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Diverse and varied crop genetic resources are necessary (though not sufficient) for adequate food production in a rapidly changing world. Since the scientific community first raised public concern several decades ago, modern cultivars have been viewed as the cause of declining diversity in the world's crop genetic resources. This paper tests the hypothesis of increasing genetic uniformity in modern spring bread wheat (Triticum aestivum L.) cultivars from 1965, a year which marks the release of some of the first modern semidwarf cultivars carrying Rht1 and Rht2 genes in the developing world. Results from previously published studies are summarized. Preliminary molecular analyses, and new analyses of cultivar numbers, areas, ages, and genealogies are presented. An estimated 77% of the spring bread wheat area in the developing world today is sown to CIMMYT-related wheats, but this does not imply that they are genetically uniform. The hypothesis of increasing genetic uniformity is tested by assessing changes in the diversity of leading progenitors over three decades, in terms of several dimensions of diversity. Latent dimensions include genetic distance and genealogies. Apparent dimensions include performance with respect to yield potential, maintenance and stability across management (input use), and growing environments. The data are not consistent with the view that the genetic diversity of modern semidwarf wheat grown in the developing world has decreased over time. Moreover, since national programs in developing countries cross CIMMYT lines with their own materials before releasing them, the genetic diversity in their cultivars is at least as great as that present among CIMMYT lines., NEARLY 30 YR HAVE PASSED since in a landmark study, the National Research Council (1972) alerted the scientific community and the public about the dangers of restricting crop improvement to [...]

The fall armyworm, Spodoptera frugiperda (J. E. Smith), is an agronomically important pest that severely limits maize (Zea mays (Linnaeus) [Poales: Poaceae]) production. This migrant insect devastates maize plants in many countries threatening the livelihood of millions. Quantitative trait loci (QTL) were mapped to identify chromosomal regions that control resistance to fall armyworm leaf-feeding and to identify molecular markers linked to the target loci for use in marker-assisted selection (MAS). A bi-parental mapping population, comprising 243 F2:3 families from the cross Mp705 (resistant) × Mp719 (susceptible), was evaluated for fall armyworm leaf-feeding damage under artificial infestation over 3 yr. A linkage map comprised of 1,276 single-nucleotide polymorphism and simple sequence repeat molecular markers was constructed. Quantitative trait loci analyses identified two major QTL in bins 4.06 and 9.03 that when combined, explained 35.7% of the phenotypic variance over all environments. Mp705 was responsible for the leaf-feeding damage reducing alleles for both large effect QTL and most of the small effect QTL identified in this study. The QTL identified in bin 9.03 co-locates with a previously identified QTL that controls resistance to leaf-feeding damage in maize by fall armyworm and other lepidopteran insects. The QTL in bin 4.06 is a new source of resistance identified in this study. Beneficial alleles derived from Mp705 for the application of an integrated QTL-MAS approach could accelerate breeding efforts to minimize fall armyworm leaf-feeding in maize. [ABSTRACT FROM AUTHOR]

Fungal mycotoxins are important contaminants of agricultural commodities that pose serious concerns to producers, consumers and exporters. Aflatoxin is a carcinogenic metabolite produced by the fungi Aspergillus flavus and A. parasiticus. These fungi and other mould species living in the soil contaminate several crops including maize. This study was undertaken with the following objectives: (i) to assess the presence of A. flavus and other moulds in Ghanaian soil; (ii) to determine the distribution and density of A. flavus under three agro‐ecologies noted for major maize production; and (iii) to assess the effect of percentage of carbon (C) and nitrogen (N) and soil pH on A. flavus population densities and diversity in the isolates found across the agro‐ecologies. The data showed seven moulds that were common across the agro‐ecologies. Significant differences (P < 0.05) were observed in the A. flavus density and distribution within and across these agro‐ecologies. Fumesua soils recorded the highest levels of A. flavus (1.185 × 103 cfu g−1) while Akomadan recorded the least (9.76 × 102 cfu g−1). Percentage available C, N and soil pH did not significantly influence A. flavus density. The A. flavus isolates identified in this study varied in genetic sequence within the aflatoxin gene cluster, but these differences were not distinguishable by origin. [ABSTRACT FROM AUTHOR]

