Submitted to: Proceedings Sunflower Research Workshop
Publication Type: Proceedings
Publication Acceptance Date: March 17, 2005
Publication Date: March 17, 2005
Citation: Rojas-Barros, P., Jan, C.C., Gulya Jr, T.J. 2005. Transferring powdery mildew resistance genes from wild helianthus into cultivated sunflower. Proceedings Sunflower Research Workshop. Available: http://www.sunflowernsa.com/research/research-workshop/documents/Rojas_PowderyMildew_05.pdf Interpretive Summary: Powdery mildew (PM) (Erysiphe chicoracearum D.C.) may cause economic loss in warmer regions where the sunflower crop can be expanded. Several wild annual and perennial sunflower species have been reported to be sources of resistance genes to PM. However, there are no reported resistant cultivars, and only a germplasm population with incomplete dominant genes for this resistance, PM1, has been released. Two wild annual sunflower species have been reported as important sources of PM resistance, which can be easily incorporated into cultivated sunflower. Preliminary inheritance studies of these resistances showed that they were dominant and controlled by at least two genes, and new PM resistant germplasm can be developed from the resistant plant material.
Technical Abstract: Hybrids between the PM resistant plants of Helianthus argophyllus and Helianthus debilis ssp. debilis and the susceptible line HA 89 were obtained. In the H. debilis ' HA 89 cross, the seed set of F1 and BC1F1 was very low, and F2 seeds were not obtained. The F1, BC1F1 plants were obtained using embryo rescue technique. Also, due to the improved pollen fertility after each backcross to the cultivated species, BC1F2 seeds were produced by selfing BC1F1 plants. In the H. argophyllus x HA 89 cross, the percentage of viable F1 seeds was higher, and embryo rescue technique was only used to obtain F1 plants. BC1F1 to HA 89 plants were produced from developed seeds, which had 90% germination. Parents, F1, and 15 BC1F1 plants from each F1 of the H. argophyllus x HA 89 cross, and 20 BC1F2 plants from each of six H. debilis x HA 89 BC1F2 plants were grown in the greenhouse during the summer of 2004, and were inoculated with PM inoculum for preliminary study of the inheritance of their PM resistances. The levels of PM resistance of the plants were assigned to the three classes: i) resistant (R), ii) susceptible (S), and iii) highly susceptible (HS), based on the frequency distribution found in the parents and F1 grown under the same environment. The F1 derived from the cross H. argophyllus x HA 89 was resistant to PM. In the BC1F1 to the susceptible line HA 89, we found two different segregations patterns: for one gene 1:1 and for two genes 1:3 (R: S classes). Previously, we found that the PM resistance from H. debilis was partially dominant. In the present study, the proportions of the phenotypic classes in the BC1F2 families from the H. debilis x HA 89 cross were adjusted to four expected ratios: 1R:2S:1HS, 3S:1HS, 1S:3HS and 9R:6S:1HS. These results confirm the heterozygosity of wild parents and suggest a polygenic nature for both PM resistances. Future inheritance studies using appropriate population size for a polygenic inheritance are needed in order to determine the number of genes involved in PM resistance. The introgression of the PM resistance into cultivated sunflower appears to be easier using H. argophyllus than H. debilis ssp. debilis. This could be explained by the fact H. argophyllus is a closer relative to the cultivated sunflower. Resistant plant material obtained will be used for the development of new PM resistant germplasm.