Research Highlights of the CIMMYT Wheat Program 1999-2000

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environments with strong disease pressure, in particular rusts, it is important to alternate screening under BYD pressure with other diseases, such as leaf and stem rusts (Cd. Obregon) and yellow rust (Toluca). We have obtained a set of 19 lines (Table 3) combining BYDV resistance and (apparently) a certain level of tolerance. Tolerance to BYD in wheat is polygenic in nature, based on the action of minor genes. It is more important to have uniform infection when selecting for minor gene resistance than for major gene resistance (Qualset, 1984). In crosses with Th. intermediumderived material, escape from infection is more common than in susceptible wheat, resulting in non-uniform infection. A sensitive plant might be rated as tolerant if it did not get infected. To minimize the error due to the escape mechanism and because BYD expression is strongly associated with the environment, it is important to confirm the tolerance identified in this work through another cycle of testing. The molecular marker gwm37 has proven to be a reliable tool for incorporating BYDV resistance, accelerating the process, and reducing the need for continuous testing under BYDV infection. This marker has been used successfully in selecting other populations, such as backcrosses with tolerant BYD germplasm. Table 3. List of F6 lines carrying both resistance and tolerance to BYDV. Pedigree TC14/2*HTG//HUITES TC14/2*HTG//HUITES TC14/2*HTG//HUITES TC14/2*HTG//HUITES TC14/2*HTG//HUITES TC14/2*HTG//HUITES TC14/2*HTG//HUITES TC14/2*HTG//TRAP#1/BOW TC14/2*HTG/3/VEE/PJN//2*TUI TC14/2*HTG/3/VEE/PJN//2*TUI TC14/2*HTG/3/VEE/PJN//2*TUI TC14/2*SPEAR//HUITES TC14/2*SPEAR//MILAN TC14/2*SPEAR//MILAN TC14/2*SPEAR//MILAN TC14/2*SPEAR//MILAN TC14/2*SPEAR/3/BOW/URES//KEA TC14/2*SPEAR/3/BOW/URES//KEA TC14/2*SPEAR/3/BOW/URES//KEA Selection history CMSS97M00087S-030M-020Y-10BYB-010Y CMSS97M00087S-030M-020Y-11M-010Y CMSS97M00087S-030M-020Y-13BYB-010Y CMSS97M00087S-030M-020Y-17M-010Y CMSS97M00087S-030M-020Y-3BYB-010Y CMSS97M00087S-030M-020Y-5BYB-010Y CMSS97M00115S-030M-020Y-22BYB-010Y CMSS97M00095S-030M-020Y-12M-010Y CMSS97M00089S-030M-020Y-10M-010Y CMSS97M00089S-030M-020Y-1BYB-010Y CMSS97M00089S-030M-020Y-5BYB-010Y CMSS97M00115S-030M-020Y-16BYB-010Y CMSS97M00168S-030M-020Y-12M-010Y CMSS97M00168S-030M-020Y-16M-010Y CMSS97M00168S-030M-020Y-1BYB-010Y CMSS97M00168S-030M-020Y-3BYB-010Y CMSS97M00151S-030M-020Y-10M-010Y CMSS97M00151S-030M-020Y-14M-010Y CMSS97M00151S-030M-020Y-1M-010Y References Ayala, L., Khairallah, M., González-de-Leon, D., van Ginkel, M., Mujeeb-Kazi, A., Keller, B., and Henry, M. 2001. Identification and use of molecular markers to detect barley yellow dwarf virus resistance derived from Th. intermedium in bread wheat. Theoretical and Applied Genetics (in press). Banks, P.M., Larkin, P.J., Bariana, H.S., Lagudah, E.S., Appels, R., Waterhouse, P.M., Brettell, R.I.S., Chen, X., Xu, H.J., Xin, Z.Y., Qian, Y.T., Zhou, X.M., Cheng, Z.M., and Zhou, G.H. 1995. The use of cell culture for subchromosomal introgressions of barley yellow dwarf virus resistance from Thinopyrum intermedium to wheat. Genome 38:395-405. Burnett P.A., Comeau, A., and Qualset, C.O. 1995. Host plant tolerance or resistance for control of barley yellow dwarf. In: Barley yellow dwarf: 40 years of progress. D’Arcy, C.J., Burnett, P.A. (eds.). St. Paul, MN, USA: APS Press. pp. 321-343. Cooper, J.I., and Jones, A.T. 1983. Responses