Laboratory studies of crust development in irish and iraqi soils: I. moisture content,penetration resistance,aggregate size and seedling emergence of spring barley (hordeum vulgare L.)

Thirty soils differing widely in origin, texture and organic carbon content were used to study crust properties and development under laboratory conditions. Crust strength was measured as penetration resistance to an upward moving probe both with and without artificial rain treatment. The patterns of penetration resistance with time of drying under infra-red lamps varied considerably, the time taken to reach maximum and steady values for penetration resistance varying from 4 to 10 days. Maximum penetration resistance values ranged from approximately 50 to 500 kPa with one Iraqi soil recording a value of 800 kPa. The soils separated into 3 fairly distinct groups when penetration resistance was plotted against moisture content: Group I showed a sudden and sharp increase, Group II a gradual increase, whereas Group III did not show a definite relationship. A positive linear relationship was found between maximum penetration-resistance values of soils with and without artificial rain treatment. There was also a high positive correlation between small (2?0.53 mm) water-stable aggregates and penetration resistance and a negative correlation between penetration resistance and percentage water-stable aggregates of > 2 mm in size.In seedling emergence trials with spring barley (Hordeum vulgare L.), maximum emergence (90–98%) was recorded at penetration resistance (no rain treatment) of 75–110 kPa and zero emergence at approximately 300 kPa, with a good negative relationship between these values. There was a positive relationship between seedling emergence and penetration resistance values < 75 kPa, failure to emerge being due to a lack of anchorage and radial support for the shoot. Simulated rain treatment, which led to additional crust strength, reduced seedling emergence further for the limited number of soils tested.     

Acid-base analysis of dissolved organic matter in surface waters

A mono-protic multi-site model is developed to obtain a pK(acid) — concentration distribution. Dense and equal interval pH data are required for an accurate characterization. A computer driven titrimetric system is used to obtain the data. The technique is applied to dissolved organic carbon (> 15 mg C L^-1) samples from the Kejimkujik region, Nova Scotia. A calculation shows that the acidic (pH=4.6) dystrophic waters can result from mixing 15 mg C L^-1 of the organic acids with an initial inorganic system of about 75 peq L^-1 alkalinity.     

Bayesian inferences for receiver operating characteristic curves in the absence of a gold standard

Sensitivity and specificity are used to characterize the accuracy of a diagnostic test. Receiver operating characteristic (ROC) analysis can be used more generally to plot the sensitivity versus (1-specificity) over all possible cutoff points. We develop an ROC analysis that can be applied to diagnostic tests with and without a gold standard. Moreover, the method can be applied to multiple correlated diagnostic tests that are used on the same individual. Simulation studies were performed to assess the discrimination ability of the no-gold-standard method compared with the situation where a gold standard exists. We used the area under the ROC curve (AUC) to quantify the diagnostic accuracy of tests and the difference between AUCs to compare their accuracies. In particular, we can estimate the prevalence of disease/infection under the no-gold-standard method. The method we proposed works well in the absence of a gold standard for correlated test data. Correlation affected the width of posterior probability intervals for these differences. The proposed method was used to analyze ELISA test scores for Johne’s disease in dairy cattle.     

Variation among androgenic and gynogenic doubled haploids of tobacco (Nicotiana Tabacum L.)

Summary Agronomic field performance traits and leaf chemical characteristics of gynogenic doubled haploids (GDH) and androgenic double haploids (ADH) were compared with selfed lines of a burley tobacco cultivar to determine which type of doubled haploids was superior. Three sets of ADH and GDH lines performed similar to their selfed lines, but one set each of ADH and GDH lines had reduced yield, plant height, leaf number, stalk diameter, and leaf length in comparison to the respective selfed lines of KY 17.Contribution from the Department of Agronomy, University of Kentucky, Lexington, KY 40546. This paper (No. 87-3-287) is published with the approval of the Director of the Kentucky Agricultural Experiment Station.     

Genetic Diversity in Tall Fescue Ecotypes from Alabama I. Maturity, Morphological Traits, and Disease Reaction

There is a large hectarage of tall fescue in Alabama. Recognition of the deleterious effects of the endophytic fungus Acremonium coenophialum has resulted in substantial acceptance of new endophyte-free cultivars. Destruction of old pastures and the concomitant loss of potentially valuable adapted germplasm could be a valid cause for concern. The objectives of this study were to evaluate genetic variation for maturity and plant morphological traits, both among and within tall fescue cv. ‘Kentucky 31’ populations from 18 to 38 year-old pastures in Alabama. Ten populations of approximately 50 plants each were collected from old Alabama tall fescue pastures. Two pastures were sampled in each of five counties, representing the five major land use areas of the state. In 1990, spaced plants of all populations were evaluated at heading time for maturity, morphological, and disease traits at two locations in central Alabama. Endophyte infection level of the populations ranged from 2 to 100 %. Maturity was highly correlated with tiller length and flag leaf width and was used as a covariate for these traits in the analysis of variance. Leaf rust and net blotch ratings were negatively correlated. Significant variation among populations was observed for maturity and flag leaf dimensions, most variation being due to differences among source counties. Significant variation was observed within all populations for maturity and morphological traits, but only in seven populations for leaf rust. No within-population variation was detected for net blotch. The average precipitation for the month of May explained 81 % of the variation among populations for maturity. Age of the pasture sampled had a significant effect on tiller diameter (r²= 0.55), and latitude of the pasture sampled was the best individual predictor of leaf width (r²= 0.42). This study reveals that considerable genetic diversity, largely influenced by climatic conditions, exists among ‘Kentucky 31’ tall fescue ecotypes from Alabama.     

Identification of incompatibility genotypes in almond (Prunus dulcis Mill.) using specific primers based on the introns of the S-alleles

Identification of the incompatibility genotypes of almond cultivars is important in breeding programmes for designing crosses and for selecting progeny. This paper describes a novel molecular technique for the identification of S‐alleles in almond based on the use of PCR primers designed from the sequences of the introns without the need for restriction enzyme digestion. Nine specific pairs of primers have been designed for the S1, S2, S5, S7, S8, S9, S10 (putative), S23 and Sf alleles, and these confirmed the S‐allele specificities for 22 of the 23 accessions for which published information is available. This technique provides a precise method for identifying S‐alleles from the genomic DNAs of almond cultivars, and will be useful for confirming the segregation of alleles in breeding progeny.     

A conceptual production model for freshwater crayfish pond culture incorporating detrital forage

A production model is presented for semi-intensive freshwater crayfish culture ponds incorporating detrital forage. The conceptual model is developed from five submodels of trophic-dynamic interactions within the pond ecosystem. The model includes microbially enhanced detrital forage (MEDF) produced from plant matter grown in the pond as a significant component of nutrition. The model is proposed as an aid to understanding pond-based aquaculture techniques that rely upon manipulating the characteristics of MEDF. The significance of MEDF as a source of nutrition in aquaculture is discussed.