131 USM R & D 17(2): 131-135 (2009) ISSN 0302-7937 Marker-assisted introgression of opaque 2 gene into elite maize inbred lines Efren E Magulama and Emma K Sales Associate Professor IV and Professor V, Department of Plant Breeding and Genetics, College of Agriculture, University of Southern Mindanao, Kabacan, Cotabato, Philippines, Email: emagulama@yahoo.com Abstract Marker assisted backcrossing can greatly accelerate the introgression of modiied opaque2 gene into elite inbred lines. This study aimed to transfer opaque 2 gene into elite maize inbred lines using SSR markers. Two backcross maize (white and yellow) populations were developed by crossing quality protein (QP) line with non-QP lines and subsequently backcrossed to non-QP lines until BC 3 generation. Among the three SSR markers (phi 057, umc 1066, and phi 112) used for opaque2 gene selection, only SSR phi 057 marker was employed in segregating populations owing to its good discriminatory power in the survey of parental polymorphism. Using marker assisted selection, we transferred opaque 2 gene into USM elite breeding lines. Of the 26 converted QPM lines (16 white, 10 yellow) selected from the BC 3 F 3 populations, seven lines (4 white, 3 yellow) were inally selected as quality protein inbred lines, having satisied the minimum standard criteria for protein quality. These converted QPM lines could be used as parent lines in the development of QPM varieties. Key words: backcrossing, corn breeding, elite inbred lines, QPM lines (quality protein maize), and ssr marker. Introduction Maize plays a very important role in human and animal nutrition. Superior QPM hybrids are extremely valuable for the white-maize food industry and yellow maize for the animal feed industry. In the Philippines, 80% of the maize produced is used as feed for swine and poultry. Eleven percent (11%) and 13 % are used as human food and for other industrial purposes, respectively (Gerpacio 2001). The development of well-adapted QPM germplasm will have tremendous value for the food and feeds industry. Moreover, it does provide a nutritionally balanced source of protein. The opaque 2 (o2) mutation increases the lysine and tryptophan contents in maize endosperm by decreasing the synthesis of zein proteins and increasing the level of other lysine-rich proteins. Scientists in CIMMYT and South Africa systematically introgressed mo2 (o2 modiiers) genes into o2 germplasm and developed hard endosperm o2 populations to produce so-called “Quality Protein Maize” (QPM). The potential of QPM to dramatically improve nutrition was recognized in the award of the World Food Prize in 2000 (Cordova 2001). Three SSR markers, phi57, phi112, and umc1066, identiied as internal repetitive sequences within the o2 gene, were used successfully to convert normal maize lines into QPM and CIMMYT (Dreher et al 2003). The markers could be used in conirming the homozygous o2 gene, thus avoiding the need to determine lysine content in QPM breeding program. Moreover, the marker-assisted breeding strategy obviates the need for seling and lysine examination after each backcross, thus markedly shortening the breeding duration. With the new research thrust focusing on maize hybrid breeding program of the University of Southern Mindanao Agricultural Research Center (USMARC), inbred lines developed by USM maize breeders are increasing in number these recent years. However, no local-version of QPM lines are available. To utilize the nutritional potential of QPM in Southern Philippines, efforts are being made by USMARC to introgress opaque mutation and its associated modiier into elite breeding lines. Therefore, this study aimed to transfer the QPM allele (opaque2) to an elite USM inbred through marker assisted backcrossing. Methodology Survey of parental polymorphism To determine which parental lines should be used for marker-aided selection, survey of parental polymorphism were conducted using three SSR markers for opaque 2 gene. These markers were phi 057, phi 112, and umc 1066. QPM lines and non QPM lines were used to survey parental polymorphism on these three SSR markers. Primer sequences (F=forward and R=reverse) used were as follows (www.maizegdb.org): phi057: F, 5’-CTCATCAGTGCCGTCGTCCAT-3’; R, 5’-CAGTCGCAAGAAACCGTTGCC-3’: umc1066: F, 5’-ATGGAGCACGTCATCTCAATGG-3’; R, 5’-AGCAGCAGCAACGTCTATGACACT-3’: phi112: F, 5’-TGCCCTGCAGGTTCACATTGAGT3’; R, 5’-AGGAGTACGCTTGGATGCTCTTC- 3’: