Changes in the rate of photosynthesis accompanying the yield increase in wheat cultivars released in the past 50 years

Photosynthetic rates in different development stages were carefully investigated in 18 cultivars of winter wheat released in the period between 1945 and 1995 in the area of Beijing, China. During this period, the recorded grain yield has increased eightfold. However, when those cultivars were planted and managed in the same environment, the difference was reduced to only 36%, indicating that agronomic practices are the most important factors for grain yield. Agronomic features have changed greatly in the past 50 years, through increasing the harvest index (R²=0.89, P<0.05), shortening plant height (R²=0.77, P<0.05) and slightly increasing flag leaf areas (R²=0.45, P<0.05), which is mostly in agreement with many other researchers. In contrast to many reports, however, this study found a genetic increase in the rate of photosynthesis per unit leaf area. From the mid-stem elongation to soft dough stages, the average photosynthetic rates at saturated photosynthetic photon flux density (P_sat) increased by 44%. In the process, the stomatal conductance (g_s) also increased by 122%. Grain yield was positively related to the mean values of P_sat (R²=0.61, P<0.01) and g_s (R²=0.67, P<0.01) in the six development stages. Our experiment may suggest that increase in grain yield was associated with the elevation of leaf photosynthetic rate and stomatal conductance over the past 50 years.     

Transglutaminases and their substrates in biology and human diseases: 50 years of growing

Transglutaminase is an enzyme able to play more than one enzymatic action, acting on a variety of different substrates. The growth of knowledge about the members of the enzyme transglutaminase’s family and its substrates since the last 50 years indicates a large interest and curiosity about this protein, whose function and structure was, but still is, an important object of research. On the other hand, the involvement in a number of human diseases together with the lack of knowledge about the biological functions played by some of the most studied members of this family, make this enzyme a fascinating field of study. The history of this enzyme and its substrates, whose cross-linking action was reported for the first time 50 years ago, suggests that an effort to increase knowledge and communication among researchers is required. To achieve this important result, 10 years ago an internet web page called worldwide happening around transglutaminase (WHAT) was created. Driven by these experiences, novel points-of-view to look at Transglutaminase and its substrates may be identified.     

Limited genetic diversity and high differentiation among the remnant adder (Vipera berus) populations in the Swiss and French Jura Mountains

Although the adder (Vipera berus) has a large distribution area, this species is particularly threatened in Western Europe due to high habitat fragmentation and human persecution. We developed 13 new microsatellite markers in order to evaluate population structure and genetic diversity in the Swiss and French Jura Mountains, where the species is limited to only a few scattered populations. We found that V. berus exhibits a considerable genetic differentiation among populations (global F_ST = 0.269), even if these are not geographically isolated. Moreover, the genetic diversity within populations in the Jura Mountains and in the less perturbed Swiss Alps is significantly lower than in other French populations, possibly due to post-glacial recolonisation processes. Finally, in order to minimize losses of genetic diversities within isolated populations, suggestions for the conservation of this species in fragmented habitats are proposed.     

A dendroclimatic analysis of regional moisture variation in the northeastern Tibetan Plateau during the past 150 years

As a transitional zone between westerlies and the Asian Monsoon system, the northeastern part of the Tibetan Plateau (NETP) is highly sensitive to climate change. The record of historical regional moisture variation in the NETP is essential for understanding climatic variation and its relationship with different climate systems in this area. Using principal component analysis, a time series was extracted from sixteen moisture-sensitive tree-ring series to investigate the regional moisture variation in the NETP over the past 150 years. We find that the first principal component (PC1) represents 46.9 % of the total variance, reflecting a common growth response to the climate factor. A spatial correlation analysis of PC1 with the gridded meteorological data demonstrated that the precipitation in May–June was the major factor in controlling tree-ring growth. Further analysis indicated that the westerlies had a sustained influence on rainfall in the NETP over the past 150 years. In addition, the rainfall in the NETP may be closely associated with the East Asian Monsoon (EAM). Severe drought years commonly correspond to years of a negative phase of the North Atlantic Oscillation and stronger EAM years over the past 150 years.     

