Detection of Quality Protein Maize (QPM) using Simple Sequence Repeat (SSR) Markers and Analysis of Tryptophan Content in Endosperm

Abstract

Quality protein maize (QPM) controlled by opaque-2 (o₂) gene was detected using two simple sequence repeat (SSR) markers and further confirmed by tryptophan content in the endosperm. Three populations, i.e., Pop61C1, Pop62C6 and Pop65C6 from the International Maize and Wheat Improvement Center (CIMMYT) were used. S0-plants were selected for the presence of QPM using two markers (phi057 and phi112) as indicated by the amplified products of 140-160 bp. The phi057 marker identified 24 out of 40 Pop61C1 plants (60%), 34 out of 35 Pop62C6 plants (97%) and 24 out of 30 Pop65C6 plants (80%) to be opaque-2 positive while phi112 marker identified 34 (85%), 35 (100%) and 30 (100%) to be opaque-2 plants from the respective populations. Since phi112 was a dominant marker not for detecting the heterozygous genotype, it could only indicate the difference between QPM inbreds and normal maize. The phi057, on the other hand, is a co-dominant marker and could identify the heterozygote of maize plants and therefore, the contamination of non-QPM presented in CIMMYT population. The endosperms of selected S1-seed were further analyzed for the tryptophan and protein content. The three maize populations were found containing the same protein quantity, but different in tryptophan content. The average tryptophan contents in endosperm of QPM and non-QPM as detected by phi057 marker were 0.66% (for QPM), 0.38% (for non-QPM), 0.38% for Suwan 1 (a non-QPM) and 0.80% for the opaque-2 control variety. Moreover, those QPM and non-QPM plants detected by phi112 showed the same result of total protein and tryptophan content in endosperm. To detect heterozygote maize for backcross breeding program, phi057 was considered more feasible than phi112 as a marker assisted selection (MAS) for opaque-2 and to identify QPM line in the short period of time.