Marker-based screening of maize inbred lines using support vector machine regression

The phenomenon of heterosis is widely used in hybrid breeding programmes, despite the fact that no satisfactory molecular explanation is available. Estimators of quantitative genetic components like GCA and SCA values are tools used by the plant breeder to identify superior parental individuals and to search for high heterosis combinations. Obtaining these estimators usually requires the creation of new parental combinations and testing their offspring in multi-environment field trials. In this study we explore the use of ɛ-insensitive Support Vector Machine Regression (ɛ-SVR) for the prediction of GCA and SCA values from the molecular marker scores of parental inbred lines as an alternative to these field trials. Prediction accuracies are obtained by means of cross-validation on a grain maize data set from the private breeding company RAGT R2n. Results indicate that the proposed method allows the routine screening of new inbred lines despite the fact that predicting the SCA value of an untested hybrid remains problematic with the available molecular marker information and standard kernel functions. The genotypical performance of a testcross hybrid, originating from a cross between an untested inbred line and a well-known complementary tester, can be predicted with moderate to high accuracy while this cannot be said for a cross between two untested inbred lines.     

Induction of 2n pollen formation in <Emphasis Type="Italic">Begonia</Emphasis> by trifluralin and N<Subscript>2</Subscript>O treatments

In this study, treatments of both trifluralin (at 10, 100 and 1000 μM) and N₂O (in the form of gas under pressure) were applied to Begonia flower buds to induce the formation of 2n pollen. Three male fertile species (B. cucullata, B. subvillosa var. leptotricha and B. fischeri) and two male sterile hybrids (B. schmidtiana × B. cucullata and B. subvillosa var. leptotricha × B. cucullata) were treated. Pollen size, which is related to pollen DNA content, increased after both N₂O and trifluralin treatments, but the induction of large pollen was genotype dependent. Trifluralin induced large pollen only in the male fertile species, while N₂O treatments induced fertile 2n pollen in the male sterile B. schmidtiana × B. cucullata. Cytological studies showed that trifluralin induced multinuclear monads that resulted in 4n gametes in stead of 2n gametes. In general, large pollen obtained after trifluralin treatments showed low germination capability, while large pollen obtained after N₂O treatments retained high germination capability. Seedlings with raised ploidy level could only be obtained after crosses were performed with large pollen obtained from N₂O treatments. Hence, N₂O treatments are preferable to the use of trifluralin to induce 2n gametes in Begonia.     

Nutrition, xylem cavitation and drought resistance in hybrid poplar

Effects of mineral nutrition on susceptibility to cavitation were examined in four hybrid poplar clones. Two drought-sensitive and two drought-resistant hybrid clones of black cottonwood (Populus trichocarpa Torr. & Gray) and eastern cottonwood (P. deltoides Bartr.) were grown at three concentrations of nitrogen (N) applied factorially with two concentrations of phosphorus (P) in a greenhouse, and subjected to varying degrees of drought stress before measurement of cavitation and of anatomical features that might affect cavitation. Mean vessel pit pore diameters were 0.132 micro m at low P, and 0.074 micro m at high P, but no other significant effects of mineral nutrition on vessel dimensions were observed. Vessel diameter and specific conductivity were greater in the drought-resistant clones than in the drought-susceptible clones. Drought-resistant clones did not reach such low water potentials as drought-sensitive clones during the cavitation induction experiments, suggesting better stomatal and cuticular control of water loss. Scanning electron microscope observations showed less damage to pit membranes, also suggesting greater membrane strength in drought-resistant clones than in drought-sensitive clones. High concentrations of N increased cavitation, whereas high concentrations of P decreased cavitation as measured by both hydraulic flow apparatus and dye perfusion techniques. For one test, cavitation was 48% at high N and low P, but only 28% at high N and high P. We consider that N fertilization may make poplars more susceptible to cavitation on dry sites, but P fertilization may reduce this effect.     

Persistent Acacia savannas replace Mediterranean sclerophyllous forests in South America

Mediterranean ecosystems are global hotspots of biodiversity threaten by human disturbances. Growing evidence indicates that regeneration of Mediterranean forests can be halted under certain circumstances and that successional stages can become notoriously persistent. The Mediterranean sclerophyllous forest in central Chile is been largely transformed into savannas dominated by the invasive legume tree Acacia caven as result of interacting management and ecological factors. We used multi-temporal satellite imagery to study the transition dynamics of these major vegetation types over the last four decades (1975-2008). Vegetation changes were related to indicators of resource availability (topography, water availability, solar radiance), potential propagule availability (distance to forest remnant patches) and disturbance regimes (grazing, fire occurrence and distance to roads and cities). During this study period, forests were mostly converted into Acacia savannas (46.1%). Acacia savanna was the most persistent natural vegetation type. The probability of sclerophyllous forest degradation into Acacia savanna increased on drier northern-exposed slopes, close to roads and further away from forest remnants. In contrast, forest regeneration from Acacia savanna was higher on moister southern-exposed slopes and closer to forest remnants. Acacia savannas are increasingly being converted into cultivated land on the moister locations or switching into a bare soil state in locations close to cities and further away from forest remnants. These results highlight the vulnerability of diverse sclerophyllous forests and its increasing conversion into persistent Acacia savannas in the Mediterranean region of central Chile and identify the ecological conditions for successful conservation and restoration of the native sclerophyllous forest vegetation that can be used for sensible land use planning.     

Weighted analysis methods for mapped plot forest inventory data: Tables,regressions, maps and graphs

Weighted estimation methods for analysis of mapped plot forest inventory data are discussed. The appropriate weighting scheme can vary depending on the type of analysis and graphical display. Both statistical issues and user expectations need to be considered in these methods. A weighting scheme is proposed that balances statistical considerations and the logical expectations of users. The methods described here are being used in an online forest carbon estimation tool. Example applications are presented to demonstrate the methods.     

Effects of short-term ozone exposure and soil water availability on the carbon economy of juvenile Douglas-fir

Effects of ozone and soil water availability on partitioning and translocation of assimilates were studied in three-year-old Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) seedlings exposed, in separate experiments, to 0 and 106 or 0 and 514 micro g m(-3) ozone for 8 h day(-1) for 9 days. The dynamics of carbon from assimilated (14)CO(2) were followed. No interactions between ozone and soil water content were observed. Total net uptake of carbon was reduced by low soil water content, but was unaffected by ozone. Both ozone and low soil water content increased the amount of (14)C-photosynthates retained in the current-year needles. Total starch content in old and current-year needles was unaffected by ozone, but was reduced by low water availability. Translocation of carbon to the root-soil compartment was additively affected by ozone and low soil water content. The results suggest that dry periods in summer combined with high ozone concentrations cause the greatest reduction in the supply of carbon compounds to the root-soil compartment.     

Leaf growth characteristics of fast-growing poplar hybrids Populus trichocarpa x P. deltoides

Fast-growing hybrid poplar trees (Populus trichocarpa Torr. & A. Gray x P. deltoides Bartr. ex Marsh.) were compared with slower-growing parental types in both field and laboratory experiments to determine physiological components of leaf growth that could be closely related to biomass production. Stem volume was correlated with individual leaf area (r = 0.81) and leaf growth rate (r = 0.82). Hybrids had a greater total leaf area, not because they produced more leaves, but because they had larger leaves than either parental type. The greater leaf size of the hybrids may be explained by inheritance of larger cell number from P. deltoides and larger cell size from P. trichocarpa. Rates of enlargement of isolated leaf discs in liquid culture were approximately 50% of those observed in intact leaves of field-grown plants.