Genotype-dependent sulphite tolerance of Australian Dekkera (Brettanomyces) bruxellensis wine isolates

Aims: The aim of this study was to determine sulphite tolerance for a large number of Dekkera bruxellensis isolates and evaluate the relationship between this phenotype and previously assigned genotype markers. Methods and Results: A published microplate‐based method for evaluation of yeast growth in the presence of sulphite was benchmarked against culturability following sulphite treatment, for the D. bruxellensis type strain (CBS 74) and a reference wine isolate (AWRI 1499). This method was used to estimate maximal sulphite tolerance for 41 D. bruxellensis isolates, which was found to vary over a fivefold range. Significant differences in sulphite tolerance were observed when isolates were grouped according to previously assigned genotypes and ribotypes. Conclusions: Variable sulphite tolerance for the wine spoilage yeast D. bruxellensis can be linked to genotype markers. Significance and Impact of the Study: Strategies to minimize risk of wine spoilage by D. bruxellensis must take into account at least a threefold range in effective sulphite concentration that is dependent upon the genotype group(s) present. The isolates characterized in this study will be a useful resource for establishing the mechanisms conferring sulphite tolerance for this industrially important yeast species.     

COMPUTATION OF MODEL-DEPENDENT TOLERANCE BANDS FOR AMBULATORILY MONITORED BLOOD PRESSURE

The construction of time-specified reference limits requires systematic sampling in clinical health, particularly for those variables characterized by a circadian rhythm of large amplitude, as it is the case for blood pressure (BP). For the detection of false negatives, tolerance intervals (limits that will include at least a specified proportion of the population with a stated confidence) are important and should substitute when possible for prediction limits. We have previously described a nonparametric method for the computation of model-independent tolerance intervals that are constructed by first dividing the sampling range in several time spans in which no appreciable changes in population characteristics (namely, mean and variance) take place. The tolerance interval is then computed for each of the time spans. The limits thus computed, as well as results of any comparison of a given individual's profile against such tolerance intervals, are highly dependent on the sampling scheme of both the reference individuals and the test subject. To avoid this problem, we have developed an alternative method that allows the computation of model-dependent tolerance bands for hybrid time series. Assuming that a set X of longitudinal series monitored from a given group of reference individuals can be fitted with the same individual model, a population model C(X,t) can be also determined, as well as the deviation S(X,t) of each individual curve from the population model. The tolerance band will then have the form C(X,t) ± kS(X,t), where k is here estimated following a nonparametric approach based on bootstrap techniques. Alternatively, two different values of k can be estimated (for the lower and upper limits of the tolerance interval, respectively) in cases for which we cannot assume symmetry. The method is generally applicable for any population model describing the reference population (including the fit of multiple significant components, nonsinusoidal waveforms, and/or trends). The method was used to establish time-specified tolerance bands for time series of blood pressure monitored automatically in healthy individuals of both genders. Model-dependent intervals are preferred to the model-independent limits when reliance on a specified sampling rate needs to be avoided. These limits may serve for an objective and positive definition of health, for the screening and diagnosis of disease, and for gauging the subject's response to treatment. (Chronobiology International, 17(4), 567–582, 2000)     

Freezing tolerance, cold acclimation and oxidative stress in potato. Paraquat tolerance is related to acclimation but is a poor indicator of freezing tolerance

