars can be used for future breeding programes to develop Al‐tolerant, cultivars that subsequendy can be recommended for planting in acidic, infertile soils of the tropics.     

Acid soil tolerances of two wheat cultivars related to soil Ph,KCl‐extractable aluminum and degree of aluminum saturation

Aluminum toxicity, associated with soil acidity, is a major growth‐limiting factor for plants in many parts of the world. More precise criteria are needed for the identification of potential Al toxicity in acid soils. The objective of the current study was to relate the acid soil tolerances of two wheat cultivars to three characteristics of an acid Tatum subsoil (clayey, mixed, thermic, typic Hapludult): pH in a 1:1 soil to water suspension; KCl‐extractable Al; and degree of Al saturation. Aluminum‐tolerant ‘BH 1146’ (Brazil) and Al‐sensitive ‘Sonora 63’ (Mexico) wheat cultivars were grown in greenhouse pots of soil treated with CaCO₃ to establish final soil pH levels of 4.1, 4.6, 4.7, 4.9, 5.2 and 7.3. Soil Al, Ca and Mg were extracted with 1 N KCl, and Al saturation was calculated as KCl‐Al/KCl Al + Ca + Mg%.

Within the soil pH range of 4.1 to 4.9, BH 1146 tops and roots produced significantly more dry matter than did those of Sonora 63; however, at pH 5.2 and 7.3, the top and root yields of the two cultivars were not significantly different. Significant cultivar differences in yield occurred over a range of 36 to 82% saturation of the Tatum soil. Graphs of relative top or root yields against soil pH, KCl‐extractable Al and Al saturation indicated that the two cultivars could be separated for tolerance to Tatum soil under the following conditions: pH less than 5.2 (1:1 soil‐water); KCl‐Al levels greater than 2 c mole kg^‐1 and Al saturations greater than 20%. Results demonstrated that any soil test used to predict Al toxicity in acid soils must take into account the Al tolerances of the plant cultivars involved.     

Aluminum effects on micronutrient uptake by annual ryegrass

Abstract

Four ryegrass (Lolium multiflorumLam.) cultivars were grown in 1/5 Steinberg nutrient solution supplemented with six Al levels (0, 37, 74, 148, 296, or 592 umol L^‐1) at pH initially adjusted to 4.2. Average net Fe influx was stimulated at low nutrient solution Al levels. This stimulation was larger for more Al‐tolerant cultivars Marshall and Gulf. Decreases in average net Mn and Zn influxes were brought about by increasing Al levels in the nutrient solution. The average net influx of Fe, Mn, and Zn was positively correlated with the root tolerance index (relative root yield of plants grown with and without Al added to the nutrient solution). For more Al‐tolerant cultivars, increased total uptake of Fe and Cu was brought about by increased nutrient solution Al levels up to 74 umol L^‐1. Decreases in total uptake of Mn and Zn were generally noted with increased nutrient solution Al levels. Percentage inhibition of total Fe, Mn, Zn, and Cu uptake was negatively correlated with the mean pH of the Al‐containing nutrient solutions. The higher average net influx and the smaller percentage inhibition of total Fe uptake at nutrient solution Al levels up to 74 umol L^‐1can be used as indicators in ranking ryegrass cultivars as more Al‐tolerant     

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.     

Aluminum tolerance of segregating wheat populations in acidic soil and nutrient solutions

Abstract

Increased demand for wheat (Triticum aestivum L.) cultivars tolerant to acid‐soil stress has accelerated genetic research on aluminum (Al) tolerance in soil and solution media. Our objective was to characterize the genetic segregation of tolerant and susceptible plants from two populations in an Al‐toxic Porters soil (coarse‐loamy, mixed, mesic Umbric Dystrochrepts), and in nutrient solutions with 0.09, 0.18, 0.36, 0.72, and 0.90 mM Al. Rapid bioassays were applied to determine seedling responses of two Al‐tolerant (Cardinal and Becker) and two susceptible cultivars (GK Zombor and GK Kincso) and their F₂ progenies. In the Al‐toxic soil, Becker/Kincso F₂ and Cardinal/Zombor F₂ exhibited contrasting segregation patterns but with similar heritability values (0.60 and 0.57, respectively). Higher values of root length in soil were dominant in Cardinal/Zombor F₂ (degree of dominance, d = 0.98), but dominance was absent (d = 0.07) for Becker/Kincso F₂. The results of the soil and nutrient‐solution experiments were not entirely consistent; gene expression appeared to be influenced by the concentration of Al in the nutrient solution. The frequency of susceptible F₂ plants increased proportionately to the increase in Al concentration for both populations. This unexpected pattern provides further evidence that segregation in wheat populations cannot always be explained by single‐gene inheritance.     

