Genetic Analysis of Resistance to Stem Rust in Ten Durum Wheats

Singh, R. P., Bechere, E., and Abdalla, 0. 1992. Genetic analysis of resistance to stem rust in ten durum wheats. Phytopathology 82:919-922. Durum wheat (Triticum turgidum L.) cultivars derived from CIMMYT present in Mexicali 75, Diver, Somorguho, and Morus together with (International Maize and Wheat Improvement Center) germplasm are an unidentified gene, SrC, and in Altar 84, Carcomun, Totanus, and currently grown on more than 8 million ha worldwide. Because negligible Woodrail together with SrD. Kingfisher and eight other durums (except information is available on their genes for resistance to stem rust, crosses Woodrail) also possessed gene SrE, which conferred resistance to in a diallel arrangement (without reciprocals) were made among nine pathotype RTR, but not to GFC. Genes Sr9e and SrD conferred immune resistant CIMMYT-derived durums, and Kingfisher, which was susand high levels of adult plant resistance, respectively; Sr12 conferred only ceptible to one Mexican pathotype of Puccinia graminis f. sp. tritici. moderate levels of resistance, and SrC was ineffective under field condiParents, F, plants, F2 populations, and F3 lines were evaluated as seedlings tions despite its effectiveness at the seedling stage to the same pathotypes. in the greenhouse with two pathotypes and in the field with one pathotype. Because resistance was based on few genes, immediate measures are being Cultivar Yavaros 79 possibly carried Sr9e and Sr12, which were also undertaken to increase genetic diversity in CIMMYT germplasm. Durum wheat (Triticum turgidum L.) is currently grown on 9f,9g,15,17,21,28,34 and RTR: Sr7a,9e,J0,12,13,14,22,23,24,25, more than 21 million ha worldwide (15). High-yielding cultivars, 26,27,29,30,31,32,33,35/5,6,7b,8a,8b,9a,9b,9d,9f,9g, 11, derived from the CIMMYT germplasm, occupy approximately 15,17,21,28,34,36. These two pathotypes were selected because 40% of this area. Although the stem rust disease (caused by Singh (unpublished data) found that GFC occurred most Puccinia graminis Pers. f. sp. tritici Eriks & E. Henn.) is one frequently on durums and because RTR possesses the widest of the most important wheat diseases worldwide, there is only virulence range among pathotypes present in Mexico (13). limited information about the genetic basis of resistance to stem Seedlings of the parents were also evaluated with four additional rust in durum wheats. This is despite the fact that durable pathotypes, MCC, QFC, RKQ, and RTQ. Avirulence/virulence resistance to stem rust in bread wheats (T. aestivum L.) based formulae of these pathotypes are described in Singh (13). on the 'Sr2 gene complex' was transferred from emmer cultivar Crosses were made in a diallel arrangement without the Yaroslav by McFadden (3,6,7,10,11). Similarly, stem rust reciprocals. The inheritance studies were based on F1, F 2, and resistance from Khapli emmer (T. dicoccum L.) resulted in useful, individual F 2 plants derived F 3 lines. F, plants and approximately resistant bread wheats (1,4). Also, five durum wheats and two 100 plants of each F2 were evaluated only in the adult plant emmers were widely used as differentials for characterization of stage in the field with pathotype GFC. Eighty F 3 lines in crosses pathogenic variation in P. g. tritici (16). Recently, Bolat and Roelfs involving Kingfisher, and 50 lines in all other crosses, were (2) identified and isolated several genes present in these classified for their seedling reactions with pathotypes GFC and differentials. RTR, and for their adult plant field response with pathotype The current study was conducted to assess the degree of genetic GFC. Between 40 and 60 plants of each F 3 line were used in variability for stem rust resistance in CIMMYT durum wheat each test. Seedlings (8-9 days old) of the parents and F 3 lines germplasm using a selection of three released cultivars and six were inoculated by spraying urediospores suspended in a lightbreeding lines. weight mineral oil (Soltrol 170), placed in a dew chamber overnight at 18-20 C, and then transferred to a greenhouse. Unless otherwise MATERIALS AND METHODS mentioned, the greenhouse temperature was maintained at 18-20 C. The rust reaction data were recorded approximately Of the nine resistant durum cultivars included in the study, 2 wk after inoculation and were based on a 0-4 scale described Mexicali 75 (CIMMYT accession DW2158), Yavaros 79 by Stakman et al (16). (DW2159), and Altar 84 (DW2885) were released for cultivation The field evaluations were carried out at Ciudad Obregon in in Mexico and various other countries (under different names). northwestern Mexico. The plots of parents, F, plants and F3 The number following the name indicates the year of release, lines consisted of two 1-m rows seeded 20 cm apart with 70 cm e.g., Mexicali 75 was released for cultivation during 1975. The between plots. F 2 plants were space planted (15-20 cm between other six durums represent a set of recent high-yielding and stem plants) in paired rows of 11 m. The stem rust epiphytotic was rust-resistant breeding lines. These were Carcomun (DW2902), created by inoculating spreader rows of Kingfisher planted at Diver (DW5036), Somorguho (DW3014), Morus (DW5544), 20-row intervals. The adult plant stem rust responses were based Totanus (DW6822), and Woodrail (DW5509). The susceptible on the modified Cobb scale (9). parent was Kingfisher (DW6823). The F 3 seedling and adult plant data in the crosses involving The two Mexican-derived P. g. tritici pathotypes used in genetic Kingfisher were used in deriving the genotypes of the parental studies were GFC and RTR. The pathotypes' nomenclature is F2 plants. Chi-square analyses were carried out to test the based on that described by Roelfs and Martens (12). The avirudistribution of observed F2 genotypic frequencies with those lence/virulence formulae are GFC: Sr5,6,7a,7b,8b,9b,9e,10, expected for each cross. 11,12,13,14 , , 3 , , 5, 2 6,27,29,30,31,32,33,35,36/8a,9a,9d,