Potato is a species commonly cultivated in temperate areas where the growing season may be interrupted by frosts, resulting in loss of yield. Cultivated potato, Solanum tuberosum, is freezing sensitive, but it has several freezing-tolerant wild potato relatives, one of which is S. commersonii. Our study was aimed to resolve the relationship between enhanced freezing tolerance, acclimation capacity and capacity to tolerate active oxygen species. To be able to characterize freezing tolerant ideotypes, a potato population (S1), which segregates in freezing tolerance, acclimation capacity and capacity to tolerate superoxide radicals, was produced by selfing a somatic hybrid between a freezing-tolerant Solanum commersonii (LT₅₀=-4.6°C) and -sensitive S. tuberosum (LT₅₀=-3.0°C). The distribution of non-acclimated freezing tolerance (NA-freezing tolerance) of the S1 population varied between the parental lines and we were able to identify genotypes, having significantly high or low NA-freezing tolerance. When a population of 25 genotypes was tested both for NA-freezing and paraquat (PQ) tolerance, no correlation was found between these two traits (R = 0.02). However, the most NA-freezing tolerant genotypes were also among the most PQ tolerant plants. Simultaneously, one of the NA-freezing sensitive genotypes (2022) (LT₅₀=-3.0°C) was observed to be PQ tolerant. These conflicting results may reflect a significant, but not obligatory, role of superoxide scavenging mechanisms in the NA-freezing tolerance of S. commersonii. The freezing tolerance after cold acclimation (CA-freezing tolerance) and the acclimation capacity (AC) was measured after acclimation for 7 days at 4/2°C. Lack of correlation between NA-freezing tolerance and AC (R =-0.05) in the S1 population points to independent genetic control of NA-freezing tolerance and AC in Solanum sp. Increased freezing tolerance after cold acclimation was clearly related to PQ tolerance of all S1 genotypes, especially those having good acclimation capacity. The rapid loss of improved PQ tolerance under deacclimation conditions confirmed the close relationship between the process of cold acclimation and enhanced PQ tolerance. Here, we report an increased PQ tolerance in cold-acclimated plants compared to non-acclimated controls. However, we concluded that high PQ tolerance is not a good indicator of actual freezing tolerance and should not be used as a selectable marker for the identification of a freezing-tolerant genotype.     

Genetic improvement of the biological control nematode Heterorhabditis bacteriophora (Rhabditidomorpha: Heterorhabditidae): heterosis effect enhances desiccation but not heat tolerance

The entomopathogenic nematode Heterorhabditis bacteriophora is commercially used in biological control of soil dwelling insect pests. It reproduces by autogamy (hermaphrodites) enabling the production of inbred lines, but also by amphimixis (through mating of male and female) which allows cross-breeding. When H. bacteriophora is produced in liquid culture, copulation of male and female is prevented and reproduction is solely by self-fertilisation of hermaphrodites. When reared in insects, crosses are possible resulting in heterozygous offspring. Heat and desiccation tolerance of these nematodes have been successfully improved by selective breeding. Trait deterioration was prevented by producing homozygous inbreds through consecutive reproduction in liquid culture, the method also used for commercial mass production. In this study, we investigated possible heterosis effects in desiccation and heat tolerance after cross-breeding of homozygous inbred lines of H. bacteriophora. Increased desiccation tolerance of the heterozygous progeny in comparison to homozygous inbred lines was recorded indicating that heterosis is a possible means for further improvement of this trait. In contrast, the heat tolerance of the heterozygous offspring was lower than that of the homozygous population. The results provide evidence for the tremendous potential of classical genetics to improve beneficial traits of a biological control agent and carry domestication of H. bacteriophora a significant step forward.     

Quantification of the Role of Acclimation Temperature in Temperature Tolerance of Fishes

The relative effect of acclimation temperature on temperature tolerance was estimated from a geometrical partitioning of the temperature tolerance polygon of a fish species into three distinct zones relative to four key tolerance temperatures. This approach yields a middle tolerance zone which is independent of acclimation temperature bounded by upper and lower acclimation dependent zones. Acclimation dependent and independent temperature tolerance zones can be quantified by either areal or linear methods. Both methods were applied to quantify the effect of acclimation temperature in 21 species of temperate fishes for which temperature tolerance polygons were available. Temperature tolerance polygon areas of these 21 species ranged from 468 to 1380°C² and are linearly related (r ²=0.93, p<0.001) to ultimate incipient upper lethal temperatures. Although areal and linear partitioning methods yielded similar acclimation independent and dependent tolerances, estimates from the areal method incorporates additional information concerning the shape of the temperature tolerance polygon, in particular lower and upper lethal temperature plateaus. Mean combined acclimation dependent and independent tolerance areas of these 21 species were not different, indicating that acclimation effectively doubles the temperature tolerance polygon. Mean lower acclimation dependent area was nearly three times greater than mean upper acclimation dependent area, suggesting that acclimation plays a larger role in tolerance of low rather than high temperatures. Among these 21 species, temperature tolerance of brook charr and sheepshead minnow were the least and most affected by acclimation temperature, respectively.     