Minor changes in orthopteran assemblages of Central European protected dry grasslands during the last 40 years

During the past 50 years development of farming practices caused tremendous changes in European agricultural landscapes and many insect species became increasingly restricted to protected areas. Yet little is known about long-term trends of insect diversity and community composition in these often small reserves. We performed a comparative study on changes in orthopteran communities of protected dry grasslands in East Germany, which had been surveyed in the 1960s. Applying the same sampling techniques, we revisited 26 of the original sites in 2008 and 2009. Nearly all sites are controlled by conservation policies and changes in vegetation composition were relatively small, although some sites showed shrub encroachment. Changes in orthopteran diversity were not significant. Community composition showed minor changes which were correlated with evidence of woody plant encroachment as derived from historical and recent aerial imagery. The frequency of some Caelifera species decreased from the 1960s to 2008/2009 with one species inhabiting bare soils (Myrmeleotettix maculatus) showing the strongest decline. Some Ensifera, especially two species inhabiting open woodland and scrub (Tettigonia viridissima, Phaneroptera falcata) showed positive trends. Nevertheless, three different regions (each belonging to a different German federal state) had shown distinct orthopteran assemblages in the 1960s, and these were equally different 40 years later. We conclude that the orthopteran fauna of Central European protected dry grasslands showed small changes in species composition, and overall diversity remained rather constant during the past 40 years, which is in accordance with the minor changes in the surrounding landscape. Consequently, the applied conservation management practises—mainly sheep grazing and trimming—are largely effective.     

Assessment of testcross performance and genetic diversity of yellow endosperm maize lines derived from adapted × exotic backcrosses

Introduction of exotic maize (Zea mays L.) into adapted tropical germplasm may enhance genetic variability and lead to greater progress from selection. The first objective of this study was to determine if yellow endosperm lines derived from adapted × exotic backcrosses contain exotic alleles that are superior to the recurrent adapted parental line for yield and other agronomic traits in tropical environments. Thirteen exotic yellow maize inbred lines were crossed to an adapted orange line (KUSR) and the F₁s were backcrossed to KUSR to generate the first backcrosses. Fifty BC₁F₄ lines derived from these backcrosses and the recurrent parent were crossed to a common inbred tester (L4001) to form testcrosses, which were evaluated at eight environments in Nigeria. Testcrosses of the BC-derived lines differed significantly for grain yield and other agronomic traits. Only two testcrosses yielded significantly less than L4001 × KUSR, with the best 15 testcrosses producing between 289 and 1,056 kg/ha more grain yield than L4001 × KUSR. The best testcrosses were similar to or better than L4001 × KUSR for other agronomic traits. The second objective of this study was to assess the extent of genetic diversity present among the BC-derived lines. We genotyped 46 BC-derived lines including KUSR and L4001 with 10 AFLP primer pairs and found 491 polymorphic fragments. The average allelic diversity of the lines was 0.30 ± 0.01. The genetic distance of each BC-derived line from KUSR ranged between 0.49 and 0.91. The average genetic distance for all pairs of the BC-derived lines was 0.68 ± 0.004, varying from 0.34 to 0.92. The increased grain yield and genetic diversity observed in these studies provide evidence that exotic germplasm can contribute new alleles to expand the genetic base of tropical maize and develop high-yielding hybrids.     

