Heterosis and combining ability of seven maize germplasm populations

Understanding the combining ability and heterosis of available germplasm is a prerequisite for successful maize improvement and breeding. The objectives of this study were to analyze the combining ability and heterosis of seven representative maize germplasm populations, and further, to evaluate their potential utility in germplasm improvement. A total of 21 crosses were made among these seven populations in a complete diallel without reciprocals. The parental populations and 21 crosses were evaluated for days to silking (DS), ear height (EH), and grain yield (GY) in the Northeast and Yellow and Huai River maize growing areas in China in 2012. Csyn5, Csyn7, Cpop.11, and Cpop.12 had desirable general combining ability (GCA) effects for DS and EH in both the Northeast China mega-environment (NCM) and the Yellow and Huai River Regions of China mega-environment (YHCM). Cpop.11 possessed a favorable GCA effect for GY in the NCM, as did Csyn5, Cpop.17, and Cpop.18 in the YHCM. Csyn6 and Csyn7 exhibited tremendous yield-enhancing potential in both mega-environments. Additionally, six combinations including Csyn7 × Csyn6, Csyn5 × Csyn6, Cpop.11 × Cpop.18, Cpop.12 × Cpop.17, Csyn7 × Cpop.17, and Csyn5 × Csyn7 exhibited better specific combining ability effects for GY, yield performance, and mid-parent heterosis in the appropriate mega-environment. These results indicated that the seven populations would be very useful for the improvement of related agronomic traits, and the six candidate combinations possessed great potential for further improvement and utilization.     

Genetics and molecular mapping of the naked grains in hexaploid oat

Avena sativa L. subsp. nudisativa has the ability to produce naked grains. Genetic studies on the naked trait of oat began over a century ago, but the genetic and molecular factors associated with the expression of this trait have not been fully clarified. The objectives of this study were to evaluate the naked trait in two oat populations of recombinant inbred lines (RILs), to determine the number of genes, to estimate the heritability, and to map genomic regions associated with the naked trait in hexaploid oat. Parental lines and RILs of each population were screened for the naked trait from plants grown in the field over a 2 year period. Based on the phenotypic data, the oat RILs were classed as naked, partially naked, partially hulled and hulled. In both populations and years, a great number of RILs showed variable expressivity for the naked trait. The genetic analysis indicated the action of a major gene (N1) with the action of modifying genes controlling the formation of naked grains. The results of the estimate of heritability show that environmental conditions do not have a great influence in determining the naked trait. The quantitative trait loci analysis detected a genomic region with a large effect on the naked trait that explained more than 50% of the phenotypic variation. Further studies are needed to validate the use of these molecular markers to assist breeding programs to select high quality and stable naked oat cultivars.     

Two reported cytotypes of the emergent orchid model species <Emphasis Type="Italic">Erycina pusilla</Emphasis> are two different species

Each species is characterized by a specific set of chromosomes, which is described as the chromosome portrait or karyotype. In general, such a karyotype is the same for all individuals in the population. An exception to that rule has recently been found in the orchid Erycina pusilla, which has been reported to have two cytotypes with chromosome numbers of 2n = 10 and 2n = 12. Here, we examined the karyotypes of the two cytotypes and found differences in arm ratios and heterochromatin patterns as well as in the presence of satellite chromosomes and in the number and location of rDNA and telomeric repeat sites. These differences are extensive and would have required multiple chromosome rearrangements to generate the differences between the two karyotypes. We also found that F1 hybrids between the parents with the two different chromosome numbers resulted in sterile offspring, in accordance with our previous findings. The combination of hybrid sterility and extensively rearranged chromosomes supports the hypothesis that these two reported cytotypes are, in fact, two different species.     

Flavan-3-ols and procyanidins in grape seeds: biodiversity and relationships among wild and cultivated vines