A novel and high-throughput approach to assess photosynthetic thermal tolerance of kelp using chlorophyll α fluorometry

Foundation seaweed species are experiencing widespread declines and localized extinctions due to increased instability of sea surface temperature. Characterizing temperature thresholds are useful for predicting patterns of change and identifying species most vulnerable to extremes. Existing methods for characterizing seaweed thermal tolerance produce diverse metrics and are often time-consuming, making comparisons between species and techniques difficult, hindering insight into global patterns of change. Using three kelp species, we adapted a high-throughput method – previously used in terrestrial plant thermal biology – for use on kelps. This method employs temperature-dependent fluorescence (T–F₀) curves under heating or cooling regimes to determine the critical temperature (T_crit) of photosystem II (PSII), i.e., the breakpoint between slow and fast rise fluorescence response to changing temperature, enabling rapid assays of photosynthetic thermal tolerance using a standardized metric. This method enables characterization of T_crit for up to 48 samples per two-hour assay, demonstrating the capacity of T–F₀ curves for high-throughput assays of thermal tolerance. Temperature-dependent fluorescence curves and their derived metric, T_crit, may offer a timely and powerful new method for the field of phycology, enabling characterization and comparison of photosynthetic thermal tolerance of seaweeds across many populations, species, and biomes.     

Improving salinity tolerance in crop plants: a biotechnological view

Salinity limits the production capabilities of agricultural soils in large areas of the world. Both breeding and screening germplasm for salt tolerance encounter the following limitations: (a) different phenotypic responses of plants at different growth stages, (b) different physiological mechanisms, (c) complicated genotype × environment interactions, and (d) variability of the salt-affected field in its chemical and physical soil composition. Plant molecular and physiological traits provide the bases for efficient germplasm screening procedures through traditional breeding, molecular breeding, and transgenic approaches. However, the quantitative nature of salinity stress tolerance and the problems associated with developing appropriate and replicable testing environments make it difficult to distinguish salt-tolerant lines from sensitive lines. In order to develop more efficient screening procedures for germplasm evaluation and improvement of salt tolerance, implementation of a rapid and reliable screening procedure is essential. Field selection for salinity tolerance is a laborious task; therefore, plant breeders are seeking reliable ways to assess the salt tolerance of plant germplasm. Salt tolerance in several plant species may operate at the cellular level, and glycophytes are believed to have special cellular mechanisms for salt tolerance. Ion exclusion, ion sequestration, osmotic adjustment, macromolecule protection, and membrane transport system adaptation to saline environments are important strategies that may confer salt tolerance to plants. Cell and tissue culture techniques have been used to obtain salt tolerant plants employing two in vitro culture approaches. The first approach is selection of mutant cell lines from cultured cells and plant regeneration from such cells (somaclones). In vitro screening of plant germplasm for salt tolerance is the second approach, and a successful employment of this method in durum wheat is presented here. Doubled haploid lines derived from pollen culture of F₁ hybrids of salt-tolerant parents are promising tools to further improve salt tolerance of plant cultivars. Enhancement of resistance against both hyper-osmotic stress and ion toxicity may also be achieved via molecular breeding of salt-tolerant plants using either molecular markers or genetic engineering.     

