RESUMO

Various insect pests attack wheat (Triticum aestivum L.) that can cause significant grain yield losses to the crop. Farmers usually depend on pesticides, however, smallholder farmers often have limited and ill-timed access to control methods, including insecticides. Host plant resistance is an alternative to protect grain yield and reduce costs to farmers. Three of the most serious pests of wheat are Diuraphis noxia (Kurdjumov), Mayetiola destructor (Say), and Cephus pygmeaus L. These pests occur in most of the wheat growing areas. However, they are of high importance in North Africa and West Asia. The aim of this study was to evaluate a set of wheat-alien translocations for resistance against D. noxia, M. destructor and C. pygmeaus. Genotypes of this germplasm set have already been reported to carry resistance against certain wheat aphid species. Genotypes 1RSam.1AL and MA1S.1RLe(1B), displayed high levels of resistance against D. noxia and C. pygmeaus, respectively. While three genotypes showed resistance reaction against M. destructor: 1Re(1D), 7A.7S-L5, and 7A.7S-Gb5. Except for the resistant genotype to C. pygmeaus, the other four genotypes were previously reported to carry resistance against Sitobion avenae Fabricius, Rhopalosiphum padi L. and Schizaphis graminum (Rondani). These five wheat-alien translocations are currently being used in the bread-wheat breeding programs at CIMMYT and ICARDA to transfer the multiple pest resistance in elite germplasm.

RESUMO

Wheat (Triticum aestivum L.) is a major staple food crop grown worldwide on >220 million ha. Climate change is regarded to have severe effect on wheat yields, and unpredictable drought stress is one of the most important factors. Breeding can significantly contribute to the mitigation of climate change effects on production by developing drought-tolerant wheat germplasm. The objective of our study was to determine the annual genetic gain for grain yield (GY) of the internationally distributed Semi-Arid Wheat Yield Trials, grown during 2002-2003 to 2013-2014 and developed by the Bread Wheat Breeding program at the CIMMYT. We analyzed data from 740 locations across 66 countries, which were classified in low-yielding (LYE) and medium-yielding (MYE) environments according to a cluster analysis. The rate of GY increase (GYC) was estimated relative to four drought-tolerant wheat lines used as constant checks. Our results estimate that the rate of GYC in LYE was 1.8% (38.13 kg ha-1 yr-1), whereas in MYE, it was 1.41% (57.71 kg ha-1 yr-1). The increase in GYC across environments was 1.6% (48.06 kg ha-1 yr-1). The pedigrees of the highest yielding lines through the coefficient of parentage analysis indicated the utilization of three primary sources-'Pastor', 'Baviacora 92', and synthetic hexaploid derivatives-to develop drought-tolerant, high and stably performing wheat lines. We conclude that CIMMYT's wheat breeding program continues to deliver adapted germplasm for suboptimal conditions of diverse wheat growing regions worldwide.

RESUMO

Since 1984, the 'Chilero' spring wheat line developed by CIMMYT has proven to be highly resistant to leaf rust and stripe rust. Amid efforts to understand the basis of resistance of this line, a recombinant inbred line (RIL) population derived from a cross between Avocet and Chilero was studied. The parents and RILs were characterized in field trials for leaf rust and stripe rust in three locations in Mexico between 2012 and 2015 and genotyped with DArT-array, DArT-GBS, and SSR markers. A total of 6,168 polymorphic markers were used to construct genetic linkage maps. Inclusive composite interval mapping detected four colocated resistance loci to both rust diseases and two stripe rust resistant loci in the Avocet × Chilero population. Among these, the quantitative trait locus (QTL) on chromosome 1BL was identified as a pleotropic adult plant resistance gene Lr46/Yr29, whereas QLr.cim-5DS/QYr.cim-5DS was a newly discovered colocated resistance locus to both rust diseases in Chilero. Additionally, one new stripe rust resistance locus on chromosome 7BL was mapped in the current population. Avocet also contributed two minor colocated resistance QTLs situated on chromosomes 1DL and 4BS. The flanking SNP markers can be converted to breeder friendly Kompetitive Allele Specific PCR (KASP) markers for wheat breeding programs.

