Determination of the relative combining abilities of com (Zea mdYs L) inbred lines is an important feature of applied mm breeding programs. Combining ability is measured by the relative performance of a tine in testcrosses to one or more testers. lnbred lines from BS13(52)Cl and BSCBl(R)C7 corn populations were evaluated at the S2 and later generations of ínbreeding. Incense selection was practiced among and within lines during inbreedjng to develop the S-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 lour Iowa locations. Genetic correlations between the S2 and later generation of inbreeding, Testcross trials were 0.97 for BS13(S) (] and 0.86 for BSCBl(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 abiliries at later generations of inbreeding.

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