RAPD polymorphism in the prebreeding material for cultivation of synthetic variations of lucerne (Medicago sativa L.)

Genetic diversity between synthetic cultivars (Syn5, Syn7), inbred lines (D₃, D₅, E_1/2, G_1/1, G_1/2) and ecotypes (E16, E51, E182, E231) of lucerne (Medicago sativa L.) was studied using the RAPD-PCR method. The plants differed in the efficiency of seed set and in the yield of green mass. The ecotypes E182 and E231 and the synthetic population Syn5 showed the highest fertility. Additionally, Syn5 also showed the highest efficiency of seed set and the yield of green mass. Among the inbred lines, D3 was characterised by the highest yield of green mass and E1/2 by the highest fertility. An optimal combination of yield and biomass was observed for the synthetic population Syn5, obtained by crossing the lines D₃, D₅ and G_1/1, as demonstrated using comparative analysis. A total of 338 polymorphic products were generated using 20 arbitrary primers. Cluster analysis using the Unweighted-Pair Group Method with Arithmetic Mean (UPGMA) in the Molecular image Gel Doc? XR (Bio-Rad) software based on the Dice’s coefficient of genetic similarity showed a division of the studied forms into two groups based on genetic similarity. The ecotype E16 formed one of the groups whereas all of the other ecotypes observed in this study clustered into the second group. A high level of polymorphism among the studied lucerne forms was detected indicating an interesting gene pool awaiting future exploration. Analysis of variance also supported a high diversity among the studied forms. This study provides insightful information into the heterosis effect of synthetic populations or hybrids of F1 lucerine by providing correlations between the genetic background of the inbred lines and their ability to produce a specific yield.     

Molecular Diversity and Population Structure of a Worldwide Collection of Cultivated Tetraploid Alfalfa (Medicago sativa subsp. sativa L.) Germplasm as Revealed by Microsatellite Markers

Information on genetic diversity and population structure of a tetraploid alfalfa collection might be valuable in effective use of the genetic resources. A set of 336 worldwide genotypes of tetraploid alfalfa (Medicago sativa subsp. sativa L.) was genotyped using 85 genome-wide distributed SSR markers to reveal the genetic diversity and population structure in the alfalfa. Genetic diversity analysis identified a total of 1056 alleles across 85 marker loci. The average expected heterozygosity and polymorphism information content values were 0.677 and 0.638, respectively, showing high levels of genetic diversity in the cultivated tetraploid alfalfa germplasm. Comparison of genetic characteristics across chromosomes indicated regions of chromosomes 2 and 3 had the highest genetic diversity. A higher genetic diversity was detected in alfalfa landraces than that of wild materials and cultivars. Two populations were identified by the model-based population structure, principal coordinate and neighbor-joining analyses, corresponding to China and other parts of the world. However, lack of strictly correlation between clustering and geographic origins suggested extensive germplasm exchanges of alfalfa germplasm across diverse geographic regions. The quantitative analysis of the genetic diversity and population structure in this study could be useful for genetic and genomic analysis and utilization of the genetic variation in alfalfa breeding.     

Genetic structure and diversity among maize inbred lines as inferred from DNA microsatellites

Two hundred and sixty maize inbred lines, representative of the genetic diversity among essentially all public lines of importance to temperate breeding and many important tropical and subtropical lines, were assayed for polymorphism at 94 microsatellite loci. The 2039 alleles identified served as raw data for estimating genetic structure and diversity. A model-based clustering analysis placed the inbred lines in five clusters that correspond to major breeding groups plus a set of lines showing evidence of mixed origins. A "phylogenetic" tree was constructed to further assess the genetic structure of maize inbreds, showing good agreement with the pedigree information and the cluster analysis. Tropical and subtropical inbreds possess a greater number of alleles and greater gene diversity than their temperate counterparts. The temperate Stiff Stalk lines are on average the most divergent from all other inbred groups. Comparison of diversity in equivalent samples of inbreds and open-pollinated landraces revealed that maize inbreds capture <80% of the alleles in the landraces, suggesting that landraces can provide additional genetic diversity for maize breeding. The contributions of four different segments of the landrace gene pool to each inbred group's gene pool were estimated using a novel likelihood-based model. The estimates are largely consistent with known histories of the inbreds and indicate that tropical highland germplasm is poorly represented in maize inbreds. Core sets of inbreds that capture maximal allelic richness were defined. These or similar core sets can be used for a variety of genetic applications in maize.     