The genetic base of soybean [Glycine max (L.) Merr.] cultivars developed for North America is very narrow. This may threaten the ability of breeders to sustain improvement and increase vulnerability of the crop to pests. The objective of this research was to assess the relationship of 18 major ancestors of North American soybean germplasm with 87 plant introductions (PIs) that are potential new sources of genetic variation for soybean breeding programs. Genetic distances (GD) among the 105 genotypes analyzed were calculated from 109 polymorphic DNA fragments amplified with random oligonucleotide primers and simple sequence repeat (SSR) primer pairs. Two hierarchical clustering algorithms were combined with data resampling and multidimensional scaling (MDS) to evaluate relationships among the genotypes. Genetic distances ranged from 0.08 to 0.76, with a mean of 0.52. Genotypes were placed in 11 clusters on the basis of a consensus of the different methods utilized. Co-occurrence values calculated from the resampling iterations showed that the stability of clusters varied. The most stable grouping was among ancestors that corresponded with known relationships based on pedigree and maturity. Several groups of PIs are distinct from the majority of the ancestors. These genotypes may be useful to breeders wanting to utilize genetically diverse introductions in soybean improvement., SOYBEAN BREEDING PROGRAMS in the USA have successfully developed hundreds of improved cultivars through hybridization of elite cultivars and breeding lines that trace back to a small number of original [...]

Global average surface temperature has increased by approximately 0.74 °C over the most recent 100-year period. At a regional level in South Africa, detectable changes in both the rainfall and temperature patterns have occurred in the past 50 years. Climate change has become a reality that can no longer be ignored. Given the relatively long timescales of plant-to-harvest rotations in the commercial production forestry sector in South Africa, and the significant investment implied, climate change has the potential to have substantial impacts on forestry productivity and profitability. Under climate change conditions the climatically optimum areas for specific forest species are hypothesised to shift, with optimum areas changing in extent and location between and within provinces. This paper focuses on the Eucalyptus and Pinus genera. From the ICFR Forestry Productivity Toolbox, climate criteria for three Pinus species plus one hybrid, and four Eucalyptus species plus one hybrid, were used in combination with gridded maps of present mean annual temperature and mean annual rainfall to assess climatically optimum, moderate- and high-risk growth areas, as well as unsuitable growth areas over southern Africa. The temperature and rainfall variables were then perturbed through plausible ranges of projected future climates to determine the potential impacts of climate change on the climatically optimum, moderate and unsuitable growth areas of the Pinus and Eucalyptus families. For both families, rising temperatures may slightly increase the optimum growth area in Mpumalanga and the Eastern Cape, whereas in KwaZulu-Natal the area may reduce. The Pinus species showed less sensitivity to rising temperatures than eucalypts. The two hybrids exhibited less sensitivity than other species of their genera. The hybrid Pinus ExC emerged as least sensitive to increasing temperature. Declining rainfall concomitant with rising temperature will have an especially negative effect on total area of optimal growth. An increase in rainfall will, however, offset all negative impacts of temperature and increase total optimum growth area for both families. [ABSTRACT FROM AUTHOR]

CIMMYT is the source of improved maize (Zea mays L.) breeding material for a significant portion of the nontemperate maize growing world. Landraces which did not serve as sources for improved maize germplasm may contain untapped allelic variation useful for future breeding progress. Information regarding levels of diversity in different germplasm would help to identify sources for broadening improved breeding pools and in seeking genes and alleles that have not been tapped in modern maize breeding. The objectives of this study were to examine the diversity in maize landraces, modern open pollinated varieties (OPVs), and inbred lines adapted to nontemperate growing areas to find unique sources of allelic diversity that may be used in maize improvement. Twenty-five simple sequence repeat markers were used to characterize 497 individuals from 24 landraces of maize from Mexico, 672 individuals from 23 CIMMYT improved breeding populations, and 261 CIMMYT inbred lines. Number of alleles, gene diversity per locus, unique alleles per locus, and population structure all differ between germplasm groups. The unique alleles found in each germplasm group represent a great reservoir of untapped genetic resources for maize improvement, and implications for hybrid breeding are discussed. [ABSTRACT FROM AUTHOR]

Characterization of genetic diversity of maize (Zea mays L.) germplasm is of great importance in hybrid maize breeding. The objectives of this study were to (i) investigate genetic diversity in CIMMYT subtropical, tropical midaltitude and highland inbreds with simple sequence repeat (SSR) markers, (ii) identify appropriate testers for the development of new inbred lines, (iii) compare this sample to U.S. and European elite maize lines and CIMMYT tropical lowland inbreds, and (iv) use the marker and pedigree information as a guide to understanding the heterotic relationship among the CIMMYT maize lines (CMLs) and their potential practical use in maize breeding pro- grams worldwide. Inbreds included in the study were assayed with 79 SSR markers. The CIMMYT inbred lines originated from 35 mostly broad-based populations and pools with mixed origins. A total of 566 alleles were scored, (averaging 7.2 and ranging from 2 to 16 alleles per locus). The modified Roger's distance (MRD) between pairs of inbreds averaged 0.78, with a range of 0.45 to 0.93. Unweighted paired group method using arithmetic averages (UPGMA) cluster analysis revealed no clear clustering. This reflects a mixed composition of CIMMYT subtropical, tropical midaltitude and highland maize populations and pools, and indicates that large amounts of variation have been incorporated into CIMMYT germplasm. Temperate heterotic groups were separated based on the markers, and nontemperate CIMMYT maize was genetically distinct from temperate lines. Discrete clusters were difficult to identify within and often between megaenvironments. Specific recommendations for nontemperate hybrid maize breeding are made. [ABSTRACT FROM AUTHOR]