Flavan-3-ol monomers and polymers composition of seeds from wild (17) and autochthonous (8) Vitis vinifera grapes growing in northern Tunisia were evaluated. Wild grape seeds were spherical with a small beak and relatively a high seed/berry ratio (~ 18.1%w/w). Local cultivars developed pyriform-shaped seeds with a well-developed beak representing on average 2.2% of total weight of the berry. Flavanol concentrations ranged between 40.9 and 67.5 mg/g FW in seeds from wild accessions and between 48.9 and 96.7 mg/g FW in seeds from cultivated grapes. Differences between accessions were highly significant (p < 0.01) and seeds from cultivar ‘Boukhasla’ showed the highest polyphenols content. Among flavan-3-ol monomers, (+)-catechin was predominant for all ecotypes and generally their abundance was: (+)-catechin (Cat) > (?)-epicatechin (Ec) > (?)-epicatechin-3-O-gallate (EcG). The Cat/Ec ratio was approximately 1.7 for wild grapes while it was about 2.5 for cultivated grapes. Procyanidins in wild seeds differed from cultivated ones by a lower mDP and higher proportions of galloylated derivatives, likely to affect fruit bitterness and astringency. (?)-epicatechin was the main extension subunit in grape seed procyanidins, reaching on average 52% in wild and 58% in cultivated seeds. Hierarchical cluster analysis based on seeds morphometry and procyanidin profile indicated close proximity between some wild and cultivated grapes suggesting that some cultivars derived from ancestral events of local domestication or cross hybridization with native wild plants.     

Identification and validation of root length QTLs for water stress resistance in hexaploid wheat (<Emphasis Type="Italic">Titicum aestivum</Emphasis> L.)

Thorough understanding of the genetic mechanisms governing drought adaptive traits can facilitate drought resistance improvement. This study was conducted to identify chromosome regions harbouring QTLs contributing for water stress resistance in wheat. A RIL mapping population derived from a cross between W7984 (Synthetic) and Opata 85 was phenotyped for root length and root dry weight under water stress and non-stress growing conditions. ANOVA showed highly significant (p ≤ 0.01) variation among the RILs for both traits. Root length and root dry weight showed positive and significant (p ≤ 0.01) phenotypic correlation. Broad sense heritability was 86% for root length under stress and 65% for root dry weight under non-stress conditions. A total of eight root length and five root dry weight QTLs were identified under both water conditions. Root length QTLs Qrln.uwa.1BL, Qrln.uwa.2DS, Qrln.uwa.5AL and Qrln.uwa.6AL combined explained 43% of phenotypic variation under non-stress condition. Opata was the source of favourable alleles for root length QTLs under non-stress condition except for Qrln.uwa.6AL. Four stress specific root length QTLs, Qrls.uwa.1AS, Qrls.uwa.3AL, Qrls.uwa.7BL.1 and Qrls.uwa.7BL.2 jointly explained 47% of phenotypic variation. Synthetic wheat contributed favourable alleles for Qrls.uwa.1AS and Qrls.uwa.3AL. Two stable root dry weight QTLs on chromosomes 4AL and 5AL were consistently found in both water conditions. Three validation populations were developed by crossing cultivars Lang, Yitpi, and Chara with Synthetic W7984 to transfer two of the QTLs identified under stress condition. The F_2.3 and F_3.4 validation lines were phenotyped under the same level of water stress as RILs to examine the effect of these QTLs. There were 13.5 and 14.5% increases in average root length due to the inheritance of Qrls.uwa.1AS and Qrls.uwa.3AL, respectively. The result indicated that closely linked SSR markers Xbarc148 (Qrls.uwa.1AS) and Xgwm391 (Qrls.uwa.3AL) can be incorporated into MAS for water stress improvement in wheat.     

Landscape dynamics of floral resources affect the supply of a biodiversity-dependent cultural ecosystem service

Context

Cultural ecosystem services, many of which depend on biodiversity, are recognized as important but seldom quantified biophysically across landscapes. Furthermore, many ecosystem service models are static, and the supply of cultural ecosystem services may be misrepresented if seasonal shifts in biotic communities are ignored.

Objectives

We modeled landscape dynamics of wildflower blooms in a temperate montane landscape to determine (1) how floral resources (wildflower species richness, abundance, timing, and presence of charismatic species) changed over the growing season, (2) how projected wildflower viewing hotspots varied over space and time, and (3) how spatial shifts in floral resources affected potential public access to wildflower viewing.

Methods

Data were collected at 63 sites across a rural-to-urban gradient in the Southern Appalachian Mountains (USA). Generalized linear models were used to identify factors affecting floral resources at two temporal scales. Floral resources were projected across the landscape and hotspots of wildflower viewing were quantified using overlay analysis.

Results

Floral resources were affected by topoedaphic conditions, climate, and surrounding building density and changed seasonally. Seasonal models revealed locational shifts in ecosystem service hotspots, which changed the proportion of hotspots accessible to the public and identified wildflower-viewing opportunities unnoticed by static models.

