Differential aluminum tolerance in some tropical rice cultivars. II. mechanism of aluminum tolerance

Ten‐day‐old seedlings of 22 rice (Oryza sativa L.) cultivars were subjected to aluminum (Al) stress in nutrient solutions with an initial pH of 4.0±0.1. The rice cultivars exhibited a wide range of response by changing the rhizosphere pH, and the uptake and efficiency ratio (ER) of utilization of nutrients both in the presence (222 μM Al) and absence of Al. In the presence of Al, the cultivars Co 37 and Basmati 370 recorded maximum uptake and highest ER's for calcium (Ca), potassium (K), magnesium (Mg), manganese (Mn), phosphorus (P), and iron (Fe). The cultivars Damodar and ADT 36 performed very poorly in terms of nutrient uptake. The tolerant cultivars (Al‐insensitive) efficiently took up and utilized Ca and P in the presence of Al. The susceptible (Al‐sensitive) and intermediate cultivars exhibited less Ca and P uptake and utilization. There was no apparent relationship between foliar Al content and the efficiency ratios. However, the Al‐tolerant cultivars, Co 37 and Basmati 370, accumulated less Al in their foliage which was the reverse in case for the Al‐susceptible cultivars. Among the 22 rice cultivars tested, Co 37 and Basmati 370 emerged as the most Al‐tolerant. Hence, they would be recommended for cultivation in acidic, infertile soils of the tropics. The results of this study are discussed in terms of identifying the mechanism of Al tolerance or sensitivity among the studied rice cultivars as related to their nutrient metabolism.     

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.     

Varietal diversity of upland rice in sensitivity to aluminium

A rapid and simple nutrient addition technique was used for evaluating Al tolerance of six local upland rice (Oryza sativa L.) cultivars (BG35, BR21, DA25, DA26, DA14, and DA22) from Bangladesh and three IRRI rice, IR46, IR97, and IR45, cultivars from the Philippines. The plants were grown for 21 days with Al (0 μM, 140 μM, 280 μM or 560 μM) at pH 4.1. The roots were more affected by Al than the shoots. In rating cultivars for Al sensitivity, relative shoot weight (RSW) was found to be the best parameter due to the severe damage of the roots, irrespective of Al sensitivity. The cultivars were rated as Al tolerant (BG35, BR21, DA25, and DA26), mid‐tolerant (DA14, DA22, and IR46) and sensitive (IR97 and IR45) . More Al was retained in the roots of tolerant cultivars than in the mid‐tolerant or sensitive cultivars. In shoots, the Al concentration of tolerant cultivars was less than in the mid‐tolerant or in the sensitive cultivars and the inhibition of growth was proportional to Al concentration irrespective of Al tolerance. Therefore, the variation among cultivars in Al sensitivity could be related to the capacity of roots to retain Al from transport to the shoots.     

Aluminum toxicity and high bulk density: Role in limiting shoot and root growth of selected aluminum indicator plants and eastern gamagrass in an acid soil

Abstract

Shallow rooting and susceptibility to drought are believed to be caused, at least in part, by strongly acidic (pH <5.5, 1:1 soil‐water), aluminum (Al)‐toxic subsoils. However, this hypothesis has not been clearly confirmed under field conditions. The Al toxicity hypothesis was tested on a map unit of Matawan‐Hammonton loam (0–2% slope) on unlimed and limed field plots (pH range 5.1 to 5.8) at Beltsville, MD, during 1994 to 1998. Aluminum‐tolerant and sensitive pairs of barley (Hordeum vulgare L.), wheat [Triticum aestivum (L.)], snap bean (Phaseolus vulgaris L.), and soybean [Glycine max (L.) Merr.] cultivars were used as indicator plants. Eastern gamagrass [Tripsacum dactyloides (L.) L.], cultivar ‘Pete’, reported to tolerate both chemical and physical stress factors in soils, was grown for comparison. Shoots of Al‐sensitive ‘Romano’ snap beans showed a significant response to liming of the 0–15 cm surface layer, but those of Al‐tolerant ‘Dade’ did not, indicating that Al toxicity was a growth limiting factor in this acid soil at pH 5.1. Lime response of the Al‐tolerant and sensitive cultivars of barley, wheat, and soybean were in the same direction but not significant at the 5% level. Aluminum‐tolerant and sensitive cultivars did not differ in abilities to root in the 15–30 cm soil depth. Only 9 to 25% of total roots were in this layer, and 75 to 91% were in the 0–15 cm zone. No roots were found in the 30–45 cm zone which had a pH of 4.9. Soil bulk density values of 1.44 and 1.50 g cm^?3 in the 15–30 and 30–45 cm zones, respectively, indicated that mechanical impedance was a primary root barrier. Results indicated that restricted shoot growth and shallow rooting of the Al‐indicator plants studied in this acid soil were due to a combination of Al toxicity and high soil bulk density. Confounding of the two factors may have masked the expected response of indicator plants to Al. These two growth restricting factors likely occur in many, if not most acid, problem subsoils. Studies are needed to separate these factors and to develop plant genotypes that have tolerance to multiple abiotic stresses. Unlike the Al indicator cultivars, eastern gamagrass showed high tolerance to acid, compact soils in the field and did not respond to lime applications (pH 5.1–5.8).     

