Silverleaf sunflower (Helianthus argophyllus, Torrey and Grey) in sunflower breeding
Rey, Juan Ignacio
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Cultivated sunflower (Helianthus annuus L.) is the fourth most important oil crop worldwide and its genus Helianthus comprises 50 species which are native to North America. Due to a genetic bottleneck during domestication, cultivated sunflower lacks the necessary variability to adapt to changing biotic and abiotic conditions. To overcome this deficiency in the domesticated germplasm, breeders have utilized wild species to expand the genetic variability to be incorporated into elite sunflower breeding populations. H. argophyllus is the closest relative of H. annuus and has been extensively used in sunflower breeding. We developed a H. argophyllus high density genetic linkage map with 1549 EST-SNP markers. Through comparative mapping with a consensus H. annuus map sharing 1445 EST-SNP markers we were able to identified 11 colinear chromosomes and four chromosomes rearrangements (two non-reciprocal translocation, one reciprocal translocation and one inversion). In spite of these rearrangements affecting gene-flow between species most of the H. argophyllus genome is colinear with H. annuus facilitating its introgression and use in sunflower breeding. Since H. argophyllus has been reported to be salt tolerant, we also studied the feasibility of using this species as a source of salt tolerance alleles. We performed QTL analysis in two generations (F2 and BC1S1) of a cross between H. annuus and H. argophyllus using Bayesian QTL interval mapping to elucidate the complexity of salt tolerance in sunflower. We were able to identify 5 and 10 QTL for the F2 and BC1S1 generations, respectively, responsible for salt tolerance rating, weighted salt tolerance rating, and SPAD value. QTL analysis using two generations of the same cross and QTL comparison with other salt tolerance studies in sunflower allowed us to identify three important genomic regions for salt tolerance. We also discovered that salt tolerance in sunflower is highly complex and epistatic interactions are of greatly importance in the expression of the trait. In addition, we performed QTL analysis of a BC2 Testcross set of families growing under saline and non-saline conditions. This experiment helped us make inferences about the best strategy to be use in the improvement of salt tolerance in sunflower. We found 22 and 26 QTL responsible for nine traits related to productivity and salt tolerance under saline and non-saline conditions, respectively. We found only two QTL in common between both saline treatments which indicated a large genotype by salt condition interaction. The QTL found were also of small effect which it will affect their utility in marker-assisted-selection.