Many wheat (Triticum aestivum L.) landrace cultivars (LCs) conserved in seed banks are not sufficiently characterized to inspire breeders' interest for their efficient exploitation. Patterns of genetic variation within and among wheat LCs are usually unknown. Two sets of wheat LCs stored in CIMMYT's plant genetic resources center were assessed for genetic diversity by means of 76 (Set 1) and 44 simple sequence repeat (SSR) markers (Set 2). Set 1 included 36 LC accessions originating from different countries, either collected as bulks, composed of a single LC subline, or an unknown collection method. Set 2 consisted of three to 25 sublines of five Mexican and four Turkish LCs already included in Set 1. In a principal coordinate analysis based on modified Rogers' distance (MRD), only three Turkish LC accessions formed a distinct cluster in Set 1. The Mexican accessions clustered together with a Spanish accession and a close relationship between a Chilean and Nigerian accession was observed. In Set 2, gene diversity (He) among the Turkish LCs (0.43) was higher than among the Mexican LCs (0.35). Analyses of molecular variance (AMOVA) revealed considerable genetic diversity within Mexican (52.7%) and within Turkish (67.6%) LCs. Pairwise fixation indices (FsT) were significant, except between two Turkish LCs. Results were discussed in relation to the most suitable collection method of wheat LCs (bulk or individual sublines) as well as to the use of SSRs as a tool for seed bank management. [ABSTRACT FROM AUTHOR]

Detailed knowledge about the genetic diversity among germplasm is important for hybrid maize (Zea mays L.) breeding. The objectives of our study were to (i) investigate the genetic diversity among tropical lowland inbred lines and (ii) delimit heterotic groups in this germplasm. Simple sequence repeat (SSR) analysis of 79 markers distributed uniformly throughout the maize genome was performed for 155 tropical lowland inbred lines from the International Maize and Wheat Improvement Center (CIMMYT). Inbred lines were extracted from 60 broad-based populations and pools with mixed origin. We observed an average of 7.4 deles per marker with a range from 2 to 18. The polymorphic information content (PIC) of the 79 SSRs ranged from 0.13 to 0.87, with an average of 0.60. Cluster analysis of the tropical yellow and white lines revealed a lack of structure within this germplasm, which can be explained by the mixed origin of the populations used to extract these lines and the specific choice of testers for reciprocal recurrent selection (RRS). An SSR analysis can support the choice of representative testers for evaluating inbred lines in such broad-based populations. Thus, a more complete exploitation of the out-standing flint-dent heterotic pattern is possible. [ABSTRACT FROM AUTHOR]

