Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 21, 2012
Publication Date: August 1, 2012
Citation: Wasonga, C.J., Pastor Corrales, M.A., Porch Clay, T.G., Griffiths, P.D. 2012. Multi-environment selection of small sieve snap beans reduces production constraints in East Africa and subtropical regions. HortScience. 47:1000-1006. Interpretive Summary: Common bean rust, a fungal foliar disease, and high temperature stress lower the yield and quality of snap beans (Phaseolus vulgaris L.) in East Africa. Snap beans combining resistance to rust and heat tolerance are needed to improve and expand snap bean production in this region. Four snap bean lines were previously developed to combine rust resistance genes, and were confirmed to be resistant across diverse geographies in East Africa. The same lines were also confirmed as heat tolerant following testing across multiple tropical, high temperature stress environments. These four breeding lines were crossed with three varieties currently targeted for production in East Africa and two varieties targeted for production in North America, all lacking effective rust resistance and heat tolerance. From these populations, twenty breeding lines were selected and evaluated in 2010 at four distinct field sites in East Africa: Arusha, Tanzinia, and Homabay, Kakamega and Kitale, Kenya. Four lines (‘L5’, ‘L9’, ‘L13’ and ‘L17’) that combined rust resistance and heat tolerance in desired plant types (high yielding and high pod quality), were selected from the evaluation of the 20 breeding lines. Three of the selections were confirmed to be heat tolerant based on evaluation trials carried out at two distinct high temperature environments: a controlled environment greenhouse in Geneva, NY and a field site in Juana Diaz, Puerto Rico. Continued testing and subsequent release of the breeding lines as cultivars, and their utilization in breeding programs will improve and expand the production of snap bean in East Africa and other tropical environments with similar production constraints.
Technical Abstract: Common bean rust caused by Uromyces appendiculatus, and heat stress lower the yield and quality of snap beans (Phaseolus vulgaris L.) in East Africa. Four snap bean breeding lines previously selected for broad-spectrum rust resistance (involving Ur-4 and Ur-11 rust genes) and heat tolerance following testing across multiple tropical environments were used as sources for the two traits. The four breeding lines were crossed with five cultivars (including three that are currently targeted for production in East Africa) that lack effective rust resistance and heat tolerance. Resultant hybrid combinations were advanced through trait selection at the F2, F3 and F4 generations with selection for heat tolerance, rust resistance, and pod quality categorized by sieve size. Twenty breeding lines selected from the F4 populations and 16 controls were evaluated in 2010 at four field sites in East Africa, a high temperature field site in Juana Diaz, Puerto Rico, and at a controlled temperature greenhouse environment. The sites in East Africa differed in altitude, climate (especially in mean temperatures), soils, and in virulence diversity of the bean rust pathogen (comprising of races 21-1, 29-1 and 31-3). Four lines, ‘L5’, ‘L9’, ‘L13’ and ‘L17’, that combined rust resistance and heat tolerance in desired plant types (high yielding and high pod quality), were selected from the 20 breeding lines. Spearman’s rank correlations between the controlled temperature testing for heat tolerance in the greenhouse and field testing at the high temperature field site in Puerto Rico were significant for seed yield per plant (p=0.001) and seeds per pod (p=0.05) which are two yield components that are most predictive of heat tolerance. The correlation results underscore the potential of a controlled greenhouse testing of the snap bean genotypes in predicting performance in a high temperature field environment. Additional testing and subsequent release of these breeding lines as cultivars, and their utilization in breeding programs will improve production of snap bean in East Africa and other tropical environments with similar production constraints by contributing rust resistance and heat tolerance.