No abstract

Nitrogen (N) is the most yield-limiting crop nutrient worldwide. Industrially produced N has increased in cost over the past years, and is unavailable in many regions around the globe. Biological N fixation by rhizobial bacteria is a great underutilized resource that this project aims to maximize. Grain legumes fix approximately 20 to 100 kg·N·haThe amount of N supplied by fixation is affected by genes and traits of both the bacterial and plant partners. The objectives of this study are to identify Pisum sativum varieties with high nitrogen fixation efficiency. This is achieved by germplasm screening and phenotypic evaluation of nodule formation, total plant nitrogen, and residual nitrogen in soil. Significant differences in plant total nitrogen among the various cultivated genotypes were found, with heritability of 0.57. These pea varieties left in the soil a residual N that varies between 11.21 to 65.018 kg·N·ha −1. Our findings reveal a unique opportunity for improving N fixation through genetic crossing and selection.

No abstract

Selection of cell lysis methodology is critical to microbial community analyses due to the inability of any single extraction technology to recover the absolute genetic structure from environmental samples. Numerous methodologies are currently applied to interrogate soil communities, each with its own inherent bias. Here we compared the efficacy and bias of three physical cell lysis methods in conjunction with the PowerLyzer PowerSoil DNA Isolation Kit (MO BIO) for direct DNA extraction from soil: bead-beating, vortex disruption, and hydrostatic pressure cycling technology (PCT). PCT lysis, which is relatively new to soil DNA extraction, was optimized for soils of two different textures prior to comparison with traditional bead-beating and vortex disruption lysis. All cell lysis methods successfully recovered DNA. Although the two traditional mechanical lysis methods yielded greater genomic, bacterial, and fungal DNA per gram soil than the PCT method, the latter resulted in a greater number of unique terminal restriction fragments by terminal RFLP (T-RFLP) analysis. These findings indicate the importance of diversity and quantity measures when assessing DNA extraction bias, as soil DNA retrieved by PCT lysis represented populations not found using traditional mechanical lysis methods.

Chickpeas (Cicer arietinum L.) are native to the Middle East (ME) and must be inoculated with symbiotic bacteria (Mesorhizobium ciceri) to fix nitrogen (N) in North American soils. Whether commercial M. ciceri strains are more or less effective than wild strains from ME soils when paired with various chickpea hosts must be elucidated. Wild N-fixing bacterial strains were isolated from ME soils, and their effectiveness was compared against commercial strains on US and ME chickpea varieties. Chickpeas were inoculated with individual strains and grown in chambers for 8 weeks. Plants received 2 mM ( 15 NH 4 ) 2 SO 4 (5% atom excess) to measure N fixation by isotope dilution. Plant below-and above-ground biomass and proportion of N fixed (PNF) were determined. Commercial and wild ME strains were examined for genetic diversity by sequencing their 16 S rDNA region. The PNF was significantly influenced by inoculant strains and chickpea varieties. Among varieties, Sierra, Troy, and Almaz had the highest PNF of 86.7%, 85.3%, and 85.2%, respectively. Among strains, Jord-M1 contributed to greater PNF (84.7%) compared to Syr-M1 (81.4%). Overall, chickpea varieties had greater effect on PNF than strain selection. These findings support efforts focusing on varietal breeding and strain selection to increase agricultural N fixation.