The bean rust disease in Sri Lanka: Identification of the pathogen’s first races and genes for the development of rust-resistant snap beans

Authors: KUMARI, H - Department Of Agriculture Government Of Sri Lanka; Pastor Corrales, Marcial; RAJAPAKSHA, R - Department Of Agriculture Government Of Sri Lanka; BANDARANAYAKE, P - University Of Peradeniya; WEEBADDE, CHOLANI - Michigan State University

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/19/2023
Publication Date: 8/18/2023
Citation: Kumari, H., Pastor Corrales, M.A., Rajapaksha, R., Bandaranayake, P., Weebadde, C. 2023. The bean rust disease in Sri Lanka: Identification of the pathogen’s first races and genes for the development of rust-resistant snap beans. Plant Disease. (107)8:2431-2439. https://doi.org/10.1094/PDIS-08-22-1942-RE.
DOI: https://doi.org/10.1094/PDIS-08-22-1942-RE

Interpretive Summary: Bean rust is a significant threat to dry and snap bean production worldwide. It is a devastating disease limiting snap bean production in Sri Lanka. Snap bean producers in Sri Lanka apply alarming rates of fungicides to manage the disease. This study endeavored to identify the rust strains that cause bean rust in Sri Lanka. Using published methodologies, we purified 57 isolates of the pathogen. The virulence of these isolates segregated into four different groups based on their virulence in comparison to other known races of the rust pathogen. All races caused more extensive disease on the Andean than on the Middle American common beans with rust resistance genes. This is important because most snap beans are of Andean origin. A common bean designated as PI 1819966 and of Middle American origin containing the Ur-11 gene, conferred resistance to all four races of rust that we discovered in Sri Lanka. Three other Middle American cultivars were resistant to three races. Conversely, five well known Andean cultivars were susceptible to all four races. The results suggest that development of snap bean varieties in Sri Lanka combining rust resistance genes of Middle American origin with genes such as Ur-11of Andean origin, will more likely confer broad and durable resistance to all races of the bean rust pathogen in Sri Lanka.

Technical Abstract: Bean rust is a devastating disease of snap beans in Sri Lanka. Our study endeavored to develop snap beans with resistance to Uromyces appendiculatus, the bean rust pathogen reported to have numerous virulent races. Accordingly, we needed a detailed understanding of the virulence of U. appendiculatus and to identify genes conferring effective rust resistance. To investigate the virulence, we collected leaves of snap bean with rust symptoms from four snap bean producing districts of Sri Lanka. From these samples we established 57 single pustule isolates. Each isolate was inoculated on a set of 12 differential cultivars, six from the Andean and six from the Middle American gene pools of common bean. The virulence of the isolates segregated into four distinct groups that comprised the first four reported races of U. appendiculatus in Sri Lanka, 23-5, 31-1, 31-11, and 63-21. All races were significantly more virulent on the Andean than on the Middle American differential cultivars. PI 1819966, a Middle American differential cultivar containing the Ur-11 gene, conferred resistance to all four races. Three other Middle American cultivars were resistant to three races. Conversely, five Andean differential cultivars were susceptible to all four races. PI 160418 was the only Andean differential cultivar with resistance to three races. The results suggested that rust resistance genes from the Middle American differential cultivars could be combined in different ways with the resistance of Andean PI 260418 to develop snap bean varieties with broad resistance to all races of U. appendiculatus in Sri Lanka.