of plants to viruses: Proposals for the use of terms. Phytopathology 73:127-128. Henry, M. 1997. Evaluation of resistance to BYDV in Thinopyrum intermedium translocated lines. In: Barley Yellow Dwarf Newsletter. No. 6. Henry, M. (ed.). Mexico, D.F.: CIMMYT. p 8. Henry, M., and Segura, J. 1999. Estimation of yield losses due to BYDV in wheat under artificial inoculation. Phytopathology 89:S33. Hohmann, U., Badaeva, K., Bush, W., Friebe, B., and Gill, B.S. 1996. Molecular cytogenetic analysis of Agropyron chromatin specifying resistance to barley yellow dwarf virus in wheat. Genome 39:336-347. Qualset, C.O. 1984. Evaluation and breeding methods for barley yellow dwarf resistance. In: Barley Yellow Dwarf. A Proceedings of the Workshop. P. Burnett (ed.). Mexico, D.F.: CIMMYT. pp. 72-82. Waterhouse, P.M., Gildow, F.E., and Johnstone, G.R. 1988. Luteovirus group. C.M.I./ A.A.B. Description of plant viruses 339. Zadoks, J.C., Chang, T.T., and Konzak, C.F. 1974. A decimal code for the growth stages of cereals. Weed Research 14:415-421. 44
Durable Resistance to Yellow (Stripe) Rust in Wheat R.P. Singh, S. Rajaram, J. Huerta-Espino, and M. William Yellow (or stripe) rust, caused by Puccinia striiformis tritici, is an important disease of wheat in most cool wheat-producing regions. Using resistant cultivars is the best disease control strategy, since it comes at no extra cost to the farmer and is environmentally safe. Historically, race-specific major genes have been used to breed rust resistant wheat cultivars. At present 30 resistance genes have been catalogued (McIntosh et al., 1998). Most are race-specific in nature, and virulence for several of them has been identified somewhere in the world. One of the main objectives of CIMMYT’s wheat improvement program is to generate genetically diverse germplasm that has high yield potential, wide adaptation, and durable resistance to important diseases such as the rusts. Durable resistance as defined by Johnson (1978) is one that has remained effective in a cultivar during its widespread cultivation for a long sequence of generations or period of time in an environment favorable to a disease or pest. Johnson (1978; 1988) described the presence of durable resistance in some European wheat cultivars and indicated that such resistance is quantitative in nature. The moderate level of adult plant resistance of CIMMYT-derived North American cultivar ‘Anza’ and good level of resistance in Mexican cultivar ‘Pavon 76’ have shown durability (Rajaram et al., 1988). During the early 1990s research was initiated to identify CIMMYT wheats that may carry durable resistance, understand the genetic basis of such resistance, and develop selection strategies to breed such resistance in newer CIMMYT wheats. Key knowledge developed during the last decade of research is summarized here. Yr18 and other minor genes for durable resistance to stripe rust Independent results obtained by Singh (1992) and McIntosh (1992) indicated that the moderate level of durable adult plant resistance in Anza and winter wheats such as Bezostaja is controlled in part by the Yr18 gene. Gene Yr18 is completely linked with gene Lr34, known to confer durable leaf rust resistance. The level of resistance it confers is usually not adequate when present alone. However, combinations of Yr18 and 2-4 additional slow rusting genes result in adequate resistance levels in most environments (Singh and Rajaram, 1994). Results of genetic analyses indicate that the level of resistance increases