Efficacy of a dual fluorescence method in detecting the viability of overwintering cyanobacteria

Chill in the light is the major environmental stress that cyanobacteria encounter in winter. Cyanobacterial cells may acquire chill‐light tolerance upon exposure to low temperature in autumn and early winter. We sought to establish the efficacy of the dual fluorescence method in detecting the viability of overwintering cyanobacteria and to provide further evidence for the chill‐light tolerance of preconditioned cyanobacteria. Synechocystis sp. PCC 6803 and Microcystis aeruginosa PCC 7806 were exposed to chill (5°C)‐light stress with or without pretreatment at 15°C and stained with SYTO 9 and propidium iodide. Live and dead cells were observed under a fluorescence microscope, and the percentage of viable cells was quantified on a microplate reader. The dual fluorescence method showed consistent results with tests of the ability to reinitiate growth. Cell viability was quantitatively correlated with ratio of SYTO 9/propidium iodide fluorescence. Previously, Microcystis colonies in Lake Taihu had been found to accumulate RNA‐binding protein 1 in autumn and winter. Use of this method directly showed the viability of such Microcystis colonies throughout the winter.

Significance and Impact of the Study

This study established the efficacy of the dual fluorescence method in evaluating the viability of cyanobacteria under chill‐light stress. The results provided the direct evidence for acquired chill‐light tolerance and the viability of overwintering Microcystis colonies. Such information can be useful in prediction of cyanobacterial blooms.     

Overexpression of the Escherichia coli catalase gene, katE, enhances tolerance to salinity stress in the transgenic indica rice cultivar, BR5

Salinity stress is a major limiting factor in cereal productivity. Many studies report improvements in salt tolerance using model plants, such as Arabidopsis thaliana or standard varieties of rice, e.g., the japonica rice cultivar Nipponbare. However, there are few reports on the enhancement of salt tolerance in local rice cultivars. In this work, we used the indica rice (Oryza sativa) cultivar BR5, which is a local cultivar in Bangladesh. To improve salt tolerance in BR5, we introduced the Escherichia coli catalase gene, katE. We integrated the katE gene into BR5 plants using an Agrobacterium tumefaciens-mediated method. The introduced katE gene was actively expressed in the transgenic BR5 rice plants, and catalase activity in T₁ and T₂ transgenic rice was approximately 150% higher than in nontransgenic plants. Under NaCl stress conditions, the transgenic rice plants exhibited high tolerance compared with nontransgenic rice plants. T₂ transgenic plants survived in a 200 mM NaCl solution for 2 weeks, whereas nontransgenic plants were scorched after 4 days soaking in the same NaCl solution. Our results indicate that the katE gene can confer salt tolerance to BR5 rice plants. Enhancement of salt tolerance in a local rice cultivar, such as BR5, will provide a powerful and useful tool for overcoming food shortage problems.     

PCR based fingerprinting of Westiellopsis cultures with short tandemly repeated repetitive (STRR) and highly iterated palindrome (HIP) sequences

The presence of repetitive DNA sequences viz., short tandemly repeated repetitive (STRR) and highly iterated palindrome (HIP), in the cyanobacterial genome were used to generate a PCR-based fingerprint pattern of nine cyanobacterial cultures (both stress tolerant and non-tolerant), belonging to the genus Westiellopsis. By this method it was possible to generate distinguishing fingerprint patterns for all the isolates and cluster isolates with similar stress tolerance properties. This study reveals the utility of repetitive DNA sequences in the cyanobacterial genome, for differentiation of Westiellopsis cultures and clustering strains that posses similar stress tolerance properties.     

