Genetic architecture of novel traits in the hopi sunflower.

Following domestication, crop lineages typically undergo diversification either to adapt to disparate habitats or to fill novel agricultural roles. This process has produced the numerous varieties found in modern-day crop germplasm collections. Here, we mapped quantitative trait loci (QTLs) underlying unique traits in the Hopi sunflower, a primitive, Native American domesticate. These traits included a variety of achene (i.e., single-seeded fruit) characters as well as the extremely late flowering time of the Hopi sunflower. Composite interval mapping identified 42 QTLs underlying the 12 traits of interest. Although these QTLs were found on 10 of the 17 sunflower linkage groups, strong genetic correlations were evidenced by the clustering of QTLs across traits in certain genomic regions. The number of QTLs per trait ranged from 2 to 6, and the average QTL explained 14.7% of the variance (range: 2.5-46.9%). The apparent contribution of epistasis was minor, as has previously been observed for domestication-related traits. Unlike typical domestication-related traits in sunflower, the traits under consideration here exhibited a relatively simple genetic basis, with 2 QTL clusters being largely responsible for the unique characteristics of the Hopi sunflower. Based on the rarity of these traits in domesticated sunflower, it would appear that they evolved within the Hopi lineage following domestication. The simple genetic architecture of these traits may be a by-product of genetic constraints imposed by the genetically complex nature of domestication-related traits in sunflower, with the large number of domestication-related QTLs limiting the fraction of the genome that is available for subsequent diversification.