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.     

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.     

Role of water stress in differential aluminum tolerance of six sunflower cultivars grown in an acid soil

Six cultivars of sunflower (Helianthus annuus L.), were screened under controlled environmental conditions for tolerance to Al stress and water stress imposed separately and in combination with one another. Plants were grown for 4 weeks in waxed cartons containing 1 kg of acid, Al‐toxic Tatum, subsoil (clayey, mixed, thermic, Typic Hapludult) at high (pH 4.3) or low (pH 6.3) Al stress. During the final 2 weeks they were also subjected to low (‐20 to ‐40 kPa) or high (‐60 to ‐80 kPa) water stress. Plant growth responses and symptoms of Al toxicity suggested that a wide range of cultivar sensitivity existed. ‘Manchurian’, ‘S‐212’, ‘S‐254’, and ‘S‐265’ were relatively tolerant to Al toxicity while cultlvars ‘Romania HS‐52’ and ‘RM‐52’ were extremely sensitive. Under high Al stress and high water stress, chloroplasts in cells from the Al‐sensitive cultivar ‘Romania HS‐52’ were smaller and contained less starch than chloroplasts from the Al‐tolerant cultivar ‘Manchurian’. Furthermore, the smaller chloroplasts tended to have fewer grana stacks per unit area than did the chloroplasts from tolerant plants. These differences were not apparent when the Al‐sensitive cultivar was grown either in the absence of Al or water stress. In general, Al‐sensitive cultivars of sunflower were more tolerant to water stress than were Al‐tolerant cultivars. Increasing the soil moisture level reduced Al toxicity in Al‐sensitive cultivars. Similarly, decreasing Al stress partially overcame the detrimental effects of high water stress. Hence, Al stress and water stress are interrelated factors which must be considered in the characterization and breeding of plants for better adaptation to acid soils.     

高光谱反射率与大豆叶面积及地上鲜生物量的相关分析

以ASD FieldSpec光谱仪实测了不同生长季大豆的冠层高光谱，同期采集了对应大豆LAI、地上鲜生物量。逐波段分析了冠层光谱反射率、导数光谱与大豆LAI、地上鲜生物量的相关关系；采用单变量线性回归逐波段分析了冠层光谱反射率、导数光谱与大豆LAI、地上鲜生物量确定性系数随波长的变化趋势；并建立了以近红外与可见光波段的冠层光谱反射率的比值植被指数RVI与大豆LAI、地上鲜生物量的高光谱遥感估算模型。结果表明，冠层光谱反射率在350～680 nm、760～1050 nm波谱区与大豆LAI、地上鲜生物量相关性     

Physiological basis of differential aluminum tolerance in rice genotypes

Abstract

Two rice genotypes, aluminum (Al)‐tolerant Co 37 and Al‐susceptible ADT 36, were evaluated for their physiological responses in the presence of Al stress in a hydroculture experiment. Two levels of Al (0 and 222 μmol/L) were supplied in the nutrient solution and the two rice genotypes were subjected to Al for two weeks. Root growth parameters, relative growth reduction in roots (RGRR), effects of calcium (Ca²⁺) nitrate metabolism, Al content in roots, and pH shift patterns were recorded. The Al treatments had a lesser effect on Co 37 in terms of reduction in root growth and root dry matter production as compared to ADT 36. While Co 37 did not show significant differences in response to various levels of Ca²⁺ added in the medium under Al stress, ADT 36 registered a dose‐dependent effect in circumventing the injurious effects of Al. Further, reduction in nitrate content and in vivo nitrate reductase (NR) activity in the leaf tissue in Co 37 under Al treatment was less than that in ADT 36. Moreover, Co 37 had a lower content of Al in its root tissue than did ADT 36. Co 37 was also able to shift the pH of the medium more efficiently than ADT 36, thereby minimizing the uptake of Al, and eventually reducing Al toxicity. The higher level of tolerance to Al of Co 37 seems to have emanated from an efficient nitrate metabolism and its capacity to shift the pH of the medium. It is also evident that Al toxicity in ADT 36 can be circumvented by a Ca treatment to a considerable extent. Our results offer a possible physiological basis for Al tolerance in crop plants.     

