Common beans (Phaseolus vulgaris) form a relationship with nitrogen-fixing rhizobia and through a process termed symbiotic nitrogen fixation (SNF) which provides them with a source of nitrogen. However, beans are considered poor nitrogen fixers, and modern production practices involve routine use of N fertilizer, which leads to the down-regulation of SNF. High-yielding, conventionally bred bean varieties are developed using conventional production practices and selection criteria, typically not including SNF efficiency, and may have lost this trait over decades of modern breeding. In contrast, heirloom bean genotypes were developed before the advent of modern production practices and may represent an underutilized pool of genetics which could be used to improve SNF. This study compared the SNF capacity under low-N field conditions, of collections of heirloom varieties with and conventionally bred dry bean varieties. The heirloom-conventional panel (HCP) consisted of 42 genotypes from various online seed retailers or from the University of Guelph Bean Breeding program seedbank. The HCP was genotyped using a single nucleotide polymorphism (SNP) array to investigate genetic relatedness within the panel. Field trials were conducted at three locations in ON, Canada from 2014 to 2015 and various agronomic and seed composition traits were measured, including capacity for nitrogen fixation (using the natural abundance method to measure seed N isotope ratios). Significant variation for SNF was found in the panel. However, on average, heirloom genotypes did not fix significantly more nitrogen than conventionally bred varieties. However, five heirloom genotypes fixed >60% of their nitrogen from the atmosphere. Yield (kg ha^-1) was not significantly different between heirloom and conventional genotypes, suggesting that incorporating heirloom genotypes into a modern breeding program would not negatively impact yield. Nitrogen fixation was significantly higher among Middle American genotypes than among Andean genotypes, confirming previous findings. The best nitrogen fixing line was Coco Sophie, a European heirloom white bean whose genetic makeup is admixed between the Andean and Middle American genepools. Heirloom genotypes represent a useful source of genetics to improve SNF in modern bean breeding.

Synthetic biology and metabolic engineering promise to deliver sustainable solutions to global problems such as phasing out fossil fuels and replacing industrial nitrogen fixation. While this promise is real, scale matters, and so do knock-on effects of implementing solutions. Both scale and knock-on effects can be estimated by 'Fermi calculations' (aka 'back-of-envelope calculations') that use uncontroversial input data plus simple arithmetic to reach rough but reliable conclusions. Here, we illustrate how this is done and how informative it can be using two cases: oilcane (sugarcane engineered to accumulate triglycerides instead of sugar) as a source of bio-jet fuel, and nitrogen fixation by bacteria in mucilage secreted by maize aerial roots. We estimate that oilcane could meet no more than about 1% of today's U.S. jet fuel demand if grown on all current U.S. sugarcane land and that, if cane land were expanded to meet two-thirds of this demand, the fertilizer and refinery requirements would create a large carbon footprint. Conversely, we estimate that nitrogen fixation in aerial-root mucilage could replace up to 10% of the fertilizer nitrogen applied to U.S. maize, that 2% of plant carbon income used for growth would suffice to fuel the fixation, and that this extra carbon consumption would likely reduce grain yield only slightly.

Common bean (Phaseolus vulgaris L.) provides critical nutrition and a livelihood for millions of smallholder farmers worldwide. Beans engage in symbiotic nitrogen fixation (SNF) with Rhizobia. Honduran hillside farmers farm marginal land and utilize few production inputs; therefore, bean varieties with high SNF capacity and environmental resiliency would be of benefit to them. We explored the diversity for SNF, agronomic traits, and water use efficiency (WUE) among 70 Honduran landrace, participatory bred (PPB), and conventionally bred bean varieties (HON panel) and 6 North American check varieties in 3 low-N field trials in Ontario, Canada and Honduras. Genetic diversity was measured with a 6K single nucleotide polymorphism (SNP) array, and phenotyping for agronomic, SNF, and WUE traits was carried out. STRUCTURE analysis revealed two subpopulations with admixture between the subpopulations. Nucleotide diversity was greater in the landraces than the PPB varieties across the genome, and multiple genomic regions were identified where population genetic differentiation between the landraces and PPB varieties was evident. Significant differences were found between varieties and breeding categories for agronomic traits, SNF, and WUE. Landraces had above average SNF capacity, conventional varieties showed higher yields, and PPB varieties performed well for WUE. Varieties with the best SNF capacity could be used in further participatory breeding efforts.

