Copper uptake and phytotoxicity as assessed in situ for durum wheat (Triticum turgidum durum L.) cultivated in Cu-contaminated, former vineyard soils

This work assessed in situ, copper (Cu) uptake and phytotoxicity for durum wheat (Triticum turgidum durum L.) cropped in a range of Cu-contaminated, former vineyard soils (pH 4.2–7.8 and total Cu concentration 32–1,030 mg Cu kg⁻¹) and identified the underlying soil chemical properties and related root-induced chemical changes in the rhizosphere. Copper concentrations in plants were significantly and positively correlated to soil Cu concentration (total and EDTA). In addition, Cu concentration in roots which was positively correlated to soil pH tended to be larger in calcareous soils than in non-calcareous soils. Symptoms of Cu phytotoxicity (interveinal chlorosis) were observed in some calcareous soils. Iron (Fe)–Cu antagonism was found in calcareous soils. Rhizosphere alkalisation in the most acidic soils was related to decreased CaCl₂-extractable Cu. Conversely, water-extractable Cu increased in the rhizosphere of both non-calcareous and calcareous soils. This work suggests that plant Cu uptake and risks of Cu phytotoxicity in situ might be greater in calcareous soils due to interaction with Fe nutrition. Larger water extractability of Cu in the rhizosphere might relate to greater Cu uptake in plants exhibiting Cu phytotoxic symptoms.     

Production of doubled haploids in durum wheat (Triticum turgidum L.) through isolated microspore culture

The objective of this work was to produce doubled haploid plants from durum wheat through the induction of androgenesis. A microspore culture technique was developed and used to produce fertile doubled haploid plants of agronomic interest. Five cultivars, one selected line, plus a collection of 20 F₁ crosses between different genotypes of high breeding value were used. Studies on several factors such as pre-treatments and media components were carried out in order to develop a protocol to regenerate green haploid plantlets. Anthers were pre-treated in 0.7 M mannitol. Microspores, from anther maceration, were plated on a C₁₇ induction culture medium with ovary co-culture. The optimum regeneration medium J25–8 was used. From 35 microspore isolations, 407 green plantlets were obtained. With this technique mature embryos were obtained. Green plants were regenerated from all genotypes used and approximately 67% of them were spontaneously doubled haploids. Some haploids and a very few polyploids plants were obtained. From the 407 plants, 275 were completely fertile and gave enough seeds to be assayed in the field. This protocol could be used complementary to or instead of the intergeneric crossing with maize as an economically feasible method to obtain doubled haploids from most durum wheat genotypes.     

Biofortification of durum wheat (Triticum turgidum L. ssp. durum (Desf.) Husnot) grains with nutrients

Durum wheat (Triticum turgidum L. ssp. durum (Desf.) Husnot) was grown under conditions to promote mineral biofortification at the grain level. Along plant development, biomass accumulation and the kinetics of nutrients accumulation were assessed, identifying the nutrient fluxes of roots and shoots, and the timescale constraints of crop biofortification. Plants were grown under environmentally controlled conditions, submitted to four increasing concentrations of nutrient solutions (1-, 2-, 4- and 6-fold) of micro- (Fe, Zn, Cu and Mn) and macronutrients (Ca, K, P and Mg). The threshold of mineral toxicity was not reached as evaluated through plant biomass accumulation, but considering grain yield, the twofold nutrient concentration was the best treatment for biofortification. In the different treatments, the contents and the mineral unrests of roots uptake and shoots translocation varied, at different magnitudes and trends, before the onset of booting and from the physiological maturity onwards. Except for Cu, all mineral nutrients were mainly detected in the bran and embryo of the grains; therefore, the production of biofortified pasta for human consumption requires the use of integral semolina.     

EST-SSR DNA polymorphism in durum wheat (Triticum durum L.) collections

SSRs derived from EST were molecular markers belonging to the transcribed region of the genome. Therefore, any polymorphism detected using EST-SSRs might reflect the better relationship among species or varieties. Using wheat EST-SSR markers, 60 durum wheat (Triticum durum L.) accessions from seven countries were investigated. Twenty-five primer pairs could amplify successfully in the 60 durum wheat accessions, of which tri-nucleotide repeats were the dominant type, and revealed 26 loci on all seven wheat homologous chromosome groups. A total of 87 eSSR alleles were detected, and the number of alleles detected by a single pair of primers ranged from 1 to 11, with an average of 3.3 alleles per locus. Higher numbers of alleles and PIC were identified on the B genome than those on the A genome.     

