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Peer Reviewed

© 2009 Plant Management Network.
Accepted for publication 4 February 2009. Published 25 March 2009.

First Report of Bean Rust Caused by Uromyces appendiculatus Race 19-63 in Puerto Rico

Byron Vega, Department of Crop Protection, James S. Beaver, Department of Agronomy and Soils, Consuelo Estévez de Jensen, Department of Crop Protection, University of Puerto Rico, Mayagüez, PR 00681; and James R. Steadman, Department of Plant Pathology, University of Nebraska, Lincoln, NE 68583

Corresponding author: Byron Vega.

Vega, B., Beaver, J. S., de Jensen, C. E., and Steadman, J. R. 2009. First report of bean rust caused by Uromyces appendiculatus race 19-63 in Puerto Rico. Online. Plant Health Progress doi:10.1094/PHP-2009-0325-01-BR.

Bean rust caused by Uromyces appendiculatus (Pers.) Unger is an important disease in common bean (Phaseolus vulgaris L.) worldwide. The first report of physiological races was published in 1935, and by 1996 the number of races described were more than 300 (1).

Fig. 1. U. appendiculatus race 19-63 fourteen days after inoculation on differential ‘Aurora’.


In 1976, a survey of bean rust identified 12 different races in Puerto Rico (3). In 1984, a new virulent race to lines B-190 and L-226 was collected in Isabela (4). Rust races from the Caribbean and South Africa have been shown to be more virulent than races from temperate zones (2).

In June 2007, an outbreak of common bean rust on the cultivar ‘Verano’ occurred in northwestern Puerto Rico. Percentage of leaf area infected in the field ranged from 20 to 50% (Fig. 1). Field collections of U. appendiculatus were obtained from the central area of Puerto Rico in five locations and three municipalities. In Naranjito an isolate from a single uredinium was increased on the cultivar ‘Verano.’ First symptoms were observed 7 to 9 days after inoculation as small chlorotic spots developing to erupted pustules.

Morphological observations were conducted using light and scanning electron microscopy (Figs. 2 and 3). The race identification and the virulence tests were carried out on a set of 12 standard differentials, including Middle American and Andean lines. Rust reactions were evaluated using a grading scale (1 to 6). A suspension of 2.4 × 104 urediniospores per ml was suspended in a water solution of 0.1% Tween 20 (vol/vol). Fourteen-day-old plants of each differential were inoculated on the adaxial side of the primary leaf using a hand sprayer. Plants were incubated in a moist chamber with sprinkler irrigation for 12 h at 20°C, and then transferred to a screenhouse with an average temperature of 23.3°C. Evaluation was conducted 14 days after inoculation.


Fig. 2. Uredinial pustule of U. appendiculatus race 19-63 on the adaxial side of the cultivar 'Verano' (40×). Bar = 500 µm.


Fig. 3. Scanning Electron Microscopy (SEM) of the adaxial side of the leaf of P. vulgaris showing numerous sori throughout the leaf surface (75×).

Resistant reactions were observed on the Middle American differentials ‘Mexico 309’ with the resistant gene Ur-5, ‘Mexico 235’ (Ur-3+) and ‘PI 181996’ (Ur-11). Susceptible reactions were observed on the Andean differentials ‘Early Gallatin’ (Ur-4), ‘Redlands Pioneer’ (Ur-13), ‘Montcalm’ and ‘PC-50’ (Ur-9, Ur-12), ‘Golden Gate Wax’ (Ur-6), and ‘PI 260418’ and Middle American differentials ‘GN 1140’ (Ur-7), ‘Aurora’ (Ur-3) (Fig. 4), and ‘Compuesto Negro Chimaltenango’ (CNC).


Fig. 4. SEM of U. appendiculatus race 19-63 showing typical ornamentation of uredospores (2000×).


The Andean differentials were all susceptible to the isolate collected but half of the Middle American differentials were resistant. Based on the reaction of the differentials with the isolate, we identified a highly virulent 19-63 new race of U. appendiculatus in Puerto Rico. To our knowledge this is the first report of a new race of U. appendiculatus (19-63) in Puerto Rico and in the Western Hemisphere.

Literature Cited

1. Araya, C. M., Alleyne, A. T., Steadman, J. R., Eskridge, K. M., and Coyne, D. P. 2004. Phenotypic and genotypic characterization of Uromyces appendiculatus from Phaseolus vulgaris in the Americas. Plant Dis. 88:830-836.

2. Jochua, C., Amane, M. I. V., Steadman, J. R., Xue, X., and Eskridge, K. M. 2008. Virulence diversity of the common bean rust pathogen within and among individual bean fields and development of sampling strategies. Plant Dis. 92:401-408.

3. López Guadamuz, M. A. 1976. Identificación de las razas fisiológicas más comunes de la roya [Uromyces appendiculatus (Pers.) Unger] del frijol (Phaseolus vulgaris L.) en Puerto Rico. M.S. thesis. Univ. of Puerto Rico, Mayaguez, Puerto Rico.

4. Stavely, J. R., Steadman, J. R., and McMillan, R. T., Jr. 1989. New pathogenic variability in Uromyces appendiculatus in North America. Plant Dis. 73:428-432.