Assessment of ecosystem health during the past 40 years for Lake Taihu in the Yangtze River Delta,China

An assessment of the ecosystem health of Lake Taihu in eastern China from 1960 to 2005 was conducted using separate and aggregated chemical and biological indicators. The chemical oxygen demand, the total nitrogen, total inorganic nitrogen and total phosphorus concentrations, and the molar ratio of TN to TP (N/P) have all significantly increased (P < 0.05) since 1980. The trophic state index increased from 35.0 in 1960 to >60.0 in 1990, confirming that Lake Taihu changed from being oligotrophic to being eutrophic. These changes in water quality have led to corresponding changes in species composition and in the densities and biomasses of many aquatic species. Algal blooms have occurred frequently since the late 1980s, leading to the dominance of small zooplankton and benthic invertebrates. About 41 fish, 65 zooplankton and 16 macrophyte species were estimated to have disappeared from the lake since the late 1980s. Buffer capacity increased for phytoplankton and zooplankton but decreased for zoobenthos. These results suggest that the Lake Taihu ecosystem was in better health in 1960, and has deteriorated since 1980.     

Changes in the impact of anthropogenic effects on river water quality during the last 50 years in Japan

Japan’s rapid urbanisation over the last 50 years has resulted in land use and lifestyle changes, all of which are likely to have changed the quality of river water, and consequently the wetland and coastal environment. We examined changes in river water quality over this period by means of a review of previous studies. Around the 1950s, the weighted average of chloride using discharge of Japan’s 30 major rivers was 6.1 mg/l while in the 2000s it was 11.3 mg/l. Because there were no significant changes in the natural conditions, we have attributed the increase to the urbanisation of the last 50 years. Nitrate levels in the mountain streams of southern Japan have increased, particularly in the western part of the Kanto region. As this area is located on the leeward side of the Tokyo Metropolitan Area, depositions from aerosols are thought to be the main cause of the increased nitrate concentration. These two findings suggest that certain uses of land may affect river water quality differently over time, and that changes in land use may also affect river water quality in remote areas.     

Adaptive responses in resurgent Lake Victoria cichlids over the past 30 years

Textbook examples of adaptive radiation like the Galapagos finches and the East-African cichlids form a subject of major interest in evolutionary biology. Many of these species often show rapid morphological changes in response to a perturbed environment. The dramatic ecological changes in Lake Victoria during the past three decades, e.g. Nile perch predation and eutrophication, provide a unique opportunity to study environmental effects on cichlid morphology. Preliminary research has revealed that the lake’s haplochromines tend to be extremely plastic and sensitive to these environmental changes. So far, long-term ecomorphological studies at short-term intervals are extremely rare. In this study, we examined morphological changes over a 30 year period in six haplochromine species. Geometric morphometric analyses at intervals of approximately 3 years revealed adaptive responses. Three out of four resurgent haplochromines had a smaller head surface/caudal peduncle area (HS/CPA) ratio during the upsurge of the predatory Nile perch. During the same period, all four resurgent species had a larger cheek depth and a smaller eye size. The smaller HS/CPA ratio and larger cheek depth are likely to be adaptive responses to a high predation pressure and a diet shift to larger prey. The smaller eye size seems to be the result of a trade off between the eyes and other morphological structures in the smaller head of these species. Interestingly, the direction of the morphological changes was different between the four resurgent cichlid species and two species that became extremely rare or even may have gone extinct. The HS/CPA ratio increased in the extinct species where it decreased in the resurgent species. This study suggests that predation is a major driver of these morphological changes, which may be due to either phenotypic plasticity or adaptive changes.     

Resilience and regime change in a southern Rocky Mountain ecosystem during the past 17?000 years

