`BeltGlade RR-1', `BeltGlade RR-2', and `BeltGlade RR-3': Rust-resistant Snap Bean Breeding Lines with the Ur-4 and Ur-11 Genes

Abstract

Received for publication 21 Sept. 1999. Accepted for publication 18 Feb. 2000. Florida Agricultural Experiment Station Journal Series No. R-07072. This research was supported in part by the Florida Foundation Seed Service. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact. Associate Professor, Plant Breeding and Genetics. Biological Scientist. Extension Agent. Research Plant Pathologist. To whom reprint requests should be addressed. Bean rust, incited by the fungus Uromyces appendiculatus (Pers.) Unger var. appendiculatus [formerly U. phaseoli (Ruben) Wint.] is a common disease of Phaseolus vulgaris L. It has the potential to cause serious crop losses, and is particularly troublesome in warm, humid production regions such as Florida (Stavely, 1999a, 1999b; Stavely and Pastor-Corrales, 1989). Currently, the Florida snap bean industry is valued at over $100 million annually, and generally relies on just over a half-dozen cultivars. The major source of rust resistance in these popular cultivars is the Ur-4 gene (Kelly et al., 1996), previously identified in ‘Early Gallatin’ as Up-2 (Christ and Groth, 1982). Unfortunately, this gene is not completely effective against the races that now infect snap beans in Florida, and growers must routinely apply fungicides to control bean rust and a number of other foliar diseases. In the past few years, 90 of the estimated 150 worldwide bean rust races have been identified and are curated at Beltsville, Md. (Stavely, 1998a, 1999b). To date, 11 dominant resistant genes have been identified to control these pathogenic races. They confer various host plant resistance reactions, including immunity, hypersensitivity, and/or reduced uredina size (Stavely, 1998a). The Ur-4 gene confers a hypersensitve type resistance, with necrotic lesions of 0.3–1.0 mm in diameter, to 30 of these races (Stavely, 1998a). Another gene, the dominant Ur-11 allele, confers hypersensitive or reduced uredinium (≤0.3 mm) type resistance to 89 of these races (Stavely, 1998a). The Ur-11 gene was previously identified as Ur-3 and later found to be linked in repulsion phase with the Ur-3 locus (Stavely, 1998b). The Ur-11 allele is not protective against Race 108 from Honduras (= H951, Steadman, pers. comm.), but Ur-4 is effective. When combined, the Ur-4 and Ur-11 genes concurrently provide either immunity, chlorotic or necrotic hypersensitive, or tiny uredinium resistance to all of the 90 races, with duplicate resistance to 29 of these races (Stavely, 1998b). Given the dynamic epidemiology of bean rust, more races will likley arise in the United States, Central America, and the Caribbean basin. A prudent strategy for the management of this disease is the deployment of different genes that confer resistance to a wide array of races, thereby diversifing the genetic basis of resistance. The primary objective of this breeding effort was to generate broad-spectrum bean rust resistance in subtropically adapted, fresh market, snap bean germplasm. To accomplish this objective, the Ur-11 gene was introgressed into snap bean germplasm with existing resistance based on the Ur-4 gene. Additional emphasis was placed on the retention of resistance to bean common mosaic virus as conferred by the I gene (Drijfhout, 1978 ) and presently deployed in many of the important cultivars grown in Florida. These breeding lines are intended for use as a combined source of rust resistance based on Ur-11 and Ur-4 genes.