The dissection of quantitative traits into their underlying Mendelian factors has become possible with the aid of molecular markers. In this study, we mapped and characterized quantitative trait loci (QTL) affecting testcross performance of maize (Zea mays L.) and discussed the consistency of these QTL across environments and testers. Two homozygous flint inbred lines were crossed to produce 380 F2 individuals which were genotyped at 89 restriction fragment length polymorphism (RFLP) marker loci. By selfing the F2 plants 380 F3 lines were produced and subsequently crossed to two diverse dent inbred testers (T1 and T2). Each series of testcrosses (TC) was evaluated in field trials with two replications in four environments. Three traits were analyzed: protein content, kernel weight, and plant height. Genotypic and genotype‐by‐environment interaction variances were highly significant for all traits in both TC series and heritabilities ranged between 0.71 and 0.85. Genotypic correlations between the two TC series were 0.80 (protein content), 0.88 (kernel weight), and 0.84 (plant height). The method of interval mapping was used for characterization of QTL. Protein content was significantly affected by four QTL in TC with T1 explaining 32% of the phenotypic variance (trueσ^normalp2) and five QTL in TC with T2 explaining 42% of trueσ^normalp2. For kernel weight, eight putative QTL were found in TC with T1 and six were found for T2, explaining about 60% of trueσ^normalp2. Seven QTL explained 52% and four 60% of trueσ^normalp2 for plant height. Results from QTL mapping agreed well across environments. Highly consistent results across testers were obtained for kernel weight and plant height but not for protein content. No significant evidence for epistasis among QTL was found.

Information on genetic relationships among genotypes is of great importance to breeders. In this study we analyzed 29 maize (Zea mays L.) inbreds (18 flint and 11 dent lines) from the European germplasm by means of pedigree and RFLP analyses. Our main objective was to compare Malécot's coancestry (f based on pedigree data with genetic similarity (GS) based on RFLP data of 188 clone‐enzyme combinations (CECs) for their ability to quantify the degree of relatedness among inbreds. Rank correlations between f and GS were highly significant (P < 0.01) for 87 related (f > 0) pairs of flint lines (rs = 0. 71) an for 30 related pairs of dent lines (rs = 0.86). One dent line was excluded because of likely errors in pedigree detected by RFLP data and confirmed by heterosis data. Based on linear regression of GS on f, coancestry explained 82 and 70% of the variation in GS for related pairs of flint and dent lines, respectively. Therefore, both the coancestry and marker approach are well‐suited to (i) measure the average level of relatedness and (ii) identify closely related lines. Observed deviations of GS from its regression on f for individual pairs of lines can be explained by (i) random genetic drift and selection causing unequal genomic contributions of the parents, (ii) random variation of GS estimates due to sampling of the genome by the CECs used, (iii) wide variation in the GS estimates of unrelated lines, and (iv) experimental errors. Provided the genome is sampled by an adequate number (> 100) of CECs, RFLP‐based GS estimates reflect more accurately the true genetic similarity of a given line pair than f.

Restriction fragment length polymorphisms (RFLPs) have been proposed for characterizing genetic diversity of maize (Zea mays L.) germplasm. Fifty‐seven elite inbred lines representative of early‐maturing European flint and dent heterotic groups were assayed for RFLPs with 188 clone—enzyme combinations (98 genomic DNA clones, 2 restriction enzymes). Objectives of this study were to (i) investigate the amount of variation for RFLPs in these materials, (ii) determine the level of genetic diversity within and between heterotic groups, and (iii) examine the usefulness of RFLPs for assigning inbred lines to heterotic groups. All DNA clones detected polymorphism with at least one enzyme. About half of all RFLP patterns were common to the flint and dent lines, and a quarter was specific to the lines of each heterotic group. Genetic similarity (GS), calculated from RFLP data as Dice's similarity coefficient, ranged from 0.25 to 0.72 between unrelated pairs of lines. Mean GS for unrelated line combinations within the flint (0.425) and dent (0.414) heterotic groups were considerably greater than for flint × dent line combinations (0.344). All flint and dent inbreds showed a smaller mean GS to lines from the other hererotic group than to unrelated lines from the same heterotic group. For lines of mixed origin, the difference in mean GS to flint lines and to dent lines was consistent with the expected genomic proportions from each heterotic group based on pedigrees. Principal coordinate analysis of GS estimates resulted in a separate grouping of flint and dent lines. Results from this study corroborate the usefulness of RFLPs for identification of lines for assigning inbreds into heterotic groups. For the latter purpose, it seems possible to confine RFLP assays to a smaller number of clone—enzyme combinations with increased discriminatory power between lines from different heterotic groups.