Paleoecological records indicate that subalpine forests in western North America have been resilient in response to multiple influences, including severe droughts, insect outbreaks, and widely varying fire regimes, over many millennia. One hypothesis for explaining this ecosystem resilience centers on the disruption of forest dynamics by frequent disturbance and climatic variability, and the resulting development of non-steady-state regimes dominated by early-successional conifers with broad climatic tolerances, such as lodgepole pine (Pinus contorta var. latifolia Engelm. ex Wats.). To evaluate this hypothesis, we independently reconstructed the vegetation, fire, and effective-moisture histories of a small, forested watershed at 2890 m elevation in southeastern Wyoming, USA, using sedimentary pollen and charcoal counts in conjunction with sedimentary lake-level indicators. The data indicate that prominent vegetation shifts (from sagebrush steppe to spruce–fir parkland at ca. 10.7 ka and spruce–fir parkland to pine-dominated forest at ca. 8.5 ka [ka stands for thousands of years before the present, defined as AD 1950]) coincided with changes in effective moisture. However, after lodgepole pine forests established at ca. 8.5 ka, similar hydroclimatic changes did not produce detectable vegetation responses. Fire history data show that other aspects of the ecosystem were responsive to changes in effective moisture at centennial timescales with prolonged fire-free episodes coinciding with periods of low effective moisture ca. 7.2–5.6 and 3.7–1.6 ka. Throughout our record, the ratio of ecosystem perturbation time (i.e., fire frequency and changes in effective moisture) to recovery time (assuming 200–600-year successional processes) falls within estimates of the ratio for non-steady state ecosystems. Frequent perturbations, therefore, may have prevented this ecosystem from reaching compositional equilibrium with the varied climatic conditions over the past 8.5 ka. Equilibrium states could have included more abundant spruce (Picea spp.) and fir (Abies spp.) than presently observed based on brief increases in pollen abundances of these taxa during prolonged dry, fire-free intervals. Our results show that, although current climate changes favor widespread disturbance in Rocky Mountain forests, the composition of these ecosystems could be highly resilient and recover through successional dynamics over the next few decades to centuries.     

Comorbidity among HHT patients and their controls in a 20 years follow-up period

Background

Hereditary Haemorrhagic Telangiectasia (HHT) is an autosomal dominant genetic disorder with a wide variety of clinical manifestations due to the presence of multiple arteriovenous malformations in various tissues and organs.

Objective

To study the need for hospital admittance in a group of HHT patients and matched controls during a 20?years follow-up period commencing in 1995.

Methods

All HHT patients in the County of Funen, Denmark, were included. For each patient, three age and sex matched controls were identified at the time of enrolment. Data on all hospitalisations were extracted from the national health registers and compared with clinical records. The hospitalisations were grouped as HHT relevant or not HHT relevant based on the discharge diagnosis (International Classification of Diseases, ICD10) and with particular focus on infections, bleedings and thromboembolic events.Patients with HHT were compared with controls concerning the first time incidence of each discharge diagnosis.

Results

We included 73 HHT patients and 219 controls of which one control was lost to follow-up. HHT-patients had significantly more hospitalisations per person caused by infections in joints and bones, but not caused by infections in general. Bleeding episodes were, as expected, more frequent among the HHT-patients. The study revealed a similar incidence of abscesses and thromboembolisms, including in the central nervous system, among the HHT patients and controls.

Conclusions

Based on this study Danish HHT patients had an increased comorbidity of infections in joints and bones and of bleeding episodes. However, the incidence of thromboembolisms, cerebral abscesses and other conditions commonly considered related to HHT was comparable between the patients and the controls. The patients included in this study were closely monitored at a highly specialised HHT Centre where they received relevant diagnostic evaluation, treatment and counselling. Since this is assumed to benefit the overall health of the patients, it may explain why these patients were less prone to comorbidity than other studies have suggested.

     

Recent advances in lactoferrin research and development during the past two years (2007–2009): in lieu of a preface of the special issue lactoferrin

This is a short preface of this Special Issue Lactoferrin, it described the major points of key reporters in ‘The 9th International Conference on LF Structure, Function and Applications’ in Beijing in late Autumn 2009, and the major articles published in this issue. A panaroma and the lastest advances of lactoferrin R&D during past two years (2007–2009) was tried to extract.     

