Karim Ammar

COMPARISON OF LEAF, SPIKE, PEDUNCLE AND CANOPY TEMPERATURE DEPRESSION IN WHEAT UNDER HEAT STRESS

Abstract This study examines genotype×organ–temperature depression (TD) interactions and whether differences in plant morphology influence organ-TD and its correlation with canopy temperature depression (CTD) and grain yield. Field experiments were conducted with 13 spring wheat genotypes planted on three dates in the 2000–2001 winter cropping cycle in NW Mexico. Surface temperatures of flag leaves, peduncles, spikes and canopy were measured with a hand-held infrared thermometer. Morphological and yield components were also measured. Results indicated that there is genetic variability for organ-TD. CTD showed strong positive correlations with organ-TD and grain yield. Organ-TD and CTD were positively correlated with leaf area index, and CTD was probably little affected by leaf rolling. Spike temperature was generally higher than leaf temperature, but lower than ambient air temperature. The interactions between grain yield and spike-TD and CTD were not significant. Results of this study indicate that CTD does not mask confounding interactions between organ temperatures and thus can be used reliably to measure TD during grain filling under heat stress conditions.

Identification and mapping of leaf, stem and stripe rust resistance quantitative trait loci and their interactions in durum wheat.

Leaf rust (Puccinia triticina Eriks.), stripe rust (Puccinia striiformis f. tritici Eriks.) and stem rust (Puccinia graminis f. sp. tritici) cause major production losses in durum wheat (Triticum turgidum L. var. durum). The objective of this research was to identify and map leaf, stripe and stem rust resistance loci from the French cultivar Sachem and Canadian cultivar Strongfield. A doubled haploid population from Sachem/Strongfield and parents were phenotyped for seedling reaction to leaf rust races BBG/BN and BBG/BP and adult plant response was determined in three field rust nurseries near El Batan, Obregon and Toluca, Mexico. Stripe rust response was recorded in 2009 and 2011 nurseries near Toluca and near Njoro, Kenya in 2010. Response to stem rust was recorded in field nurseries near Njoro, Kenya, in 2010 and 2011. Sachem was resistant to leaf, stripe and stem rust. A major leaf rust quantitative trait locus (QTL) was identified on chromosome 7B at Xgwm146 in Sachem. In the same region on 7B, a stripe rust QTL was identified in Strongfield. Leaf and stripe rust QTL around DArT marker wPt3451 were identified on chromosome 1B. On chromosome 2B, a significant leaf rust QTL was detected conferred by Strongfield, and at the same QTL, a Yr gene derived from Sachem conferred resistance. Significant stem rust resistance QTL were detected on chromosome 4B. Consistent interactions among loci for resistance to each rust type across nurseries were detected, especially for leaf rust QTL on 7B. Sachem and Strongfield offer useful sources of rust resistance genes for durum rust breeding.

Variability in glutenin subunit composition of Mediterranean durum wheat germplasm and its relationship with gluten strength

SUMMARY The allelic composition at five glutenin loci was assessed by one-dimensional sodium dodecyl sulphate polyacrylamide gel electrophoresis (1D SDS–PAGE) on a set of 155 landraces (from 21 Mediterranean countries) and 18 representative modern varieties. Gluten strength was determined by SDS-sedimentation on samples grown under rainfed conditions during 3 years in north-eastern Spain. One hundred and fourteen alleles/banding patterns were identified (25 at Glu-1 and 89 at Glu-2/Glu-3 loci); 0·85 of them were in landraces at very low frequency and 0·72 were unreported. Genetic diversity index was 0·71 for landraces and 0·38 for modern varieties. All modern varieties exhibited medium to strong gluten type with none of their 13 banding patterns having a significant effect on gluten-strength type. Ten banding patterns significantly affected gluten strength in landraces. Alleles Glu-B1e (band 20), Glu-A3a (band 6), Glu-A3d (bands 6 + 11), Glu-B3a (bands 2 + 4+15 + 19) and Glu-B2a (band 12) significantly increased the SDS-value, and their effects were associated with their frequency. Two alleles, Glu-A3b (band 5) and Glu-B2b (null), significantly reduced gluten strength, but only the effect of the latter locus could be associated with its frequency. Only three rare banding patterns affected gluten strength significantly: Glu-B1a (band 7), found in six landraces, had a negative effect, whereas banding patterns 2 + 4+14 + 15 + 18 and 2 + 4+15 + 18 + 19 at Glu-B3 had a positive effect. Landraces with outstanding gluten strength were more frequent in eastern than in western Mediterranean countries. The geographical pattern displayed from the frequencies of Glu-A1c is discussed.

