Agronomic Performance and Nitrogen Fixation of Heirloom and Conventional Dry Bean Varieties Under Low-Nitrogen Field Conditions

Abstract

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.

Evaluation of beneficial and inhibitory effects of nitrate on nodulation and nitrogen fixation in common bean (Phaseolus vulgaris)

“…Common bean has been noted in several studies to be a weak N 2 fixer in comparison with other leguminous plants; however, genotypic effects (genetic variability) play a large role in common beans ability to fix nitrogen as several P. vulgaris genotypes have been reported to have higher SNF capability when compared with other genotypes. (Farid & Navabi, 2015;Kamfwa et al, 2015;Farid et al, 2016;Farid et al, 2017;Wilker et al, 2019). It is possible that, compared with other legumes, common bean can take better advantage of low N quantities present in the soil under field conditions.…”

Abiotic treatment to common bean plants results in an altered endophytic seed microbiome

“…Another consideration is the definition and directness of abiotic treatment, and whether an abiotic treatment is expected to act on the plant, the microbiome, or both. In this pilot study, we applied two different abiotic treatments: one that was expected to stress the plant directly (water-withholding to simulate mild drought) and one that was expected to weaken a legume’s relationship with its root-associated microbiome and symbiotic nitrogen fixers as nitrogen fixers are down-regulated by nitrogen application (Müller & Pereira, 1995; Wilker et al, 2019) (nutrient addition). Thus, the addition of nutrients was a benefit to the plant, rather than a stress, as indicated by the increased root and shoot masses.…”

Genetic Diversity, Nitrogen Fixation, and Water Use Efficiency in a Panel of Honduran Common Bean (Phaseolus vulgaris L.) Landraces and Modern Genotypes

“…Strong nitrogen-fixers would have a competitive advantage in the low input environments and would likely be preferentially selected over time. There may be parallels between the selection pressures during landrace evolution and the selection of heirloom bean varieties, which have also been shown to have strong SNF capacity [18].…”

“…Preplant fertilizer (0-20-20) at a rate of 200 kg ha −1 was applied approximately one week prior to planting. Preplant herbicide was applied to control broadleaf weeds, and pesticides were applied as needed throughout the growing season at standard rates to control leafhoppers, anthracnose, and root rot (see details in Wilker et al [18]). Plots were manually weeded once before canopy closure each year.…”

“…Seed from each plot was processed and analyzed as detailed in Wilker et al [18]. Briefly, seed was finely ground, precisely measured, and the isotope analyses were carried out using mass spectrometry at the Agriculture and Agri-food Canada (AAFC) gas chromatography mass spectrometry facility in Lethbridge, Alberta.…”