|Cadle Davidson, Molly|
Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/15/2010
Publication Date: 4/1/2011
Citation: Ramming, D.W., Gabler, F., Smilanick, J.L., Cadle Davidson, M., Barba, P., Consolie, N.H., Mahanil, S., Cadle Davidson, L.E. 2011. A single dominant locus Ren4 confers non-race-specific penetration resistance to grapevine powdery mildew. Phytopathology. 101(4):502-508. Interpretive Summary: Powdery mildew is one of the most important diseases of grapes. Grape growers in the U.S. routinely apply 30 million pounds of sulfur every year on grapes to control powdery mildew. A new form of resistance that prevents powdery mildew from infecting grape leaves and fruit clusters was identified and described by the USDA/ARS laboratories at Parlier, CA and Geneva, NY. This resistance is conferred by a single genetic locus and is inherited as a dominant gene in several related families. This means that just one copy of the gene is required for full resistance. The resistance remained effective when tested in California and New York, the center of pathogen diversity. It also remained resistant even late into the growing season. This is the first case of a dominant powdery mildew gene that prevents infection and is effective against all known powdery mildew races. Grapes with this form of resistance will drastically reduce the number of sprays for powdery mildew.
Technical Abstract: Most powdery mildew resistance genes act after formation of the haustorial feeding cell and secretion of effector proteins into the host epidermis, enabling some degree of hyphal growth. The few genes identified to-date that act to prevent penetration, haustorial formation, and hyphal growth are, with the exception of the race-specific barley gene Mlg, recessive alleles or non-host resistance genes with intermediate resistance in the susceptible allele. Here we describe the resistance phenotype of a single dominant locus, Ren4, introgressed from a Chinese grape species Vitis romanetii into an otherwise susceptible V. vinifera background. The Ren4 locus confers extreme resistance to the grapevine powdery mildew fungus Erysiphe necator. In each of nine Ren4 breeding populations (1030 progeny), resistance fit a 1:1 segregation ratio (p-value=0.596) and overall segregated as 543 resistant progeny to 487 susceptible. In full-sib progeny, microscopic observations revealed the reduction of penetration success rate from 86% in susceptible progeny to below 10% in resistant progeny; similarly extreme differences were seen macroscopically. Ratings for population 03-3004 screened using natural infection in a California vineyard and greenhouse and using artificial inoculation of an aggressive New York isolate were fully consistent among all three pathogen sources and environments. From 2006-2010, Ren4 vines were continuously screened in California and New York (part of the center of diversity for E. necator), and no sporulating colonies were observed. For population 03-3004, severity ratings on leaves, shoots, berries, and rachises were highly correlated (R2 = 0.875 to 0.996) in the vineyard. Together, these data document a powdery mildew resistance mechanism not previously described, in which a dominantly inherited penetration resistance is non-race-specific and tissue-independent. In addition to its role in breeding for durable resistance, Ren4 may provide mechanistic insights into the early events that enable powdery mildew infection.