Genome-wide association study for electrolyte leakage in rapeseed/canola (Brassica napus L.)

Authors: FIEBELKORN, DANIELLE - North Dakota State University; Horvath, David; RAHMAN, MUKHLESUR - North Dakota State University

Submitted to: Molecular Breeding
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/24/2018
Publication Date: 10/24/2018
Citation: Fiebelkorn, D., Horvath, D., Rahman, M. 2018. Genome-wide association study for electrolyte leakage in rapeseed/canola (Brassica napus L.). Molecular Breeding. 38:129. https://doi.org/10.1007/s11032-018-0892-0.
DOI: https://doi.org/10.1007/s11032-018-0892-0

Interpretive Summary: Canola is an important crop for the northern Great Plains, but frost damage can limit yield and cost growers money. In order to develop canola lines with superior frost tolerance, breeders need to know which portions of the genome contain genes that control the level of freezing tolerance. One way to do this is to collect a large number of cultivars (called a mapping population or sometimes a diversity panel) and evaluate their freezing tolerance of each cultivar, and then use DNA sequences that mark 10s of 1000s of places all over the genome to look for genome locations that are statistically associated with the level of freezing tolerance. We used a method called electrolyte leakage which measures how much damage is caused to the cell membranes by ice formation to evaluate the damage caused by freezing in our diversity panel of 157 different cultivars of canola. We identified 10 genomic regions that were associated with differences in freezing tolerance among our canola cultivars. We found 33 genes located within these 10 regions that we suspect may play a role in freezing–induced membrane damage.

Technical Abstract: Freezing temperature/frosts can cause significant damage to plants by rupturing plant cells. Rapeseed/canola (Brassica napus L.) is susceptible to freezing temperature at early seedling stage. The degree of cell rupture or seedling damage can be evaluated through the measurement of electrolyte leakage. Here we measured the electrolyte leakage of a diversity panel of B. napus germplasm accessions under simulated freezing conditions. Preliminary data for electrolyte leakage measurement indicated cold acclimation of two-week old seedlings for 7 days at 4°C followed by freezing treatment at -12°C for 2 h provided a reasonable diversity in response. With this protocol for electrolyte leakage, a genome-wide association study was conducted on 157 winter, semi-winter and spring types B. napus accessions that originated from 17 countries. A total of 37,454 single nucleotide polymorphism (SNP) markers based upon genotyping-by-sequencing were used for the analysis. Ten QTL were identified as associated with electrolyte leakage of canola seedlings, which together explained 43% phenotypic variation. Five of the QTL were located on A-genome. We identified at least 33 orthologs of the functional candidate genes. Although no well characterized cold regulatory genes were identified, there were some indications that genes involved in membrane structure, developmental processes, and extracellular transport may be involved in altering the electrolyte leakage following the short term hard freeze and rapid defrosting suffered by the plants in our protocol.