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

Jennifer Wilker,Frédéric Marsolais,Davoud Torkamaneh,Brett Hill,Alireza Navabi,Istvan Rajcan,K Peter Pauls

doi:10.3389/fpls.2019.00952

Jennifer Wilker, Frédéric Marsolais + Show 5 more

Open Access

https://doi.org/10.3389/fpls.2019.00952

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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.

Highlights

Since its origin in central Mexico some 2 My ago, common bean (Phaseolus vulgaris L.) has diverged into two genepools in Central America and South America, been domesticated and spread throughout the world (Kaplan and Lynch, 1999; Gepts et al, 2000; Bitocchi et al, 2017)
The objectives of this study were to compare heirloom and conventionally bred bean genotypes from both the Andean and Middle American genepools for their capacity for symbiotic nitrogen fixation (SNF), to assess whether genetic diversity has been lost over years of modern breeding, and to assess agronomic characteristics to determine the suitability of using heirloom varieties in modern breeding programs
Amish Gnuttle (Amish Nuttle; known as Cornhill Bean or Mayflower) is described by some retailers as a variety that was introduced to America with the early settlers and has been grown by Amish communities for generations, while other variety descriptions suggest that Amish Gnuttle originated with the Seneca First Nation

Summary

Introduction

Since its origin in central Mexico some 2 My ago, common bean (Phaseolus vulgaris L.) has diverged into two genepools in Central America and South America, been domesticated and spread throughout the world (Kaplan and Lynch, 1999; Gepts et al, 2000; Bitocchi et al, 2017). Before the establishment of formal bean breeding programs, landraces maintained by First Nations groups and European settlers were grown throughout North America (Kelly, 2010). Aside from their historical origin and association with early farming systems, bean landraces are characterized by having local genetic adaptation, high genetic diversity and a lack of formal genetic improvement (Villa et al, 2005). Market demands and producer requirements are believed to have led to narrow breeding objectives and reduced genetic diversity in modern bean cultivars (Singh, 1988). This reduction in genetic diversity may have led to a reduction in diversity and capacity for nitrogen fixation in modern bean genotypes

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