Search

In hybrid breeding a high correlation between per se performance of parental lines and hybrid performance can help to reduce the efforts for testcross trials. Our objectives were (i) to investigate the correlation between per se and testcross performance of rye (Secale cereale L.) candidate introgression lines (pre-lLs) for thousand-kernel weight, test weight, failing number, starch, pentosan, and protein content; and (ii) to investigate the consistency of quantitative trait loci (QTL) determined in pre-ILs and their testcross progenies. Eighty pre-ILs carrying donor chromosome segments (DCS) from the Iranian primitive rye Altevogt 14160 in the genetic background of elite line L2053-N, were evaluated at four locations over 2 yr. Genetic correlations between per se and testcross performance were estimated with a bivariate mixed linear model. Putative QTL regions were detected by comparing the performance of pre-ILs carrying certain DCS with the performance of the recurrent parent. Genotypic variances and heritabilities were higher for per se than for testcross performance. Genetic correlations between per se and testcross performance were mostly intermediate. Common QTL regions were observed for test weight, starch, pentosan, and protein content. Our results revealed that a superior per se performance of rye pre-ILs is not indicative for a superior hybrid performance. Consequently, using rye pre-ILs in hybrid breeding programs requires testcross trials. doi: 10.2135/cropsci2009.06.0309

Heterotic groups are an essential prerequisite for efficient hybrid breeding. The present study in winter triticale (xTriticosecale Wittmack) was performed to (i) evaluate the magnitude of heterosis, (ii) investigate the efficiency of the prediction of hybrid performance based on midparent value or general combining ability (GCA)effects, and(iii)identify two heterotic groups by employing principle coordinate analysis and an enumeration algorithm for maximizing [F.sub.1] performance, midparent heterosis, and [[sigma].sup.2.sub.GCA]/ [[sigma].sup.2.sub.SCA] ratio for grain yield. Twenty-one inbred lines and their 210 diallel crosses were field-evaluated for grain yield at five agroecologically diverse locations in Germany. On average, the hybrids yielded 8.6% higher than the midparent performance, and the maximum superiority was 12.4%. Hybrid performance was predicted more reliably with GCA effects rather than with midparent performance. An enumeration algorithm based on optimum allocation of parents to heterotic groups, improved all three criteria. [F.sub.1] performance, midparent heterosis, and [[sigma].sup.2.sub.GCA]/[[sigma].sup.2.sub.SCA] ratio increased by about 3, 24, and 70%, respectively, as compared with the base situation of having no heterotic groups. These improvements substantiate the potential advantages, when heterotic groups are developed in hybrid breeding. doi: 10.2135/cropsci2009.04.0225

The objective of our study was to examine the influence of genetic divergence on the ratio of the components of variance for specific ([[sigma].sup.2.sub.SCA]) and general [[sigma].sup.2.sub.GCA]) combining ability using experimental data in triticale (xTriticosecale Wittm.). In total, 21 lines and their 210 crosses were evaluated for grain yield in field trials. Published molecular data were reanalyzed, indicating an optimum of two subgroups. The estimates of [[sigma].sup.2.sub.SCA] and [[sigma].sup.2.sub.GCA] were determined for the total diallel and between the two subgroups. The ratio of [[sigma].sup.2.sub.SCA] VS. [[sigma].sup.2.sub.GCA] tended to be lower for crosses between than within genetically distinct groups. Our experimental findings can be interpreted as an indicator of a more favorable ratio of [[sigma].sup.2.sub.SCA] vs. [[sigma].sup.2.sub.GCA] in situations with two genetically distinct populations than in situations with populations that are not genetically distinct. doi: 10.2135/cropsci2008.12.0689

Series of plant breeding trials are often unbalanced and have a complex genetic structure. To reduce computing cost, it is common practice to employ a two-stage approach, where adjusted means per location are estimated and then a mixed model analysis of these adjusted means is performed. An important question is how means from the first step should be weighted in the second step. Our objective therefore was the comparison of different weighting methods in the analysis of four typical series of plant breeding trials using mixed models with fixed or random genetic effects. We used four published weighting methods and proposed three new methods. Four evaluation criteria were computed to compare methods, using onestage analysis as benchmark. We found that the two-stage analysis gave acceptable results with fixed genetic effects. When genetic effects were taken as random in stage two, in three of four datasets the two-stage analysis gave acceptable results. In both cases differences between weighting methods were small and the best weighting method depended on the dataset but not on the evaluation criteria. A two-stage analysis without weighting also produced acceptable results, but weighting mostly performed better. In the fourth dataset the missing data pattern was informative, resulting in violation of the missing-at-random (MAR) assumption in one- and two-stage analysis. In this case both analyses were not strictly valid. doi: 10.2135/cropsci2009.02.0083

Heterosis is widely used in breeding, but the genetic basis of this biological phenomenon has not been elucidated. We postulate that additive and dominance genetic effects as well as two-locus interactions estimated in classical QTL analyses are not sufficient for quantifying the contributions of QTL to heterosis. A general theoretical framework for determining the contributions of different types of genetic effects to heterosis was developed. Additive x additive epistatic interactions of individual loci with the entire genetic background were identified as a major component of midparent heterosis. On the basis of these findings we defined a new type of heterotic effect denoted as augmented dominance effect [d.sub.i.sup.*] that comprises the dominance effect at each QTL minus half the sum of additive x additive interactions with all other QTL. We demonstrate that genotypic expectations of QTL effects obtained from analyses with the design III using testcrosses of recombinant inbred lines and composite-interval mapping precisely equal genotypic expectations of midparent heterosis, thus identifying genomic regions relevant for expression of heterosis. The theory for QTL mapping of multiple traits is extended to the simultaneous mapping of newly defined genetic effects to improve the power of QTL detection and distinguish between dominance and overdominance.