First Report of Leaf Spot Caused by Cercospora bizzozeriana on Hoary Cress in Russia.

Hoary cress (Lepidium draba (L.) subsp. draba (synonym = Cardaria draba (L.) Desv.) (1), family Brassicaceae, is a common weed in Russia but it is an aggressive invasive weed in the northwestern United States. In the summer of 2006, dying hoary cress plants were found near Kugoyeyskoye in the Krylovskoy area of the Krasnodar Region of Russia. Plants had grayish white leaf spots on most of the leaves. In some cases, the diseased leaf spots dropped out of the leaves producing shot-holes. In most cases, the leaf spots coalesced and the leaves wilted and died. Diseased leaves were collected, air dried, and sent to the quarantine facility of the Foreign Disease-Weed Science Research Unit (FDWSRU), USDA/ARS, Fort Detrick, MD. The air-dried leaves were observed microscopically, and numerous conidiophores and conidia were observed on both sides of leaves within and around the lesions. The fungus isolated (DB06-018) conformed to the description of Cercospora bizzozeriana Saccardo & Berlese (2). Conidiophores were 1 to 5 geniculate, unbranched, pale olive-brown, and uniform in color and width (4 µm). Conidia were multiseptate, hyaline, cylindric, straight to slightly curved, and measured 57 to 171 µm (average 103) long × 3.8 to 6.7 µm (average 4.6) wide. Leaves of rosettes (10 to 15 cm in diameter) of four hoary cress plants were spray inoculated with an aqueous suspension of conidia (1 × 105/ml) and mycelia harvested from 6- to 8-day-old cultures grown on V8 medium. Inoculated plants and two noninoculated plants were placed in a dew chamber at 20°C in darkness and continuous dew. After 96 h, plants were moved from the dew chamber to a greenhouse bench. All plants were watered twice daily. After 12 days, symptoms were observed on all inoculated plants. Symptoms were identical to those observed in the field in Russia. No symptoms were observed on noninoculated plants. C. bizzozeriana was reisolated from the leaves of all symptomatic plants. Nucleotide sequences were obtained for the internal transcribed spacer regions ITS1 and ITS2 and the 5.8S ribosomal RNA gene (GenBank Accession No. EU031780) and aligned with the same sequences obtained from another C. bizzozeriana isolate (GenBank Accession No. DQ370428) collected in Tunisia. There was 100% alignment of the two sequences with no gaps. Both isolates of C. bizzozeriana are destructive pathogens on hoary cress and locally severe epidemics have been observed in both Russia and Tunisia (4). This fungus has also been reported in North America (3) and has the potential as a biological control agent where the weed is a problem. To our knowledge, this is the first report of C. bizzozeriana on L. draba subsp. draba in Russia. A voucher specimen has been deposited with the U.S. National Fungus Collections (BPI 878175). Live cultures are being maintained at FDWSRU. References: (1) I. A. Al-Shehbaz and K. Mummenhoff. Novon 12:5, 2002. (2) C. Chupp. A Monograph of the Fungus Genus Cercospora. C. Chupp, Ithaca, New York, 1953. (3) I. L. Conners. Res. Bra. Can. Dep. Agric. 1251:1, 1967. (4) T. Souissi et al. Plant Dis. 89:206, 2005.

First Report of Leaf Spot Caused by Colletotrichum cf. linicola on Field Bindweed in Turkey.