Assessment of genetic diversity among Syrian durum (Triticum turgidum ssp. durum) and bread wheat (Triticum aestivum L.) using SSR markers

Genetic diversity among 49 wheat varieties (37 durum and 12 bread wheat) was assayed using 32 microsatellites representing 34 loci covering almost the whole wheat genome. The polymorphic information content (PIC) across the tested loci ranged from 0 to 0.88 with average values of 0.57 and 0.65 for durum and bread wheat respectively. B genome had the highest mean number of alleles (10.91) followed by A genome (8.3) whereas D genome had the lowest number (4.73). The correlation between PIC and allele number was significant in all genome groups accounting for 0.87, 074 and 0.84 for A, B and D genomes respectively, and over all genomes, the correlation was higher in tetraploid (0.8) than in hexaploid wheat varieties (0.5). The cluster analysis discriminated all varieties and clearly divided the two ploidy levels into two separate clusters that reflect the differences in genetic diversity within each cluster. This study demonstrates that microsatellites markers have unique advantages compared to other molecular and biochemical fingerprinting techniques in revealing the genetic diversity in Syrian wheat varieties that is crucial for wheat improvement.     

Dynamics of phosphorus fractions in the rhizosphere of common bean (Phaseolus vulgaris L.) and durum wheat (Triticum turgidum durum L.) grown in monocropping and intercropping systems

The main objective of the present study was to investigate phosphorus (P) dynamics in the rhizosphere of durum wheat (Triticum turgidum durum L.) and common bean (Phaseolus vulgaris L.) grown in monocropping and intercropping systems with nitrate supply. Wheat and common bean were grown either alone or in association in a cropping device with a thin (1 mm) soil layer sandwiched between large root mats. Wheat intercropped with common bean exhibited a 33% increase in shoot biomass and a 22% increased root biomass, without significantly affecting common bean growth. After 12 days of culture, rhizosphere pH decreased by 1.66 and 1.13 units in monocropping system of common bean and intercropping system, respectively. Wheat increased intercropped common bean proton release by 36% compared with monocropped beans. Common bean and wheat exhibited different behaviors in rhizosphere P dynamics. Monocropped wheat decreased Resin-P, NaHCO₃-P and NaOH-P in its rhizosphere by 24, 96 and 10%, respectively. However, NaHCO₃-P and NaOH-P were increased by 61 and 10% in the rhizosphere of intercropping. Almost all values about P fraction in intercropping system were between those in monocropped common bean and monocropped wheat. Through taping different P fraction, different plants species possibly can alleviate competition for phosphorus in intercropping system.     

AFLP and pedigree-based genetic diversity estimates in modern cultivars of durum wheat [ Triticum turgidum L. subsp. durum (Desf.) Husn.

A substantial amount of between and within cultivar genetic variation was detected in all the 13 registered modern Canadian durum wheat (Triticum turgidum L. ssp. durum (Desf.) Husn.) cultivars based upon amplified restriction fragment polymorphism (AFLP). Of the approximately 950 detected AFLP markers, only 89 were polymorphic, with 41 between cultivars whereas the remaining 48 showed polymorphism within at least one cultivar. The ancestry of Canadian durum wheat cultivars was traced back to 125 cultivars, selections, and breeding lines including 17 landraces. Mean pair-wise genetic distance based on the kinship coefficient was 0.76. On the other hand, AFLP-based mean pair-wise genetic distance was 0.40. Even though there was a large difference between the means of the two diversity measures, a moderate positive correlation (r=0.457, p<0.002) was detected between the two distance matrices. Cluster analysis with the entire AFLP data divided all cultivars into three major groups reflecting their breeding origins. One group contained ’Pelissier’ alone, which was a selection from a landrace introduced into the US from Algeria. On the other hand such groupings among cultivars were not evident when KIN was used for genetic diversity measures instead. The level of genetic variation among individuals within a cultivar at the breeders’ seed level was estimated based on an inter-haplotypic distance matrix derived from the AFLP data. We found that the level of genetic variation within the most-developed cultivars is fairly substantial despite rigorous selection pressure aimed at cultivar purity in breeding programs. Comparison of AFLP and pedigree-based genetic diversity estimates in crop species such as durum wheat can provide important information for plant improvement. Received: 26 January 2001 / Accepted: 31 May 2001     

