Image processing-based study of soil porosity and its effect on water movement through Andosol intact columns

The soil pore network and marcoporosity are important factors affecting water and solute transport. The transfer of contaminants to water resources is of particular importance in the Valle de Bravo watershed as it provides 10% of the drinking water for the 20 million inhabitants of Mexico City. This watershed is composed mainly of Andosols with unique mineralogical and physical characteristics. Soil porosity is usually examined on thin sections, using various image analysis techniques. We propose a novel methodology combining image analysis and a displacement experiment to study relationships between soil structure and water tracer transport parameters. H₂¹⁸O displacement experiments were conducted through intact soil columns sampled at three depths from a representative cultivated Andosol profile. The soil structure and pore characteristics were obtained by image analysis on thin sections obtained from each column at the end of the displacement experiment. The total 2D porosity (for pores larger than 50 μm) varied from 80% of the total section area in the topsoil to around 60% in the subsoil. Tubular pores were the most abundant in the soil profile, but ploughing of the topsoil had destroyed sections of these pores and replaced them with packing pores. Water transport in the intact subsoil columns was always in physical non-equilibrium, showing the existence of preferential flow pathways. In the topsoil, one column out of three showed no preferential flow, demonstrating that soil ploughing also homogenised pore connections. Pore connectivity was larger in the ploughed topsoil than in their deeper soil horizon counterparts. Our methodology offers a 2D quantitative characterisation of the macroporous network at 50 μm resolution and the determination of water transport parameters on the same intact soil samples. 3D characterisation of soil porosity using X-ray computed tomography (CT) gives a better picture of pore connection but usually has lower spatial resolution and a larger cost.     

Simulation of transpiration, drainage, N uptake, nitrate leaching, and N uptake concentration in tomato grown in open substrate

Free-drainage or “open” substrate system used for vegetable production in greenhouses is associated with appreciable NO₃⁻ leaching losses and drainage volumes. Simulation models of crop N uptake, N leaching, water use and drainage of crops in these systems will be useful for crop and water resource management, and environmental assessment. This work (i) modified the TOMGRO model to simulate N uptake for tomato grown in greenhouses in SE Spain, (ii) modified the PrHo model to simulate transpiration of tomato grown in substrate and (iii) developed an aggregated model combining TOMGRO and PrHo to calculate N uptake concentrations and drainage NO₃⁻ concentration. The component models simulate NO₃⁻-N leached by subtracting simulated N uptake from measured applied N, and drainage by subtracting simulated transpiration from measured irrigation. Three tomato crops grown sequentially in free-draining rock wool in a plastic greenhouse were used for calibration and validation. Measured daily transpiration was determined by the water balance method from daily measurements of irrigation and drainage. Measured N uptake was determined by N balance, using data of volumes and of concentrations of NO₃⁻ and NH₄⁺ in applied nutrient solution and drainage. Accuracy of the two modified component models and aggregated model was assessed by comparing simulated to measured values using linear regression analysis, comparison of slope and intercept values of regression equations, and root mean squared error (RMSE) values. For the three crops, the modified TOMGRO provided accurate simulations of cumulative crop N uptake, (RMSE = 6.4, 1.9 and 2.6% of total N uptake) and NO₃⁻-N leached (RMSE = 11.0, 10.3, and 6.1% of total NO₃⁻-N leached). The modified PrHo provided accurate simulation of cumulative transpiration (RMSE = 4.3, 1.7 and 2.4% of total transpiration) and cumulative drainage (RMSE = 13.8, 6.9, 7.4% of total drainage). For the four cumulative parameters, slopes and intercepts of the linear regressions were mostly not statistically significant (P < 0.05) from one and zero, respectively, and coefficient of determination (r²) values were 0.96-0.98. Simulated values of total drainage volumes for the three crops were +21, +1 and −13% of measured total drainage volumes. The aggregated TOMGRO-PrHo model generally provided accurate simulation of crop N uptake concentration after 30-40 days of transplanting, with an average RMSE of approximately 2 mmol L⁻¹. Simulated values of average NO₃⁻ concentration in drainage, obtained with the aggregated model, were −7, +18 and +31% of measured values.     

