Phenotypic Recurrent Selection for Increased Endosperm Hardness in Two High-Lysine Maize Synthetics

The agronomic problems associated with high lysine opaque-2 maize (Zea mays L.) could be eliminated with the development of opaque-2 genotypes with harder endosperm texture. Two opaque-2 maize synthetics Illinois Disease Oil Opaque-2 and Illinois Elite Single Cross Opaque-2 were selected for increased endosperm modification or kernel hardness. Phenotypic recurrent selection was used to select for increased endosperm modification for five cycles. Seed from 200 individual selfed plants in each synthetic was evaluated for endosperm modification each cycle, and seed from 40 plants with the highest endosperm modification were intermated to produce the next cycle of selection. Progeny representing each of the five cycles of each synthetic were evaluated for 2 yr (1991–1992) in replicated field experiments at Urbana, IL. A split plot experiment, using a randomized complete block design, with synthetics as main plots and cycles as sub-plots, was used to evaluate selection response. Traits evaluated were endosperm modification, grain yield and moisture, 100-kernel-weight, plant height, oil, protein, starch, lysine content, and lysine/protein ratio. Five cycles of selection showed a significant increase in endosperm modification, Disease Oil Opaque-2 showing a 42% increase and Elite Single Cross Opaque-2 a 31% increase. Significant cycle effects were observed for protein and starch content. Significant years × cycles and years × synthetics × cycles interactions were observed for several traits but were all of the non-crossover type. No changes in the nutritional characteristics of both synthetics were observed as a result of selection for increased endosperm modification. The results were obtained without monitoring lysine or tryptophan during selection. Results indicate Corn Belt adapted opaque-2 synthetics with a high degree of endosperm modification can be developed with appropriate selection procedures