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Title: Appearance of Powdery Mildew of Wheat (caused by Blumeria graminis f. sp. Tritici) on Pm17-bearing Cultivars in North Carolina

Author
item Cowger, Christina
item Parks, Wesley
item Marshall, David

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/9/2009
Publication Date: 11/2/2009
Citation: Cowger, C., Parks, W.R., Marshall, D.S. 2009. Appearance of Powdery Mildew of Wheat (caused by Blumeria graminis f. sp. Tritici) on Pm17-bearing Cultivars in North Carolina. Plant Disease. 93:1219

Interpretive Summary: Pm17 is a gene for resistance to powdery mildew (caused by Blumeria graminis f. sp. tritici) that was first confirmed in the wheat-rye translocation cultivar Amigo (1). In Amigo, the translocation is T1AL-1RS, and the 1RS arm has the gene Pm17. In the Mid-Atlantic USA, at least two widely deployed soft red winter wheat (Triticum aestivum L.) cultivars, McCormick (2) and Vigoro Tribute (3), possess Pm17 inherited from Amigo. In April 2009, moderately severe powdery mildew was observed for the first time throughout plots of McCormick, Tribute, and other cultivars in both Kinston and Raleigh, North Carolina. At Kinston, Pm17 virulence was observed at two research sites, separated by approximately 10 km, throughout plots of Amigo, McCormick, Tribute, and the hard red winter wheat cultivar TAM 303 (which also contains Pm17). In the same month, virulence to Pm17 was observed in Raleigh throughout rows and plots of Amigo and TAM 303. In both Kinston and Raleigh, ratings of powdery mildew severity on the Pm17-containing cultivars were 4 or 5 on a scale of 0-9, with 0 being the absence of mildew pustules and 9 the most severe mildew infection. Mildew was observed on leaves of all ages. Mildewed leaves were collected from field plots of all four Pm17-bearing cultivars, and an assay to confirm Pm17 virulence was conducted in the laboratory. Mixed-isolate cultures were derived from the leaves, and a detached-leaf assay was performed using Amigo, which is the standard Pm17 differential (4). All tested cultures were fully to moderately virulent on Pm17, and all were fully virulent on the susceptible control Chancellor. In the field, cleistothecia were observed on Pm17-bearing cultivars. Together with the quantitatively varying Pm17 virulence detected in the laboratory assay, this suggests that multiple strains of Pm17-virulent B. graminis f. sp. tritici may be expected in the field, although that has not yet been formally demonstrated. Pm17 has protected wheat from powdery mildew over a substantial area in the Mid-Atlantic USA. Isolates with Pm17 can be expected to spread geographically and increase in average fitness, and thus there is heightened urgency to develop and release wheat cultivars with other sources of mildew resistance.

Technical Abstract: Pm17 is a gene for resistance to powdery mildew (caused by Blumeria graminis f. sp. tritici) that was first confirmed in the wheat-rye translocation cultivar Amigo (1). In Amigo, the translocation is T1AL-1RS, and the 1RS arm has the gene Pm17. In the Mid-Atlantic USA, at least two widely deployed soft red winter wheat (Triticum aestivum L.) cultivars, McCormick (2) and Vigoro Tribute (3), possess Pm17 inherited from Amigo. In April 2009, moderately severe powdery mildew was observed for the first time throughout plots of McCormick, Tribute, and other cultivars in both Kinston and Raleigh, North Carolina. At Kinston, Pm17 virulence was observed at two research sites, separated by approximately 10 km, throughout plots of Amigo, McCormick, Tribute, and the hard red winter wheat cultivar TAM 303 (which also contains Pm17). In the same month, virulence to Pm17 was observed in Raleigh throughout rows and plots of Amigo and TAM 303. In both Kinston and Raleigh, ratings of powdery mildew severity on the Pm17-containing cultivars were 4 or 5 on a scale of 0-9, with 0 being the absence of mildew pustules and 9 the most severe mildew infection. Mildew was observed on leaves of all ages. Mildewed leaves were collected from field plots of all four Pm17-bearing cultivars, and an assay to confirm Pm17 virulence was conducted in the laboratory. Mixed-isolate cultures were derived from the leaves, and a detached-leaf assay was performed using Amigo, which is the standard Pm17 differential (4). All tested cultures were fully to moderately virulent on Pm17, and all were fully virulent on the susceptible control Chancellor. In the field, cleistothecia were observed on Pm17-bearing cultivars. Together with the quantitatively varying Pm17 virulence detected in the laboratory assay, this suggests that multiple strains of Pm17-virulent B. graminis f. sp. tritici may be expected in the field, although that has not yet been formally demonstrated. Pm17 has protected wheat from powdery mildew over a substantial area in the Mid-Atlantic USA. Isolates with Pm17 can be expected to spread geographically and increase in average fitness, and thus there is heightened urgency to develop and release wheat cultivars with other sources of mildew resistance.