Molecular tagging and genetic mapping of the disease resistance gene RppQ to southern corn rust

Southern corn rust (SCR), Puccinia polysora Underw, is a destructive disease in maize ( Zea mays L.). Inbred line Qi319 is highly resistant to SCR. Results from the inoculation test and genetic analysis of SCR in five F(2) populations and five BC(1)F(1 )populations derived from resistant parent Qi319 clearly indicate that the resistance to SCR in Qi319 is controlled by a single dominant resistant gene, which was named RppQ. Simple sequence repeat (SSR) analysis was carried out in an F(2) population derived from the cross "Qi319x340". Twenty SSR primer pairs evenly distributed on chromosome10 were screened at first. Out of them, two primer pairs, phi118 and phi 041, showed linkage with SCR resistance. Based on this result, eight new SSR primer pairs surrounding the region of primers phi118 and phi 041 were selected and further tested regarding their linkage relation with RppQ. Results indicated that SSR markers umc1,318 and umc 2,018 were linked to RppQ with a genetic distance of 4.76 and 14.59 cM, respectively. On the other side of RppQ, beyond SSR markers phi 041 and phi118, another SSR marker umc1,293 was linked to RppQ with a genetic distance of 3.78 cM. Because the five linkage SSR markers (phi118, phi 041, umc1,318, umc 2,018 and umc1,293) are all located on chromosome 10, the RppQ gene should also be located on chromosome 10. In order to fine map the RppQ gene, AFLP (amplified fragment length polymorphism) analysis was carried out. A total 54 AFLP primer combinations were analyzed; one AFLP marker, AF1, from the amplification products of primer combination E-AGC/M-CAA, showed linkage with the RppQ gene in a genetic distance of 3.34 cM. Finally the RppQ gene was mapped on the short arm of chromosome 10 between SSR markers phi 041 and AFLP marker AF1 with a genetic distance of 2.45 and 3.34 cM respectively.