Tall fescue (Festuca arundinacea Schreb), a predominant cool-season perennial grass, is widely used as forage and turf grasses in China. In July 2013, powdery mildew was observed on 10 F. arundinacea lawns (about 0.5 ha in total) in Urumchi, Xinjiang Province, China, with 20 to 30% of the area being infected. Signs of the disease initially appeared as irregular white mycelial colonies on the adaxial surface of infected leaves. As the disease progressed, the colonies covered the whole adaxial surface and white patches appeared on the abaxial surface of infected leaves. Conidiophores were unbranched and cylindrical with swollen bases, measuring 13.3 to 15 × 16.7 to 20 μm, and borne vertically on hyphae. Each conidiophore produced 10 to 18 conidia in a chain. The conidia were oval, one-celled, and colorless, measuring 8.1 to 9.8 × 26 to 29.7 μm. Cleistothecia were black, spherical, and 164.3 to 207.3 μm in diameter, each of which contained 9 to 26 asci. Asci were oblong or ovate, measuring 32.1 to 40 × 85.7 to 96.4 μm. Asci were petiolate, containing eight ascospores. Ascospores were round to oval, colorless, one-celled, measuring 19.1 to 22.5 × 11.7 to 13.6 μm. Based on morphological characteristics of the anamorph and the teleomorph, the fungus was identified as Blumeria graminis (DC.) Speer. Additionally, the internal transcribed spacer (ITS) of 563 bp was amplified from DNA of conidia using ITS1 and ITS4 primers (4). The ITS sequence was deposited in GenBank (Accession No. KF545644). The ITS sequence showed 100% homogeneity with those of B. graminis on Poa pratensis in Swizerland (AB273540) and on P. bulbosa in Iran (AB273551) (1), which further confirmed the identification. Ten 3-week-old healthy plants were inoculated by spraying a spore suspension (1 × 105 conidia ml−1) made from conidia brushed from infected plants, and 10 plants sprayed with sterile distilled water were served as controls. All the plants were placed in the same growth chamber at 20°C, 80% humidity, and 16-h photoperiod. Twenty days after inoculation, typical signs and symptoms of powdery mildew were observed on all the inoculated plants, whereas no symptoms were observed on the controls. Microscopic and ITS analysis showed that the fungus on the inoculated plants is identical to that on diseased field plants. B. graminis on F. arundinacea has been observed in a few European countries (1), Israel (3), and the United States (2). To our knowledge, this is the first report of powdery mildew caused by B. graminis on F. arundinacea in China, which will increase the difficulty to prevent powdery mildew on grasses including cereals. References: (1) U. Braun. The Powdery Mildews (Erysiphales) of Europe. Gustav Fischer Verlag, Jena-Stuttgart-New York, 1995. (2) F. M. Dugan and G. Newcombe. Pacific Northwest Fungi. 2:1-5, 2007. (3) S. O. Voytyuk et al. Biodiversity of the Powdery Mildew Fungi (Erysiphales, Ascomycota) of Israel Vol. 7. Biodiversity of Cyanoprocaryotes, Algae and Fungi of Israel. Koeltz Scientific Books, 2009. (4) T. J. White et al. Page 315 in: PCR Protocols: A Guide to Methods and Applications. M. A. Innis et al., eds. Academic Press, San Diego, 1990.
Carrot (Daucus carota) is an important root vegetable crop in China, which accounted for 46% of global production in 2011. Carrot was grown in Henan Province on >20,000 ha/year, which ranks first in China for area of carrots harvested. In October 2012, a powdery mildew outbreak was observed in 16 investigated carrot production fields in Zhoukou, Henan Province, in central China. White colonies typical of powdery mildew were seen on leaves of affected plants. The colonies enlarged and finally coalesced. Small, scattered fruiting bodies found on the adaxial and abaxial leaf surfaces were determined microscopically to be chasmothecia. Examining the pathogen morphologically revealed that appressoria were lobed, conidiophores were straight and bore single conidia, and cylindrical foot cells were followed by one to three shorter cells in the conidiophores. Conidiophores were subhyaline and 54.1 to 66.1 × 6.1 to 8.1 μm. Conidia were barrel-cylindrical and 28.8 to 38.6 × 11.4 to 14.8 μm. Chasmothecia were subspherical, dark brown to black, formed hyphoid appendages, and 110 to 122 μm in diameter. Appendages typically had one to five branches, which were nearly dichotomous or irregular, flexuous or almost straight, and 30 to 165 μm long. Each chasmothecium contained multiple asci that were saccate, multiguttulate, short-stipitate or not, 62.5 to 63.8 × 43.2 to 45.9 μm, and each contained two to six ascospores. Ascospores were subhyaline, ovoid to ellipsoid, and 16.5 to 17.7 × 11.2 to 12.7 μm. Based on characteristics of the anamorphic and teleomorphic stages, the fungus was identified as Erysiphe heraclei (2,4). To verify the identity, the internal transcribed spacer (ITS) region of ribosomal DNA was amplified with universal primers ITS1 and ITS4, and sequenced. The ITS sequence was assigned GenBank Accession No. KC480605, and showed 100% similarity to ITS sequences of E. heraclei on carrot in GenBank (EU371725 and GU252368). Koch's postulates were completed by using detached infected leaves from 10-week-old carrot plants growing in a field to inoculate 10 healthy, 5-week-old plants of the carrot cultivar Dinghong, growing in a growth chamber under 22/16°C (day/night) cycle at 50% relative humidity with 120 μmol/m2/s light and a 14-h photoperiod. Ten non-inoculated plants served as replicates of a control treatment. Symptoms consistent with those in the field were observed on inoculated plants 20 days post-inoculation. No symptoms were observed on the control plants. Microscopic observation of the pathogen growing on the inoculated plants revealed that it was the same as the original fungus. Powdery mildew on carrot has been observed in many countries including Australia (1), Mexico (3), and the United States (2). To our knowledge, this is the first report of E. heraclei infection on carrot in central China, a major region of carrot production, although the disease has previously been observed in northwestern China (4). Further research should help to reduce losses in carrot crops caused by E. heraclei in central China. References: (1) J. H. Cunnington et al. Australas. Plant Dis. Notes 3:38, 2008. (2) D. A. Glawe et al. Plant Health Progress doi: 10.1094/PHP-2005-0114-01-HN, 2005. (3) G. Rodríguez-Alvarado et al. Plant Dis. 94:483, 2010. (4) R. Zheng and G. Chen. Pp. 97-99 in: Flora Fungorum Sinicorum Vol. 1. Erysiphales. R. Zheng et al., eds. Science Press, Beijing, 1987.
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