Responses to Selection for Endosperm Hardness and Associated Changes in Agronomic Traits after Four Cycles of Recurrent Selection in Maize

Abstract

Increased endosperm hardness of grain in maize (Zea mays L.) is desirable for dry milling, storage, and expert purposes. This study was conducted to evaluate changes in endosperm hardness resulting from four cycles of visual recurrent selection for increased hardness in two dent corn synthetics representative of U.S. Corn Belt germplasm, and to determine associated responses in other agronomic traits. Testcrosses of random S1 lines from each cycle of selection were grown in replicated trials at four locations in each of 2 yr for determination of grain hardness and evaluation of agronomic traits. Evaluation of grain hardness 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 changes corresponding to altered endosperm hardness were detected for any of five agronomic traits measured in testcross hybrids from S1 lines representing each cycle of selection. Estimated genetic correlation coefficients indicated a negative, nonsignificant trend between grain yield and grain hardness. These results indicate increases in grain hardness can be achieved through selection in dent corn germplasm common to the U.S. Corn Belt. However, continual progress in recurrent selection may require quantification of hardness by measurements such as kernel density and the Stenvert hardness test, rather than simple visual judgment of relative hardness. Genetic correlation coefficients indicate selection progress can be simultaneously made for both grain yield and grain quality.