Medicago truncatula EST-SSR MARKERS LINKED TO APHID RESISTANCE IN ALFALFA

¹ Forage Improvement Division, The Samuel Roberts Noble Foundation, 2510 Sam Noble Parkway, Ardmore, OK 73401, USA

Spotted alfalfa aphid (SAA), Therioaphis trifolii, is a serious pest of many crop plants including alfalfa (Medicago sativa L.) and barrel medics (Medicago truncatula). The objectives of this study were to identify M. truncatula EST-SSR markers linked to SAA resistance in alfalfa and locate the resistance gene(s) on the alfalfa genome. A pseudo testcross population of 111 F1 progeny was developed by crossing an SAA susceptible alfalfa line with an SAA resistant line. The parents and the progeny segregated for SAA resistance. The susceptible and resistant DNA bulks were created by pooling the DNA from 12 susceptible and 12 resistant progeny, respectively. Two hundred M. truncatula EST-SSR markers were used for bulk segregate analyses (BSA) of DNA of the parents, the susceptible and the resistant bulks. From the BSA, several (8-10) markers appeared to be linked SAA resistance in this alfalfa population. All progeny in the population are being screened with these putatively linked markers to locate the SAA resistance gene(s) on the alfalfa genome. EST-SSR markers tightly linked to SAA resistance will be useful for marker assisted breeding of alfalfa for SAA resistance. Such markers will also be useful for comparative mapping of SAA resistance between alfalfa and M. truncatula.