LAUSR

Significance Life is a product of many genes that interact to enhance fitness. Genetics has made much progress in mapping quantitative trait loci (QTLs) that affect complex traits while the probing of epistasis is still rudimentary. To characterize epistasis—the nonlinear interaction of genes—we developed interspecific backcross inbred lines of unparalleled size and mapping resolution. Of the 80 cases of QTL epistasis, we selected validation of QTLs on chromosomes 1 and 7 that independently had no effect on yield, but surprisingly, together they increased yield by 20 to 50% over a period of 4 y in irrigated and dry fields. Our work demonstrates the power of a very large interspecific population to highlight rare epistatic QTLs that improve productivity via heterosis.