中国十倍体割手密资源抗逆功能标记的遗传多样性分析

整倍体割手密是现代甘蔗品种重要的野生亲本和抗逆性状基因源,为了明确其抗逆相关基因的遗传背景,该研究选用来自脱水绑定因子DREB、水通道蛋白AQP、热激蛋白HSP70、WRKY1转录因子和随机引物组成的5对抗旱和耐高温相关功能标记,以63份甘蔗常用亲本材料和8份甘蔗原种作为对照,对中国保育的50份十倍体割手密(Saccharum spontaneum L.)进行遗传多样性分析。结果显示:(1)5对引物共获得119个扩增片段,其中110个为多态性条带,平均多态性条带比例为92.44%,平均多态信息量为92.53%,十倍体割手密抗旱功能标记多态性最高,甘蔗常用亲本材料耐高温功能标记多态性最高。(2)十倍体割手密在抗旱功能标记上具有较低的平均相似性系数值(0.541)和最大的分布范围(0.347~0.800),且主要集中在0.400~0.600之间,而在耐高温功能标记上甘蔗常用亲本材料虽拥有最大的分布范围(0.238~1.000),但甘蔗原种具有最低的平均相似性系数值(0.481),且相似性系数范围主要集中在0.400~0.600之间。(3)UPGMA聚类可将参试材料划分为较明显的两个大组,十倍体割手密与甘蔗常用亲本和甘蔗原种在聚类关系上表现出明显的不同。研究表明,十倍体割手密资源无论是在抗旱功能标记DBF、Aqua方面,还是在耐高温功能标记SCB174、SCB190方面都与甘蔗常用亲本和甘蔗原种具有较大的遗传差异,而且在抗旱功能标记方面表现出更为丰富的遗传变异,因此在后续甘蔗品种抗逆性状改良和亲本创新上应进一步加大十倍体割手密资源的利用。     

Phytochelatin is not a primary factor in determining copper tolerance

Phytochelatin (PC) is involved in the detoxification of harmful, non-essential heavy metals and the homeostasis of essential heavy metals in plants. Its synthesis can be induced by either cadmium (Cd) or copper (Cu), and can form stable complexes with either element. This might suggest that PC has an important role in determining plant tolerance to both. However, this is not clearly apparent, as evidenced by a PC-deficient and Cd-sensitiveArabidopsis mutant (cad1-3) that shows no significant increase in its sensitivity to copper. Therefore, we investigated whether the mechanism for Cu tolerance differed from that for Cd by analyzing copper sensitivity in Cd-tolerant transgenics and Cd-sensitive mutants ofArabidopsis. Cadmium-tolerant transgenic plants that over-expressedA. thaliana phytochelatin synthase 1 (AtPCS1) were not tolerant of copper stress, thereby supporting the hypothesis that PC is not primarily involved in this tolerance mechanism. We also investigated Cu tolerance incad2-1, a Cd-sensitive and glutathione (GSH)-deficientArabidopsis mutant. Paradoxically,cad2-1 was more resistant to copper stress than were wild-type plants. This was likely due to the high level of cysteine present in that mutant. However, when the growth medium was supplemented with cysteine, the wild types also exhibited copper tolerance. Moreover,Saccharomyces cerevisiae that expressedAtPCS1 showed tolerance to Cd but hypersensitivity to Cu. All these results indicate that PC is not a major factor in determining copper tolerance in plants.     

Genes/QTLs affecting flood tolerance in rice

The adaptation of deepwater rice to flooding is attributed to two mechanisms, submergence tolerance and plant elongation. Using a QTL mapping study with replicated phenotyping under two contrasting (water qualities) submergence treatments and AFLP markers, we were able to identify several genes/QTLs that control plant elongation and submergence tolerance in a recombinant inbred rice population. Our results indicate that segregation of rice plants in their responses to different flooding stress conditions is largely due to the differential expression of a few key elongation and submergence tolerance genes. The most important gene was QIne1 mapped near sd-1 on chromosome 1. The Jalmagna (the deepwater parent) allele at this locus had a very large effect on internal elongation and contributed significantly to submergence tolerance under flooding. The second locus was a major gene, sub1(t), mapped to chromosome 9, which contributed to submergence tolerance only. The third one was a QTL, QIne4, mapped to chromosome 4. The IR74 (non-elongating parent) allele at this locus had a large effect for internal elongation. An additional locus that interacted strongly with both QIne1 and QIne4 appeared near RG403 on chromosome 5, suggesting a complex epistatic relationship among the three loci. Several QTLs with relatively small effects on plant elongation and submergence tolerance were also identified. The genetic aspects of these flooding tolerance QTLs with respect to patterns of differential expression of elongation and submergence tolerance genes under flooding are discussed. Received: 13 December 1999 / Accepted: 14 March 2000<@head-com-p1a.lf>Communicated by G. Wenzel     

