Powdery mildew (barley)

Powdery mildew is a fungal disease of barley caused by Blumeria graminis f. sp. hordei. The disease has a worldwide distribution and is most damaging in cool, wet climates. The host range of the form species hordei is restricted to barley and other Hordeum species.^[1][2]

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Symptoms

At first, powdery mildew can be observed as small greyish patches of fluffy fungal growth (mycelium) on the upper surface of the lower leaves. These spots resemble small cushions of white powder. Leaf tissue on the opposite side of an infected leaf turns pale green to yellow. The fungus only infects the epidermal layer and can be easily scrapped off with a fingernail. Infections can also occur on the leaf sheaths and ears. Leaves remain green and active for some time following infection, then gradually become chlorotic and die off. As the disease progresses, the mycelium often becomes dotted with minute black points (cleistothecia), which are the sexual fruiting bodies of the fungus.

Disease cycle

The fungus ovewinters as cleistothecia on straw, and in milder climates, also as mycelium and conidia on stubble and straw or volunteer barley and certain grasses. Windborne ascospores or conidia are the primary inoculum and can be dispersed over considerable distances. Infection by conidia requires high humidity, but not free water on the leaf surface. Sporulation and spore dispersal are favored by drier conditions. Thus the disease does well under alternating wet and dry conditions. Production of conidia declines markedly as the colony ages. Cleistothecia develop on older leaves as the plant matures. Low temperatures, together with the wetting of the cleistothecia for at least 72 hours, induces the maturations of the ascospores. Ascospores are released following rains, but are relatively sparse in comparison to the condia.

Research articles

Blatter, R.H.E; J.K.M. Brown, M.S. Wolfe (1998). "Genetic control of the resistance of Erysiphe graminis f.sp. hordei to five triazole fungicides". Plant Pathology 47(5): 570–579.

Bousset, L.; M.S. Hovmøller, V. Caffier, C. de Vallavieille-Pope, H. Østergård (2002). "Observed and predicted changes over eight years in frequency of barley powdery mildew avirulent to spring barley in France and Denmark". Plant Pathology 51(1): 33–44.

Bousset, L.; B. Schaeffer, C. de Vallavieille-Pope (2001). "Effect of early infection on pathotype frequencies in barley powdery mildew (Blumeria graminis f.sp. hordei) populations in field plots". Plant Pathology 50(3): 317–324.

Boyd, L.A.; P.H. Smith, R.M. Green, J.K.M. Brow (1994). "The relationship between the expression of fefense-related Genes and mildew development in barley". MPMI 7: 401-410.

Caffier, V; T. Hoffstadt M. Leconte, C. de Vallavielle-Pope (1996). "Seasonal changes in pathotype complexity in French populations of barley powdery mildew". Plant Pathology 45(3): 454–468.

Dreiseitl, A.; A. Dinoor, E. Kosman (2006). "[[1] Virulence and Diversity of Blumeria graminis f. sp. hordei in Israel and in the Czech Republic]". Plant Dis. 87: 99.

Duggal, V.; G.J. Jellis, T.W. Hollins, R. Stratford (2000). "Resistance to powdery mildew in mutant lines of the susceptible wheat cultivar Hobbit 'sib'". Plant Pathology 49(4): 468–476.

El-Zahaby, H.M.; G. Gullner, Z. Király (1995). "Effects of powdery mildew infection of barley on the ascorbate-glutathione cycle and other antioxidants in different host-pathogen interactions". Phytopathology 85: 1225-1230.

Fraaije,, B.A.; J.A. Butters, J.M. Coelho, D.R. Jones, D.W. Hollomon (2002). "Following the dynamics of strobilurin resistance in Blumeria graminis f.sp. tritici using quantitative allele-specific real-time PCR measurements with the fluorescent dye SYBR Green I". Plant Pathology 51(1): 45–54.

Haugaard, H.; H.J. Lyngs Jørgensen, M.F. Lyngkjær, V. Smedegaard-Petersen, D.B. Collinge (2001). "Control of Blumeria graminis f.sp. hordei by treatment with mycelial extracts from cultured fungi". Plant Pathology 50(5): 552–560.

Heide, M.; V. Smedegaard-Petersen (1985). "Common antigens between barley and barley powdery mildew and their relation to resistance and susceptibility". CJPP 7: 341-346.

Hückelhoven, R.; K.-H. Kogel (1998). "Tissue-specific superoxide generation at interaction sites in resistant and susceptible near-isogenic barley lines attacked by the powdery mildew fungus (Erysiphe graminis f. sp. hordei)". MPMI 11: 292-300.

O'Hara, R.B.; J.K.M. Brown (1996). "Immigration of the barley mildew pathogen into field plots of barley". Plant Pathology 45(6): 1071-1076.

O'Hara, R.B.; J.K.M. Brown (1997). "Spatial aggregation of pathotypes of barley powdery mildew". Plant Pathology 46(06): 969–977.

O'Hara, R.B.; J.K.M. Brown (1998). "Movement of barley powdery mildew within field plots". Plant Pathology 47(4): 394–400.

O'Hara, R.B.; B.J. Nielsen, H. Østergård (2000). "The effect of fungicide dose on the composition of laboratory populations of barley powdery mildew". Plant Pathology 49(5): 558–566.

Oslash;stergård; M.F. Lyngkjær (1998). "Interaction between powdery mildew and barley with mlo5 mildew resistance". Plant Pathology 47(3): 252–258.

Schiffer, R.; R. Görg, B. Jarosch, U. Beckhove, G. Bahrenberg, K.-H. Kogel, P. Schulze-Lefert (1997). "Tissue dependence and differential cordycepin sensitivity of race-specific resistance responses in the barley-powdery mildew interaction". MPMI 10: 830-839.

Vallélian-Bindschedler, L.; J-P. Métraux, P. Schweizer (1998). "Salicylic acid accumulation in barley is pathogen specific but not required for defense-gene activation". MPMI 11: 702-705.

Yahyaoui, A.H.; M. Reinhold, A.L. Scharen (1997). "Virulence spectrum in populations of the barley powdery mildew pathogen, Erysiphe graminis f. sp. hordei in Tunisia and Morocco in 1992". Plant Pathology 46(1): 139–146.

References

1. ^ Wiese, M.V. (1987). Compendium of wheat diseases. American Phytopathological Society, 124 pp. 
2. ^ Martens, J.W.; W.L. Seaman, T.G. Atkinson (1984). Diseases of field crops in Canada. Canadian Phytopathological Society, 160 pp.