Association Mapping Reveals Novel Stem Rust Resistance Loci in Durum Wheat at the Seedling Stage

Wheat stem rust rapidly evolves new virulence to resistance genes. Recently emerged races in East Africa, such as TTKSK (or Ug99), possess broad virulence to durum cultivars, and only a limited number of genes provide resistance. An association mapping (AM) study conducted on 183 durum wheat accessions has allowed us to identify 41 quantitative trait loci (QTLs; determination coefficient [R2] values from 1.1 to 23.1%) for seedling resistance to one or more of four highly virulent stem rust races: TRTTF, TTTTF, TTKSK (Ug99), and JRCQC, two of which (TRTTF and JRCQC) were isolated from Ethiopia. Among these loci, 24 are novel, while the remaining 17 overlapped with loci previously shown to provide field resistance in Ethiopia and/or chromosome regions known to harbor designated stem rust resistance designated loci (Sr). The identified loci were either effective against multiple races or race specific, particularly for race JRCQC. Our results highlight that stem rust resistance in durum wheat is governed in part by loci for resistance across multiple races, and in part by race‐specific ones (23 and 18, respectively). Collectively, these results provide useful information to improve the effectiveness of marker‐assisted selection towards the release of durum wheat cultivars with durable stem rust resistance.

Breeding progress in the pasta-making quality of durum wheat cultivars released in Italy and Spain during the 20th Century

Abstract. Genetic improvement of quality traits of durum wheat achieved in Italy and Spain during the 20th Century was investigated using an historical series of 12 cultivars from each country. The European Union durum wheat quality index increased by 6.25% (0.13% year–1 in Italian and 0.06% year–1 in Spanish cultivars). Protein content decreased by ∼10% (–0.14% year–1 in Italian and –0.19% year–1 in Spanish cultivars) but protein per ha increased at a rate of 0.35% year–1 (0.41% year–1 in Spanish and 0.26% year–1 in Italian cultivars). Yellow colour index increased by 9.9% (0.15% year–1 in Italian and 0.10% year–1 in Spanish cultivars). Test weight and vitreousness did not suffer significant changes over time. Gluten strength increased by 32.1% or 0.54% year–1 in Italian, and 27.9% or 0.33% year–1 in Spanish cultivars. Much larger genetic control on gluten strength was found in Italian than in Spanish cultivars. Changes in sedimentation index (41.1% or 0.64% year–1 in Italy, and 41.6% or 0.49% year–1 in Spain) were the consequence of the progressive incorporation into recent cultivars of favourable low molecular weight glutenin subunits (LMW-GS). Breeding increased the frequency of the LMW-GS combination aaa, which was present in 75% of all intermediate cultivars and in 100% of the modern Italian cultivars. A LMW-GS combination not previously reported (d?b) was identified in two modern Spanish cultivars. Breeding programs were also successful in increasing the stability of gluten strength and the sedimentation index.

Genome-Wide Association Mapping of Leaf Rust Response in a Durum Wheat Worldwide Germplasm Collection

Thirteen durum wheat accessions showed resistance to all Puccinia triticina races tested GWAS revealed 88 SNPs (37 loci) associated with leaf rust response in durum wheat Associations were identified on all chromosomes except 1B and 7B GWAS revealed 14 previously uncharacterized loci for leaf rust resistance

Genetic analysis of leaf rust resistance in six durum wheat genotypes.

Leaf rust, caused by Puccinia triticina, is one of the main fungal diseases limiting durum wheat production. This study aimed to characterize previously undescribed genes for leaf rust resistance in durum wheat. Six different resistant durum genotypes were crossed to two susceptible International Maize and Wheat Improvement Center (CIMMYT) lines and the resulting F1, F2, and F3 progenies were evaluated for leaf rust reactions in the field and under greenhouse conditions. In addition, allelism tests were conducted. The results of the study indicated that most genotypes carried single effective dominant or recessive seedling resistance genes; the only exception to this was genotype Gaza, which carried one adult plant and one seedling resistance gene. In addition, it was concluded that the resistance genes identified in the current study were neither allelic to LrCamayo or Lr61, nor were they related to Lr3 or Lr14a, the genes that already are either ineffective or are considered to be vulnerable for breeding purposes. A complicated allelic or linkage relationship between the identified genes is discussed. The results of the study will be useful for breeding for durable resistance by creating polygenic complexes.