Inheritance and molecular characterization of broad range tolerance to herbicides targeting acetohydroxyacid synthase in sunflower

Ahasl1 is a multilallelic locus where all the induced and natural mutations for herbicide tolerance were described thus far in sunflower (Helianthus annuus L.). The allele Ahasl1-1 confers moderate tolerance to imidazolinone (IMI), Ahasl1-2, and Ahasl1-3 provides high levels of tolerance solely to sulfonylurea (SU) and IMI, respectively. An Argentinean wild sunflower population showing plants with high level of tolerance to either an IMI and a SU herbicide was discovered and used to develop an inbred line designated RW-B. The objectives of this work were to determine the relative level and pattern of cross-tolerance to different AHAS-inhibiting herbicides, the mode of inheritance, and the molecular basis of herbicide tolerance in this line. Slight or no symptoms observed after application of different herbicides indicated that RW-B possesses a completely new pattern of tolerance to AHAS-inhibiting herbicides in sunflower. Biomass response to increasing doses of metsulfuron or imazapyr demonstrated a higher level of tolerance in RW-B with respect to Ahasl1-1/Ahasl1-1 and Ahasl1-2/Ahasl1-2 lines. On the basis of genetic analyses and cosegregation test, it was concluded that tolerance to imazapyr in the original population is inherited as a single, partially dominant nuclear gene and that this gene is controlling the tolerance to four different AHAS-inhibiting herbicides. Pseudo-allelism test permitted us to conclude that the tolerant allele present in RW-B is an allelic variant of Ahasl1-1 and was designated as Ahasl1-4. Nucleotide and deduced amino acid sequence indicated that the Ahasl1-4 allele sequence of RW-B has a leucine codon (TTG) at position 574 (relative to the Arabidopsis thaliana AHAS sequence), whereas the enzyme from susceptible lines has a tryptophan residue (TGG) at this position. The utilization of this new allele in the framework of weed control and crop rotation is discussed.     

Metal resistant rhizobia and ultrastructure of Anthyllis vulneraria nodules from zinc and lead contaminated tailing in Poland

This present paper studies the response of Anthyllis vulneraria-Rhizobium symbiosis to heavy metal stress. The symbiotic rhizobium bacteria isolated from root nodules of A. vulneraria from zinc and lead wastes were examined in this project. Light microscopy (LM) and transmission electron microscopy (TEM) were used to analyze the nodule anatomy and ultrastructure and conduct a comparison with nonmetal-treated nodules. 16S ribosomal DNA sequence analysis of bacteria isolated from metal-treated nodules revealed the presence of Rhizobium metallidurans and Bradyrhizobium sp. In regard to heavy metal resistance/tolerance, a similar tolerance to Pb was shown by both strains, and a high tolerance to Zn and a lower tolerance to Cd and Cu by R. metallidurans, whereas a high tolerance to Cd and Cu and a lower tolerance to Zn by Bradyrhizobium were found. The nodules of Anthyllis from metal-polluted tailing sites were identified as the typical determinate type of nodules. Observed under TEM microscopy changes in nodules ultrastructure like: (1) wall thickening; (2) infection thread reduction; (3) vacuole shrinkage; (4) synthesis of phenolics in vacuoles; (5) various differentiation of bacteroids and (6) simultaneous symbiosis with arbuscular mycorrhiza fungi could be considered as a form of the A.vulneraria-Rhizobium symbiosis adaptation to metal stress.     