Genotypic difference in root penetration ability by durum wheat (Triticum turgidum L. var. durum) evaluated by a pot with paraffin-Vaseline discs

Improvement of root penetration (RP) ability in durum wheat (Triticum turgidum L. var. durum) is an important breeding target to reduce yield losses due to soil compaction and drought. This study investigated the genotypic difference of RP ability in durum wheat of seven Ethiopian landraces (ET genotypes), which were presumed to adapt to soil compaction, and 17 genotypes bred in North America (NA genotypes). The pregerminated seed was planted in a pot with four paraffin-Vaseline (PV) discs of hardness 0.12, 0.24, 0.50 and 0.73 MPa. After eight weeks from planting, each plant was sampled and the number of roots penetrating through the PV discs was counted. No genotype penetrated through the PV disc of 0.73 MPa hardness. The number of roots penetrating through the PV disc of 0.50 MPa hardness showed a significant difference among the genotypes: highest in an ET genotype and lowest in a NA genotype. The mean value was also significantly higher in ET genotypes than in NA genotypes, and it significantly correlated with root weight density below the disc and plant height. The mean root diameter and root weight density above the disc showed no significant difference between NA and ET genotypes. Our results indicate that a large genotypic difference exists for RP ability in durum wheat, and that ET genotypes have a higher RP ability than NA genotypes.     

The addition of Dasypyrum villosum (L.) Candargy chromosomes to durum wheat (Triticum durum Desf.)

Summary Six monosomic addition lines were produced in which different Dasypyrum villosum (L.) Candargy chromosomes were added to the chromosome complement of Triticum durum Desf. cv. Creso. Each added alien chromosome was found to have a specific effect on plant morphology and fertility. Transmission rate varied widely (from 7.5 to 27.7%) among the six univalent chromosomes. Different monotelosomic addition plants derived by a relatively high frequency of chromosome misdivision were isolated. The addition lines should be useful for studying Dasypyrum chromosome homoeology and the introduction of alien variation into durum and common wheats.Research supported by a grant from the Italian Research Council for Finalized Project IPRA. Sub-project Plant Breeding, Paper No. 1095     

The effect of root cooling on hormone content, leaf conductance and root hydraulic conductivity of durum wheat seedlings (Triticum durum L.)

Root cooling of 7-day-old wheat seedlings decreased root hydraulic conductivity causing a gradual loss of relative water content during 45 min (RWC). Subsequently (in 60 min), RWC became partially restored due to a decrease in transpiration linked to lower stomatal conductivity. The decrease in stomatal conductivity cannot be attributed to ABA-induced stomatal closure, since no increase in ABA content in the leaves or in the concentration in xylem sap or delivery of ABA from roots was found. However, decreased stomatal conductance was associated with a sharp decline in the content of cytokinins in shoots that was registered shortly after the start of root cooling and linked to increases in the activity of cytokinin-oxidase. This decrease in shoot cytokinin content may have been responsible for closing stomata, since this hormone is known to maintain stomatal opening when applied to plants. In support of this, pre-treatment with synthetic cytokinin benzyladenine was found to increase transpiration of wheat seedlings with cooled roots and bring about visible loss of turgor and wilting.     

Behaviour of rye univalents in hybrids of 6x-triticale with Triticum turgidum (L.) ssp. turgidum conv. durum (Desf.)

In a cytological analysis of the meiotic behaviour in PMCs of five hybrids between hexaploid triticale and durum wheat, Triticum turgidum L., chromosome association at meiotic first metaphase and the behaviour of rye univalents at first anaphase were analyzed. The chromosomes of the B genome, chromosomes 4A and 7A (disomic condition), and the seven rye chromosomes, could be distinguished by their C-banding pattern. No wheat-rye paring was detected at metaphase I. Rye univalents were observed as laggards which disjoined either predominantly equationaly (2R, 3R, 4R, 5R and 7R) or predominantly reductionaly (1R and 6R). Misdivision occurred in up to 3% of rye univalents.     

