All BGRI Abstracts

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Progress in simultaneous selection for stable, high yielding, rust resistant wheat genotypes for Kenya

Macharia Kenya Agricultural and Livestock Research Organization, Kenya

In the past decade Pgt race Ug99 and its variants have been a challenge to wheat production in Kenya. Towards identifying suitable varieties, 37 lines selected from rust screening nurseries and 3 checks were tested for yield and adult plant reaction to natural stem rust epidemics across 11 diverse Kenyan environments in 2013 and 2014. Trial locations were chosen to mainly represent key wheat growing areas as well as three new sites. Evaluations based on the AMMI linear-bilinear model indicated significant (P≤0.01) genotype (G), environment (E), and GE interactions with the first three principal components (PC) explaining ~70% of the observed variation. With a contribution of over 90% to total sum of squares, environment was the predominant source of variation and the genotypic effect was approximately twofold higher than the GE effect. Based on biplot projections, clusters of lines were most closely associated with specific environments. Biplots also pointed to at least five environments, clearly those in traditional wheat growing areas that were highly correlated and associated with positive PC suggesting a similar ability to discriminate genotypes. Each non-traditional testing environment was associated with negative PC and was uncorrelated in its discriminatory ability. Combined yield and stability results achieved through classifying genotypes based on Shukla’s stability variance and Kang’s stability rating, revealed four genotypes (R1357, R1362, R1372, and R1374) as desirable candidates. The hitherto popular variety Robin, used as the ‘best check’ for yield, posted an at least 10% lower yield relative to the highest yielding genotype (R1357). Moreover, Robin which was released as a high yielding variety with adult plant resistance in 2009, was not stable in performance across environments, perhaps due its current susceptibility to a new Pgt race (TTKTT) within the race Ug99 group, that is virulent to the SrTmp-based resistance.

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Pst pathotypes and Yr gene postulation in Tunisian wheat

Hamza National Institute of Agronomy, Tunisia

Yellow rust is a widely distributed wheat disease, that is more damaging in cooler, temperate regions. Epidemics have increased worldwide due to spread of aggressive high temperature tolerant strains PstS1/S2 that reached North Africa and southern France in 2004 and the widely virulent exotic Warrior race that spread in Western Europe in 2011. Resistant varieties are effective solutions to reduce the use of pesticides. However, races of the pathogen quickly overcome resistance genes. Therefore, selection of varieties with durable resistance to yellow rust is paramount for protection of both bread wheat and durum. To conduct a genetic control strategy, it is essential to study the pathotype dynamics and the resistance genes in wheat. We identified the pathotypes using the European and world differential sets that discriminate between 23 avirulence/virulence factors as well as simple sequence repeat (SSR) diversity among 20 Pst isolates collected in Tunisia in 2014. In addition, we postulated resistance genes in 28 Tunisian varieties and accessions at the seedling stage in order to identify the resistance diversity. Race 239 E175V17 was involved in the 2014 epidemic in Tunisia. Genetic analysis revealed that this race is exotic and distinct from the Northwestern European and Mediterranean groups, previously present in Tunisia. Resistance gene postulation indicated the presence of Yr3, Yr6, Yr7, Yr9+Yr4, and Yr25 in Tunisian varieties and accessions. Durum varieties Khiar and Salim, and bread wheat variety Tahent, were resistant to the local Northwestern European and Western Mediterranean pathotypes as well as the Warrior race. These varieties are thus short-term measures to address the yellow rust problem in Tunisia. Gene identifications will be confirmed by molecular and pedigree analyses of the accessions.Yellow rust is a widely distributed wheat disease, that is more damaging in cooler, temperate regions. Epidemics have increased worldwide due to spread of aggressive high temperature tolerant strains PstS1/S2 that reached North Africa and southern France in 2004 and the widely virulent exotic Warrior race that spread in Western Europe in 2011. Resistant varieties are effective solutions to reduce the use of pesticides. However, races of the pathogen quickly overcome resistance genes. Therefore, selection of varieties with durable resistance to yellow rust is paramount for protection of both bread wheat and durum. To conduct a genetic control strategy, it is essential to study the pathotype dynamics and the resistance genes in wheat. We identified the pathotypes using the European and world differential sets that discriminate between 23 avirulence/virulence factors as well as simple sequence repeat (SSR) diversity among 20 Pst isolates collected in Tunisia in 2014. In addition, we postulated resistance genes in 28 Tunisian varieties and accessions at the seedling stage in order to identify the resistance diversity. Race 239 E175V17 was involved in the 2014 epidemic in Tunisia. Genetic analysis revealed that this race is exotic and distinct from the Northwestern European and Mediterranean groups, previously present in Tunisia. Resistance gene postulation indicated the presence of Yr3, Yr6, Yr7, Yr9+Yr4, and Yr25 in Tunisian varieties and accessions. Durum varieties Khiar and Salim, and bread wheat variety Tahent, were resistant to the local Northwestern European and Western Mediterranean pathotypes as well as the Warrior race. These varieties are thus short-term measures to address the yellow rust problem in Tunisia. Gene identifications will be confirmed by molecular and pedigree analyses of the accessions.