Estimating seasonal evapotranspiration from temporal satellite images

Estimating seasonal evapotranspiration (ET) has many applications in water resources planning and management, including hydrological and ecological modeling. Availability of satellite remote sensing images is limited due to repeat cycle of satellite or cloud cover. This study was conducted to determine the suitability of different methods namely cubic spline, fixed, and linear for estimating seasonal ET from temporal remotely sensed images. Mapping Evapotranspiration at high Resolution with Internalized Calibration (METRIC) model in conjunction with the wet METRIC (wMETRIC), a modified version of the METRIC model, was used to estimate ET on the days of satellite overpass using eight Landsat images during the 2001 crop growing season in Midwest USA. The model-estimated daily ET was in good agreement (R ²?=?0.91) with the eddy covariance tower-measured daily ET. The standard error of daily ET was 0.6?mm (20%) at three validation sites in Nebraska, USA. There was no statistically significant difference (P?>?0.05) among the cubic spline, fixed, and linear methods for computing seasonal (July–December) ET from temporal ET estimates. Overall, the cubic spline resulted in the lowest standard error of 6?mm (1.67%) for seasonal ET. However, further testing of this method for multiple years is necessary to determine its suitability.     

Evaluating irrigation strategies for lettuce by simulation: 2. Nitrogen budget

A mechanistic water-flow, solute transport and crop growth model was used to compare three irrigation strategies for lettuce in French Mediterranean conditions: (1) the current strategy based on the occurrence of rainfall, (2) a strategy based on a simplified modelling of the soil water balance and (3) a strategy based on tensiometer readings. Water and solute instantaneous fluxes versus time were simulated for two growing periods (summer and autumn) over 100 years. The climatic data were provided by a weather generator. Leenhardt et al. (1998) compared the three strategies with regard to their effects on water flows in the soil. The present paper deals with their effects on the nitrogen balance and particularly nitrate leaching.

The three strategies rank similarly for all processes of the N cycle. Strategy 1 generates soil water content conditions favourable to denitrification and nitrate leaching and less favourable to mineralisation and nitrification, leading to a low NO⁻₃ availability for the crop, and thus a low nitrate uptake. Strategy 1 minimizes the water stress but induces the maximum nitrogen stress. At the other extreme is strategy 3, whereas strategy 2 has an intermediate position, but closer, however, to strategy 3 than 1. A direct conclusion would suggest avoiding strategy 1 and choosing strategy 3.     

Molecular wheat breeding by direct gene transfer

A method for efficient genetic transformation of wheat has been developed using immature embryos as targets for microprojectile-mediated gene transfer and a helium driven particle delivery system. Screening and selection of transgenic cells, somatic embryos and regenerated plants are performed with the gus-gene and the phosphinothricin acetyl transferase (bar) gene coding for Basta-resistance as the selectable marker. On average, one fertile transgenic plant can be obtained from about 100 microprojectile treated, immature embryos. The number of integrated copies of the transferred gene ranges from 1 up to about 10. Stable integrated genes are inherited in most of the transgenic lines in a normal mendelian fashion segregating 3:1 in the F₂. Homozygous, as well as heterozygous, lines have been followed and analysed genetically at the molecular level and up to F₅. Apart from normal stable gene expression, examples have also been found which showed a loss of gene activity or unexpected segregation pattern. For applied aspects, different genes are transferred aiming for improved disease resistance, modification of quality, or other characteristics. First results from these transgenic lines are reported, and problems still existing with the production of stable transgenic wheat lines are discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Evaluation of a core collection of Brassica oleracea accessions for resistance to Brevicoryne brassicae, the cabbage aphid

A rapid, simple and reliable technique was developed for evaluating Brassica accessions in the glasshouse for resistance to Brevicoryne brassicae, the cabbage aphid. Brassica accessions were grouped into crop types with similar habit and vigour for evaluation. 401 Brassica oleracea accessions, representing the genetic and geographic diversity of the species, were evaluated for resistance to a population of B. brassicae collected originally from HRI, Wellesbourne. Ninety eight accessions were identified as being moderately resistant (grade 3) or partially resistant (grade 4). Re-testing of accessions in the glasshouse identified 12 moderately resistant and 43 partially resistant accessions. The most promising gene pool was kale, where a higher than expected number of resistant accessions were found. Three of the kales were consistently rated as moderately resistant in all tests. In contrast the broccoli gene pool was a poor source of resistance with less (one out of 46) resistant accessions than expected. Eleven of the kales graded 3 were tested in the field in 1995 and resistance to B. brassicae was confirmed. Ten accessions were also tested for resistance to two additional populations of B. brassicae, one from Greece and the other from Portugal. The results provided no evidence of aphid biotype/host specific differences in the resistance of these B. oleracea accessions. This revised version was published online in August 2006 with corrections to the Cover Date.     