The consumption of plant proteins is increasing worldwide as a viable alternative to animal‐derived proteins in the marketplace. The projected increase in global population to at least 10 billion by 2050 is placing greater pressure on the food supply, particularly due to the rising demand for large‐scale protein production. This protein transition is caused by macro‐drivers such as changing consumer demographics, environmental sustainability, animal ethics, regulatory influences, and changing dietary patterns. Research efforts worldwide have explored various food applications for plant protein ingredients, including meat analogs, dairy alternatives, beverages, bakery products, and hybrid products. We provide here a review of the potential for legume breeding programs to incorporate traits that target the emerging plant‐based protein market and aim to promote discussion among (but not limited to) plant breeders and geneticists, plant physiologists, agricultural economists, food scientists and chemists, and agricultural engineers. The prospects, progress, and tools developed when breeding for protein content, quality, structure, and functionality of several food legumes (common bean—Phaseolus vulgaris, pea—Pisum sativum, lentil—Lens culinaris, chickpea—Cicer arietinum, faba bean—Vicia faba, and mung bean—Vigna radiata) are presented. We also present some of the physiological processes that affect the accumulation of nitrogen and protein metabolism in tropical legume crop species, providing some insight into potential breeding targets for improving protein concentration, quality, and structural and functional properties. Finally, a perspective of industrial processing technologies for extracting and transforming plant proteins is discussed.

Plant breeding and genetics play a major role in the adaptation of plants to meet human needs. The current requirement to make agriculture more sustainable can be partly met by a greater reliance on biological nitrogen fixation by symbiotic diazotrophic microorganisms that provide crop plants with ammonium. Select accessions of the cereal crop sorghum (Sorghum bicolor (L.) Moench) form mucilage-producing aerial roots that harbor nitrogen-fixing bacteria. Breeding programs aimed at developing sorghum varieties that support diazotrophs will benefit from a detailed understanding of the genetic and environmental factors contributing to aerial root formation. A genome-wide association study of the sorghum minicore, a collection of 242 landraces, and 30 accessions from the sorghum association panel was conducted in Florida and Wisconsin and under 2 fertilizer treatments to identify loci associated with the number of nodes with aerial roots and aerial root diameter. Sequence variation in genes encoding transcription factors that control phytohormone signaling and root system architecture showed significant associations with these traits. In addition, the location had a significant effect on the phenotypes. Concurrently, we developed F₂ populations from crosses between bioenergy sorghums and a landrace that produced extensive aerial roots to evaluate the mode of inheritance of the loci identified by the genome-wide association study. Furthermore, the mucilage collected from aerial roots contained polysaccharides rich in galactose, arabinose, and fucose, whose composition displayed minimal variation among 10 genotypes and 2 fertilizer treatments. These combined results support the development of sorghums with the ability to acquire nitrogen via biological nitrogen fixation.

Sorghum ( Sorghum bicolor ) is a significant crop globally, serving as an important source of food, feed, and fodder, and is increasingly recognized as an energy crop due to its high potential for biomass production. Certain sorghum accessions exhibit prolific aerial root development and produce abundant carbohydrate-rich mucilage after precipitation. This aerial root mucilage bears resemblance to that found in landraces of maize ( Zea mays ) from southern Mexico, which have previously been found to harbor diazotrophs. In this study, we examined the aerial root development of specific sorghum accessions and investigated the influence of humidity on this trait. Our microbiome analysis of the aerial root mucilage of maize and sorghum revealed the presence of numerous diazotrophs in sorghum mucilage, with Pseudomonadota , Bacillota , and Bacteriodota being the predominant phyla observed. However, the community composition varied significantly depending on the host plant and location. Through acetylene reduction, ¹⁵ N ₂ gas feeding, and ¹⁵ N isotope dilution assays, we determined that these sorghum accessions can acquire approximately 40% of their nitrogen from the atmosphere through these symbiotic associations on aerial roots. The nitrogen fixation occurring in sorghum aerial root mucilage presents a promising opportunity to reduce reliance on synthetic fertilizers and advance sustainable agricultural practices for food, feed, fodder, and bioenergy production.