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Limon-Ortega A.,INIFAP CEVAMEX | Sayre K.,CIMMYT Cropping Systems Management
Agronomy Journal | Year: 2012

The planting system on permanent raised-beds for rainfed wheat (Triticum aestivum L.) production in the central highlands of Mexico is an option that needs to be documented for moderate-yield environments. Long-term plots were established under this technology in the 2002 crop season. The objective was to evaluate wheat grain yield performance as related to rainfall and soil characteristics until 2009. The experiment was conducted in rotation with maize (Zea mays L.) and monoculture. Four N rates were applied to wheat (0, 40, 80, and 120 kg ha-1) and three to maize (0, 60, and 120 kg ha-1). Nitrogen rates to the subsequent wheat crop were superimposed to each one of the preceding maize crop. Crop residues of both crops were left on the soil surface. Results showed that the amount of soil N measured as N-NO3 and N-NH4 was reduced during the first three seasons after the establishment of permanent beds. Although this reduction was substantial, stepwise regression procedures indicated that wheat grain yield was mostly determined by the amount of rainfall and distribution during the crop season, except for the 2009 season when the standard deviation of this measurement was larger. In addition to those N measurements, total soil N, available P, and exchangeable K had no effect on grain yield. The response of grain yield to N application rates >40 kg ha-1 was negligible for both crop rotations. In average, wheat grain yield in rotation was greater than wheat in monoculture. Grain yield reduction in monoculture resulted from fewer heads m-2. © 2012 by the American Society of Agronomy.

Singh R.P.,CIMMYT | Huerta-Espino J.,INIFAP CEVAMEX | Bhavani S.,CIMMYT | Herrera-Foessel S.A.,CIMMYT | And 7 more authors.
Euphytica | Year: 2011

Rust diseases continue to cause significant losses to wheat production worldwide. Although the life of effective race-specific resistance genes can be prolonged by using gene combinations, an alternative approach is to deploy varieties that posses adult plant resistance (APR) based on combinations of minor, slow rusting genes. When present alone, APR genes do not confer adequate resistance especially under high disease pressure; however, combinations of 4-5 such genes usually result in "near-immunity" or a high level of resistance. Although high diversity for APR occurs for all three rusts in improved germplasm, relatively few genes are characterized in detail. Breeding for APR to leaf rust and stripe rust in CIMMYT spring wheats was initiated in the early 1970s by crossing slow rusting parents that lacked effective race-specific resistance genes to prevalent pathogen populations and selecting plants in segregating populations under high disease pressure in field nurseries. Consequently most of the wheat germplasm distributed worldwide now possesses near-immunity or adequate levels of resistance. Some semidwarf wheats such as Kingbird, Pavon 76, Kiritati and Parula show high levels of APR to stem rust race Ug99 and its derivatives based on the Sr2-complex, or a combination of Sr2 with other uncharacterized slow rusting genes. These parents are being utilized in our crossing program and a Mexico-Kenya shuttle breeding scheme is used for selecting resistance to Ug99. High frequencies of lines with near-immunity to moderate levels of resistance are now emerging from these activities. After further yield trials and quality assessments these lines will be distributed internationally through the CIMMYT nursery system. © 2010 Springer Science+Business Media B.V.

Verhulst N.,International Maize and Wheat Improvement Center | Verhulst N.,Catholic University of Leuven | Kienle F.,Colegio de Mexico | Sayre K.D.,International Maize and Wheat Improvement Center | And 5 more authors.
Plant and Soil | Year: 2011

There is a clear need to develop conservation agriculture technologies appropriate for surface irrigated conditions, and the adoption by small-scale farmers. The objective of this paper is to evaluate the effect on soil quality of five different tillage-crop residue management systems (conventionally tilled raised beds [CTB] with residue incorporated and permanent raised beds [PB] with residue burned, removed, partly retained or fully retained). Data were collected in a long-term trial established in 1992 with a wheat-maize rotation under irrigated, arid conditions in north-western Mexico. Three groups of tillage-straw systems with different characteristics in relation to the soil environment were distinguished: PB-straw burned, CTB-straw incorporated, and PB-straw not burned. The PB-straw burned had high electrical conductivity, Na concentration and penetration resistance and low soil resilience and aggregation, showing that the combination of PB with the burning of residues is not a sustainable management option. The CTB-straw incorporated was distinguished from the PB practices by the soil physical variables, especially the low direct infiltration and aggregate stability, indicating degradation of physical soil quality in this system. The practice of PB, where all or part of the residue is retained in the field, seems to be the most sustainable option for this cropping system. © 2010 Springer Science+Business Media B.V.