Assuntos

Basidiomycota/fisiologia , Resistência à Doença/genética , Genes de Plantas/genética , Doenças das Plantas/genética , Triticum/genética , Mapeamento Cromossômico , Genótipo , México , Locos de Características Quantitativas , Triticum/microbiologia

RESUMO

Maintaining wheat productivity under the increasing temperatures in South Asia is a challenge. We focused on developing early maturing wheat lines as an adaptive mechanism in regions suffering from terminal heat stress and those areas that require wheat adapted to shorter cycles under continual high temperature stress. We evaluated the grain yield performance of early-maturing heat-tolerant germplasm developed by CIMMYT, Mexico at diverse locations in South Asia from 2009 to 2014 and estimated the breeding progress for high-yielding and early-maturing heat-tolerant germplasm in South Asia. Each year the trial comprised of 28 new entries, one CIMMYT check (Baj) and a local check variety. Locations were classified by mega environment (ME); ME1 being the temperate irrigated locations with terminal high temperature stress, and ME5 as hot, sub-tropical, irrigated locations. Grain yield (GY), days to heading (DTH) and plant height (PH) were recorded at each location. Effect of temperature on GY was observed in both ME1 and ME5. Across years, mean minimum temperatures in ME1 and mean maximum temperatures in ME5 during grain filling had significant negative association with GY. The ME1 locations were cooler that those in ME5 in the 5 years of evaluations and had a 1-2 t/ha higher GY. A mean reduction of 20 days for DTH and 20 cm in PH was observed in ME5. Negative genetic correlations of -0.43 to -0.79 were observed between GY and DTH in South Asia during 2009-2014. Each year, we identified early-maturing germplasm with higher grain yield than the local checks. A positive trend was observed while estimating the breeding progress across five years for high-yielding early-maturing heat tolerant wheat compared to the local checks in South Asia. The results suggests the potential of the high-yielding early-maturing wheat lines developed at CIMMYT in improving wheat production and maintaining genetic gains in South Asia.

RESUMO

Stripe rust, caused by Puccinia striiformis f. sp. tritici W., is a devastating disease of wheat worldwide. A new stripe rust resistance gene with moderate seedling and adult plant resistance was mapped using an F5 recombinant inbred line (RIL) population developed from the cross of the resistant parent 'Almop' with the susceptible parent 'Avocet'. The parents and RILs were phenotyped for seedling stripe rust response variation in a greenhouse and in field trials at Toluca, Mexico for 2 years. Almop showed moderate levels of resistance at both seedling and adult plant stages compared with the highly susceptible response of Avocet. The distribution of homozygous resistant, homozygous susceptible, and segregating RILs conformed to segregation at a single locus. Seedlings and adult plant responses were correlated, indicating that the same gene conferred resistance at both stages. A bulk segregant analysis approach with widely distributed simple sequence repeat (SSR) markers mapped the resistance gene to the distal region of the long arm of chromosome 4A. The SSR marker wmc776 cosegregated with this gene, whereas markers wmc219 and wmc313 were tightly linked and both located at 0.6 centimorgans. The resistance locus was designated Yr60.

RESUMO

Leaf rust and stripe rust are important diseases of wheat and can be controlled by growing resistant varieties. We investigated the genetic basis of resistance to both rusts in 198 F5 recombinant inbred lines derived from a cross between 'Avocet' and 'Francolin#1'. The population was phenotyped in greenhouse and field, and genotyped with known gene-associated molecular markers. Seedling resistance of Francolin#1 to leaf and stripe rusts was attributed to the loosely linked genes Lr16 and YrF, respectively, with a recombination frequency of 0.36. Field segregation indicated that adult plant resistance (APR) to leaf and stripe rusts was conferred by three and five additive genes, respectively. Among them, Lr46/Yr29 was associated with resistance to both rusts in Francolin#1, Lr16 reduced field leaf rust severity by 8 to 9%, and YrF contributed to 10 to 25% reductions in stripe rust severity. The Lr16 region was also associated with a 5 to 16% reduction in stripe rust severity, which is likely due to its linkage with YrF or another unidentified stripe rust APR gene. Significant additive effects on stripe rust were detected between YrF and Yr29. We conclude that APR in Francolin#1 to leaf and stripe rusts involves a combination of seedling and APR genes.

RESUMO

Leaf rust, caused by Puccinia triticina (Pt), has become a globally important disease for durum wheat (Triticum turgidum subsp. durum) since the detection of race group BBG/BN, which renders ineffective a widely deployed seedling resistance gene present in several popular cultivars including Mexican cultivars Altar C84 and Atil C2000. The resistance gene continues to play a key role in protecting durum wheat against bread wheat-predominant races since virulence among this race group has not been found. We developed F3 and F5 mapping populations from a cross between Atil C2000 and the susceptible line Atred #1. Resistance was characterized by greenhouse seedling tests using three Pt races. Segregation tests indicated the presence of a single gene, which was mapped to the distal end of 7BS by bulk segregant analysis. The closest marker, wmc606, was located 5.5 cM proximal to the gene. No known leaf rust resistance genes are reported in this region; this gene was therefore designated as Lr72. The presence of Lr72 was further investigated in greenhouse tests in a collection of durum wheat using 13 Pt races. It was concluded that at least one additional gene protects durum wheat from bread wheat-predominant Pt races.

