QTL × environment interactions underlie adaptive divergence in switchgrass across a large latitudinal gradient

Area of Science:

• Plant genetics
• Evolutionary biology
• Ecology

Background:

• Local adaptation drives species divergence along environmental gradients.
• Genetic trade-offs are theorized to cause fitness costs in non-native environments.
• Reciprocal transplant experiments are common but limited in scope.

Purpose of the Study:

• To quantify benefits and costs of locally adaptive loci in switchgrass (Panicum virgatum L.).
• To assess genetic trade-offs across a wide latitudinal gradient (17°).
• To inform breeding strategies for developing regionally adapted cultivars.

Main Methods:

• Utilized a four-grandparent outbred mapping population of switchgrass.
• Conducted quantitative trait locus (QTL) mapping across 10 field sites from Texas to South Dakota.
• Monitored biomass (fitness) and transplant performance over two years.

Main Results:

• Beneficial biomass QTL generally exhibited minimal fitness costs when transplanted across diverse sites.
• No significant trade-offs were observed for locally adaptive loci across the tested environmental gradient.
• This indicates a high degree of genetic flexibility in locally adapted alleles.

Conclusions:

• Locally advantageous alleles in switchgrass may not incur substantial fitness costs in alternative environments.
• Combining beneficial alleles across loci through breeding is a viable strategy for developing high-yielding, regionally adapted cultivars.
• Findings challenge the universality of strong genetic trade-offs in local adaptation.