Complex Growth Regulator Increases Alfalfa Seed Production

The effects of thermophilic methane fermentation products on alfalfa (Medicago sativa L.) growth, nitrogen-fixing activity, and seed production were studied in pot and field experiments. Plant treatment with the preparation at the stages of stooling and flower bud formation resulted in an increase in the root nodule weight and their nitrogen-fixing activity, the accumulation of cytokinins (zeatin and zeatin riboside), and an increase in the green mass yield and protein content, especially at a low (0.25 of the full rate) mineral nitrogen rate. Crop seed production was considerably improved during the first (pot experiments) and second (field experiments) growing seasons. The conclusion was drawn that the causes for improved alfalfa seed production were the effects of group B vitamins, phytohormones, their interaction, and the switching of metabolic pathways toward cytokinin synthesis.     

Diversity in commercial varieties and landraces of black eggplants and implications for broadening the breeders' gene pool

Black‐coloured eggplants (Solanum melongena) represent the commercially most important group of eggplants in Europe and North America. Most of the modern varieties of black eggplants correspond to F₁ hybrids, which at the same time constitute an elite gene pool for the development of new varieties. However, there are many black landraces and old varieties, which could be useful as sources of variation for black eggplant breeding programmes as well as for the broadening of the genetic diversity of the breeders’ gene pool. We have studied the morphological and molecular [amplified fragment length polymorphism and simple sequence repeat (SSR)] diversity in a collection of 38 black eggplant accessions, including commercial (modern F₁ hybrid and old nonhybrid) varieties and landraces as well as in six nonblack control eggplants, from different origins. The results show that black eggplants contain a considerable morphological and molecular diversity, but commercial varieties, and in particular F₁ hybrids, display a reduced morphological and molecular diversity when compared with landraces. The principal components analysis morphological and principal coordinates analysis molecular analyses show that commercial F₁ hybrids group together, indicating that they share a common and narrow gene pool. Commercial F₁ hybrids present a series of productive advantages, like early production, intense black colour (low L*, a* and b*) values and absence of fruit calyx prickles. However, several of the landraces and old nonhybrid varieties studied present a high yield as well as other traits of interest for eggplant breeding. Furthermore, given the low genetic diversity of F₁ hybrids and the moderate level of SSR heterozygosity found in these materials (0.382), introduction of black landraces and old varieties in the present breeding programmes could contribute to broadening the gene pool used by breeders and this could help increase the heterosis for yield of F₁ hybrids, which is greatly favoured by high heterozygosity levels.     

Genetic diversity in maize landraces from indigenous settlements of Northeastern Argentina

In South America, native maize germplasm has been extensively studied particularly for the Andean region. However, relatively few genetic diversity studies include materials from the eastern region of the continent. Herein we present a genetic diversity characterization of four Popcorn maize landraces, maintained in indigenous settlements, from Northeastern Argentina (NEA). In addition, one Popcorn landrace from Northwestern Argentina (NWA) was incorporated for comparison. We characterized these landraces using ten microsatellite markers. For the whole data set, a total of 65 alleles were found, with an average of 7.22 alleles per locus. The average gene diversity was 0.370. Global fit to Hardy–Weinberg proportions was observed in all landraces. Global estimates of F _ST revealed a significant differentiation among the populations. Individual Neighbor-joining clustering and Bayesian analyses allowed the recognition of most populations studied. Two main groups were distinguished by the Neighbor-joining clustering of populations. This grouping pattern would be consistent with a hypothesis of successive introductions of Popcorn in South America. The results presented will be useful to design strategies that maximize the utility of maize genetic resources.     

Phosphatidylinositol 4,5-Biphosphate (PIP2) Modulates Interaction of Syntaxin-1A with Sulfonylurea Receptor 1 to Regulate Pancreatic β-Cell ATP-sensitive Potassium Channels