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Up scaling seed of Ug99 resistant wheat varieties to ensure protection against stem rust in Pakistan

Hussain International Maize and Wheat Improvement Center (CIMMYT) Pakistan Office

With ongoing threats of rust from both internal and international sources it has become a priority at CIMMYT and for Pakistan national programs to accelerate the rate of seed increase and to popularize new Pgt race Ug99 resistant varieties to avert future disasters. Seed of Ug99 resistant varieties NARC-11, Pak-2013, Dharabi-2011 and BARS-09 was produced under the Wheat Productivity Enhancement Program (WPEP). The country-wide participatory approach involves a partnership of farmers, seed companies and research institutes. In 2014 16,020 and 6,085 kg of seed of NARC-11 and Pak-13, respectively, were distributed all over the country, including Azad Jammu Kashmir and Gilgit-Baltistan. Comparative yields across Pakistan show that the rust resistant varieties are equal, or superior, to current stem rust susceptible varieties grown by farmers. Deployment and use of these varieties by farmers in Balochistan will have a significant impact not only on productivity, but may also avert the consequences of possible introduction of race Ug99.

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Leaf rust on high yielding winter wheats in Chile

Madariaga National Institute of Agricultural Research [INIA], Chile

The physical environment and farming system in Chile are conducive to high yields from winter/alternate wheat cultivars. The national average yields for 2012-2014 were 6.5 t/ha for pasta wheat and 5.3 t/ha for bread wheat grown on 19,000 and 239,000 ha, respectively. The most efficient farmers obtain averages of 8-9 t/ha, and experimental plots at southern INIA sites are as high as 14 t/ha. The most important diseases are Septoria leaf blotch, stripe rust, powdery mildew, and BYDV. Recent increases of leaf rust on winter cultivars from near non-existence to the level of a major threat are a concern. Wheat cultivars such as Bicentenario INIA showed yield increases of 31.7% to reach 12.4 t/ha yield when sprayed twice with a mixture of strobilurin and triazol compared to 9.4 t/ha for the unsprayed control. Susceptible winter cultivars being introduced by private companies require complete chemical protection. In order to understand the virulences present in the pathogen population the Thatcher NILs were grown in 2014/15 under non-inoculated conditions in central [Chillan] and southern [Osorno] Chile. The Morocco check showed 100S, Thatcher 60S, TcLr1 40S, TcLr2b 30S, TcLr2c 40S, TcLr3a 30S, TcLr3ka 20S, TcLr3bg 30S, TcLr9 20S, TcLr10 60S, TcLr11 80S, TcLr12 60S, TcLr13 70S, TcLr14a 70S, TcLr15 50S, TcLr16 60S, TcLr17a 30S, TcLr18 20MR, TcLr19 0, TcLr20 30S, TcLr21 0, TcLr22a 0, TcLr23 70S, TcLr24 60S, TcLr25 0, TcLr26 60S, Lr27+31 80S, TcLr28 10MR, TcLr29 40MS, TcLr30 60S, TcLr32 70S, TcLr33 60S, TcLr34 70S, TcLr35 10MR–MS, Lr36 0, and TcLr37 0. The most significant differences (>40%) in response between the two locations were for TcLr2b, TcLr2c, TcLr11 and TcLr33. The Cereal Disease Laboratory (U.S.A.) tested 68 isolates from 55 samples from 2012/13 and identified 14 races, including one Triticum turgidum race (BBBQJ 26%). Significant breeding efforts are currently underway to address the leaf rust problem in Chile.

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Rust surveillance in Tajikistan, 2011-2014

Otambekova Research Institute of Biotechnology, Tajik Agrarian University, Tajikistan

Wheat farmers in Tajikistan measure their success by harvesting higher grain yields. However, crop yields remain very low, and losses from pests and diseases are significant. In this regard, continuous monitoring and surveillance of crops for pests and diseases and identification of resistant varieties are important. During 2011 to 2014 FAO and CIMMYT provided support for crop surveillance to obtain an overview of the most severe diseases, insects, weeds and other constraints affecting cereal crop production. Leading Tajik wheat varieties were screened for resistance to major diseases under controlled conditions in Turkey. The outcomes of the surveys demonstrated that the most devastating leaf diseases of wheat in Tajikistan are yellow rust, leaf rust and occasionally stem rust. Yellow rust was present during spike formation and flowering in most wheat growing areas. Leaf rust developed later in the season and did not significantly affect yield. In 2013 yellow rust reached epidemic levels, especially in central and central-eastern parts of the country. Stem rust was occasionally observed at moderate levels in highland spring wheat areas (above 1,000 masl). Only three varieties screened in Turkey showed resistance to yellow rust; these included Ormon and Alex that originated from CIMMYT materials. However, the majority of currently grown varieties were susceptible. Seventeen of 43 varieties were resistant or displayed only trace levels of leaf rust. Wheat crops are also damaged by powdery mildew, tan spot, Septoria leaf blotch and seed-borne diseases such as common bunt and loose smut.

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