Location: Sunflower and Plant Biology ResearchTitle: Inheritance and molecular mapping of a downy mildew resistance gene, Pl13 in cultivated sunflower (Helianthus annuus L.) Author
|Gulya Jr, Thomas|
Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/30/2009
Publication Date: 8/30/2009
Citation: Mulpuri, S., Liu, Z., Feng, J., Gulya, T.J., Jan, C. 2009. Inheritance and Molecular Mapping of a Downy Mildew Resistance Gene, Pl13 in Cultivated Sunflower (Helianthus annuus L.). Theoretical and Applied Genetics. 119(5):795-803. Interpretive Summary: Downy mildew is a major disease in all sunflower growing regions. Among the various methods of control, host-plant resistance using race-specific resistance genes, designated as Pl genes, is the most effective. The predominant races of downy mildew in the major sunflower producing countries are 700, 710, 730, and 770. HA-R5 is a germplasm with resistance to four races of rust, nine races of downy mildew, and verticillium wilt; facilitating incorporation of resistance to three major diseases from a single source. The present study investigates the inheritance of resistance of HA-R5 to four predominant races of downy mildew (300, 700, 730, and 770) and maps a resistance gene onto the sunflower linkage map using an F2 population derived from a cross between HA-R5 (resistant) and HA 821 (susceptible). The results of this study indicate a single dominant gene, Pl13, control of the resistance to the four predominant downy mildew races. The gene is flanked by two closely linked molecular markers, which will greatly enhance the efficiency of selection in breeding programs.
Technical Abstract: The inheritance of resistance to sunflower downy mildew (SDM) derived from HA-R5 conferring resistance to nine races of the pathogen has been determined and the new source has been designated as Pl13. The F2 individuals and F2-3 families of the cross HA-R5 (resistant) x HA 821 (susceptible) were screened against the four predominant SDM races 300, 700, 730, and 770 in separate tests which indicated dominant control by a single locus. Bulked segregant analysis (BSA) was carried out on 116 F2 individuals with 500 SSR primers that resulted in the identification of 10 SSR markers of linkage groups 1 (9 markers) and 10 (1 marker) of the map of Tang et al. (2002) that distinguished the bulks. Of these, the SSR marker ORS 1008 of linkage group 10 was tightly linked (0.9 cM) to the Pl13 gene. Genotyping the F2 population and linkage analysis with 20 polymorphic primers located on linkage group 10 failed to show linkage of the markers with downy mildew resistance and the ORS 1008 marker. Nevertheless, validation of polymorphic SSR markers of linkage group 1 along with six RFLP-based STS markers of linkage group 12 of the RHA 271 x HA 234 map of Jan et al. (1998) corresponding to LG1 of the SSR map, mapped seven SSR markers (ORS 1008, ORS 965-1, ORS 965-2, ORS 959, ORS 371, ORS 716, and ORS 605) and one STS marker (STS10D6) to linkage group 1 covering a genetic distance of 65.0 cM. The Pl locus (Pl1, Pl2, Pl5, and Pl6) governing downy mildew resistance has been described on linkage group 8 and has been characterized by several investigators. To examine the possible involvement of some of these loci, 12 SSR markers of linkage group 8 that identify polymorphism in parents and three STS primers specific to downy mildew resistance were tested on 12 homozygous resistant and susceptible plants. None of the markers of linkage group 8 were found to be associated with downy mildew resistance in HA-R5, which confirmed Pl13 as a different gene source with its location on linkage group 1.