RECURRENT SELECTION FOR MAIZE GRAIN-YIELD - DRY-MATTER AND NITROGEN ACCUMULATION AND PARTITIONING CHANGES

Recurrent full-sib family and reciprocal recurrent selection have resu lted in significant increases in grain weight of crosses between the v arieties of maize (Zea mays L.) Janis Golden Prolific and Indian Chief . The objectives of this study were to (i) compare increases due to 14 cycles of recurrent full-sib family selection, and reciprocal recurre nt selection for yield in maize and (ii) determine whether increased g rain weights were accompanied by parallel increases in total dry matte r and total N accumulation. Unless total dry matter acquisition increa ses in parallel with grain weight during selection, sustained root and shoot functions would be restricted by excessive diversion of carbohy drates to grain. After 14 selection cycles on sandy soils of the North Carolina coastal plain, grain weight, dry matter accumulation, and N accumulation in the population hybrid increased 23, 12, and 4%, respec tively, with full-sib family selection and 27, 21, and 10%, respective ly, with reciprocal recurrent selection. Greater proportions of the dr y matter and N accumulated were partitioned to grain after full-sib fa mily selection than after reciprocal recurrent selection. Therefore, p hotosynthate production after full-sib family selection was not suffic ient to fully satisfy both the demand by grain and the requirements fo r root and shoot processes. Reciprocal recurrent selection resulted in a greater increase in photosynthate production, so that the hybrid po pulation was able to meet the demand for carbohydrate by higher grain yield and still sustain N acquisition by roots. The conclusions were a lso supported by heterosis for grain weight, total dry matter, and tot al N accumulation, which was greater after reciprocal recurrent select ion than after full-sib family selection. Selection to increase grain weight will result in efficient N acquisition only when the greater gr ain weight is supported by an adequate increase in photosynthate produ ction.