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.     

The effect of subsurface aluminium on the growth and uptake of surface‐applied phosphorus by wheat seedlings 1

Seedlings of four cultivars of wheat (Triticum aestivum L.) differing in tolerance to aluminium (Al) were grown for 14 to 20 days using a split‐root sand/solution culture technique. Each culture tube was divided horizontally into two compartments by a root‐permeable paraffin wax barrier, so that phosphorus (P) and aluminium (Al) supply could be varied in the upper 0–80 mm (surface) and lower 80–180 mm (subsurface) compartments, respectively.

Root growth into the subsurface zone was enhanced by increased P supply to surface roots, but only in the absence of subsurface Al. Where subsurface Al was present, increased P supply to surface roots had no effect on the penetration of roots into the subsurface zone. Tolerance to Al in the cultivars used was therefore not related to the ability to translocate P to sites of Al injury.     

Magnetic resonance imaging of absorbed aluminum in alfalfa roots

An estimated 30% of the world's arable soils are acidic and aluminum (Al) toxicity is often the primary growth‐limiting factor. Excess Al is especially undesirable in sub‐soils because it reduces rooting depth and branching and predisposes plants to drought injury. Liming the plow layer does not generally neutralize subsoil phytotoxicity and Al‐tolerant cultivars offer an alternative or supplemental solution to the problem. Genetic diversity for acid soil tolerance in alfalfa (Medicago sativa L.) is limited and a better understanding of the basic tolerance mechanisms would facilitate the design of more efficacious breeding procedures. Evidence is accumulating that organic acids and proteins elicited by Al stress may complex and detoxify Al either within, or external to, the root. Because Al is a paramagnetic element that can reduce T2 relaxation times (inter‐proton interactions) markedly, the mechanism of Al tolerance in alfalfa was investigated through T2‐based Magnetic Resonance Imaging (MRI) of young lateral root sections of an Al‐sensitive and an Al‐tolerant alfalfa clone grown in nutrient solution (0 or 111 μmol Al; pH 4.5). Root sections that developed under phytotoxic levels of Al accumulated considerable Al in the epidermis and internal root tissue. Aluminum may have been complexed by low molecular weight proteins and organic acids in the tolerant clone whereas the sensitive clone appeared to have abundant free Al; however, variation among replications indicates that free Al may still have been present in tolerant roots and that other tolerance mechanisms may also be important. Root buds accumulated little Al compared to the remainder of the root, indicating that the pronounced effects of Al on lateral root development are indirect. Magnetic Resonance Imaging images evaluated in this study provided clues to the basic mechanisms of Al tolerance in alfalfa and, with further refinement, could be used as one criterion for selecting Al‐tolerant plants.     

Effect of nodulation with Bradyrhizobium japonicum and Shinorhizobium fredii on xylem sap composition of Peking (Glycine max L. Merr )

Five barley cultivars were grown together in complete, low-P·low-pH and high-Al medium containing only NO₃, only NH₄ or both NO₃ and NH₄ as N sources, respectively using an automatic control system of pH for water culture, and the relationship between the differential Al tolerance and the plant-induced pH change of medium among the barley cultivars was investigated.

The pH of the medium containing only NO₃ as N source tended to increase, whereas the pH of the other media containing only NH₄ or both NO₃ and NH₄ as N sources tended to decrease, but the fluctuations of the medium pH could be maintained within the value of 0.2 pH in the complete medium and within the value of 0.1 pH in the high-Al medium.

Barley cultivars still differed in their Al tolerance in the medium which was continuously stirred and circulated at a constant pH. The pattern of Al tolerance was not affected by the N sources in the medium. The plant-induced pH change of medium for each cultivar was influenced by the N sources in the medium, and was not correlated positively with Al tolerance. The contents of Al and Ca or other nutrient cations in roots were positively correlated with Al tolerance and positive correlations were recognized also between the contents of Al and Ca or some other nutrient cations in the roots.