with the increase in the number of these genes that individually have minor to intermediate but additive effects. Cultivars carrying such Yr18 complexes are listed in Table 1. Genes Lr34 and Yr18 occur frequently in germplasm developed at CIMMYT and in various other countries. Using Jupateco 73 near-isogenic Table 1. Seedling susceptible bread wheats that carry good adult plant resistance to stripe rust in field trials in Mexico and other countries. Usual yellow Additive for Genotype(s) rust response 1 genes 2 resistance Jupateco 73S (check) 100 MS Moderately susceptible Jupateco 73R 50 M Yr18 Parula, Cook, Trap 15 M Yr18 + 2 genes Tonichi 81, Sonoita 81, Yaco 10 M Yr18 + 2 or 3 genes Chapio, Tukuru, Kukuna, Vivitsi 1 M Yr18 + 3 or 4 genes Amadina 30 M 3 genes Pavon 76, Attila 20 M 3 genes 1 The yellow rust response data from Mexico have two components: % severity based on the modified Cobb scale (Peterson et al., 1948) and reaction based on Roelfs et al. (1992). The reactions are M = moderately resistant to moderately susceptible, sporulating stripes with necrosis and chlorosis; and S = sporulating stripes without chlorosis or necrosis. 2 Minimum number estimated from genetic analysis. 45
Page 2 and 3: Research Highlights of the CIMMYT W
Page 4 and 5: Table of Contents New Conservation
Page 6 and 7: Foreword We are pleased to initiate
Page 8 and 9: Hobbs on the zero-till planters fro
Page 10 and 11: Burning is practiced due to a lack
Page 12 and 13: (0.64 million ha), and Bolivia (0.2
Page 14 and 15: New Bread Wheats for High Rainfall
Page 16 and 17: CIMMYT scientists have published on
Page 18 and 19: Taken together these data indicate
Page 20 and 21: Evaluating Advanced Materials Targe
Page 22 and 23: this may simply reflect a lack of v
Page 24 and 25: eleased in more than 30 countries u
Page 26 and 27: Parallel enhancement of yield compo
Page 28 and 29: Taken together, these factors sugge
Page 30 and 31: of improved seed and new technologi
Page 32 and 33: The high cost of hybrid seed is one
Page 34 and 35: Only a few cultivars performed well
Page 36 and 37: in CAC. In Turkey, the advantage ov
Page 38 and 39: ows, 2 m long). One plot was inocul
Page 40 and 41: Table 2. Wheat production statistic
Page 42 and 43: Based on farmers’ preferences, 12
Page 44 and 45: Global Monitoring of Wheat Rusts, a
Page 46 and 47: Monitoring nurseries The nurseries
Page 48 and 49: controlled by several QTLs with sma
Page 52 and 53: eselections, studies at CIMMYT have
Page 54 and 55: References Johnson, R. 1978. Practi
Page 56 and 57: spike. Interaction between Lr19 and
Page 58 and 59: variation in the trait. Both grain
Page 60 and 61: the variation in yield (Figure 2).
Page 62 and 63: References Amani, I., R.A. Fischer,
Page 64 and 65: in ECSA rely heavily on CIMMYT whea
Page 66 and 67: the pivotal role of Kulumsa in the
Page 68 and 69: Regional wheat quality classificati
Page 70 and 71: Table 5. Regional screening nurseri
Page 72 and 73: In 1992-93 the CIMMYT office in Tur
Page 74 and 75: In addition to shuttle breeding sev
Page 76 and 77: the CIMMYT wheat breeding program.
Page 78 and 79: Five participants thought the level
Page 80 and 81: 35. Skovmand, B.; López C., C.; S
Page 82 and 83: 94. Tanner, D.G. 1999. Principles a
Page 84 and 85: 182. Díaz de León, J.L.; Escoppin
Page 86 and 87: 258. Mujeeb-Kazi, A.; Delgado, R.;
Page 88: CIMMYT-Derived Bread Wheat, Durum W

Research Highlights of the CIMMYT Wheat Program 1999-2000

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