Since the genome release, there has been a surplus of genomics research on beans. This research has aided in our understanding of genetic mechanisms for various traits, including better understanding pathogen response for anthracnose and common bacterial blight (Vaz Bisneta et al. 2020; Simons et al. 2021), drought stress (Diaz et al. 2020), and domestication related traits (Soltani et al. 2021), to name a few.
Marker platforms have largely moved to SNP based, with the Illumina BARCBean6K_3 SNP BeadChip (Song et al. 2015) and BARCBean12K BeadChip, which includes all SNPs from the BARCBean6K_and additional SNPs among a set of Andean accessions. The large reduction in the cost of DNA sequencing in recent years has made sequencing (whether RNA or DNA) a fairly regular aspect of bean genetics discovery work. Genotype by sequencing is also commonly applied as a SNP marker generating method that can then be used for mapping purposes, for both recombinant inbred line populations and diversity panels (Schröder et al. 2016; Katuuramu et al. 2018). Genome resequencing is also gaining popularity in bean genomics projects to gain understanding of the genetic architecture for traits such as seed yield and stress tolerance (Wu et al. 2020). Kompetitive Allele Specific PCR (KASPTM)‐based SNP marker system has been successfully integrated for marker assisted breeding tool in many labs (Raatz et al. 2019). This technology is easily outsourced to service companies, which makes it a viable option for most breeders, even those without a lab or dedicated DNA‐related equipment. The new frontier in genomics for bean breeding is genomic selection (Keller et al. 2020). Some studies are underway, although it remains to be seen how easily this will be implemented since dry bean breeding efforts occur in at least 10 different market classes, each somewhat isolated from the other, so it may not be possible to achieve the numbers necessary to make genomic prediction worth the investment.
Transgenic beans
Thus far, no commercially available bean varieties developed through genetic modification (GM) or through gene engineering are being marketed in the US. Beans have lagged behind soybeans in the utilization of this technology for a number of reasons (Veltcheva et al. 2005; Song et al. 2020). The major reason was the absence of an incentive to develop a GM bean by private industry as the acreage base is so small compared to soybean. This meant that there was limited investment or financial resources targeted to develop a GM bean, either in the public or private sector. In addition, the smaller acreage planted to dry beans is dispersed over six to eight major market classes in addition to the different horticultural types, so no economic incentive existed to pursue the development of GM bean as any financial returns would be small. Since beans are cropped with soybeans, the private sector did not want herbicide‐resistant volunteer beans appearing in the soybean or corn crop the following season. The additional hurdle was the recalcitrant nature of beans to regeneration and plant transformation.
All major grain legumes, including cowpea, peanut, and pea, have been genetically transformed, and beans continue to resist transformation using Agrobacterium. This has been a formidable hurdle, and one that was bypassed by colleagues in Brazil who have successfully transformed beans using a particle gun (Bonfim et al. 2007). This was the first use of RNA interference technology to achieve this remarkable result of engineered Gemini Virus resistance to Bean Golden Mosaic Virus in the field (Aragão and Feria 2009), which has since been moved into commercial “carioca bean” cultivars (Souza et al. 2018). These varieties were engineered to express resistance to the Gemini Virus pathogen Bean Golden Mosaic Virus. This was the first use of RNA interference technology to achieve this remarkable result of engineered Gemini virus resistance in the field (Aragão and Feria 2009).
The cost to deregulate GM beans in the US is estimated at over $10 million for each GM event but the revenue generated by the crop across diverse states and seed and pod types is insufficient to support deregulation. This bodes well for consumers who are “anti‐GMO foods” or for European markets that similarly continue to exclude GM products. The downside is that bean producers cannot avail themselves of the same production technologies as soybean producers, which will result in a competitive loss of bean acreage in many production states. Lower acreage will undoubtedly result in smaller crop production and higher prices to the consumer. This fact alone is concerning, given the new evidence of the valuable health benefits of increasing bean consumption in the US diet to help combat obesity, diabetes, and certain cancers (Thompson et al. 2009). The US bean industry with limited research support needs to address this question in a rational and reasonable fashion using science‐based research. Breeders are consistently asked to make progress and compete with GM crops such as soybean, yet they are limited in the tools they can use to address future production needs and challenges. Perhaps CRISPR (Zaidi et al. 2020) will provide an affordable consumer‐accepted gene‐editing technology to engineer improved traits for common bean in the near future.
FUTURE DIRECTIONS
Greater focus on climate change and sustainable production will be key breeding goals of the future. Global climate changes underscore the strong justification for continuous public breeding efforts to preserve bean yield potential through breeding of improved resistance to rapidly evolving biotic and abiotic stresses and the continued displacement of bean production to less favorable environments across the globe.
A 2010 study demonstrated the importance of maintenance breeding as it relates to climate. It was found the 15% reductions in present‐day yield of IR8, the miracle rice variety developed over 50 years ago resulted from the lack of adaptation to current environmental conditions (Peng et al. 2010). The authors stressed the critical role that breeding plays in improving the adaptation of newly developed varieties to changing climatic conditions that have a negative impact on older varieties. The same holds true for bean breeding.
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