In conclusion, the following mechanisms are proposed. Al tolerant barley cultivars exclude Al actively outside the plasmalemma of the root cells, and the excluded Al may polymerize and or react with P to form Al precipitates. Consequently, in the Al tolerant barley cultivars the Al content may be low in the root protoplasts, high in the whole root tissues and the contents of Ca or other nutrients may be high in the roots. The plant-induced pH change of medium is not considered to be the cause of the differential Al tolerance among barley cultivars.     

Differential tolerance of bush bean cultivars to excess manganese in solution and sand culture

Nineteen bush bean cultivars were screened for tolerance to excess Mn in nutrient solution and sand culture experiments. Seven‐day‐old seedlings were treated with full strength Hoagland No. 2 nutrient solution containing different Mn concentrations for 12 days in the greenhouse.

Cultivars showing the greatest sensitivity to Mn toxicity were ‘Wonder Crop 1’ and ‘Wonder Crop 2'; those showing the greatest tolerance were ‘Green Lord’, ‘Red Kidney’ and ‘Edogawa Black Seeded’.

Leaf Mn concentration of plants grown in sand culture was higher than that for plants grown in solution culture. The lowest leaf Mn concentration at which Mn toxicity symptoms developed, was higher in tolerant than in sensitive cultivars. The Fe/Mn ratio in the leaves at which Mn toxicity symptoms developed, was higher in the sensitive cultivars than in the tolerant ones.

We concluded that Mn tolerance in certain bush bean cultivars is due to a greater ability to tolerate a high level of Mn accumulation in the leaves.     

Mechanisms of aluminum tolerance in triticum aestivum L. (wheat) III. Long‐term pH changes induced in nutrient solutions by winter cultivars differing in tolerance to aluminum

Five winter cultivars of Triticum aestivum L., representing a known range of tolerance to aluminum (Al), were grown in nutrient solutions with and without Al for 41 days to determine long‐term changes in solution pH. Plant‐induced pH of the nutrient solutions declined for 16 to 17 days. Subsequently, the pH induced by Al‐sensitive plants grown without Al and Al‐tolerant plants grown with Al and without Al increased rapidly, presumably reflecting depletion of NH₄ ⁺ from the nutrient solutions. Aluminum‐sensitive plants grown with Al showed a less pronounced pH rise after 16 to 17 days of treatment.

After nutrient solutions were renewed on days 26 and 34, plant‐induced pH patterns were similar to those during days 1 to 26. However, the time required for the onset of the rapid rise in pH decreased. In these subsequent pH cycles, the pH patterns induced by Al‐tolerant plants grown with Al progressively approximated those induced by plants grown without Al. Aluminum‐sensitive plants grown with Al did not induce a rapid rise In pH of nutrient solutions.

Differential tolerance to Al was apparent visually after three to five days growth. Cultivar tolerance to Al was correlated with the initial rate of the pH decline (days 1 to 26) as well as final pH of solutions discarded on days 26, 34, and 41. These results support the hypothesis that differential uptake of NH₄ ⁺ and NO₃ ^‐ causes cultivar differences in plant‐induced pH of nutrient solutions and affects the relative growth of cultivars in Al‐toxic nutrient solutions.     

Aluminum effects on six wheat cultivars in Kenyan soils

Abstract

Six cultivars of wheat (Triticum aestivum L.), Kenya Nyumbu, Kenya Zabadi, Alondra, Kenya Swara, Kenya Tumbili, and Kenya Fahari, were tested for their susceptibility to Al. They were grown in a glasshouse in four Kenyan soils, two of which had high Al, low pH and supported poor field crops, and two of which had higher pH, lower Al and supported healthy field crops. Shoot, root and seed weights, and concentrations of Al, Ca, and Mn in shoots and seeds were determined at harvesting. Significant differences in Al susceptibility between varieties existed, and these differences increased with increasing soil Al. The Al‐susceptibility ratings using a root‐staining procedure for these cultivars reported by earlier workers were not fully confirmed; K. Fahari, rated as “Al‐susceptible”;, performed as well as “Al‐tolerant”; varieties. Greater uptake of Mn by all cultivars seemed to be due to anaerobiosis through poor soil drainage. The marked Al‐susceptibility of K. Swara is probably due to its inability to restrict Al uptake. Further testing of cultivars is necessary under field conditions to confirm their Al‐susceptibility to acidic, high‐Al soils.     

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.