Evaluation of maize varieties for their potential as breeding populations

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A 7-variety diallel of synthetic varieties that have not had selection for yield improvement and a 10-variety diallel of synthetic varieties that either resulted from recurrent selection for yield improvement or from the introgression of exotic germ plasm into adapted varieties were evaluated in six environments for yield and five other agronomic traits. The specific objective was to determine the relative potential of the synthetic varieties as germ plasm sources for breeding programs. Recurrent selection improved population yield in ‘BSSS CO’, ‘BSK CO’, and ‘Alph CO’ in the varieties and also in crosses with other varieties. ‘BSSS(R)C6’ and ‘BSSS(HT)C7’ yielded 11.4% and 16.1% more than ‘BSSS CO’, and the variety crosses of ‘BSSS(R)C6’ and ‘BSSS(HT)C7’ yielded 21.6% and 22.0% more than the variety crosses of ‘BSSS CO’. Recurrent selection also improved stalk-lodging resistance for ‘BSSS(R)C6’ and ‘BSSS(HT)C7’, but root lodging for ‘BSSS(HT)C7’ was significantly higher. ‘BS15’ had 61.0% higher yields than ‘Alph CO’, with 9.3% less stalk lodging. Average heterosis of the 10-variety diallel was 1120 kg/ha (19.6%) and ranged from 800 kg/ha (13.7%) for ‘BSK(S)C5’ to 1770 kg/ha (39.4%) for ‘BS12(HI)C5’. The heterosis expressed among individual variety crosses ranged from 4.3% for ‘BSK(S)C5’ x ‘BSTE(FR)C1’ to 37.6% for ‘BSSS(R)C6’ x ‘BS12(HI)C5’, which approached the yield of the two highest yielding single-cross checks. In the 7-variety diallel of unselected varieties, ‘BSTE CO’ and ‘Late Rootworm Synthetic’ were superior as varieties and in crosses for yield and stalk quality. Average heterosis for the 7-variety diallel was 950 kg/ha (18.5%). Stalk lodging was important in the performance of varieties with poor stalk quality. Although recurrent selection improved yield, development of superior breeding populations also will require selection for general agronomic performance. The performance of ‘BS16’ and the yields of ‘BSTL’ and ‘Teozea’ and their crosses suggest that exotic germ plasm should receive greater attention.