Effects of three herbicides on yields of five cultivars of winter wheat (Triticum aestivum L. em Thell)

With the development of new selective herbicides and the frequent change in commercial wheat cultivars, information is needed as to the possible interaction between cultivars and herbicides. The responses of five genotypically diverse wheat cultivars (Bezostaya, Daws, Maris Hobbit, Stephens and Yamhill) to diuron [3-(3,4-dichloropheny1)-1,1- dimethylurea], diclofop methyl 2-[4-(2,4-dichlorophenoxy)phenoxy] propanoate and 2,4-D (2,4-dichlorophenoxy acetic acid) herbicides were compared under field and greenhouse conditions during the 1979-80 growing season. Grain yield was considered as a measure of herbicide injury when compared to the control plots for each cultivar. Effect on components of yield, plant height and grain protein content also were investigated. Differences in yield performance and related agronomic characters could be attributed to specific herbicides, designated rates and growth stages at the time of application. The lower (1.4 kg/ha) rate of diuron, diclofop and 2,4-D reduced yields less than the higher rate (2.8 kg/ha). Diuron and diclofop applied at the earlier (three to to five leaf) growth stage caused greater yield reductions than when applied at the later (five to six tiller) growth stage. Differential yield responses were found among and within the five winter wheat cultivars. The higher rate of diuron (2.8 kg/ha) caused the most injury in all of the cultivars tested. Major injury from diclofop occurred on the cultivar Maris Hobbit with minor effects on the other four cultivars. The primary reduction in yield from application of 2,4-D was to the cultivar Bezostaya. Among the five wheat cultivars tested in this experiment, Daws was the most tolerant to the three herbicides tested. Among the yield components (number of spikes per unit area, kernels per spike and 1000 kernel weight), number of kernels per spike accounted for most of the variation in yield. The data showed a direct relationship between kernel number and grain yield. Grain protein percentage of Daws, Maris Hobbit, Stephens and Yamhill significantly increased at the higher rate of diuron; whereas a similar increase was noted only in Bezostaya at the lower rate of 2,4-D. These increases in protein were associated with significant decreases in yield. Yield reductions due to herbicide treatments were generally lower than those due to weed competition. Reductions in yield and corresponding changes in the other agronomic characteristics observed in this experiment were the result of concentrations which are higher than those normally used in spraying wheat for weed control. This high chemical dosage was chosen for each herbicide to assure a greater differential response among and within the wheat cultivars. It also provided information for the plant breeder as to which cultivars had higher levels of tolerance. Such information is important when making hybrid combinations for the development of future varieties if higher levels of tolerance to specific herbicides are required

Frequency of mutations associated with fungicide resistance and population structure of Mycosphaerella graminicola in Tunisia

The occurrence of fungicide resistance in Mycosphaerella graminicola populations from Tunisia was investigated by examining mutations known to be associated with strobilurin and azole resistance. Few mutations associated with fungicide resistance were detected. No evidence for strobilurin resistance was found among 357 Tunisian isolates and only two among 80 sequenced isolates carried mutations associated with azole resistance. A network analysis suggested that these mutations emerged independently from mutations found in previously described European populations. The population genetic structure of M. graminicola in Tunisia was analyzed using variation at 11 microsatellite loci. Populations in Tunisia were characterized by high gene and genotype diversity. All populations were in gametic equilibrium and mating type proportions did not deviate from the 1:1 ratio expected under random mating, consistent with regular cycles of sexual reproduction. In combination with a high degree of gene flow among sampling sites, M. graminicola must be considered a pathogens with high evolutionary potential. Thus, control strategies against Septoria blotch in Tunisia should be optimized to reduce the emergence and spread of resistant isolate

Geographical distribution of a specific mitochondrial haplotype of Zymoseptoria tritici

Severity of disease caused by the fungus Zymoseptoria tritici throughout world cereal growing regions has elicited much debate on the potential evolutionary mechanism conferring high adaptability of the pathogen to diverse climate conditions and different wheat hosts (Triticum durum and T. aestivum). Specific mitochondrial DNA sequence was used to investigate geographic distribution of the type 4 haplotype (mtRFLP4) within 1363 isolates of Z. tritici originating from 21 countries. The mtRFLP4 haplotype was detected from both durum and bread wheat hosts with greater frequency on durum wheat. The distribution of mtRFLP4 was limited to populations sampled from the Mediterranean and the Red Sea region. Greater frequencies of mtRFLP4 were found in Tunisia (87%) and Algeria (60%). The haplotype was absent within European, Australian, North and South American populations except Argentina. While alternative hypotheses such as climatic adaptation could not be ruled out, it is postulated that mtRFLP4 originated in North Africa (e.g. Tunisia or Algeria) as an adaptation to durum wheat as the prevailing cereal crop. The specialized haplotype has subsequently spread as indicated by lower frequency of occurrence in the surrounding Mediterranean countries and on bread wheat hosts

Evaluación del riesgo de contaminación por metales pesados en sedimentos superficiales de la Laguna Sur de Túnez mediante un procedimiento de extracción secuencial