Field bindweed (Convolvulus arvensis L., Convolvulaceae) is one of the most problematic weeds in the world (1) and a target of biological control efforts (2). In the summer of 2006, dying field bindweed plants were found in a wheat field near Bafra, Turkey (41°21.197'N, 36°12.524'E). Plants had water-soaked lesions that developed into necrotic leaf spots on most of the leaves, particularly along the leaf margins, and on some stems. In most cases, the leaf spots coalesced, causing the leaves and later plants to wilt and die. Diseased leaves and stems were taken to the Phytopathology Laboratory of the Faculty of Agriculture, Ondokuz Mayis University, Samsun, Turkey. Diseased tissue was surface disinfested and placed on moist filter paper in petri dishes. Numerous acervuli with setae and conidia typical of a Colletotrichum sp. were observed after 2 to 5 days. A fungus, designated 06-01, was isolated from the diseased leaves. Stems and leaves of seven 12-week-old plants were spray inoculated in the laboratory with an aqueous suspension of conidia (106 spores per ml; 10 ml per plant) harvested from 6- to 8-day-old cultures grown on malt extract agar. The plants and two noninoculated checks were placed in a dew chamber at 22°C in darkness and continuous dew. After 48 h, plants from the dew chamber were moved to a greenhouse bench. All plants were watered twice daily. Symptoms were observed 5 days after inoculation. No symptoms were observed on noninoculated plants. Isolate 06-01 was reisolated from all inoculated plants. In the field, 20 inoculated plants became diseased after 20 days with approximately 36% diseased leaf tissue from which 06-01 was consistently reisolated. Diseased tissue and cultures of the fungus were sent to the Foreign Disease-Weed Science Research Unit, USDA/ARS, Fort Detrick, MD. The fungus conformed to the description of Colletotrichum linicola Pethybr. & Laff., which was noted as distinct from C. lini (3). The original description is also different than the description of C. lini (Westerdijk) Tochinai by Sutton (4). Acervuli were sparse, subepidermal, and erumpent. Conidia were hyaline, oblong or cylindrical or somewhat spindle-shaped with dull-pointed ends, guttulate, and 14 to 19 × 4 to 5 µm (mean 17 × 4 µm). Conidiophores were short, simple, hyaline, and emerged from subepidermal stroma. Setae were simple, erect, 3-septate, and dark with hyaline tips. DNA sequences were obtained for the internal transcribed spacer regions (GenBank Accession No. EU000060) and compared with other sequences in GenBank. Sequences from 06-01 matched 100% with one isolate of C. linicola and 99% with two other isolates of C. linicola. These isolates formed a unique clade. However, 06-01 was also 99% identical to other species of Colletotrichum. Thus, species identification is inconclusive. Isolate 06-01 is a destructive pathogen on field bindweed, and severe disease can be produced by inoculation of foliage with an aqueous suspension of conidia. To our knowledge, this is the first report of Colletotrichum on field bindweed. A voucher specimen has been deposited with the U.S. National Fungus Collections (BPI 878174). References: (1) L. Holm et al. The World's Worst Weeds. University Hawaii Press, Honolulu, Hawaii, 1977. (2) G. Defago et al. BioControl 46:157, 2001. (3) G. H. Pethybridge and H. A. Lafferty. Sci. Proc. R. Dublin Soc. 15:359, 1918. (4) B. C. Sutton. The Coelomycetes. Commonw. Mycol. Inst., Kew, England, 1980.

Slender Wheatgrass is Susceptible to Smut Caused by Ustilago phrygica from Turkey.

Slender wheatgrass (Elymus trachycaulus (Link) Gould ex Shinners subsp. trachycaulus), family Poaceae, tribe Triticeae, is a native North American grass that is used as a livestock forage. Ustilago phrygica, a systemic ovary-smut fungus, is native to Turkey and West Asia and is pathogenic on Aegilops spp. and Taeniatherum caput-medusae (L.) Nevski subsp. asperum (Simonk.) Melderis (medusahead), an invasive weed in the western United States that is targeted for biological control. An isolate of the fungus (U.S. National Fungus Collections, BPI 871725; GenBank Accession No. DQ139961) was collected from medusahead in Turkey and screened for possible use in classical biological control of this weed. Screening was done in quarantine in a BSL-3 facility of the Foreign Disease-Weed Science Research Unit, USDA, ARS, Ft. Detrick, MD. The focus of screening was determination of host range of the fungus among related native and agriculturally important grasses in North America. A procedure was developed to consistently and quickly produce disease on medusahead and other grasses. Without vernalization, plants inoculated with U. phrygica will not produce smutted spikes (seedheads). Teliospores of the fungus were vacuum inoculated (1) onto caryopses (seeds) of medusahead and slender wheatgrass, which were then placed on moist germination paper in a petri dish or on moist vermiculite in plastic boxes. The dishes, sealed with Parafilm, and the boxes, covered with lids, were placed in a dark refrigerator at 3°C. After 8 weeks, all seedlings were transplanted into pots on a greenhouse bench at 22 to 25°C and 14 h light (photosynthetic photon flux density [PPFD] 620 µmol·s-1·m-2). The plants began to flower and produce smutted spikes 40 days later. These tests were repeated once. Fourteen of sixty medusahead plants from inoculated caryopses incubated on germination paper and nine of twenty-four plants from caryopses incubated on vermiculite became smutted and produced numerous smutted spikes per plant. Partial systemic infection was the norm, and all diseased plants had some spikes that were not diseased. One slender wheatgrass plant of nine plants grown from inoculated caryopses incubated on germination paper was also smutted and produced three diseased spikes. Nielsen (2) indicated susceptibility of slender wheatgrass to U. phrygica, but only as a single entry in a table under the synonym Agropyron trachycaulum (Link) Malte ex H. F. Lewis in a report on susceptibility of Aegilops spp. to U. phrygica. Because this is an obscure mention of the susceptibility of slender wheatgrass to U. phrygica, the fungus-host association does not explicitly appear in literature and is absent from relevant databases. Our tests with the fungus confirm that slender wheatgrass is susceptible to U. phrygica and lead us to conclude that the fungus would not be a good candidate for classical biological control of medusahead in North America. This formal report should establish this fungus-host association in literature and ensure reference in plant disease databases. References: (1) C. C. Allison. Univ. Minn. Agric. Exp. Stn. Tech. Bull. August:1, 1936. (2) J. Nielsen. Can. J. Bot. 70:581, 1992.

First Report of a Leaf Spot Caused by Cercospora bizzozeriana on Lepidium draba subsp. draba in Tunisia.