Singh S.,International Maize and Wheat Improvement Center | Singh R.P.,International Maize and Wheat Improvement Center | Bhavani S.,International Maize and Wheat Improvement Center | Huerta-Espino J.,INIFAP CEVAMEX | And 2 more authors.
Theoretical and Applied Genetics | Year: 2013

Races of stem rust fungus pose a major threat to wheat production worldwide. We mapped adult plant resistance (APR) to Ug99 in 141 lines of a PBW343/Muu recombinant inbred lines (RILs) population by phenotyping them for three seasons at Njoro, Kenya in field trials and genotyping them with Diversity Arrays Technology (DArT) markers. Moderately susceptible parent PBW343 and APR parent Muu displayed mean stem rust severities of 66. 6 and 5 %, respectively. The mean disease severity of RILs ranged from 1 to 100 %, with an average of 23. 3 %. Variance components for stem rust severity were highly significant (p < 0. 001) for RILs and seasons and the heritability (h2) for the disease ranged between 0. 78 and 0. 89. Quantitative trait loci (QTL) analysis identified four consistent genomic regions on chromosomes 2BS, 3BS, 5BL, and 7AS; three contributed by Muu (QSr. cim-2BS, QSr. cim-3BS and QSr. cim-7AS) and one (QSr. cim-5BL) derived from PBW343. RILs with flanking markers for these QTLs had significantly lower severities than those lacking the markers, and combinations of QTLs had an additive effect, significantly enhancing APR. The QTL identified on chromosome 3BS mapped to the matching region as the known APR gene Sr2. Four additional QTLs on chromosomes 1D, 3A, 4B, and 6A reduced disease severity significantly at least once in three seasons. Our results show a complex nature of APR to stem rust where Sr2 and other minor slow rusting resistance genes can confer a higher level of resistance when present together. © 2013 Springer-Verlag Berlin Heidelberg.

Singh R.P.,CIMMYT | Herrera-Foessel S.,CIMMYT | Huerta-Espino J.,INIFAP CEVAMEX | Singh S.,CIMMYT | And 3 more authors.
Journal of Integrative Agriculture | Year: 2014

Wheat rusts continue to cause significant losses worldwide despite major efforts given to their genetic control. This is due to frequent evolution and selection of virulence in pathogen overcoming the deployed race-specific resistance genes. Although the life of effective race-specific resistance genes can be prolonged by using gene combinations, an alternative approach being implemented at CIMMYT is to deploy varieties that posses adult plant resistance (APR) based on combinations of minor, slow rusting genes. When present alone, the APR genes do not confer adequate resistance especially under high disease pressure; however, combinations of 4 or 5 minor genes usually result in "near-immunity" or a high level of resistance. Although only a few APR genes are catalogued, various APR QTLs are now known and could lead to further characterization of additional genes. Four characterized genes have pleiotropic effects in conferring partial APR to all 3 rusts and powdery mildew, thus simplifying the task of breeding wheat varieties that are resistant to multiple diseases. Significant progress was made recently in developing high-yielding wheat germplasm that possesses high levels of APR to all three rusts by implementing a Mexico-Kenya shuttle breeding scheme. Parents with APR to Ug99 were hybridized with high-yielding parents that had adequate to high levels of APR to leaf rust and yellow rust. Segregating populations and advanced lines from these crosses were selected under high rust pressures in Mexico (leaf rust and yellow rust) and Kenya (Ug99 stem rust and yellow rust) to identify high-yielding progenies that possess high to adequate APR to all three rusts. International distribution of these high-yielding wheats is underway through CIMMYT international yield trials and screening nurseries. It is expected that several wheat varieties with APR to three rusts will be released and grown in various countries in the near-future that will allow determining the durability of resistance. © 2014 Chinese Academy of Agricultural Sciences.

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