In this study, the total concentrations and chemical forms of heavy metals (Fe, Zn, Pb, Cu, Cr, Cd, and Ni) in surface sediments of the South Lagoon of Tunis located in northeast Tunisia were investigated. Multiple geochemical indices were applied to assess the potential environmental risks. The South Lagoon is a valuable regional resource for fisheries, tourism and aquaculture. Total metal concentrations exhibited significant spatial variation attributed to the principal water circulation direction (east to west). The chemical speciation of Fe, Cr and Ni shows that they were mostly related to the residual fraction (Fe 34.8%, Cr 37.4% and Ni 37.9%), while Pb, Zn, Cu, and Cd were mostly related to the non-residual fraction (labile fraction Pb 89.4%, Zn 26.1%, Cu 71.8% and Cd 84.3%). Pb, Zn, Cu and Cr are of high potential bioavailability. The highest pollution was found on the west side of the lagoon according to the calculated global contamination factors. Besides, individual contamination factors, Pb followed by Zn and Cu, posed the highest risk of contamination. This study shows that, even after dredging, the persistence of low concentrations of some contaminants may cause environmental problems in certain physico-chemical conditions.En este estudio, se investigaron las concentraciones totales y las formas químicas de los metales pesados (Fe, Zn, Pb, Cu, Cr, Cd y Ni) en los sedimentos superficiales de la Laguna Sur de Túnez, ubicada en el noreste de Túnez. Se aplicaron múltiples índices geoquímicos para evaluar los riesgos ambientales potenciales. La Laguna Sur es un valioso recurso regional para la pesca, el turismo y la acuicultura. Las concentraciones totales de metales exhibieron una variación espacial significativa, atribuida a la dirección principal de circulación del agua (Este a Oeste). La especiación química de Fe, Cr y Ni muestra que están esencialmente relacionados con la fracción residual (Fe: 34,8%, Cr: 37,4% y Ni: 37,9%), mientras que Pb, Zn, Cu y Cd se encontraron mayoritariamente en la fracción no residual. -fracción residual (fracción lábil Pb: 89,4%, Zn: 26,1%, Cu: 71,8% y Cd: 84,3%). Estos elementos (Pb, Zn, Cu y Cr) tienen un alto potencial de biodisponibilidad. La mayor contaminación se encontró en el lado oeste de la laguna, según los factores de contaminación global calculados. Además, los factores de contaminación individuales, Pb seguido de Zn y Cu, presentaron el mayor riesgo de contaminación. Este estudio muestra que, incluso después de la operación de dragado, la persistencia de bajas concentraciones de algunos contaminantes puede causar problemas ambientales en determinadas condiciones físico-químicas

Geographical distribution of a specific mitochondrial haplotype of Zymoseptoria tritici

Severity of disease caused by the fungus Zymoseptoria tritici throughout world cereal growing regions has elicited much debate on the potential evolutionary mechanism conferring high adaptability of the pathogen to diverse climate conditions and different wheat hosts (Triticum durum and T. aestivum). Specific mitochondrial DNA sequence was used to investigate geographic distribution of the type 4 haplotype (mtRFLP4) within 1363 isolates of Z. tritici originating from 21 countries. The mtRFLP4 haplotype was detected from both durum and bread wheat hosts with greater frequency on durum wheat. The distribution of mtRFLP4 was limited to populations sampled from the Mediterranean and the Red Sea region. Greater frequencies of mtRFLP4 were found in Tunisia (87%) and Algeria (60%). The haplotype was absent within European, Australian, North and South American populations except Argentina. While alternative hypotheses such as climatic adaptation could not be ruled out, it is postulated that mtRFLP4 originated in North Africa (e.g. Tunisia or Algeria) as an adaptation to durum wheat as the prevailing cereal crop. The specialized haplotype has subsequently spread as indicated by lower frequency of occurrence in the surrounding Mediterranean countries and on bread wheat hosts

Characterization of Mediterranean durum wheat for resistance to Pyrenophora tritici-repentis

Tan spot (TS), caused by the fugus Pyrenophora tritici-repentis (Ptr), has gained significant importance in the last few years, thereby representing a threat to wheat production in all major wheat-growing regions, including Tunisia. In this context, we evaluated a Mediterranean collection of 549 durum wheat accessions under field conditions for resistance to Ptr over two cropping seasons in Jendouba (Tunisia), a hot spot for Ptr. The relative disease severities showed significant phenotypic variation from resistance to susceptibility. The correlation between disease scores over the two trials was significant, as 50% of the accessions maintained good levels of resistance (resistant–moderately resistant). Seedling-and adult-stage reactions were significantly correlated. The ANOVA analysis revealed that the genotype term is highly significant at the adult stage, thus emphasizing the high genetic variability of the tested accessions. Reaction-type comparison among and between countries revealed a high diversity of TS resistance. Plant height (PH) was negatively correlated to disease scores, indicating that PH might either have a significant effect on TS severity or that it can be potential disease escape traits. The evaluation of this collection allowed for the identification of potential diverse resistance sources to Ptr that can be incorporated in breeding programs