Genetic diversity in mung bean germplasm revealed by RAPD markers

Knowledge of the genetic relationships among landraces is useful to gene bank managers because it permits a better organization of the crop's gene pool management, more efficient sampling of the available germplasm resources and better access to useful genetic variation for breeders. Genetic diversity of 19 landraces of the cultivated mung bean, Vigna radiate, and three weedy and wild relatives including Vigna mungo, Vigna luteola and Vigna radiate var. sublobata, was investigated at the DNA level with the random amplified polymorphic DNA (RAPD) procedure. Sixty random decamer primers were employed in amplification reactions; 28 of these were informative and yielded 246 bands, of which 229 were polymorphic with a mean of 8.2 bands per primer. A genetic distance matrix based on Nei and Li coefficient was converted to a dendrogram and a two-dimensional plot using multidimensional scaling (MDS). The accessions studied were separated into three main clusters, which included V. radiate landraces, V. mungo and V. luteola, respectively. The variation of this cluster supports the view that the genetic distance of V. mungo and V. luteola varies considerably from the accession VO2955 (V. radiata). The multidimensional scaling plot confirmed that V. mungo, V. luteola and most of the accessions of V. radiata formed distinct clusters with no overlap, and two mung bean accessions (PI177493 and VO4134–1 from Turkey and India, respectively) were genetically distant from other V. radiata landraces. V. radiata and V. mungo are positioned in separate botanical species and V. radiata var. sublobata is classified within other V. radiata landraces. Based on the limited range of accessions tested, the approach holds promise for the classification of mung bean germplasm, identification of mung bean landraces and applications of molecular markers to mung bean breeding.     

Fusarium vascular wilt in lentil: Inheritance and identification of DNA markers for resistance

The inheritance of resistance to lentil (Lens culinaris Medik.) vascular wilt caused by Fusarium oxysporum f.sp. lentis was investigated in a cross between resistant (ILL5588) and susceptible (L692–16-l(s)) lines. F_2:4 progenies and F_6:8, F_6:9 recombinant inbred line (RIL) populations were assessed for their wilt reaction for three seasons in a well-established wilt-sick plot. Resistance to wilt was conditioned by a single dominant gene in the populations studied. The map location of the Fw locus was identified for the first time through linkage to a random amplified polymorphic DNA (RAPD) marker (OPK-15₉₀₀) at 10.8 cM. Two other RAPD markers (OP-BH₈₀₀ and OP-DI5₅₀₀) identified by bulked segregant analysis were associated in the coupling phase with the resistance trait, and another marker (OP-C04₆₅₀) was associated with repulsion. The DNA markers reported here will provide a starting point in marker-assisted selection for vascular wilt resistance in lentil.     

Assessment of cytoplasmic effects of cytoplasmic male-sterile lines in upland cotton

Paired A- and B-lines, cytoplasmic male-sterile (CMS)-lines and main-tainer lines, respectively, were crossed with R-lines (restorer) to produce A × R, R × B and B × R hybrids, which were used in 1993 and 1996 to predict the performance of three lypes of CMS cotton lines available in China. A significant difference in yield and yield components was revealed between paired A × R and B × R hybrids. This difference was greatly influenced by both CMS cytoplasm and the interaction between cytoplasm and nuclear genotypes. It is suggested that there are detrimental effects of CMS cytoplasm on yield and yield components. General combining ability of near-isogenic CMS lines was also affected by this negative effect. The detrimental effect was closely related to an increased number of immature seeds per boll, which might be caused by partial female sterility associated with CMS cytoplasm. The possibility of developing specific combinations of CMS Upland × Upland restorer hybrids that express enough heterosis for yield to overcome the detrimental effect of the CMS cytoplasm is discussed.     

Genetic parameters of several biochemical compounds from green coffee, Coffea canephora

A factorial crossing scheme of Cofflea canephora (two parents from the Congolese group crossed to 14 parents of the Guinean group) was used to evaluate genetic parameters of several biochemical compounds, bean weight and crop outturn (ration of dry bean weight 10 fresh berry weight). For most characters studied, additive genetic effects were preponderant. Narrow-sense heritability was high for caffeine content (h²_ns= 0.80), fat matter content (h²_ns, = 0.74), bean weight (h²_ns= 0.73) and crop outturn (h²_ns= 1). It was intermediate for trigonelline (h²_ns= 0.38) and chlorogenic acid (h²_ns= 0.36) content. Only sucrose content had a low narrow-sense heritability (h²_ns=0.11). There were few genetic and enviromnental correlations, Consequences for breeding, in relation to coffee drinking quality, are discussed.