Genetic variation of salt-stressed durum wheat (Triticum turgidum subsp. durum Desf.) genotypes under field conditions and gynogenetic capacity

Agriculture has new challenges against the climate change: the preservation of genetic resources and the rapid creation of new varieties better adapted to abiotic stress, specially salinity. In this context, the agronomic performance of 25 durum wheat (Triticum turgidum subsp. durum Desf.) genotypes (nineteen landraces and six improved varieties), cultivated in two semi-arid regions in the center area of Tunisia, were assessed. These sites (Echbika, 2.2?g?l^?1; Barrouta, 4.2?g?l^?1) differ by their degree of salinity of the water irrigation. The results showed that most of the agronomic traits (e.g. spike per meter square, thousand kernels weight and grain yield) were reduced by salinity. Durum wheat landraces, Mahmoudi and Hmira, and improved varieties, Maali and Om Rabia showed the widest adaptability to different quality of irrigation water. Genotypes including Jneh Kotifa and Arbi were estimated as stable genotypes under adverse conditions. Thereafter, salt-tolerant (Hmira and Jneh Khotifa) and the most cultivated high-yielding (Karim, Razzak and Khiar) genotypes were tested for their gynogenetic ability to obtain haploids and doubled haploid lines. Genotypes with good induction capacity had not necessarily a good capacity of regeneration of haploid plantlets. In our conditions, Hmira and Khiar exhibited the best gynogenetic ability (3.1% and 2.9% of haploid plantlets, respectively).     

Radiation induced asynaptic mutations in durum wheat (Triticum durum DESF.)

The cytological behaviour and the inheritance of two asynaptic mutations independently obtained by neutron treatment of durum wheat seeds of var. Cappelli and Aziziah are considered. Mutant individuals of both lines have normal morphology, but are completely sterile. Analysis of chromosome behaviour at the several stages of PMC meiosis has been thoroughly accomplished in mutant progenies of both varieties during two subsequent generations. A completely random chromosome disjunction was found at anaphase I, together with multipolar spindles, laggard chromosomes etc. At meiotic second division a large amount of abnormalities were found, as a consequence of previous asynapsis and irregular polarization. Some differences in cytological behaviour were found between the asynaptic mutants of Cappelli and the asynaptics of Aziziah. - Genetic analysis demonstrated that both mutations behave as monogenic recessives.Contribution No. 139 from the Laboratory for the Application of nuclear energy to Agriculture, Casaccia Nuclear Studies Centre, Roma, Italy. - Part of the investigation was supported by Consiglio Nazionale delle Ricerche (Gruppo di lavoro per il miglioramento genetico delle piante erbacee e cultivate, Sottogruppo per il grano duro).     

Lead phytotoxicity on wheat (Triticum aestivum L.) seed germination and seedlings growth

Lead (Pb) is an environmental pollutant extremely toxic to plants and other living organisms including humans. To assess Pb phytotoxicity, experiments focusing on germination of wheat seeds were germinated in a solution containing Pb (NO(3))(2) (0.05; 0.1; 0.5; 1g/L) during 6 days. Lead accumulation in seedlings was positively correlated with the external concentrations, and negatively correlated with morphological parameters of plant growth. Lead increased lipid peroxidation, enhanced soluble protein concentrations and induced a significant accumulation of proline in roots. Esterase activity was enhanced in the presence of lead, whereas α-amylase activity was significantly inhibited. Antioxidant enzymes activities, such as, ascorbate peroxidase, peroxidase, superoxide dismutase, catalase and glutathione S-transferase were generally significantly increased in the presence of lead in a dose-dependent manner. The present results thus provide a model system to screen for natural compounds able to counteract the deleterious effects of lead.     

Long-term optimized embryogenic cultures in durum wheat (Triticum durum Desf.)