Climacteric fruit ripening: Ethylene-dependent and independent regulation of ripening pathways in melon fruit

Cantaloupe melons have a typical climacteric behaviour with ethylene playing a major role in the regulation of the ripening process and affecting the ripening rate. Crossing of Cantaloupe Charentais melon with a non-climacteric melon indicated that the climacteric character is genetically dominant and conferred by two duplicated loci only. However, other experiments made by crossing two non-climacteric melons have generated climacteric fruit, indicating that different and complex genetic regulation exists for the climacteric character. Suppression of ethylene production by antisense ACC oxidase RNA in Charentais melon has shown that, while many ripening pathways were regulated by ethylene (synthesis of aroma volatiles, respiratory climacteric and degreening of the rind), some were ethylene-independent (initiation of climacteric, sugar accumulation, loss of acidity and coloration of the pulp). Softening of the flesh comprised both ethylene-dependent and independent components that were correlated with differential regulation of cell wall degrading genes. These results indicate that climacteric (ethylene-dependent) and non-climacteric (ethylene-independent) regulation coexist during climacteric fruit ripening. In addition, ethylenesuppressed melons allowed demonstrating that the various ethylene-dependent events exhibited differential sensitivity to ethylene and that ethylene was promoting sensitivity to chilling injury. Throughout this review, the data generated with melon are compared with those obtained with tomato and other fruit

Phenotyping mediterranean durum wheat landraces for resistance to Zymoseptoria tritici in Tunisia

Durum wheat landraces have huge potential for the identification of genetic factors valuable for improving resistance to biotic stresses. Tunisia is known as a hot spot for Septoria tritici blotch disease (STB), caused by the fungus Zymoseptoria tritici (Z. tritici). In this context, a collection of 3166 Mediterranean durum wheat landraces were evaluated at the seedling and adult stages for STB resistance in the 2016–2017 cropping season under field conditions in Kodia (Tunisia). Unadapted/susceptible accessions were eliminated to reach the final set of 1059 accessions; this was termed the Med-collection, which comprised accessions from 13 countries and was also screened in the 2018–2019 cropping season. The Med-collection showed high frequency of resistance reactions, among which over 50% showed an immune reaction (HR) at both seedling and adult growth stages. Interestingly, 92% of HR and R accessions maintained their resistance levels across the two years, confirming the highly significant correlation found between seedling-and adult-stage reactions. Plant Height was found to have a negative significant effect on adult-stage resistance, suggesting that either this trait can influence disease severity, or that it can be due to environmental/epidemiological factors. Accessions from Italy showed the highest variability, while those from Portugal, Spain and Tunisia showed the highest levels of resistance at both growth stages, suggesting that the latter accessions may harbor novel QTLs effective for STB resistance

The use of pentaploid crosses for the introgression of Amblyopyrum muticum and D-genome chromosome segments into durum wheat

The wild relatives of wheat provide an important source of genetic variation for wheat improvement. Much of the work in the past aimed at transferring genetic variation from wild relatives into wheat has relied on the exploitation of the ph1b mutant, located on the long arm of chromosome 5B. This mutation allows homoeologous recombination to occur between chromosomes from related but different genomes, e.g. between the chromosomes of wheat and related chromosomes from a wild relative resulting in the generation of interspecific recombinant chromosomes. However, the ph1b mutant also enables recombination to occur between the homoeologous genomes of wheat, e.g. A/B, A/D, B/D, resulting in the generation of wheat intergenomic recombinant chromosomes. In this work we report on the presence of wheat intergenomic recombinants in the genomic background of hexaploid wheat/Amblyopyrum muticum introgression lines. The transfer of genomic rearrangements involving the D-genome through pentaploid crosses provides a strategy by which the D-genome of wheat can be introgressed into durum wheat. Hence, a pentaploid crossing strategy was used to transfer D-genome segments, translocated with either the A- and/or the B-genome, into the tetraploid background of two durum wheat genotypes Karim and Om Rabi 5 in either the presence or absence of different Am. muticum (2n = 2x = 14, TT) segments. Translocations were monitored in backcross generations to the durum wheat parents via multicolour genomic in situ hybridisation (mc-GISH). Tetraploid lines carrying homozygous D-genome introgressions, as well as simultaneous homozygous D- and T-genome introgressions, were developed. Introgression lines were characterised via KASP markers and multicolour fluorescence in situ hybridisation (FISH). Results showed that new wheat sub-genomic translocations were generated at each generation in progeny that carried any Am. muticum chromosome segment irrespective of the linkage group that the segment was derived from. The highest frequencies of homoeologous recombination were observed between the A- and the D-genomes. Results indicated that the genotype Karim had a higher tolerance to genomic rearrangements and T-genome introgressions compared to Om Rabi 5. This indicates the importance of the selection of the parental genotype when attempting to transfer/develop introgressions into durum wheat from pentaploid crosses