RESPONSES TO SELECTION FOR ENDOSPERM HARDNESS AND ASSOCIATED CHANGES IN AGRONOMIC TRAITS AFTER 4 CYCLES OF RECURRENT SELECTION IN MAIZE

Increased endosperm hardness of grain in maize (Zea mays L.) is desira ble for dry milling, storage, and export purposes. This study was cond ucted to evaluate changes in endosperm hardness resulting from four cy cles of visual recurrent selection for increased hardness in two dent corn synthetics representative of U.S. Corn Belt germplasm, and to det ermine associated responses in other agronomic traits. Testcrosses of random S-1 lines from each cycle of selection were grown in replicated trials at four locations in each of 2 yr for determination of grain h ardness and evaluation of agronomic traits. Evaluation of grain hardne ss was through measurement of average kernel density and the Stenvert hardness test. Significant increase in endosperm hardness was Limited to the first cycle of selection in both synthetics. No significant cha nges corresponding to altered endosperm hardness were detected for any of five agronomic traits measured in testcross hybrids from S-1 lines representing each cycle of selection. Estimated genetic correlation c oefficients indicated a negative, nonsignificant trend between grain y ield and grain hardness. These results indicate increases in grain har dness can be achieved through selection in dent corn germplasm common to the U.S. Corn Belt. However, continual process in recurrent selecti on may require quantification of hardness by measurements such as kern el density and the Stenvert hardness test, rather than simple visual j udgment of relative hardness. Genetic correlation coefficients indicat e selection progress can be simultaneously made for both grain yield a nd grain quality.