Architecture
Preamble: Plant architecture has played an important role in the adaptation of beans to production areas in temperate regions such as Michigan. X-ray mutagenesis was first used in 1940s to develop a determinate bush navy bean better suited for local production than the prostrate vine types. Starting in the 1970s the breeding program used tropical germplasm to develop upright short vine types suited for direct harvest. Currently 90% of the bean acreage in Michigan is direct harvested due in large part to the availability of upright black, navy, pinto, pink and small red bean varieties developed by the breeding program. A history of that research is described in the article ‘Remaking bean plant architecture for efficient production’ (Kelly, 2000) and is featured in the video on bean plant architecture: http://www.youtube.com/watch?v=wf_nOs7DP-o. Current research continues to refine architectural characteristics in a wider range of seed types and combine these traits with improved performance as the two traits compete for resources. Bean plants that ‘overinvest’ in plant structural components have fewer reserves available for seed production so striking that critical balance in future varieties continues to be a breeding challenge.
REMAKING BEAN PLANT ARCHITECTURE FOR EFFICIENT PRODUCTION
The wide range of variability for plant type in cultivated beans (Phaseolus vulgarisL.) has been classified into four growth habits. Type I is the only determinate habit, whereas Types II, III and IV are indeterminate, differing in vine growth extension and climbing ability. A major focus of many bean breeding programs has been the genetic modification of growth habit to improve adaptation and yield. Earliest attempts were successful in converting pole or climbing ‘Blue Lake’ snap beans to determinate bush types suitable for mechanical harvest. In the dry edible navy bean, X-ray mutagensis was successfully used to develop an upright determinate navy bean for production in the humid Midwestern U.S. Central American black bean germplasm was used to develop of high-yielding, upright Type II navy beans, based on the ideotype concept. With the successful development of small-seeded ideotype, recurrent selection was employed to introduce the architectural traits into medium-seeded Durango race pinto beans. Durango race ideotypes are among the highest-yielding contemporary cultivars. Further refinements of later-generation recurrent selection were used to successfully transfer indeterminacy into large-seeded Andean beans grown in tropical regions. The indeterminate types proved to be both higher yielding and exhibited more yield stability across the diverse environments of the Caribbean. Genetic maps and molecular markers offer bean breeders the opportunity to access variability in related species that is presently masked by unadapted traits such as the Type IV climbing habit of wild beans.
Abstracted from: Kelly, J.D. 2000. Remaking bean plant architecture for efficient production. Advances in Agronomy 71:109-143.
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