Response of cotton cultivars to aluminum in solutions with varying silicon concentrations

Abstract

Cotton (Gossypium hirsutum L.) is extremely sensitive to Al toxicity. Increasing Si concentration in solution has been reported to alleviate AI toxicity. In this investigation the effects of varying Si concentrations (700, 1400, and 2800 μM Si) on reactive Al (defined as Al reactive with aluminon during 10‐s reaction time, without acidification and heating) was studied in solutions containing either 50, 100 or 200 μM Al during 50 d of aging. An increase in Si concentration had negligible effects on the reactive Al in solutions with 50 or 100 μM Al. However, in solutions with 200 μM Al the reactive Al decreased by 6 to 15% with an increase in Si concentration from 0 to 2800 μM.

The effects of either 700, 1400 or 2800 μM Si on root growth of Coker 208, Coker 315, DPL 90, McNair 235, Stoneville 506 and Tifcot 56 cotton cultivars were investigated in solutions containing either 0, 10, 20 or 40 μM Al with 500 μM Ca at pH 4.5. In solutions containing no Al, addition of 700 μM Si improved root growth by 69–87% in Coker 315, DPL 90 and McNair 235 cultivars but not in the other cultivars. In solutions containing 10 μM Al, an increase in Si concentration from 0 to 2800 μM improved the root growth by 15–17% in DPL 90 and McNair 235 cultivars only. An increase in Si additions failed to improve root growth of any of the cultivars in solutions with 20 or 40 μM Al.     

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.     

Effects of low aluminum activity in nutrient solutions on the organic acid concentrations in maize plants

The effects of low aluminum (Al) activity in nutrient solution on the concentrations of organic acids in two cultivars of maize (Zea mays L.), HS7777 Al‐sensitive and C525‐M Al‐tolerant, were studied. Aluminum stress increased total organic acid concentration in the roots and in the shoots for both cultivars. The relative increase of t‐aconitic, citric, formic, malic, and quinic acids was higher in the roots than in the shoots for both cultivars. The concentrations of c‐aconitic, isocitric, malonic, oxalic, and succinic organic acids were reduced by Al stress, principally for C525‐M. There were no consistent differences in organic acid concentrations between the cultivars to discriminate Al tolerance. The Al tolerance for C525‐M may be justified by lower Al concentrations in the root tips where cellular division takes place and/or by higher excretion of organic acids from roots to the rhizosphere for detoxification of Al by chelation.     

Agronomic effectiveness of phosphate rock and superphosphate for aluminum‐tolerant and non‐tolerant sorghum cultivars

Abstract

About 35% of soils in Venezuela are acid and low in available phosphorus (P). To solve this problem farmers lime and apply phosphate fertilizers to the soils, but both lime and fertilizers are expensive. A good alternative to overcome soil acidity is the use of aluminum (Al)‐tolerant cultivars. The objective of this study was to test the hypothesis, by use of a pot experiment, that sorghum cultivars tolerant to Al toxicity are able to use P from phosphate rock more efficiently than are susceptible cultivars. Three sorghum (Sorghum bicolor L. Moench) cultivars, Chaguaramas III (Ch), AI‐tolerant, Decalb D59 (D59), and Pioneer 8225 (Pi), both Al‐susceptible, were grown in the greenhouse for 20 and 35 days in two acid soils fertilized with 0 and 100 mg P kg^‐1 as triple superphosphate (SP) and Riecito phosphate rock (PR). Santa Maria soil was very low in available P (2 mg kg^‐1) and highly saturated in Al saturation (64.5%) and Pao soil was higher in available P (20 mg kg^‐1) and low in Al saturation (6.5%). Chaguaramas dry matter production, P uptake and root length was higher in Santa Maria soil as compared with Pi and D59 when grown with both SP and PR fertilization. Chaguaramas response to PR in Pao soil was not as good as in Santa Maria soil. The results of our experiment suggest that Al‐tolerant Ch is able to utilize P from PR more efficiently in soils like Santa Maria than Al‐susceptible cultivare Pi and D59.     