Identification of two closely linked quantitative trait loci for cold tolerance on chromosome 4 of rice and their association with anther length

Norin-PL8 is a cold-tolerant variety of rice (Oryza sativa L.) that was developed by introgressing chromosomal segments from a cold-tolerant javanica variety, Silewah. We previously detected quantitative trait loci (QTLs) for cold tolerance of Norin-PL8 in the introgressions on chromosomes 3 and 4. We provide fine mapping of the QTLs on chromosome 4 and the association between the QTLs and anther length, which has been reported to be a major component of cold tolerance. Interval mapping using a segregating population derived from an advanced backcross progeny indicated that a QTL for cold tolerance is probably located from the center to the proximal end of the introgression. For fine mapping, we developed a set of near-isogenic lines (NILs) from recombinants in the segregating population. Comparison of cold tolerance between the NILs indicated that either the proximal end or the center of the introgression is necessary for cold tolerance. From these results, we concluded that there are at least two QTLs for cold tolerance, tentatively designated as Ctb-1 and Ctb-2, in the introgression on chromosome 4. The map distance between Ctb-1 and Ctb-2 is estimated to be 4.7–17.2 cM. In order to investigate the mechanism underlying cold tolerance by the QTLs, we compared anther lengths of the NILs. The results indicate that both Ctb-1 and Ctb-2 are associated with anther length. Received: 17 July 2000 / Accepted: 1 February 2001     

Acetyl salicylic acid (Aspirin) and salicylic acid induce multiple stress tolerance in bean and tomato plants

The hypothesis that physiologically activeconcentrations of salicylic acid (SA) and itsderivatives can confer stress tolerance in plants wasevaluated using bean (Phaseolus vulgaris L.) andtomato (Lycopersicon esculentum L.). Plantsgrown from seeds imbibed in aqueous solutions (0.1--0.5 mM) of salicylic acid or acetyl salicylic acid(ASA) displayed enhanced tolerance to heat, chillingand drought stresses. Seedlings acquired similarstress tolerance when SA or ASA treatments wereapplied as soil drenches. The fact that seedimbibition with SA or ASA confers stress tolerance inplants is more consistent with a signaling role ofthese molecules, leading to the expression oftolerance rather than a direct effect. Induction ofmultiple stress tolerance in plants by exogenousapplication of SA and its derivatives may have asignificant practical application in agriculture,horticulture and forestry.     

Genetic diversity for aluminum tolerance in sorghum

Genetic variation for aluminum (Al) tolerance in plants has allowed the development of cultivars that are high yielding on acidic, Al toxic soils. However, knowledge of intraspecific variation for Al tolerance control is needed in order to assess the potential for further Al tolerance improvement. Here we focused on the major sorghum Al tolerance gene, Alt _SB , from the highly Al tolerant standard SC283 to investigate the range of genetic diversity for Al tolerance control in sorghum accessions from diverse origins. Two tightly linked STS markers flanking Alt _SB were used to study the role of this locus in the segregation for Al tolerance in mapping populations derived from different sources of Al tolerance crossed with a common Al sensitive tester, BR012, as well as to isolate the allelic effects of Alt _SB in near-isogenic lines. The results indicated the existence not only of multiple alleles at the Alt _SB locus, which conditioned a wide range of tolerance levels, but also of novel sorghum Al tolerance genes. Transgressive segregation was observed in a highly Al tolerant breeding line, indicating that potential exists to exploit the additive or codominant effects of distinct Al tolerance loci. A global, SSR-based, genetic diversity analysis using a broader sorghum set revealed the presence of both multiple Alt _SB alleles and different Al tolerance genes within highly related accessions. This suggests that efforts toward broadening the genetic basis for Al tolerance in sorghum may benefit from a detailed analysis of Al tolerance gene diversity within subgroups across a target population. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.