Five varieties of durum wheat: Appulo, Ofanto, Latino, Creso, and Castello (Triticum durum Desf.) adapted to the semi-arid mediterranean environment have been tested for their in vitro response. Compact, embryogenic, highly regenerable calli originated from primary callus derived through proliferation of the scutellum of immature embryos explanted in the presence of 2,4 dichlorophenoxyacetic acid. Selective subculture of the white, compact, embryogenic sectors led to the establishment of long-term cultures. Regeneration occurred on hormone-free medium either via germination of somatic embryos, or via multiple-shoot formation probably due to precocious germination of somatic embryos. The three varieties, Ofanto, Creso and Appulo, were the best responding genotypes. Callus fragmentation and two subsequent transfers onto fresh medium at 7-day intervals yielded a frequency of plant regeneration of some 25–40 plantlets per gram fresh weight callus in 21 days on Murashige and Skoog's hormone-free medium. Plantlets could be efficiently established in soil, thus confirming the possibility of biotechnological approaches with varieties of this crop species.Abbreviations E embryogenic - NE non embryogenic - MS Murashige and Skoog's (1962) medium - 2,4-D 2,4 dichlorophenoxyacetic acid - DAA days after anthesis - FWT fresh weight tissue     

Molecular linkage map for an intraspecific recombinant inbred population of durum wheat (Triticum turgidum L. var. durum)

Durum wheat (Triticum turgidum L. var. durum) is an economically and nutritionally important cereal crop in the Mediterranean region. To further our understanding of durum genome organization we constructed a durum linkage map using restriction fragment length polymorphisms (RFLPs), simple sequence repeats (SSRs) known as Gatersleben wheat microsatellites (GWMs), amplified fragment length polymorphisms (AFLPs), and seed storage proteins (SSPs: gliadins and glutenins). A population of 110 F₉ recombinant inbred lines (RILs) was derived from an intraspecific cross between two durum cultivars, Jennah Khetifa and Cham 1. The two parents exhibit contrasting traits for resistance to biotic and abiotic stresses and for grain quality. In total, 306 markers have been placed on the linkage map – 138 RFLPs, 26 SSRs, 134 AFLPs, five SSPs, and three known genes (one pyruvate decarboxylase and two lipoxygenases). The map is 3598 cM long, with an average distance between markers of 11.8 cM, and 12.1% of the markers deviated significantly from the expected Mendelian ratio 1:1. The molecular markers were evenly distributed between the A and B genomes. The chromosome with the most markers is 1B (41 markers), followed by 3B and 7B, with 25 markers each. The chromosomes with the fewest markers are 2A (11 markers), 5A (12 markers), and 4B (15 markers). In general, there is a good agreement between the map obtained and the Triticeae linkage consensus maps. This intraspecific map provides a useful tool for marker-assisted selection and map-based breeding for resistance to biotic and abiotic stresses and for improvement of grain quality. Received: 14 February 2000 / Accepted: 28 April 2000     

Accumulation of cadmium in near-isogenic lines of durum wheat (Triticum turgidum L. var durum): the role of transpiration

Concentrations of cadmium in the grain of durum wheat (Triticum turgidum L. var durum) are often above the internationally acceptable limit of 0.2 mg kg⁻¹. Cultivars that vary in concentrations of cadmium in the grain have been identified but the physiology behind differential accumulation has not been determined. Three pairs of near-isogenic lines (isolines) of durum wheat that vary in aboveground cadmium accumulation (8982-TL ‘high’ and ‘low’, W9260-BC ‘high’ and ‘low’, and W9261-BG ‘high’ and ‘low’) were used to test the hypothesis that the greater amounts of cadmium in shoots of the ‘high’ isolines are correlated with greater volumes of water transpired. In general, cadmium content was positively correlated with transpiration only in the ‘low’ isolines. Although shoots of the ‘high’ isolines of W9260-BC and W9261-BG contained higher concentrations of cadmium than did their corresponding ‘low’ isolines, they did not transpire larger volumes of water. In addition, isolines of 8982-TL transpired less water than did the other pairs of isolines yet both ‘high’ and ‘low’ isolines of 8982-TL contained higher amounts of cadmium than did the other pairs. The difference between ‘high’ and ‘low’ isolines appears to be related to the relative contribution of transpiration to cadmium translocation to the shoot. Increased transpiration was associated with increased cadmium content in the ‘low’ isolines but in the ‘high’ isolines increased cadmium in the shoot occurred independently of the volume of water transpired.