In β-cells, syntaxin (Syn)-1A interacts with SUR1 to inhibit ATP-sensitive potassium channels (K_ATP channels). PIP₂ binds the Kir6.2 subunit to open K_ATP channels. PIP₂ also modifies Syn-1A clustering in plasma membrane (PM) that may alter Syn-1A actions on PM proteins like SUR1. Here, we assessed whether the actions of PIP₂ on activating K_ATP channels is contributed by sequestering Syn-1A from binding SUR1. In vitro binding showed that PIP₂ dose-dependently disrupted Syn-1A·SUR1 complexes, corroborated by an in vivo Forster resonance energy transfer assay showing disruption of SUR1(-EGFP)/Syn-1A(-mCherry) interaction along with increased Syn-1A cluster formation. Electrophysiological studies of rat β-cells, INS-1, and SUR1/Kir6.2-expressing HEK293 cells showed that PIP₂ dose-dependent activation of K_ATP currents was uniformly reduced by Syn-1A. To unequivocally distinguish between PIP₂ actions on Syn-1A and Kir6.2, we employed several strategies. First, we showed that PIP₂-insensitive Syn-1A-5RK/A mutant complex with SUR1 could not be disrupted by PIP₂, consequently reducing PIP₂ activation of K_ATP channels. Next, Syn-1A·SUR1 complex modulation of K_ATP channels could be observed at a physiologically low PIP₂ concentration that did not disrupt the Syn-1A·SUR1 complex, compared with higher PIP₂ concentrations acting directly on Kir6.2. These effects were specific to PIP₂ and not observed with physiologic concentrations of other phospholipids. Finally, depleting endogenous PIP₂ with polyphosphoinositide phosphatase synaptojanin-1, known to disperse Syn-1A clusters, freed Syn-1A from Syn-1A clusters to bind SUR1, causing inhibition of K_ATP channels that could no longer be further inhibited by exogenous Syn-1A. These results taken together indicate that PIP₂ affects islet β-cell K_ATP channels not only by its actions on Kir6.2 but also by sequestering Syn-1A to modulate Syn-1A availability and its interactions with SUR1 on PM.     

Patterns of molecular and phenotypic diversity in pearl millet [<Emphasis Type="Italic">Pennisetum glaucum</Emphasis>(L.) R. Br.] from West and Central Africa and their relation to geographical and environmental parameters

Background  

The distribution area of pearl millet in West and Central Africa (WCA) harbours a wide range of climatic and environmental conditions as well as diverse farmer preferences and pearl millet utilization habits which have the potential to lead to local adaptation and thereby to population structure. The objectives of our research were to (i) assess the geographical distribution of genetic diversity in pearl millet inbreds derived from landraces, (ii) assess the population structure of pearl millet from WCA, and (iii) identify those geographical parameters and environmental factors from the location at which landraces were sampled, as well as those phenotypic traits that may have affected or led to this population structure. Our study was based on a set of 145 inbred lines derived from 122 different pearl millet landraces from WCA.     

Genetic diversity of maize landraces from lowland and highland agro‐ecosystems of Southern South America: implications for the conservation of native resources

The North of Argentina is one of the southernmost areas of maize landrace cultivation. Two distinct centres of diversity have been distinguished within this region: Northwestern Argentina (NWA), and Northeastern Argentina (NEA). Nowadays, maize landraces from this area are faced with two main risks. On the one hand, significant structural and functional changes have modified the rural environment with the boundaries of cropland areas experiencing a rapid expansion at the expense of northern natural forests and rangelands; and on the other, native gene pools are increasingly threatened by hybrids and commercial varieties which are more attractive relative to landraces. The first step towards any conservational action is the acquisition of an inclusive knowledge of the biological resources. For this purpose, our study assesses the genetic diversity and population dynamics of maize landraces from Northern Argentina using microsatellite markers. The Northeastern lowland region (NEA) was represented by 12 landraces (19 populations). In addition, six landraces (eight populations) from the Northwestern highland region (NWA) were used for comparison. For the NEA data set, a total of 126 alleles were found, with an average of 10.5 alleles per locus. Mean H_o, H_e and R_s were 0.350, 0.467 and 2.72, respectively. Global fit to Hardy–Weinberg proportions was observed in 7 of 19 populations. Global estimates of F_ST revealed significant differentiation among populations. Bayesian analyses of population structure allowed the recognition of two main gene pools (popcorns versus floury landraces). When NWA was added to the analysis, three clusters were distinguished: NEA popcorns, NEA flours and NWA racial complexes. Additional information on the relationships among these groups was retrieved from cluster analyses. This study shows that lowland landraces from Northern Argentina harbour considerable levels of genetic diversity, with contributions from different gene pools. Further studies encompassing a larger number of populations from the NEA region will certainly help to detect additional genetic variation, which may prove highly valuable in germplasm conservation and management. Future conservation efforts should focus on preserving NEA popcorns, NEA floury and NWA racial complexes as different management units.     

