First Detection of Virulence in Puccinia triticina to Resistance Genes Lr27 + Lr31 Present in Durum Wheat in Mexico.

Leaf rust caused by Puccinia triticina Eriks. was observed during the 2007-2008 crop season in the state of Sonora, Mexico on previously resistant durum wheat (Triticum turgidum L.) cvs. Jupare C2001 (Lr27 + 31) and Banamichi C2004. Single uredinial isolates were made from disease samples collected in the field and tested mostly on 'Thatcher' differentials at seedling or adult-plant stages (1). The isolates were identified as a new race, BBG/BP, resembling race BBG/BN predominant on durum wheat (2), but with additional virulences to resistance genes Lr27 + Lr31 in Gatcher and adult-plant resistance gene Lr12. The new race was also identified in samples collected from durum wheat in the State of Nuevo Leon during the same season. The avirulence/virulence formula of race BBG/BP is Lr1, 2a, 2b, 2c, 3, 3ka, 3bg, 9, 13, 14a, 15, 16, 17, 18, 19, 21, 22a, 24, 25, 26, 28, 29, 30, 32, 35, 37/Lr10, 11, 12, 14b, 20, 23, 27 + 31, 33. Although virulences to Lr27 + Lr31 and Lr12 is known to occur in P. triticina races predominant on bread wheat (T. aestivum L.) (1), to our knowledge, this is the first report of such virulences in the pathogen population on durum wheat. Pure isolates of race BBG/BP are stored in the CIMMYT leaf rust collection. References: (1) R. P. Singh. Plant Dis. 75:790, 1991. (2) R. P. Singh et al. Plant Dis. 88:703, 2004.

First Report of Ramularia cercosporelloides on Carthamus tinctorius in Northwestern Mexico.

Severe yield losses caused by an unidentified fungal disease occurred on safflower in Sonora, Mexico from 2001 to 2006. Leaf spots were pale at the beginning and became sunken lesions, spots turned brown, and diseased tissue became necrotic. Under continuous presence of dew, new infections occurred and the number of lesions increased, coalesced, and eventually the entire leaf and plant turned brown and dried up. The fungus appears as a whitish mold covering the lesions. Observations with a dissecting microscope revealed fungal growth on both leaf surfaces. Spots had minute, gray-to-pink tufts emerging from the host tissues. Stromata were roughly spherical, 35 to 55 µm in diameter, developed under the epidermis near the edge of the spots from which conidiophores arose. Fascicles of conidiophores emerged through stomata from colorless or slightly yellowish stroma and were simple, colorless, or slightly yellowish, as much as 85 µm long and 2.5 to 3 µm wide, with a pigmented scar at the tip. Conidia, formed in chains at scar sites on conidiophores, were colorless, obclavate, 0 to 1 septate, approximately 24 to 32 µm long, and 4.5 to 7 µm wide at the broadest part with a pigmented scar either at the base or at both ends. On the basis of symptoms and fungal morphology, the pathogen was identified as Ramularia cercosporelloides U. Braun & Crous (=Cercosporella carthami) (1). Seven specimens were deposited at the Uppsala University Herbarium as Nos. UPS F-119998 to 120004. Conidia were transferred to water agar plates from symptomatic leaves after 8 days in a humid chamber. Ten single conidia were plated onto a Septoria tritici medium (4 g each of malt extract, yeast extract, and sucrose, and 18 g of agar per liter of water). Colonies of the fungus were white-to-light pink with irregular margins and very slow in growth. Inoculum was produced by transferring 2 ml of distilled water containing conidia onto petri plates filled with Septoria medium. Plates were incubated at 18°C for 12 days. Water suspension was amended with two drops of Tween 20 per liter of inoculum. Pathogenicity of five isolates was confirmed by spraying a suspension of 1.0 × 105 conidia/ml onto five pots of four direct-seeded adult plants of cv. S-518 per isolate. Plants were kept in a dew chamber (20°C) for 48 h under 16 h of darkness and 8 h of light and then in a greenhouse (20 to 24°C). After 2 weeks, leaves developed the characteristic spots, and R. cercosporelloides was isolated from symptomatic tissue. To our knowledge, this is the first report of R. cercosporelloides on safflower, not only in Mexico, but also on the American continent. Reference: (1) U. Braun. A monograph of Cercosporella, Ramularia and allied genera (Phytopathogenic Hyphomycetes). Vol 2. IHW-Verlag. Eching bei Munchen, 1998.

Genomic prediction models for grain yield of spring bread wheat in diverse agro-ecological zones.

Genomic and pedigree predictions for grain yield and agronomic traits were carried out using high density molecular data on a set of 803 spring wheat lines that were evaluated in 5 sites characterized by several environmental co-variables. Seven statistical models were tested using two random cross-validations schemes. Two other prediction problems were studied, namely predicting the lines' performance at one site with another (pairwise-site) and at untested sites (leave-one-site-out). Grain yield ranged from 3.7 to 9.0 t ha(-1) across sites. The best predictability was observed when genotypic and pedigree data were included in the models and their interaction with sites and the environmental co-variables. The leave-one-site-out increased average prediction accuracy over pairwise-site for all the traits, specifically from 0.27 to 0.36 for grain yield. Days to anthesis, maturity, and plant height predictions had high heritability and gave the highest accuracy for prediction models. Genomic and pedigree models coupled with environmental co-variables gave high prediction accuracy due to high genetic correlation between sites. This study provides an example of model prediction considering climate data along-with genomic and pedigree information. Such comprehensive models can be used to achieve rapid enhancement of wheat yield enhancement in current and future climate change scenario.

Occurrence and Impact of a New Leaf Rust Race on Durum Wheat in Northwestern Mexico from 2001 to 2003.

Durum wheat (Triticum turgidum var. durum) is the main irrigated winter crop in northwestern Mexico. Historically, leaf rust, caused by Puccinia triticina, had not induced significant losses to durum production in the area until 2001. That year, a new race, designated as BBG/BN, was detected that caused the most widely grown cultivar, Altar C84, which had remained resistant for 16 years, to become susceptible. Other recommended cultivars also became either moderately susceptible or susceptible. Detailed characterization of avirulence/virulence characteristics on Lr genes indicated that this race possibly did not evolve from the older races, but may have been introduced. Rust epidemics during the 2000-2001, 2001-2002, and 2002-2003 crop seasons have caused estimated losses of at least US$32 million. Although a majority of cultivars from 31 different countries, including the United States and Canada, and most of CIMMYT's durum wheat germ plasm were highly susceptible, diversity for both race-specific resistance and moderate levels of slow rusting resistance were identified. Jupare C2001, a resistant cultivar released in 2001, showed high levels of resistance and negligible losses in grain yield in a trial where Altar C84 suffered over 27% losses.