|TORNQVIST, CARL-ERIK - University Of Wisconsin|
|TAYLOR, MEGAN - Purdue University|
|JIANG, YIWEI - Purdue University|
|EVANS, JOSEPH - Dupont Pioneer Hi-Bred|
|BUELL, ROBIN - Michigan State University|
|KAEPPLER, SHAWN - University Of Wisconsin|
Submitted to: BioEnergy Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2018
Publication Date: 4/12/2018
Citation: Tornqvist, C., Taylor, M., Jiang, Y., Evans, J., Buell, R., Kaeppler, S., Casler, M.D. 2018. Quantitative trait locus mapping for flowering time in a lowland x upland switchgrass pseudo-F2 population. BioEnergy Research. https://doi.org/10.3835/plantgenome2017.10.0093.
Interpretive Summary: Switchgrass is undergoing development as a dedicated biomass crop for conversion to bioenergy. To be an economically sustainable crop, biomass yields must be increased by about 100%. To accomplish this, breeding programs are focused on developing varieties of switchgrass that flower later in the season, ideally as late as possible, allowing the crop to continue accumulating biomass as long as the weather allows. The most efficient way to do this is to use DNA markers that are linked to critical genes in the flowering pathway. DNA markers can be tested on seedlings, allowing late-flowering plants to be identified early in their life history and potentially reducing the time required for each breeding cycle from 3 years to 1 year. This study identified nine candidate genes that, individually, resulted in delays in flowering from 2 to 13 days. Collectively stacking some of these genes together could potentially result in a flowering delay of up to 25 days. Several of the genes identified in this study are strongly related to known genes that influence flowering in model plants, providing some validation of the results. This research has generated a tool that can be used by any switchgrass breeder to rapidly select switchgrass plants that flower later.
Technical Abstract: Flowering is an important developmental event in switchgrass (Panicum virgatum), as the time to complete the life cycle affects overall biomass accumulation. The objective of this study was to generate a linkage map using single-nucleotide polymorphism (SNP) markers to identify quantitative trait loci (QTL) associated with flowering time. A pseudo-F2 population was created by crossing two siblings that were derived from an initial cross between the lowland population Ellsworth and the upland cultivar Summer. Heading and anthesis dates were collected for two years at two locations: DeKalb, IL and West Lafayette, IN. Overall, nine QTL for flowering time were detected, two of which were heading-associated, four were anthesis-associated, and three were associated with both heading and anthesis. One QTL on linkage group (LG) 2a was detected for heading and anthesis in each location and year when environments were analyzed separately, and in a combined analysis across both locations and years. The effect on heading and anthesis of the QTL on LG 2a ranged from 4 to 13 days and 5 to 9 days, respectively, depending on the environment. Our findings validate QTL for switchgrass flowering time from previous research, and identified additional QTL. Homologs of flowering time genes reside on chromosome 2a, based on the switchgrass reference genome version 1.1. Examining the flowering time genes in proximity to the LG 2a (chromosome 2a) QTL, candidate genes were identified including PSEUDO RESPONSE REGULATOR 5, involved in coordinating photoperiod cues with the circadian clock; SUPPRESSOR OF FRIGIDA 4, a vernalization-related gene from Arabidopsis; and APETALA 1, a floral meristem identity gene. Markers linked to the QTL can be used to improve the efficiency of breeding switchgrass for delayed flowering to increase biomass yield.