Changes in plant species diversity of aquatic ecosystems in the agricultural landscape in West Poland in the last 30 years

The aim of this study was to diagnose changes in species composition and their dynamics caused by human impact in aquatic and marsh vegetation in the contemporary agricultural landscape. The most serious threat was an increase in the nitrogen content of surface waters and groundwater which had resulted from the intensive management of the surrounding areas. Floristic data were collected in a lake, peaty pools and a drainage ditch within agricultural areas in the Wielkopolska region (West Poland) in 2006–2007, and compared with data from 1976–1980. The species richness had significantly increased and the shares of sociological and geographical–historical groups had changed clearly. This was reflected in an increase in the synanthropization index from 32.6 to 48.5. All the changes resulted from human impact, which had caused the acceleration of eutrophication in the water bodies. The natural plant succession, especially in the reed beds and sedge communities, was also accelerated due to human pressure. The vascular plant species richness in aquatic and marsh habitats increased by 40, because 15 species had disappeared and 55 new had appeared. However, six moss and four stonewort species had disappeared and only three new moss species were found. The increase in species richness did not raise the natural value of the flora, because the new species group is composed mainly of synanthropic species: native (apophytes) and alien, whereas all the lost species are endangered and rare native species (spontaneophytes), which occur only in natural or seminatural conditions. On the local scale, as species richness increases, plant communities lose their natural value. As an effect of synanthropization the stenotopic species disappear, while the widespread species spread even more. The increase in species richness is a consequence of appearance of species with a wide ecological scale that are not typical for aquatic ecosystems in patches of emergent vegetation. Finally, the species diversity of the whole landscape declines.     

Nutrient fluxes and water quality in the drainage network of the Scheldt basin over the last 50 years

and use and urban activity in the catchment of the Scheldt river system have deeply changed during the last 50 years, modifying in turn the water quality of the drainage network and the fluxes of nutrient transferred to the estuary and to the sea. Based on the RIVERSTRAHLER model, developed for establishing the link between the biogeochemical functioning of large river systems and the constraints set by the meteorology, the morphology of the drainage network and the human activity in the watershed, we reassembled the data available to document these constraints in the Scheldt basin since the last half of the XXth century and we used them to reconstruct the variations of nutrient and oxygen concentrations at the outlet of the Scheldt drainage network. We compared the results with the water quality data at the entrance of the estuarine zone available since the 1960s. Both model results and observational data show a very severe deterioration of water quality (with deep oxygen depletion) in the beginning of the 1960s, while a clear trend to improvement is apparent since the late 1980s. The budget of nutrient loadings from the watershed, retention within the drainage network and delivery to the estuarine zone is established on an annual basis for the 50 last years. The yearly fluxes of nutrient delivered by the river to the estuary and the sea show a severe depletion of silica with respect to nitrogen compared with the requirements of diatoms, and a clear shift from the early 1990s from nitrogen to phosphorus potential limitation. Seasonal variations of nutrient delivery are however much more pronounced for nitrogen, with much less inputs during the dry seasons, while phosphorus inputs, mainly from point sources are more constant, so that nitrogen limitation can still occur during summer. Compared with similar budget estimations carried out for the Seine river system, the Scheldt basin, in spite of its much higher population density, does not deliver higher specific fluxes of nutrient (presently about 2000 kgN/km²/yr, 80 kgP/km²/yr and 1000 kgSi/km²/yr), owing to very efficient processes of nutrient retention.     

Developmental consequences of water and temperature in the European corn borer — maize interaction

