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

Recurrent full-sib family and reciprocal recurrent selection have resulted in significant increases in grain weight of crosses between the varieties 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 recurrent selection for yield in maize and (ii) determine whether increased grain weights were accompanied by parallel increases in total dry matter and total N accumulation. Unless total dry matter acquisition increases in parallel with grain weight during selection, sustained root and shoot functions would be restricted by excessive diversion of carbohydrates 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%, respectively, with full-sib family selection and 27, 21, and 10%, respectively, with reciprocal recurrent selection. Greater proportions of the dry matter and N accumulated were partitioned to grain after full-sib family selection than after reciprocal recurrent selection. Therefore, photosynthate production after full-sib family selection was not sufficient to fully satisfy both the demand by grain and the requirements for root and shoot processes. Reciprocal recurrent selection resulted in a greater increase in photosynthate production, so that the hybrid population was able to meet the demand for carbohydrate by higher grain yield and still sustain N acquisition by roots. The conclusions were also supported by heterosis for grain weight, total dry matter, and total N accumulation, which was greater after reciprocal recurrent selection than after full-sib family selection. Selection to increase grain weight will result in efficient N acquisition only when the greater grain weight is supported by an adequate increase in photosynthate production.