Sources of Resistance to Common Bacterial Blight and Charcoal Rot Disease for the Production of Mesoamerican Common Beans in the Southern United States.

Daniel Ambachew,Jacqueline Joshua,Matthew W Blair,Margaret T Mmbaga

doi:10.3390/plants10050998

Daniel Ambachew, Jacqueline Joshua + Show 2 more

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https://doi.org/10.3390/plants10050998

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Abstract

The gene pool of Mesoamerican common beans (Phaseolus vulgaris L.) includes genotypes in the small-to-medium-size seeded dry beans, as well as some snap beans from hotter environments adapted to the Southeastern United States. However, the warm and humid climate of the Southeastern United States is conducive to diseases such as Common Bacterial Blight (CBB) and Charcoal Rot (CR). The pathogens for these two diseases can survive long periods in infested soil or on seeds and are difficult to control through pesticides. Hence, field-level resistance would be the best management strategy for these diseases. The goals of this study were (1) to evaluate field-level resistance from the various commercial classes and subgroups represented in the Mesoamerican gene pool as sources for breeding beans for the region and (2) to evaluate genome-wide marker × trait associations (GWAS) using genetic markers for the genotypes. A total of 300 genotypes from the Mesoamerican Diversity Panel (MDP) were evaluated for CBB and CR in field experiments for three years. CBB resistance was also tested with a field isolate in controlled greenhouse conditions. The analysis of variance revealed the presence of variability in the MDP for the evaluated traits. We also identified adapted common bean genotypes that could be used directly in Southeastern production or that could be good parents in breeding programs for CBB and CR resistance. The GWAS detected 14 significant Single-Nucleotide Polymorphism (SNP) markers associated with CBB resistance distributed on five chromosomes, namely Pv02, Pv04, Pv08, Pv10, and Pv11, but no loci for resistance to CR. A total of 89 candidate genes were identified in close vicinity (±100 kb) to the significant CBB markers, some of which could be directly or indirectly involved in plant defense to diseases. These results provide a basis to further understand the complex inheritance of CBB resistance in Mesoamerican common beans and show that this biotic stress is unrelated to CR resistance, which was evident during a drought period. Genotypes with good yield potential for the Southeastern U.S. growing conditions were found with resistant to infection by the two diseases, as well as adaptation to the hot and humid conditions punctuated by droughts found in this region.

Highlights

The common bean, Phaseolus vulgaris L., is an important species to agriculture in the United States (U.S.) primarily produced as a commodity grain crop [1] and as a vegetable crop, known as snap beans [2,3,4]
The goals of this study were (1) to evaluate field-level resistance from the various commercial classes and subgroups represented in a Mesoamerican Diversity Panel (MDP) as sources for breeding beans for the Southeast region of the United States of America (USA) and (2) to evaluate marker × trait associations using previously developed genetic markers for the genotypes and genome-wide marker × trait associations (GWAS) screening for two diseases, Common Bacterial Blight (CBB) and Charcoal Rot (CR), which are prevalent in warm climates
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Summary

Introduction

The common bean, Phaseolus vulgaris L., is an important species to agriculture in the United States (U.S.) primarily produced as a commodity grain crop [1] and as a vegetable crop, known as snap beans [2,3,4]. On the other hand, follow a seasonal worker and machine harvester migration from the Southern U.S, with the earliest and highest value fresh crops in Florida, Georgia, the Carolinas, and Tennessee, moving north to facilities that cut and freeze snap beans in Wisconsin at the height of summer [8]. The U.S southeastern states have long growing seasons and have the capacity to grow the common bean at least twice a year based on spring and summer plantings. Smaller organic farms, as well as backyard gardeners continue to produce both dry and snap beans in the region. Local consumption, and proximity to markets favor larger scale snap bean production especially on the Cumberland Plateau of Tennessee [9]

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