ARS | Publication request: INCOMPLETE DOMINANCE OF RUST RESISTANCE IN TEPARY BEAN

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 8, 1997
Publication Date: N/A

Interpretive Summary: Bean rust disease adversely effects dry-edible beans. Yield losses caused by bean rust and the costs incurred for chemical pesticides used to control them create an annual economic hardship for growers. We searched for new sources of resistance to bean rust. Seven tepary bean germplasm lines were found to possess high levels of resistance to bean rust. The resistance exhibited incomplete dominance which is rare for resistance genes in highe plants. The same resistance gene was present in all seven lines. Thus, only one of these tepary bean germplasms could contribute to the development of future bean cultivars with improved rust resistance. Rust resistant cultivars will yield more, and ensure a safer food product and cleaner environment through reduced pesticide use.

Technical Abstract: Foliar diseases are a major constraint to cultivated tepary bean (Phaseolus acutifolius A. Gray var. latifolius Freeman) production in different environments. The greenhouse reactions of 12 cultivated teparies were examined against eight individual races of the bean rust fungus Uromyces appendiculatus (Pers.) Unger var. appendiculatus maintained by USDA-ARS at Beltsville, MD. Seven lines exhibited similar high levels of resistance (immunity or necrotic spots without sporulation) to all eight races. Inheritance of resistance was examined across five susceptible x resistant (S x R) and three resistant x resistant (R x R) populations. The rust reactions in the F1, F2, and F3 generations derived from S x R crosses revealed that the immune or necrotic resistance response was conditioned by a single locus exhibiting incomplete dominance. Allelism tests in the R x R crosses indicated that the rust resistance was derived from the same locus. This apparent lack of variability for rust resistance suggests tha a single introgression event may realize the full potential for cultivated tepary bean to contribute rust resistance to common bean through interspecific hybridization.