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Evaluation of Synthetic Varieties of Maize for Yield¹

Nine maize synthetic varieties were crossed in a diallel series and evaluated for yield performance per se and in crosses. The synthetic varieties and crosses were grown at 3 locations in each of 2 years, and, on the basis of the combined analysis over locations and years, the 6 experiments were considered as representative of 6 random enviromnents.

A nonorthogonal partition of the entry sum of squares obtained estimates of average, variety, and specific heterosis. F-tests indicated that average heterosis was significant at the 1% level in 5 of the 6 experiments and for the combined analysis over experiments. Of the total sum of squares due to heterosis, 73% was attributed to average heterosis. Variety heterosis was significant in the combined analysis, but the proportion of the heterosis sum of squares due to variety heterosis was only 11%. Specific heterosis was nonsignificant.

Estimated and observed heterosis were obtained for each of the synthetic varieties. Average observed heterosis on the basis of constant, mid-parent, and high parent was 12, 11, and 6%, respectively. Estimated heterosis, obtained as average heterosis () plus variety heterosis (h_j) for each variety, ranged from 6% for C.B. Syn. #1 to 14% for Ind. Syn. A. Average estimated heterosis () was 11%.

Estimates of synthetic variety effects (v_j), obtained for each variety by least squares analysis, included the performance of a variety per se and in variety crosses. The estimates of variety effects ranged from –5.7 for Ind. Syn. A to 5.2 for L.E. Syn., and formed three distinct groups. The relatively large, positive v_j group included C.B. Syn. #3, S.S. Syn., and L.E. Syn. Pa. Int. Syn. had essentially zero variety effects. C.B. Syn. #1 and #2 and Ind. Syn. A. and B had relatively large, negative effects.

The correlation between the predicted (_j = µ_v + v_j) and observed yield performance of the nine synthetic varieties was significant (r = .92**), as was the correlation between predicted [C_jj = µ_v + 1/2 (v_j + v_j) + ] and observed variety cross performance (r = .74**).

² Research Geneticists, ARS.

Received for publication January 10, 1966.

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