RESUMO

Chapio is a spring wheat developed by CIMMYT in Mexico by a breeding program that focused on multigenic resistances to leaf rust and stripe rust. A population consisting of 277 recombinant inbred lines (RILs) was developed by crossing Chapio with Avocet. The RILs were genotyped with DArT markers (137 randomly selected RILs) and bulked segregant analysis conducted to supplement the map with informative SSR markers. The final map consisted of 264 markers. Phenotyping against stripe rust was conducted for three seasons in Toluca, Mexico and at three sites over two seasons (total of four environments) in Sichuan Province, China. Significant loci across the two inter-continental regions included Lr34/Yr18 on 7DS, Sr2/Yr30 on 3BS, and a QTL on 3D. There were significant genotype × environment interactions with resistance gene Yr31 on 2BS being effective in most of the Toluca environments; however, a late incursion of a virulent pathotype in 2009 rendered this gene ineffective. This locus also had no effect in China. Conversely, a 5BL locus was only effective in the Chinese environments. There were also complex additive interactions. In the Mexican environments, Yr31 suppressed the additive effect of Yr30 and the 3D locus, but not of Lr34/Yr18, while in China, the 3D and 5BL loci were generally not additive with each other, but were additive when combined with other loci. These results indicate the importance of maintaining diverse, multi-genic resistances as Chapio had stable inter-continental resistance despite the fact that there were QTLs that were not effective in either one or the other region.

Assuntos

Resistência à Doença/genética , Locos de Características Quantitativas , Triticum/genética , China , Cruzamentos Genéticos , Meio Ambiente , Marcadores Genéticos , Genótipo , México , Doenças das Plantas/microbiologia , Triticum/microbiologia

RESUMO

Leaf rust caused by Puccinia triticina Eriks. was observed during the 2007-2008 crop season in the state of Sonora, Mexico on previously resistant durum wheat (Triticum turgidum L.) cvs. Jupare C2001 (Lr27 + 31) and Banamichi C2004. Single uredinial isolates were made from disease samples collected in the field and tested mostly on 'Thatcher' differentials at seedling or adult-plant stages (1). The isolates were identified as a new race, BBG/BP, resembling race BBG/BN predominant on durum wheat (2), but with additional virulences to resistance genes Lr27 + Lr31 in Gatcher and adult-plant resistance gene Lr12. The new race was also identified in samples collected from durum wheat in the State of Nuevo Leon during the same season. The avirulence/virulence formula of race BBG/BP is Lr1, 2a, 2b, 2c, 3, 3ka, 3bg, 9, 13, 14a, 15, 16, 17, 18, 19, 21, 22a, 24, 25, 26, 28, 29, 30, 32, 35, 37/Lr10, 11, 12, 14b, 20, 23, 27 + 31, 33. Although virulences to Lr27 + Lr31 and Lr12 is known to occur in P. triticina races predominant on bread wheat (T. aestivum L.) (1), to our knowledge, this is the first report of such virulences in the pathogen population on durum wheat. Pure isolates of race BBG/BP are stored in the CIMMYT leaf rust collection. References: (1) R. P. Singh. Plant Dis. 75:790, 1991. (2) R. P. Singh et al. Plant Dis. 88:703, 2004.

RESUMO

Leaf rust resistance gene Lr9 was transferred to wheat from Triticum umbellulatum (1). In 1971, 4 years after cultivars with this gene were released in the United States, leaf rust races with virulence to Lr9 were detected. In Mexico, cultivars with Lr9 have not been released and leaf rust races with Lr9 virulence have not been detected. Resistance gene Lr25 was transferred to wheat from Rosen rye (1) and has been effective worldwide, but this gene has not been used commercially because of possible negative effects on yield (1). Rust samples collected at different locations in Nuevo Leon State of Mexico during the 2004-2005 and 2005-2006 wheat crop seasons were analyzed on seedlings of wheat leaf rust differentials in the greenhouse from single pustule isolates. The race nomenclature used is described in Singh (2). Among the races identified from this area, seven, MLJ/SP, TNM/JP, TLB/JP, TNM/KP, TNR/JP, TNB/JN, and TMB/JP, were virulent to both of these genes. Virulence to Lr9 and Lr25 were confirmed by repeating tests using Lr9 differentials 'RL6010' and 'McNair 701' and Transec and three other Lr25 wheat lines developed at CIMMYT, which carry Lr25. To our knowledge, this is the first confirmed report of virulence to Lr9 in Mexico and virulence to Lr25 in the world. These isolates are conserved at CIMMYT for future reference. References: (1) R. A. McIntosh et al. Wheat Rusts: An Atlas of Resistance Genes. CSIRO Publishing, Melbourne, Australia, 1995. (2) R. P. Singh. Plant Dis. 75:790, 1991.

