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.

Com o objetivo de verificar os efeitos de diferentes tipos de despendoamento no desenvolvimento de plantas e produção de sementes de milho, foi conduzido, um ensaio durante três anos agrícolas. Esse trabalho consistiu de cinco tipos de despendoamento (manual, macho-estéril, arranquio do cartucho, mecânico e testemunha) e três genótipos (linhagens A e B e o híbrido CMS 355), em suas versões férteis e estéreis. Esses tratamentos foram combinados num fatorial 5x3 com quatro repetições, num delineamento experimental de blocos ao acaso. As variáveis avaliadas, após a imposição dos tratamentos foram: altura da planta, área foliar e peso da matéria seca total. Na colheita, foram avaliados: altura de inserção de espiga, índice de espiga e produção de sementes. Os resultados revelaram que num campo de produção de sementes híbridas o despendoamento manual ou o uso de macho-esterilidade são as técnicas recomendadas. Arranquio do cartucho e despendoamento mecânico afetam negativamente a produção de sementes.

The study of inbreeding depression is important for breeding strategies such as use of inbred progenies or extraction of inbreed lines. A diallel of 28 maize open-pollinated varieties was evaluated in 10 environments in the early 1990s. At the same time, S 1 populations for each of the 28 varieties were evaluated in the same 10 experiments (environments). Yield reductions of the populations from S 0 to S 1 (mean of the 10 environments), varied from 34.6% (CMS-01) to 59.2% (CMS-30), with an average of 49.1%. Inbreeding depression was greater in populations with a wider genetic base, which had never been exposed to inbreeding (CMS-30, BR-107, PH4, Cunha, Saracura, Nitrodent, and Nitroflint). Inbred lines with greater yield means should be obtained from the BR-105, BR-111, CMS-01, CMS-03, BR-106, CMS-14c, and CMS-28 populations. The use of parameter estimates generated by analysis of inbreeding depression, allow to make inferences about frequencies of deleterious alleles in the population. The frequencies of favorable alleles in the parents can be obtained by diallel analysis. The association of these two types of information, can provide a better interpretation of the genetic parameters and also can improve the process of selection of parents for either an intra-or an inter-populational breeding program.

Interpopulation and intrapopulation single‐cross hybrids of maize (Zea mays L.) produced from selected and unselected lines were compared [or grain yield productivity and stability. Selected lines were chosen from paired plant interpopulation crosses tested from S0 ✕ S0 through S4 ✕ S4 generations, whereas unselected lines were derived by single‐seed descent from the S0 plants. Our objective was to compare relative stability of grain yield among hybrids produced from selected and unselected lines. Mean grain yield and stability analysis of variance, which included linear regression coefficient (bl) and deviations from the regression (sd2), were used to determine relative stability of the single‐cross hybrids. Simple correlation coefficients among mean grain yield, bl, and sd2 also were determined.Hybrids of selected lines produced significantly greater grain yield than did hybrids of unselected lines. Significant hybrid‐environment interactions were detected for both groups of hybrids, and both groups had similar contributions to total hybrid‐environment variances. Hybrids of selected and unselected lines had significantly different regression coefficients, as indicated by the hybrid‐environment (linear) mean squares. Both groups hybrids had similar number of stable hybrids when both stability parameters (bl and sd2) were considered. Simple correlations between mean yield and bl and mean yield and sd2 for both groups of hybrids were highly significant (P ⩽ 0.01), but they were not great enough to have predictive value. It seems selection of hybrids for mean yield across environments should be emphasized first, and then the relative stability of the elite hybrids over environments should be determined.

No abstract