The genetic linkage map of Prunus constructed earlier and based on an interspecific F[sub 2] population resulting from a cross between almond (Prunus dulcis D.A. Webb) and peach (Prunus persica L. Batsch) was extended to include 8 isozyme loci, 102 peach mesocarp cDNAs, 11 plum genomic clones, 19 almond genomic clones, 7 resistance gene analogs (RGAs), 1 RGA-related sequence marker, 4 morphological trait loci, 3 genes with known function, 4 simple sequence repeat (SSR) loci, 1 RAPD, and 1 cleaved amplified polymorphic sequence (CAP) marker. This map contains 161 markers placed in eight linkage groups that correspond to the basic chromosome number of the genus (x = n = 8) with a map distance of 1144 centimorgans (cM) and an average marker density of 6.8 cM. Four more trait loci (Y, Pcp, D, and SK) and one isozyme locus (Mdh1) were assigned to linkage groups based on known associations with linked markers. The linkage group identification numbers correspond to those for maps published by the Arús group in Spain and the Dirlewanger group in France. Forty-five percent of the loci showed segregation distortion most likely owing to the interspecific nature of the cross and mating system differences between almond (obligate outcrosser) and peach (selfer). The Cat1 locus, known to be linked to the D locus controlling fruit acidity, was mapped to linkage group 5. A gene or genes controlling polycarpel fruit development was placed on linkage group 3, and control of senesced leaf color (in late fall season) (LFCLR) was mapped to linkage group 1 at a putative location similar to where the Y locus has also been placed.Key words: Prunus, molecular markers, RFLPs, resistance gene analogs (RGAs), polycarpel fruit, stone fruits.La carte génétique du genre Prunus produite précédemment à l'aide d'une population F2 issue d'un croisement interspécifique entre l'amandier (Prunus dulcis D.A. Webb) et le pêcher (Prunus persica L. Batsch) a été bonifiée et compte maintenant : 8 locus isoenzymatiques, 102 ADNc du mésocarpe du pêcher, 11 clones génomiques du prunier, 19 clones génomiques de l'amandier, 7 analogues de gène de résistance (RGA), 1 marqueur correspondant à un gène ressemblant à un gène de résistance, 4 caractères morphologiques, 3 gènes de fonction connue, 4 microsatellites (SSR), 1 marqueur RAPD et 1 marqueur CAPS (« cleaved amplified polymorphic sequence »). Cette carte comprend 161 marqueurs formant huit groupes de liaison, ce qui correspond au nombre haploïde de chromosomes (x = n = 8), et totalise 1144 centimorgans (cM), ce qui se traduit par une densité moyenne d'un marqueur à tous les 6,8 cM. Quatre autres caractères morphologiques (Y, Pcp, D et SK) et un locus isoenzymatique (Mdh1) ont été assignés à un groupe de liaison sur la base d'une liaison connue avec un marqueur. La numérotation des groupes de liaison est conforme à celle employée par les groupes de Arús en Espagne et de Dirlewanger en France. Quarante-cinq pour cent des locus montraient une distorsion de la ségrégation vraisemblablement en raison de la nature interspécifique du croisement et de différences quant au mode de reproduction des deux espèces, l'amandier étant une espèce à allofécondation obligatoire et le pêcher à autofécondation. Le locus Cat1, connu comme étant lié au locus D qui contrôle l'acidité des fruits, a été assigné au groupe de liaison 5. Un gène ou des gènes déterminant le nombre de carpelles au sein du fruit a été situé sur le groupe de liaison 3 et le contrôle de la couleur des feuilles senescentes à l'automne (LFCLR) a été placé sur le groupe de liaison 1 à un endroit semblable à celui où se trouve le locus Y.Mots clés : Prunus, marqueurs moléculaires, RFLP, analogues de gène de résistance (RGA), fruit à carpelles multiples, fruits à noyau.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

Immunocytochemical stains for three epithelial cell markers--keratin, epithelial membrane antigen (EMA) and carcinoembryonic antigen (CEA)--have been examined on paraffin-embedded material from 14 patients with nasopharyngeal carcinoma (NPC). Tumour cells staining positively for keratin were found in all cases and for EMA in eight; two tumours contained CEA-positive cells. Seven cases of Hodgkin's disease and 24 non-Hodgkin's lymphomas were uniformly negative. Keratin is the most reliable epithelial marker for identifying NPC and excluding lymphoma. The regular finding of stainable keratin in non-keratinising and anaplastic NPC supports the view that NPC is a homogeneous group exhibiting variable degrees of squamous differentiation. [ABSTRACT FROM PUBLISHER]

Haemagglutinin was extracted from H. pertussis with alkaline 1 M NaCl and adsorbed on aluminium phosphate at slightly acid pH. The antigen was purified by elution and readsorption. Haemagglutinin in the adsorbed form was more resistant to destruction by heat or agitation than in solution. Mice immunized actively with the adsorbed antigen, or passively with sera of animals immunized with it, were protected against the lethal effects of intranasally introduced infection with H. pertussis. [ABSTRACT FROM AUTHOR]

HAPA (pertussis haemagglutinin, aluminium phosphate adsorbed), injected into babies in single subcutaneous or intramuscular doses of 1 ml., or two subcutaneous doses of 0·1 ml. or 0·3 ml. spaced 1 to 2½ months apart, produced mean serum antihaemagglutinin titres between 11·3 and 32. Single subcutaneous doses of 0·1 ml. or 0·3 ml. resulted in significantly lower serum antibody levels. Local and general toxic effects, observed in over 270 subjects, were mild in babies and young children with no history of previous immunization against whooping cough. The reactions were more marked in older children and in those previously sensitized with H. pertussis, but were no more severe than those associated with administration of bacterial pertussis vaccine in customary doses. [ABSTRACT FROM AUTHOR]