Intravarietal level of aluminum resistance in cereal crops

The relative growth parameters of seedlings of some oat (Avena sativa L.) and barley (Hordeum vulgare L.) varieties from different intravarietal seed fractions in the absence or presence of 1–2 mM aluminum (Al) sulfate were investigated in several experiments using the solution‐paper culture technique. There were statistically significant differences in Al‐resistance level of seeds, which differ by its weight, place on ear, place, and year of reproduction and rate of germination. The data suggest that the level of Al resistance/susceptibility is not determined by genotype exactly, but may be modified by some endogenous chemical and biochemical factors (for example, content of seed storage proteins, inhibitors of germination, natural plant growth regulators, etc.). Such non‐uniformity of seeds within cultivars may be used for investigation of plant Al‐resistance mechanisms.     

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.     

Effects of low aluminium levels on growth and nutrient relations in three rice cultivars with different tolerances to aluminium

Reports on varietal diversity of upland rice in relation to relatively low aluminium (Al) levels are limited. Therefore, effects were examined of 35, 70, and 140 μM Al on plant growth and uptake of macro‐ and micro‐nutrients (K, P, Ca, Mg, Fe, Zn, Cu, and Mn) and their distribution in three upland rice (Oryza saliva L.) cultivars (BG35, DA14, and IR45) with different Al sensitivity. After an initial growth period of 5 days without Al, the plants were grown for 21 days in nutrient solutions containing Al at pH 4.1. Cultivar BG35 showed the highest and IR45 the lowest tolerance to Al when fresh weights of shoots or roots were considered. Except for IR45 at 140 μM Al, total dry weight was unaffected by Al, and the cultivars could not be clearly distinguished with respect to Al tolerance. Net Al uptake rate was higher in Al tolerant BG35 than in DA14 or IR45. Conversely, in IR45 the absorbed Al was rapidly transported to the shoots and accumulated there. In BG35, net P and Ca uptake rates in Al‐treated plants were high enough to maintain the P and Ca status of the shoots at all Al levels. Irrespective of Al sensitivity, there was a general depression of internal Mg concentration in Al‐reated plants. The Fe, Zn, Cu, and Mn concentrations of the plants were not negatively affected by Al in any of the cultivars.     

Effects of aluminum stress on alfalfa root proteins 1

An estimated 40% of arable soils worldwide contain phytotoxic levels of aluminum (Al). Recent evidence indicates that Al‐stress‐induced low molecular weight proteins may bind Al in Al‐tolerant plants. The objective of this study was to investigate protein patterns in young roots of two Al‐sensitive and two Al‐tolerant alfalfa (Medicago sativa L.) clones grown at 0 and 111 μmol Al in pH 4.5 nutrient solution. Based on SDS‐PAGE of supernatant, Al stress resulted in an increase in detectable root proteins in all clones and results are consistent with results reported for other plant species. A proliferation of new low‐molecular‐weight proteins in the tolerant clones could be related to Al tolerance. One protein (18.7 kD) was produced in both tolerant clones yet not detected in the sensitive clones. Protein levels were more often reduced than enhanced under Al stress and reduction was more prevalent in sensitive than in tolerant clones. Aluminum stress may initiate the production of some of the same proteins in alfalfa and wheat (Triticum aestivum L. Thell.). General stress proteins could be produced in reaction to a variety of chemical, environmental, and pathological stresses.     

Differential response of two taro cultivars to aluminum: I. Plant growth

Abstract

Aluminum (Al) toxicity is one of the major factors limiting plant growth in acid soils. To determine the response of taro [Colocasia esculenta (L.) Schott] to Al‐toxicity, cultivars (cv.) Lehua maoli and Bun long were grown in hydroponic solution at six initial levels of Al (0, 110, 220, 440, 890, and 1330 uM Al). Increasing Al levels significantly depressed fresh and dry weights of taro leaf blades, petioles, and roots, as well as leaf areas and root lengths. No significant cultivar differences were found for plant dry weights. However, significant cultivar differences were found for expansion growth parameters, with cv. Lehua maoli exhibiting greater leaf fresh weights and root lengths in the presence of Al, compared to cv. Bun long. Apparently, differential response of taro cultivars to Al is related to the ability of the Al‐tolerant cultivar to maintain water uptake and cell expansion in the presence of Al. The initial solution Al level that resulted in the greatest separation of growth differences between taro cultivars in their response to Al was 890 μM Al.     

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.     

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.