Wide variability in kernel composition, seed characteristics, and zein profiles among diverse maize inbreds, landraces, and teosinte

All crop species have been domesticated from their wild relatives, and geneticists are just now beginning to understand the consequences of artificial (human) selection on agronomic traits that are relevant today. The primary consequence is a basal loss of diversity across the genome, and an additional reduction in diversity for genes underlying traits targeted by selection. An understanding of attributes of the wild relatives may provide insight into target traits and valuable allelic variants for modern agriculture. This is especially true for maize (Zea mays ssp. mays), where its wild ancestor, teosinte (Z. mays ssp. parviglumis), is so strikingly different than modern maize. One obvious target of selection is the size and composition of the kernel. We evaluated kernel characteristics, kernel composition, and zein profiles for a diverse set of modern inbred lines, teosinte accessions, and landraces, the intermediate between inbreds and teosinte. We found that teosinte has very small seeds, but twice the protein content of landraces and inbred lines. Teosinte has a higher average alpha zein content (nearly 89% of total zeins as compared to 72% for inbred lines and 76% for landraces), and there are many novel alcohol-soluble proteins in teosinte relative to the other two germplasm groups. Nearly every zein protein varied in abundance among the germplasm groups, especially the methionine-rich delta zein protein, and the gamma zeins. Teosinte and landraces harbor phenotypic variation that will facilitate genetic dissection of kernel traits and grain quality, ultimately leading to improvement via traditional plant breeding and/or genetic engineering.     

Allelic forms of mouse transcobalamin 2

Transcobalamin 2 is the only vitamin B12-binding protein found in mouse serum. Two allelic forms of mouse transcobalamin 2 are described. The two forms differ in their mobilities on polyacrylamide gel electrophoresis. The slowly migrating form has been found in serum from 25 inbred mouse strains. The more rapidly migrating form was detected in 3 inbred mouse strains (NZB, ST/bJ, and CPB-WV). Both parental variants were expressed in F₁ progeny of appropriate interstrain crosses, showing codominant expression of the transcobalamin 2 alleles. In backcrosses between F₁ and parental individuals, the two electrophoretic variants were inherited as single Mendelian traits. The strain distribution pattern of the two variants in recombinant inbred lines likewise suggested a single-gene mode of inheritance and indicated a lack of close linkage with a number of genetic loci on chromosomes 1, 2, 4, 5, 6, 7, 9, 12, 14, 15, and 17. We propose the symbol Tcn-2 for the polymorphic gene locus coding for transcobalamin 2 in the mouse and Tcn-2 ^s and Tcn-2 ^f for the two alleles.     

Patterns of genetic and eco-geographical diversity in Spanish barleys

The pool of Western Mediterranean landraces has been under-utilised for barley breeding so far. The objectives of this study were to assess genetic diversity in a core collection of inbred lines derived from Spanish barley landraces to establish its relationship to barleys from other origins, and to correlate the distribution of diversity with geographical and climatic factors. To this end, 64 SSR were used to evaluate the polymorphism among 225 barley (Hordeum vulgare ssp. vulgare) genotypes, comprising two-row and six-row types. These included 159 landraces from the Spanish barley core collection (SBCC) plus 66 cultivars, mainly from European countries, as a reference set. Out of the 669 alleles generated, a large proportion of them were unique to the six-row Spanish barleys. An analysis of molecular variance revealed a clear genetic divergence between the six-row Spanish barleys and the reference cultivars, whereas this was not evident for the two-row barleys. A model-based clustering analysis identified an underlying population structure, consisting of four main populations for the whole genotype set, and suggested further possible subdivision within two of these populations. Most of the six-row Spanish landraces clustered into two groups that corresponded to geographic regions with contrasting environmental conditions. The existence of wide genetic diversity in Spanish germplasm, possibly related to adaptation to a broad range of environmental conditions, and its divergence from current European cultivars confirm its potential as a new resource for barley breeders, and make the SBCC a valuable tool for the study of adaptation in barley. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Identification of Indian Landraces of Opium Poppy Papaver somniferum Resistant to Damping-off and Downy Mildew Fungal Diseases

A set of 32 landraces (traditional local cultivars) of poppy Papaver somniferum originating in the Indian states of Rajasthan, Madhya Pradesh, Uttar Pradesh and Tamilnadu, and four Indian commercial varieties were screened over four cropping seasons for their reaction to downy mildew disease caused by Peronospora arborescens and damping-off disease caused by Pythium dissotocum under both field and artificial inoculation conditions. The landrace 1018 was found to be resistant to damping-off disease and the landraces 1014 and N3 were resistant to downy mildew disease. A yield trial conducted over two seasons showed that the damping-off disease-resistant landrace 1018 was superior to all the commercial varieties in seed, morphine and/or codeine yield. The experiments provided further evidence that there is considerable genetic variability between the landraces.     

