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Remarks (public):For a complete description including images see www.cababstractsplus.org/dfb 
Remarks (internal):The minutely echinulated outer surface of the spore distinguishes the loose smut pathogen from the covered smut pathogen, U. hordei (Pers.) Lagerh., which has smooth spores. The production of oat cvs. resistant to the pathogen was pioneered by Reed (20: 525; 21: 251, 367; 27: 180) and this work still continues in cereal breeding programmes. Cultural methods of control include early sowing of susceptible oat cvs. in spring as germination of infected seed at 7°C reduces disease incidence (max. at 0-2,5ºC) (37: 717). Seed treatments with volatile fungicides such as Ceresan L & M, Chipcote, Panogen and Ortho LM have given good control in U.S.A. with minimum damage to seedlings (48, 1659) and Vitavax has been reported to give complete protection in France (47, 1480; 48, 2872a, 2873). Hot water treatment is not considered commercially justified unless infection is >2% (46, 1176c; 47, 3406).
 
Description type:Non-original description 
Description:Ustilago avenae (Pers.) Rostr., Overs. K. danske Vidensk. Sesik. Forh. 1890, p. 13, 1890.
= Uredo segetum (Pers.) Ditmar subsp. avenae Pers., 1801.
= Reticularia segetum Bull., 1791, pro parte.
= Uredo segeTum e decipiens Wallr., 1815, fide Liro, 1924, pro parte.
= Ustilago decipiens (Wallr.) Liro, 1924.
= Uredo carbo DC., 1815, pro parte.
= Ustilago carbo (DC.) Tul., 1847, pro parte.
= Uredo auenae Corda, 1846.
= Ustilago segetum (Pers.) Ditmar, 1817
(as Ustilago segetum Link).
=Erysibe vera holci-avenacei Wallr., 1833, fide Ciferri.
= Ustilago holci-avenacei (Wallr.) Cifferi, 1938.
= Ustilago perennans Rostr., 1890, fide Fischer, 1943.
= Ustilago nigra Tapke, 1932, fide Fischer, 1943.
For further synonyms see Fischer, 1953; Zundel, 1953.
Sori in spikelets often completely destroying the ovaries, eventually becoming dissipated leaving the bare rachis; occasionallyon the leaves; spore mass powdery, dark greenish-brown. Spores spherical to subspherical, pale greenish-brown paler to oneside, minutely echinulate, 5-8 µm diam.Sporidial cultures may be obtained on potato-dextrose or potato-dextrose victor grain extract agar (Horton, 1932; Narain,1964).
Hosts: On species of Arrhenatherum, Avena, Hordeum. Also on Trisetum flavescens on inoculation (44, 3328).
Disease: Loose smut of oats, tall oat grass and barley. Characterized by abortion of the panicles which remain stunted, erect, compact, with the transformation of the ovary and glumes into a dark greenish-brown powdery spore mass. Seedlings may show necrotic lesions developing on the coleoptile and first leaf and may die at an early stage (15: 346). Lesions may also develop on the blade of the flag leaf producing spore masses (15: 358). Symptoms vary according to the pathogenic race and host cv. Sterile white spikelets known as 'blast' have been experimentally produced in glasshouse inoculations under low light intensity (45, 1362). Abnormally dwarfed oats have been induced by inoculation with the F1 generation of a smut hybrid U. avenae x U. hordei (45, 428).
Geographical distribution: World wide (CMI Map 238, ed. 2, 1967).
Physiological specialization: A large number of races have been reported showing great diversity in pathogenicity. Reed (19: 466) listed 29 races on 17 oat differentials in U.S.A. and Welsh et al. (34: 592) found over 20 races in Canada. Races with a wide host range have been found to contain more free amino acids and reducing sugars than those with a narrow one (43, 2594) and some races exhibit genetic heterogeneity leading to break down in resistance of their hosts (47 502). Inter-racial hybrids are more virulent than races derived from their selfed parents (44, 1066) and pathogenicity may be dominant or recessive depending on the heterozygosity of the parent stock (43, 3918; 44, 397j). The genetic controls of host-parasite interaction have been reviewed by Holton (1959).
Transmission: By wind-borne spores from smutted panicles which emerge shortly before healthy panicles begin to flower. Spores lodge within and on open flower parts which serve as infection courts. Max. dispersal occurs when there is an increase in wind accompanying rain (47, 143). Seedborne spores lodged between the caryopsis and the glumes (37: 717; 17: 309; 15: 790) and resting mycelium produced from spores which germinate at anthmis in the outer part of the seed enable the pathogen to over-winter and develop in seedlings in the following spring (12: 431; 19: 83).
Literature: Ainsworth & Sampson, The British smut fungi, 1950; Fischer, Manual of rhe North American smut fungi: 242-243, 1953; Fischer & Holton, Biology and control of the smut fungi, 1957; Holton, Tech. Bull. Minn. agric. Exp. Stn 87, 34 pp., 1932; Holton, Plant pathology problems and progress (Holton et al., eds, chapt. 5, pp. 145- 156, 1959; Mills, Trans. Br. mycol. Soc. 49: 651-663, 1966; Mordvinkina, Trudy prikl. Bot., Genct. Selek. 39: 233-242, 1969; Walker, Plant pathology, ed. 3; 433-438, 1970; Zundel, Ustilaginales of the World: 141-142, 1953 (biology, genetics, techniques and nomenclature); Noble & Richardson, An annotated list of seed-borne diseases, ed. 2 (Phytopath. Pap. 8), 1968 (seed treatment); Narain, Indian Phytopath. 17: 157-161, 1964 (culture).
 
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