Restriction fragment length polymorphisms (RFLPs) have been proposed as a tool for assigning inbreds to heterotic groups and predicting heterosis and performance of single‐cross hybrids in maize (Zea mays L.). Such use was evaluated in 11 flint and 11 dent inbred lines from the European maize germplasm and in 66 F1 hybrids produced between them according to an incomplete factorial mating scheme. Inbreds and hybrids were evaluated for 12 forage yield and quality traits in three and six environments, respectively, in Germany. The RFLP assays of the 22 inbreds were performed with two restriction enzymes and 101 DNA probes distributed throughout the maize genome. Most (>97%) clone‐enzyme combinations revealed polymorphisms (⊄5.0 variants per clone‐enzyme combination). Genetic distances (GD) between lines, calculated from RFLP data, had a significantly greater mean for flint × dent (0.65) than for flint x flint (0.58) or dent × dent (0.59) line combinations. Cluster analysis based on GDs revealed associations among lines consistent with their origin from different heterotic groups and known pedigrees. The GD values pertaining to the 66 F1 hybrids were partitioned into general (GGD) and specific (SGD) genetic distances; GGD explained ⊄30% of the variation among GD values. Neither GD nor SGD was significantly correlated (|r|≤ 0.25) with F1 performance or midparent heterosis for any trait examined. Results from this study support previous investigations with U.S. maize germplasm in that RFLP data can be used for assigning inbreds into heterotic groups. However, RFLP‐based genetic distance measures are apparently not indicative of the performance of single‐cross hybrids between lines from different heterotic groups for forage traits.

Restrictionfragment length polymorphisms (RFLPs) have been proposed for predicting the yield potential of different types of cross. Their has been evaluated in 15 flint and 12 dent inbreds from the European maize {Zea mays L.) germplasm as well as in 68 F, crosses (21 flint X flint, 14 dent X dent, and 33 flint X dent) produced between them. The materials were evaluated for Fi performance and midparent heterosis of grain yield, dry matter content (DMC) and plant height in two environments in Germany. Genetic distances (GDs) between parental lines, calculated from RFLP data of 194 cloneenzyme combinations, showed greater means for flint X dent (0.67) than dent X dent (0.62) and flint X flint (0.55) crosses. Cluster analysis based on GDs resulted in a clear separation of flint and dent hnes and agreed well with pedigree information. For the complete set of 64 crosses analyzed (excluding 4 crosses between closely related lines) correlations of GD with Fi performance and heterosis were significant for all traits except F] performance of DMC. When separate calculations were performed for individual subjets of crosses, correlations of GD with Fi performance and heterosis were significantly positive (0.48 < r < 0.80) for all traits in the flint x flint crosses, but not significant for the subsets of flint x dent and dent x dent crosses. Our results confirm those of previous investigations in that the predictive value of RFLP data is restricted to crosses between lines from the same heterotic group, and cannot be applied to crosses between lines from genetically divergent heterotic groups.Recognition of inbred lines with superior performance in crosses is a key for the success of hybrid breeding programme. Traditional methods have relied primarily on extensive field evaluation of crosses in topcross of diallel tests and are very time-consuming and costly. The efficiency of hybrid breeding programme would be improved if superior crosses could be predicted reliably (before field tests) by the simple screening of inbred lines.Parental genetic distance, determined from assays of inbreds for isozymes or restriction fragment length polymorphisms (RFLPs), has been suggested as a potential tool for predicting the hybrid performance of crosses. This approach has been stimulated by quantitativegenetic theory and empirical studies indicating that the amount of heterosis in crosses is, within limits, positively related to the parental genetic divergence (see HALLAUER and MIRAN-U.S.