新疆自然高温环境下玉米自交系开花期耐热性鉴定与评价

在新疆夏季自然高温环境下,以田间玉米空秆率、果穗结实率、相对结实率为主要评价指标,综合籽粒产量与穗部性状,对26份国内外玉米骨干自交系连续2年进行耐热性鉴定与评价,结合新疆当地高温干燥的气候特点,建立一套适宜玉米种质资源大田耐热性的鉴定、评价体系,为中国玉米耐热种质资源的遗传改良和新品种选育提供参考。结果表明:(1)不同基因型玉米自交系空秆率、果穗结穗率、相对结实率和耐热性差异较大,其中GW5F、GW4F、GW7F和PH6WC耐热性最强,在高温胁迫下空秆率最低,果穗结实率与相对结实率最高;其次为PHBA6、新自351等8份自交系,在高温胁迫下籽粒产量及综合表现较好;其余自交系对高温均表现敏感。(2)高温胁迫导致玉米穗部性状严重衰退,其中的穗重、穗行数和行粒数所受影响最大。(3)在年份或材料之间,玉米自交系籽粒产量与其主要农艺性状相关性差异较大,并以果穗重与籽粒产量相关性最高。(4)以相对结实率为主要指标通过层次聚类可将参试材料分为两大群,耐热性最强的GW5F、PH6WC、GW4M聚为第Ⅰ群,其余自交系聚为第Ⅱ群;第Ⅱ群中‘吉63’、Mo17等6份自交系可聚为第1亚群,PHBA6、LH82等6份自交系聚为第2亚群,郑58、新农育6390M等11份自交系聚为第3亚群。综合分析来看,该研究中表现极耐高温的4份自交系均为国外优异种质,可用于玉米耐高温基础研究和遗传改良;表现较强耐热性的8份品系多来自于新疆本地选育的材料,其遗传基础较为广泛,适应当地的高温环境,也是优异的耐热育种资源。     

Unlocking the Genetic Diversity of Maize Landraces with Doubled Haploids Opens New Avenues for Breeding

Landraces are valuable genetic resources for broadening the genetic base of elite germplasm in maize. Extensive exploitation of landraces has been hampered by their genetic heterogeneity and heavy genetic load. These limitations may be overcome by the in-vivo doubled haploid (DH) technique. A set of 132 DH lines derived from three European landraces and 106 elite flint (EF) lines were genotyped for 56,110 single nucleotide polymorphism (SNP) markers and evaluated in field trials at five locations in Germany in 2010 for several agronomic traits. In addition, the landraces were compared with synthetic populations produced by intermating DH lines derived from the respective landrace. Our objectives were to (1) evaluate the phenotypic and molecular diversity captured within DH lines derived from European landraces, (2) assess the breeding potential (usefulness) of DH lines derived from landraces to broaden the genetic base of the EF germplasm, and (3) compare the performance of each landrace with the synthetic population produced from the respective DH lines. Large genotypic variances among DH lines derived from landraces allowed the identification of DH lines with grain yields comparable to those of EF lines. Selected DH lines may thus be introgressed into elite germplasm without impairing its yield level. Large genetic distances of the DH lines to the EF lines demonstrated the potential of DH lines derived from landraces to broaden the genetic base of the EF germplasm. The comparison of landraces with their respective synthetic population showed no yield improvement and no reduction of phenotypic diversity. Owing to the low population structure and rapid decrease of linkage disequilibrium within populations of DH lines derived from landraces, these would be an ideal tool for association mapping. Altogether, the DH technology opens new opportunities for characterizing and utilizing the genetic diversity present in gene bank accessions of maize.     

Genetic parameters estimation for some wild wheat species and their F1 hybrids grown in different regions of Saudi Arabia

Wheat (Triticum aestivum L.) is the most important crop for human nutrition that underpins the food safety of Saudi Arabia. The investigation here was to determine heterosis effects using different genetic methods: heterosis over better, mid parents, the genetic advance, and genotype, phenotypic coefficient of variation for estimation some traits among six wheat landraces and their F₁ hybrids. In 2019, these landraces were sown using hand and after 100 days, the emasculation and crossing were made among these six landraces using hand emasculation of anthers. In 2020, seeds for these genotypes (six wheat landraces and their F₁) were sown under normal irrigation accordingly done in 2019. The results showed that the most important parent was Mabia resulted with the highest value in number of tiller/ plant, 1,000-grain weight, and fresh shoot weight. The highest value of plant height among six parents was Naqra while highest value at the same trait among F₁ hybrids was P₃ XP₆. The estimations of heterosis showed that out of 15 crosses, one cross (P₁XP₅) was significantly better yield than all crosses for these four traits. The genotype coefficient of variation (GCV) ranged from 12.5% to 8.7% while phenotypic coefficient of variation ranged from 17.7% to 11.3%. The correlation coefficients was found between fresh shoot weight and number of tiller and plant height and umber of tiller. Wild wheat still serve as a source of useful germplasm with proven adaption and productivity and thus assembles of the wild wheat assortments are the initial step of breeding program.     