Maize plants were grown under four moisture regimes (wet to extreme deficit) and three constant temperatures (20°, 25° & 30°C) in a phytotron. Each plant was infested with one E-race European corn borer [Ostrinia nubilalis (Hubn.)] (ECB) egg mass at pollen shed. ECB development, location, and establishment were recorded over the course of 12 destructive sample dates (4/temperature). ECB developmental rates were not significantly affected by soil moisture treatments, but were significantly affected by temperature. In spite of successful establishment of four distinctly different soil moisture regimes, the maize stalk tissue water levels were not significantly different among soil water treatments. Instead, the maize plants exhibited accelerated leaf senescence in response to the water deficit conditions. Among the soil water treatments, differences were found in larval establishment, vertical distribution and dispersion, and feeding site selection; however, those effects were slight and could not explain the similarity in ECB developmental rates observed in these treatments.In maize, the larval environment within the stalk was effectively insulated from changes in the external environment by the plant's ability to maintain a relatively high and stable stalk tissue water content. Thus, large changes to the soil environment had essentially no effect on ECB development, though drastic consequences for the plant. This study indicates that ECB rates of development are relatively insensitive to changes in the soil water environment as well as the associated changes in the maize plant that accompany severe drought stress. The significance of these findings to insect modelling, crop physiology, and insect-crop interactions is discussed.

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Résumé Des plants de maïs se développent dans un phytotron dans 4 conditions d'humidité du sol (de la saturation à la dessication) et à 3 températures constantes (20°, 25° & 30°C). Chaque pied est contaminé au moment de l'émission du pollen, par une ooplaque d'O. nubilalis Hübn. (ECB) de race européenne E. L'installation, la colonisation et le développement des chenilles sont notés lors de 12 périodes de prélèvements destructifs (4 par température). La vitesse de développement d'O. nubilalis est affectée par la température, main non par l'humidité du sol. Les 4 niveaux d'humidité du sol n'ont aucun effet sur la teneur en eau des tiges de maïs. En fait, les feuilles de maïs présentent une senescence précoce lorsqu'il y a déficit en eau dans le sol. La teneur en eau du sol agit sur l'installation, sur la distribution verticale, la dispersion et le lieu d'alimentation des chenilles; mais ces effets sont légers et ne modifient pas la vitesse de développement.L'environnement larvaire dans la tige de maïs est efficacement isolé des variations externes par l'aptitude de la plante à maintenir la teneur en eau des tiges relativement élevée et stable. Ainsi, des changements importants au niveau du sol n'ont pratiquement pas d'effets sur le développement d'O. nubilalis, malgré les conséquences brutales pour la plante. Cette étude montre que la vitesse de développement d'O. nubilalis est relativement insensible aux modifications de la teneur en eau du sol ainsi qu'aux effets de ce stress de sécheresse sévère sur le pied de maïs. La discussion porte sur l'importance de ces résultats pour la modélisation de la dynamique de l'insecte, la physiologie de la culture et les interactions entre insecte et plante.

     

Genetic relationships between resistance to stalk-tunneling by the European corn borer and cell-wall components in maize population B73×B52

The objective of this study was to assess the relationships among quantitative trait loci (QTL) detected for European corn borer (ECB) tunneling and cell-wall components (CWC) neutral detergent fiber (NDF), acid detergent fiber (ADF), and acid detergent lignin (ADL) content in leaf-sheath and stalk tissues in a maize recombinant inbred line population derived from inbred lines B73 and B52. Most of the QTL for ECB resistance (10/13) were at QTL positions for one or more CWC. Of the 12 QTL for NDF and ADF in leaf-sheaths, five for each trait were at or near QTL for ECB tunneling. Four of these five QTL for NDF and ADF mapped to common locations. Four of the eight leaf-sheath ADL QTL were detected in the same genomic regions as ECB QTL. For stalk tissue, four regions contained common/overlapping QTL for ECB tunneling, NDF, and ADF. Six such regions were observed for stalk ADL and ECB tunneling. Seven of the ten QTL associated with both CWC and ECB tunneling contributed to the negative correlations observed between these traits, while relatively few QTL effects were positively correlated. This suggests that while CWC contribute to ECB resistance in this population, other mechanisms and other genes also are involved. Several QTL contributing to the negative correlations between ECB tunneling and CWC in the leaf-sheaths mapped to similar positions as QTL detected in tropical maize populations for resistance to leaf-feeding by Diatraea grandiosella Dyar and Diatraea saccharalis Fabricus. These regions may contain genes involved in the synthesis of cellulose, hemicellulose, and lignin in the leaf-blades and leaf-sheaths of maize.     