RESUMO

Leaf (brown) and stripe (yellow) rusts, caused by Puccinia triticina and Puccinia striiformis, respectively, are fungal diseases of wheat (Triticum aestivum) that cause significant yield losses annually in many wheat-growing regions of the world. The objectives of our study were to characterize genetic loci associated with resistance to leaf and stripe rusts using molecular markers in a population derived from a cross between the rust-susceptible cultivar 'Avocet S' and the resistant cultivar 'Pavon76'. Using bulked segregant analysis and partial linkage mapping with AFLPs, SSRs and RFLPs, we identified 6 independent loci that contributed to slow rusting or adult plant resistance (APR) to the 2 rust diseases. Using marker information available from existing linkage maps, we have identified additional markers associated with resistance to these 2 diseases and established several linkage groups in the 'Avocet S' x 'Pavon76' population. The putative loci identified on chromosomes 1BL, 4BL, and 6AL influenced resistance to both stripe and leaf rust. The loci on chromosomes 3BS and 6BL had significant effects only on stripe rust, whereas another locus, characterized by AFLP markers, had minor effects on leaf rust only. Data derived from Interval mapping indicated that the loci identified explained 53% of the total phenotypic variation (R2) for stripe rust and 57% for leaf rust averaged across 3 sets of field data. A single chromosome recombinant line population segregating for chromosome 1B was used to map Lr46/Yr29 as a single Mendelian locus. Characterization of slow-rusting genes for leaf and stripe rust in improved wheat germplasm would enable wheat breeders to combine these additional loci with known slow-rusting loci to generate wheat cultivars with higher levels of slow-rusting resistance.

Assuntos

Basidiomycota/patogenicidade , Triticum/genética , Triticum/microbiologia , Mapeamento Cromossômico , Cromossomos de Plantas/genética , Cruzamentos Genéticos , Genes de Plantas , Marcadores Genéticos , Escore Lod , Fenótipo , Doenças das Plantas/genética , Doenças das Plantas/microbiologia , Locos de Características Quantitativas

RESUMO

Resistance based on slow-rusting genes has proven to be a useful strategy to develop wheat cultivars with durable resistance to rust diseases in wheat. However this type of resistance is often difficult to incorporate into a single genetic background due to the polygenic and additive nature of the genes involved. Therefore, markers, both molecular and phenotypic, are useful tools to facilitate the use of this type of resistance in wheat breeding programs. We have used field assays to score for both leaf and yellow rust in an Avocet-YrA x Attila population that segregates for several slow-rusting leaf and yellow rust resistance genes. This population was analyzed with the AFLP technique and the slow-rusting resistance locus Lr46/Yr29 was identified. A common set of AFLP and SSR markers linked to the Lr46/Yr29 locus was identified and validated in other recombinant inbred families developed from single chromosome recombinant populations that segregated for Lr46. These populations segregated for leaf tip necrosis (LTN) in the field, a trait that had previously been associated with Lr34/Yr18. We show that LTN is also pleiotropic or closely linked to the Lr46/Yr29 locus and suggest that a new Ltn gene designation should be given to this locus, in addition to the one that already exists for Lr34/Yr18. Coincidentally, members of a small gene family encoding beta-1 proteasome subunits located on group 1L and 7S chromosomes implicated in plant defense were linked to the Lr34/Yr18 and Lr46/Yr29 loci.

Assuntos

Basidiomycota/patogenicidade , Genes de Plantas , Imunidade Inata/genética , Doenças das Plantas/microbiologia , Folhas de Planta/microbiologia , Complexo de Endopeptidases do Proteassoma/análise , Mapeamento Cromossômico , Cromossomos de Plantas , Cruzamentos Genéticos , DNA de Plantas/isolamento & purificação , Etiquetas de Sequências Expressas , Marcadores Genéticos , Repetições de Microssatélites , Necrose/patologia , Doenças das Plantas/genética , Polimorfismo Conformacional de Fita Simples , Complexo de Endopeptidases do Proteassoma/química , Complexo de Endopeptidases do Proteassoma/genética , Locos de Características Quantitativas , Técnica de Amplificação ao Acaso de DNA Polimórfico

