Determination of the relative combining abilities of corn (Zea mays L.) inbred lines is an important feature of applied corn breeding programs. Combining ability is measured by the relative performance of a line in testcrosses to one or more testers. Inbred lines from BS13(S2)Cl and BSCB1(R)C7 corn populations were evaluated at the S2 and later generations of inbreeding. Intense selection was practiced among and within lines during inbreeding to develop the S5-equivalent and S8 generation lines. The objective of this study was to determine if the combining ability of lines in early generations (S2) of inbreeding was similar to the combining ability of lines at later generations of inbreeding. Testcross trials were conducted at four Iowa locations. Genetic correlations between the S2 and later generation testcrosses for gram yield were 0.9.7 for BS13(S)Cl and 0.86 for BSCB1(R)C7. The S2 testcross data were highly predictive of S8 testcross data, suggesting that early testing was effective in discriminating among these lines for relative combining abilities at later generations of inbreeding
