ABSTRACT
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.
ABSTRACT
In much of the world, resistance to stem rust in wheat, caused by Puccinia graminis f. sp. tritici, is based at least in part on the gene Sr31. During February 1999, high levels of stem rust infection were observed on entries in wheat (Triticum aestivum) grown in a nursery at Kalengyere Research Station in Uganda. Because several of the rusted entries were known to carry the 1BL-1RS chromosome translocation containing the Sr31, Lr26, and Yr9 genes for rust resistance, virulence to Sr31 was suspected. Urediniospores, collected in bulk from rusted stems of seven entries containing Sr31, were suspended in light mineral oil and sprayed on primary leaves of 7-day-old seedlings of South African wheat cv. Gamtoos (=Veery #3, pedigree: Kvz/Buho'S'//Kal/BB). Plants were kept overnight at 19 to 21°C in a dew chamber before placement in a greenhouse at 18 to 25°C. After ≈14 days, urediniospores were collected from large, susceptible-type stem rust pustules and subsequently increased on Gamtoos, which served as a selective host for the new rust culture, designated Pgt-Ug99. Pathogenicity of Pgt-Ug99 was studied in seedling tests of available wheats containing Sr31, as well as other stem rust differential lines. All seedling tests were conducted at least three times in independent inoculations. Isolate Pgt-Ug99 was not virulent to Avocet'S'/Yr9 (Australian line containing Sr26) or Oom Charl (South African cultivar) but was virulent to the other Sr31 testers: Alondra 'S', Bobwhite, Chokka, Clement, Federation/Kavkaz, Gamtoos, Grebe, Kavkaz, Letaba, Line E/Kavkaz, RL6078, and Veery 'S'. Virulence to Sr31 (infection types [ITs] 3-3 to 3++4) was clearly contrasted by the low reactions (ITs 0; to 1) produced by UVPgt53, a South African pathotype avirulent to Sr31. According to the reactions of the differential lines, Pgt-Ug99 is avirulent to Sr21, -22, -24, -25, -26, -27, -29, -32, -33, -34, -35, -36, -39, -40, -42, and -43, Agi, and Em and virulent to Sr5, -6, -7b, -8a, -8b, -9b, -9e, -9g, -11, -15, -17, -30, -31, and -38. Virulence to the T. ventricosum-derived gene Sr38, which is linked to Lr37 and Yr17 and occurs in cultivars from Australia, the United Kingdom, and the United States, was not known previously (1). Both Pgt-Ug99 and UVPgt53 produced a continuum of ITs (; to 2+3) on Petkus rye (obtained from the USDA-ARS National Small Grains Collection, Aberdeen, ID), the original Sr31 donor source. Pgt-Ug99 did not appear more virulent than UVPgt53 on Petkus. All triticales tested, as well as oat cv. Overberg, were highly resistant to Pgt-Ug99. According to McIntosh et al. (1), Huerta-Espino mentioned a Sr31-virulent culture from Turkey, but this could not be confirmed. Should the Sr31-virulent pathotype migrate out of Uganda, it poses a major threat to wheat production in countries where the leading cultivars have resistance based on this gene. Reference: (1) R. A. McIntosh et al. 1995. Wheat Rusts: An Atlas of Resistance Genes. Kluwer Academic Publishers, Dordrecht, the Netherlands.
ABSTRACT
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.
ABSTRACT
A simple laser-based instrument is described which produces output voltages proportional to displacements in orthogonal directions. This instrument and the associated experimental techniques have been used to measure biaxial displacements across 400-mum slots at various angles in sheet specimens of various widths.
