Relation Between Inbred and Hybrid Traits in Maize1

We conducted correlation studies between plant and ear traits of inbred lines and single‐cross hybrids of maize (Zea mays L.) developed from Iowa Stiff Stalk Synthetic. We included 160 S7 lines and 320 single‐cross hybrids produced among the lines by use of the cross‐classification mating design. The 160 S7 lines were partitioned into 20 sets of eight lines to produce the 320 single‐cross hybrids (16 hybrids per set). Objectives of our study were to determine the relation between plant and ear traits of the inbred lines and their single‐cross hybrids and to determine the relation of plant and ear traits of the inbred lines with yield of the single‐cross hybrids. Two procedures were used: (1) correlations of inbred lines themselves with means of hybrids that had one inbred line in common and (2) correlations of the means of two inbred lines with their specific hybrids. Simple and multiple correlations were computed for each set of eight inbred lines and 16 single‐cross hybrids and combined across the 20 sets. Simple correlations of plant and ear traits of inbred lines and single‐cross hybrids were small in all instances for both procedures when combined across sets. The coefficient of determination (r2) was less than 0.16 in all instances. Correlations for individual sets for all traits ranged from significantly (P ≤ 0.01) negative to significantly positive. Sampling error was high among individual sets, indicating that small sample sizes can give misleading associations of traits. Multiple correlations of plant and ear traits of inbred lines with yield of singlecross hybrids were only 0.23 (Procedure 1) and 0.21 (Procedure 2). Our results showed that plant and ear traits of inbred lines were not good indicators of their performance in single‐cross hybrids. Correlations of yield of inbred lines with yields of single‐cross hybrids were 0.09 and 0.11. It seems that yield testing of inbred lines in single‐cross hybrids is the only procedure for determining the potential usefulness of an inbred line in single‐cross hybrids. Visual selection of morphological traits in inbred lines will not insure development of higher yielding single‐cross yields.