Lepidium draba (L.) subsp. draba (synonym = Cardaria draba (L.) Desv.), commonly known as white-top or hoary-cress (1), family Brassicaceae, is a common weed and emerging problem in wheat in Tunisia. It is also a problematic invasive weed in the northwestern United States and a target of biological control efforts. During the summer of 2002, dying L. draba plants were found around Tunis, Tunisia. Plants had grayish white leaf spots on most of the leaves. In some cases, the leaf spots dropped out of the leaves producing "shot-holes". In most cases, the leaf spots coalesced, and the leaves wilted and died. Diseased leaves were collected, air-dried, and sent to the quarantine facility of the Foreign Disease-Weed Science Research Unit (FDWSRU), USDA/ARS, Fort Detrick, MD. The air-dried leaves were observed microscopically, and numerous conidiophores and conidia were observed on both sides of the leaves within and around the lesions. The fungus isolated (DB03-009) conformed to the description of Cercospora bizzozeriana Saccardo & Berlese (2). Conidiophores were unbranched, pale olive-brown, 1 to 5 geniculate, and uniform in color and width. Conidia were hyaline, straight to slightly curved, multiseptate, and 57 to 171 × 3.8 to 6.7 µm (average 103 to 4.6 µm). Stems and leaves of 12 rosettes (10 to 15 cm in diameter) of 6-week-old L. draba plants were spray inoculated with an aqueous suspension of conidia (1 × 105/ml) harvested from 6- to 8-day-old cultures grown on carrot leaf decoction agar. Six of the plants and two noninoculated plants were placed in a dew chamber at 22°C in darkness and continuous dew. The other half of the plants and two noninoculated plants were placed on a greenhouse bench at approximately 25°C and covered with clear polyethylene bags. After 72 h, plants from the dew chamber were moved to a greenhouse bench, and the bagged plants were uncovered. All plants were watered twice daily. After 9 days, symptoms were observed on the plants that had been bagged but not on the plants from the dew chamber. Symptoms were identical to those observed in the field in Tunisia and included "shot holes". No symptoms were observed on noninoculated plants. C. bizzozeriana was reisolated from the leaves of all symptomatic plants. Completion of Koch's postulates was repeated with an additional five plants. This isolate of C. bizzozeriana is a destructive pathogen on L. draba subsp. draba, and severe disease can be produced by inoculation of foliage with an aqueous suspension of conidia. This isolate is a good candidate for mycoherbicide development in Tunisia where the weed and pathogen are indigenous. However, some commercially grown Brassica species were found susceptible to this isolate, which will preclude its use as a classical biological control agent in the United States. To our knowledge, this is the first report of C. bizzozeriana on L. draba subsp. draba in Tunisia. A voucher specimen has been deposited at the U.S. National Fungus Collections (BPI 843753). Live cultures are being maintained at FDWSRU and the Institut National Agronomique de Tunisie, Tunis, Tunisia. References: (1) I. A. Al-Shehbaz and K. Mummenhoff. Novon 12:5, 2002. (2) C. Chupp. A Monograph of the Fungus Genus Cercospora. C. Chupp, Ithaca, New York, 1953.

Estimating the Economic Impact of Breeding Nonspecific Resistance to Leaf Rust in Modern Bread Wheats.

Breeding for resistance to rust diseases in wheat is an example of productivity maintenance research. Productivity maintenance research is necessary to avoid contractions in the wheat supply curve that result from changes in the biological or physical environment. In this study, the benefits of incorporating nonspecific resistance to leaf rust caused by Puccinia recondita into modern bread wheats (Triticum aestivum) have been estimated using data on resistance genes identified in cultivars, trial data, and area sown to cultivar in the Yaqui Valley, Sonora State, Mexico. In the most pessimistic scenario, the gross benefits generated in the Yaqui Valley from 1970 to 1990 were 17 million U.S. dollars (in 1994 real terms). Even when costs were overstated and benefits were understated, the internal rate of return on capital invested was 13%, well within the range recommended for use in project evaluations by the World Bank. Substantial economic benefits likely are associated with deployment of nonspecific resistance in many wheat-producing areas of developing countries where farmers change cultivars slowly because of delays in cultivar release, incomplete seed markets, and economic factors related to adoption or where disease pressure is heavy and the costs of treating disease outbreaks is high.

Breeding disease-resistant wheats for tropical highlands and lowlands.

Wheat is grown on about 10 million ha in the tropical highlands and lowlands of the world, where it is an important food source. Many farmers in these areas work under subsistence conditions. Wheat diseases in tropical regions can be severe and require significant efforts to control. For economic and environmental reasons, host plant resistance is the most appropriate and sustainable disease control method. We describe highland and lowland tropical wheat regions and discuss CIMMYT's breeding strategies, philosophies, and progress in developing resistance to the major diseases such as rusts, foliar blights, fusarium scab, BYD, and spot blotch. Additionally, we review the role of national wheat research programs and beneficial spillovers of our combined breeding efforts to other wheat production areas of the world.