Confirmation of QTL controlling seed yield in spring canola (Brassica napus L.) hybrids

Allelic effects observed in QTL discovery experiments must be confirmed to be useful in subsequent breeding efforts. Two QTL affecting seed yield of spring hybrid canola (Brassica napus L.) were previously identified in two populations of inbred backcross lines (IBLs) containing germplasm introgressed from a winter cultivar. The effects of favorable alleles at these QTL were retested by crossing two selected IBLs (M5 and M31) to three spring canola lines having different genetic backgrounds. Doubled haploid (DH) lines derived from each F₁ were genotyped with RFLP markers flanking the QTL and grouped into the four possible QTL genotypes. For the first field experiment, DH lines derived by crossing the M5 line to one spring line were crossed to two female testers and evaluated as individual testcross progenies in one environment. QTL genotypes had large variances and were not significantly different. A second field experiment was conducted using the DH lines from the first experiment and two other sets of DH lines derived from the M31 line crossed to two different spring canola lines. Individual lines within each QTL genotype of each set were bulked and crossed to the same testers used in Experiment 1. Bulked hybrid seeds of each QTL genotype were planted in a split-split plot randomized block design and 12 replicates. QTL genotypes had smaller variances in this experiment, and the effects of one QTL were confirmed in some genetic backgrounds. These results suggest that bulking of QTL genotypes and use of an appropriate experimental design with many replicates are needed to detect small differences between QTL genotypes.     

Genotyping of DNA pools identifies untapped landraces and genomic regions to develop next-generation varieties

Landraces, that is, traditional varieties, have a large diversity that is underexploited in modern breeding. A novel DNA pooling strategy was implemented to identify promising landraces and genomic regions to enlarge the genetic diversity of modern varieties. As proof of concept, DNA pools from 156 American and European maize landraces representing 2340 individuals were genotyped with an SNP array to assess their genome-wide diversity. They were compared to elite cultivars produced across the 20th century, represented by 327 inbred lines. Detection of selective footprints between landraces of different geographic origin identified genes involved in environmental adaptation (flowering times, growth) and tolerance to abiotic and biotic stress (drought, cold, salinity). Promising landraces were identified by developing two novel indicators that estimate their contribution to the genome of inbred lines: (i) a modified Roger's distance standardized by gene diversity and (ii) the assignation of lines to landraces using supervised analysis. It showed that most landraces do not have closely related lines and that only 10 landraces, including famous landraces as Reid's Yellow Dent, Lancaster Surecrop and Lacaune, cumulated half of the total contribution to inbred lines. Comparison of ancestral lines directly derived from landraces with lines from more advanced breeding cycles showed a decrease in the number of landraces with a large contribution. New inbred lines derived from landraces with limited contributions enriched more the haplotype diversity of reference inbred lines than those with a high contribution. Our approach opens an avenue for the identification of promising landraces for pre-breeding.     

Comparison of methods for calculating the heritability of adult field resistance to yellow rust and grain yield in spring wheat

Several methods are available for estimating heritability in disomic species, including parent-offspring regression, realized heritability, intraclass correlations of recombinant inbred lines, and diallel-cross analysis. Estimates were obtained by these various methods for a set of eight bread wheat (Triticum aestivum) lines adapted to the East African highlands, which had been intercrossed and selfed in a half-diallel arrangement to give F₁, F₂ and F₃ generations, and F₆ recombinant inbred lines. Significant genetic variation existed among parents and crosses for both grain yield and yellow rust resistance in all generations. Based on the heritability calculated from the analysis of F₆ recombinant inbred lines, analysis of the F₂ diallel crosses was recommended for determining the heritability of both characters in early segregating generations. The results also suggest that a form of tandem selection may be effective in developing locally adapted germplasm which combines high grain yield with yellow rust resistance. Received: 15 February 1999 / Accepted: 11 March 1999