RESUMO

Durum wheat (Triticum turgidum var. durum) is the main irrigated winter crop in northwestern Mexico. Historically, leaf rust, caused by Puccinia triticina, had not induced significant losses to durum production in the area until 2001. That year, a new race, designated as BBG/BN, was detected that caused the most widely grown cultivar, Altar C84, which had remained resistant for 16 years, to become susceptible. Other recommended cultivars also became either moderately susceptible or susceptible. Detailed characterization of avirulence/virulence characteristics on Lr genes indicated that this race possibly did not evolve from the older races, but may have been introduced. Rust epidemics during the 2000-2001, 2001-2002, and 2002-2003 crop seasons have caused estimated losses of at least US$32 million. Although a majority of cultivars from 31 different countries, including the United States and Canada, and most of CIMMYT's durum wheat germ plasm were highly susceptible, diversity for both race-specific resistance and moderate levels of slow rusting resistance were identified. Jupare C2001, a resistant cultivar released in 2001, showed high levels of resistance and negligible losses in grain yield in a trial where Altar C84 suffered over 27% losses.

RESUMO

Leaf rust, caused by Puccinia triticina, is an important disease of wheat (Triticum aestivum) in China. Sixty-one spring and 102 facultative or winter growth habit wheat cultivars from China and a set of testers, carrying named Lr genes, were evaluated for resistance at the seedling growth stage with an array of Mexican Puccinia triticina races. Variation in seedling infection types of the cultivars was compared with that of the testers, and genes conferring low infection types were postulated. In total, nine named genes, Lr1 (in 13 cultivars), Lr3 (12), Lr3bg (2), Lr10 (1), Lr13 (4), Lr14a (1), Lr16 (49), Lr23 (9), and Lr26 (81), were identified. Thirty-one cultivars displayed intermediate reactions to one or more races that could not be attributed to any named gene. Twenty-eight spring cultivars were also evaluated at two field sites in Mexico using two common races. About half of them displayed good to moderate adult resistance that may be partly due to the presence of slow rusting gene Lr34 in at least seven cultivars. Diversity in adult plant responses of these wheats indicated the presence of additional slow rusting genes. Presence of 1B.1R translocation in 12 wheat cultivars, supposedly derived from intergeneric crosses involving T. durum, Haynaldia villosa, and Avena fatua, indicated that their pedigrees were incorrect.

RESUMO

Breeding for resistance to rust diseases in wheat is an example of productivity maintenance research. Productivity maintenance research is necessary to avoid contractions in the wheat supply curve that result from changes in the biological or physical environment. In this study, the benefits of incorporating nonspecific resistance to leaf rust caused by Puccinia recondita into modern bread wheats (Triticum aestivum) have been estimated using data on resistance genes identified in cultivars, trial data, and area sown to cultivar in the Yaqui Valley, Sonora State, Mexico. In the most pessimistic scenario, the gross benefits generated in the Yaqui Valley from 1970 to 1990 were 17 million U.S. dollars (in 1994 real terms). Even when costs were overstated and benefits were understated, the internal rate of return on capital invested was 13%, well within the range recommended for use in project evaluations by the World Bank. Substantial economic benefits likely are associated with deployment of nonspecific resistance in many wheat-producing areas of developing countries where farmers change cultivars slowly because of delays in cultivar release, incomplete seed markets, and economic factors related to adoption or where disease pressure is heavy and the costs of treating disease outbreaks is high.

RESUMO

A study of spring bread wheat (Triticum aestivum) germ plasm developed at the International Maize and Wheat Improvement Center (CIMMYT) showed highly significant phenotypic variability for each component of partial resistance (namely, uredial appearance period, latency period, uredial number and uredial size) to Puccinia recondita f. sp. tritici. All of the wheat genotypes displayed longer uredial appearance and latency periods and decreased uredial number and uredial size when compared to the susceptible check cultivar 'Morocco'. Positive correlations between uredial appearance period and latency period, and uredial number and uredial size, and negative correlations between uredial appearance and latency periods and uredial number and uredial size, inclusive, suggested that the components of partial resistance were either tightly linked or under pleiotropic genetic control. Compared to 'Morocco', all entries had slow disease progress in the field and variation occurred in the germ plasm for the area under the leaf rust progress curve. Disease progress was negatively correlated with uredial appearance and latency periods, whereas a positive correlation was observed with uredial number and uredial size. Certain genotypes displayed high levels of partial resistance resulting in low disease incidence in the field.