Rapid morphological divergence in two closely related and co-occurring species over the last 50 years

We studied morphological variation in two closely related and ecologically similar species of mice of the genus Peromyscus, the deer mouse (P. maniculatus) and white-footed mouse (P. leucopus), over the last 50 years in Southern Quebec. We found that contemporary populations of the two species are distinct in morphology and interpret this differentiation as a reflection of resource partitioning, a mechanism favouring their local coexistence. While there was no size trend, geographic or temporal, both species displayed a concomitant change in the shape of their skull over the last 50 years, although this change was much more apparent in the white-footed mouse. As a result, the two species diverged over time and became more distinct in their morphology. The observed changes in morphology are large given the short time scale. During this period, there was also a shift in abundance of the two species in Southern Quebec, consistent with the northern displacement of the range of the white-footed mouse in the last 15 years. Our study thus reports the changes in morphology of two co-occurring mammal species that were accompanied by changes in distribution and local abundance, potentially in response to rapid climate change.     

Tropical maize germplasm: what can we say about its genetic diversity in the light of molecular markers?

Knowledge about genetic variability of a crop allows for more efficient and effective use of resources in plant improvement programs. The genetic variation within temperate maize has been studied extensively, but the levels and patterns of diversity in tropical maize are still not well understood. Brazilian maize germplasm represents a very important pool of genetic diversity due to many past introductions of exotic material. To improve our knowledge of the genetic diversity in tropical maize inbred lines, we fingerprinted 85 lines with 569 AFLP bands and 50 microsatellite loci. These markers revealed substantial variability among lines, with high rates of polymorphism. Cluster analysis was used to identify groups of related lines. Well-defined groups were not observed, indicating that the tropical maize studied is not as well organized as temperate maize. Three types of genetic distance measurements were applied (Jaccard’s coefficient, Modified Rogers’ distance and molecular coefficient of coancestry), and the values obtained with all of them indicated that the genetic similarities were small among the lines. The different coefficients did not substantially affect the results of cluster analysis, but marker types had a large effect on genetic similarity estimates. Regardless of genetic similarity coefficient used, estimates based on AFLPs were poorly correlated with those based on SSRs. Analyses using AFLP and SSR data together do not seem to be the most efficient manner of assessing variability in highly diverse materials because the result was similar to using AFLPs alone. It was seen that molecular markers can help to organize the genetic variability and expose useful diversity for breeding purposes.     

Further characterization of AFLP® data as a tool in genetic diversity assessments among maize (Zea mays L.) inbred lines

AFLP® markers generated by CNG methylation sensitive (PstI/MseI) and CNG methylation insensitive (EcoRI/MseI) enzyme combinations and AFLP markers collected from hypomethylated (PstI/MseI) and hypermethylated (^m PstI/MseI) regions were compared for their polymorphism information content, sampling variance and patterns of genetic diversity in a representative sample of 33 inbred lines of maize (Zea mays L.). We demonstrate that the mean polymorphism information content generated by sets of PstI/MseI and ^m PstI/MseI markers (0.38) is significantly higher than by sets ofEcoRI/MseI markers (0.33). Also the sampling variance highlighted the distinctive nature of the ^(m) PstI/MseI markers: to achieve a mean standard deviation of 5% in the estimation of genetic distance among the 33 inbreds, the PstI/MseI and ^m PstI/MseI marker sets (135 and 129 markers, respectively) are clearly smaller than the EcoRI/MseI marker set (173 markers). A further minimizing of the sampling variance of AFLP data in the estimation of genetic similarities was obtained by reducing marker information redundancy by selecting markers evenly distributed over each chromosome: a set of only 106 AFLP markers, sampled conditionally on their genetic map position, was required for a mean standard deviation of 5% in the estimation of genetic distance among the 33 inbreds.