Effect of Ppd-1 genes on durum wheat flowering time and grain filling duration in a wide range of latitudes

Understanding the effect of genetic factors controlling flowering time is essential to fine-tune crop development to each target environment and to maximize yield. A set of 35 durum wheat genotypes of spring growth-habit involving different allelic combinations at Ppd-A1 and Ppd-B1 genes was grown for 2 years at four sites at latitudes ranging from 19°N to 41°N. The emergence-flowering period was reduced from north to south. The frequency in the collection of the insensitive allele GS-105 at Ppd-A1 was greater (34%) than that of allele GS-100 (20%). Genotypes that flowered earlier due to the presence of alleles causing photoperiod insensitivity extended their grain-filling period, but less than the shortening in flowering time. The effect of the allele conferring photoperiod sensitivity at Ppd-A1 was stronger than that at Ppd-B1 ( Ppd-A1b > Ppd-B1b ). The effect of photoperiod insensitivity alleles was classified as GS-100 > GS-105 > Ppd-B1a . The phenotypic expression of alleles conferring photoperiod insensitivity at Ppd-A1 increased at sites with average day length from emergence to flowering lower than 12 h. An interaction effect was found between Ppd-A1 and Ppd-B1 . Differences between allelic combinations in flowering time accounted for c . 66% of the variability induced by the genotype effect, with the remaining 34% being explained by genes controlling earliness per se . The shortest flowering time across sites corresponded to the allelic combination GS-100/ Ppd-B1a , which reduced flowering time by 11 days irrespective of the Ppd-A1b/Ppd-B1b combination. The current study marks a further step towards elucidation of the phenotypic expression of genes regulating photoperiod sensitivity and their interaction with the environment.

Variability and expression profile of the DRF1 gene in four cultivars of durum wheat and one triticale under moderate water stress conditions

The dehydration responsive element binding (DREB) proteins are important transcription factors that contribute to stress endurance in plants triggering the expression of a set of abiotic stress-related genes. A DREB2-related gene, previously referred to as dehydration responsive factor 1 (DRF1) was originally isolated and characterized in durum wheat. The aim of this study was to monitor the expression profiles of three alternatively spliced TdDRF1 transcripts during dehydration experiments and to evaluate the effects of genetic diversity on the molecular response, using experimental conditions reflecting as closely as possible water stress perceived by cereals in open field. To investigate the effect of moderate water stress conditions, time-course dehydration experiments were carried out under controlled conditions in the greenhouse on four durum wheat and one triticale genotypes. Differences were observed in molecular patterns, thus, suggesting a genotype dependency of the DRF1 gene expression in response to the stress induced. The biodiversity of the transcripts of the DRF1 gene was explored in order to assess the level of polymorphism and its possible effects on structure and function of putative proteins. A total of nine haplotypes were identified in the sequences cloned, seven of which encompassing polymorphisms in exon 4, including the region codifying for the DNA binding Apetala2 (AP2) domain. The 3D structural models of the AP2 domain were generated by homology modelling using the variability observed. The polymorphisms analysed did not significantly affect the structural arrangement of the DNA binding domains, thus resulting compatible with the putative functionality.

Molecular analyses of a dehydration-related gene from the DREB family in durum, wheat and triticale

Abiotic stresses are the primary cause of crop loss worldwide. They result in average yield losses of more than 50% in major crops. The negative effects of abiotic stresses are thought to be increasing due to global climate change and the resulting erratic weather patterns. Improving crops’ ability to tolerate abiotic stresses through conventional breeding has been successful, especially in the case of wheat, as new cultivars better adapting to increasingly difficult growing conditions are being released regularly. However, as many stress-inducible genes have been identified, sequenced, characterized and insights into their functional roles in stress tolerance are being obtained, breeding programs have much to gain by exploring ways to target those stress-related genes that may be useful in their selection. If, or when, the relationship between different alleles or expression patterns of some stress-related genes is demonstrated, perfect markers for assisting breeder in selection for stress-tolerant lines can be readily obtained. Previously, we isolated and characterized the gene designated as TdDRF1 encoding for a dehydration responsive factor in durum wheat. Results obtained using plant samples of different cultivars in time-course experiments conducted in the greenhouse suggested that the expression profile of TdDRF1 upon water stress was genotype dependent. In the present paper we report results from field experiments carried at CIMMYT’s experimental fields near Obregon in Mexico, in which quantitative RT-PCR was used to monitor the expression profile of the three transcripts produced by the TdDRF1 gene under stressed (minimally irrigated) and non-stressed (fully irrigated) conditions. Tolerant and susceptible cultivars were analyzed and the results from these field experiments are compared with those from greenhouse testing.