Conclusion

Relationships between landscape gradients, biodiversity, and ecosystem service supply varied seasonally, and our models identified cultural ecosystem service hotspots otherwise obscured by simple proxies. Landscape models of biodiversity-based cultural ecosystem services should include seasonal dynamics of biotic communities to avoid under- or over-emphasizing the importance of particular locations in ecosystem service assessments.

     

Edge effects in tropical dry forests of Madagascar: additivity or synergy?

Context

The study of habitat fragmentation is complex because multiple, potentially synergistic, ecological processes may be acting simultaneously. Further, edge effects themselves may be complex in that additivity from multiple edges can give rise to heterogeneous nearest–edge gradients.

Objectives

We used heat diffusion as a proxy for additive edge effects in two study landscapes in order to test whether two key observations recently attributed to synergy between edge and area effects could be more simply explained by additivity; namely, steeper edge gradients in larger fragments and variation in slopes of species–area relationships as a function of distances to fragment edges.

Methods

We sampled forest structure in northwestern Madagascar at various distances from the edge in fragments and continuous forest and used an inverse modelling approach to parameterize the model. In addition, we applied the model to data from a published study of beetle communities in fragmented forests in New Zealand.

Results

With increasing proximity to edges, woody stem densities decreased and, as predicted, smaller fragments had lower stem densities and less steep edge gradients than larger ones. The model successfully predicted shifts in species–area relationships as a function of nearest–edge distances for beetle species, although observed richness for forest specialists in the smallest fragments was lower than predicted.

Conclusions

Two key observations attributed to synergy between edge and area effects were explained by edge additivity. The model is particularly useful in that it can help to disentangle the complex sets of processes acting in fragmented landscapes.

     

Using operating area size and adjacency constraints to mitigate the effects of harvesting activities on boreal caribou habitat

Context

Sustained timber harvesting conflicts with the long-term viability of boreal caribou (Rangifer tarandus caribou) populations. The spatial arrangement of harvest blocks in the landscape could mitigate the impact of logging on caribou populations. For the forest industry, however, these measures represent constraints that reduce the annual allowable cut (AAC).

Objective

Estimate the long-term impacts of spatial constraints to harvesting, applied alone or in combination, on AAC and boreal caribou populations.

Methods

We divided a 30,000 km² region into 20 harvest block sizes varying from 50 to 1000 km², and modeled the implementation of spatially explicit harvest schedule plans in combination with wildfire and caribou population dynamics. We then evaluated the probability of persistence of boreal caribou populations.

Results

The probability of maintaining an AAC target declined with increasing target AAC, increasing size of operating area, and increasing adjacency constraints. In contrast, the probability of maintaining caribou populations declined with increasing AAC, decreasing size of operating areas, and decreasing adjacency constraints. An increase in operating area size from 50 to 300 km² produced a considerable gain in AAC for all adjacency constraints.

Conclusions

Because adjacency constraints led only to a small increase in the probability of maintaining caribou populations, we recommend adopting less constraining landscape management actions, such as a 70-year period between two consecutive harvests in the same ~300-km² operating area.

     

Multi-model comparison on the effects of climate change on tree species in the eastern U.S.: results from an enhanced niche model and process-based ecosystem and landscape models

Context

Species distribution models (SDM) establish statistical relationships between the current distribution of species and key attributes whereas process-based models simulate ecosystem and tree species dynamics based on representations of physical and biological processes. TreeAtlas, which uses DISTRIB SDM, and Linkages and LANDIS PRO, process-based ecosystem and landscape models, respectively, were used concurrently on four regional climate change assessments in the eastern Unites States.

Objectives

We compared predictions for 30 species from TreeAtlas, Linkages, and LANDIS PRO, using two climate change scenarios on four regions, to derive a more robust assessment of species change in response to climate change.

Methods

We calculated the ratio of future importance or biomass to current for each species, then compared agreement among models by species, region, and climate scenario using change classes, an ordinal agreement score, spearman rank correlations, and model averaged change ratios.

Results

Comparisons indicated high agreement for many species, especially northern species modeled to lose habitat. TreeAtlas and Linkages agreed the most but each also agreed with many species outputs from LANDIS PRO, particularly when succession within LANDIS PRO was simulated to 2300. A geographic analysis showed that a simple difference (in latitude degrees) of the weighted mean center of a species distribution versus the geographic center of the region of interest provides an initial estimate for the species’ potential to gain, lose, or remain stable under climate change.

Conclusions

This analysis of multiple models provides a useful approach to compare among disparate models and a more consistent interpretation of the future for use in vulnerability assessments and adaptation planning.