A Continuous Time-and-State Epidemic Model Fitted to Ordinal Categorical Data Observed on a Lattice at Discrete Times

We consider a spatio-temporal model to describe the spread of apple scab within an orchard composed of several plots. The model is defined on a regular lattice and evolves in continuous time. Based on ordinal categorical data observed only at some discrete instants, we adopt a continuous-time approach and apply a Bayesian framework for estimating unknown parameters.     

Mineralogy and nutrient desorption of suspended sediments during a storm event

Purpose

This study investigated desorption of potassium (K) and phosphorus (P) from soil and river suspended sediments sampled during a storm event in a Brazilian watershed traditionally used for tobacco plantations.

Material and methods

Suspended sediment samples were collected automatically at the outlet of the watershed and were grouped into three phases: beginning (phase a), middle (phase b) and final stages (phase c) of the storm event. Granulometric and mineralogical characterisation of soils (0 to 0.20 m depth) and suspended sediments was determined, and K and P extractions were performed using a cation and anion exchange resin (CAER) membrane. A kinetic modelling approach was used to estimate the amount of K and P desorbed.

Results and discussion

Clay-sized (<2 μm) content of the soils were all <21 %. Kaolinite, smectite (partially with hydroxy-Al interlayer) and a small amount of illite were found in the clay fraction of the different soils. The clay-sized fractions in sediments of phases a, b and c of the storm event were 49, 52 and 72 %, respectively. Smectite (>90 %) and kaolinite (<10 %) were the dominant clay minerals in the suspended sediments. The values of labile P and potentially available P of suspended sediments were higher than those for soils. In sediments, the highest values of labile P (325 mg kg^?1) and labile K (4,458 mg kg^?1) were found in phase c and in phase a, respectively.

Conclusions

Particle size distribution and clay mineralogy of soils differed from those of suspended sediments collected during the storm event. By comparison with the watershed soils, suspended sediments collected during the storm event were enriched in fine particles composed mainly of smectite, and this may explain their P and K desorption behaviour. This suggests particle size and clay species selectivity processes during the transfer of sediment particles from soils to aquatic systems. The amounts of P and K desorbed from the suspended sediments in the three phases of the storm event were much larger than those desorbed from soils. This indicates that rainfall promoted the transfer of these nutrients to the watercourses.     

Validation and use of a qPCR protocol to quantify the spread of Ralstonia solanacearum in susceptible and resistant eucalypt plants

Bacterial wilt caused by Ralstonia solanacearum is a serious disease of eucalypt in humid and high temperature areas worldwide. Spreading of the bacterium in the field or to other nurseries occurs mainly by symptomless infected plant material. The use of pathogen-free propagating material as well as planting of resistant genotypes are currently the only strategies used for disease control. Therefore, a reliable and sensitive method for detection of low titres of R. solanacearum in infected plant tissue is essential for the success of management programmes. In this work, we adapted an efficient intercalating dye-based real-time PCR protocol to detect the bacterium in symptomless eucalypt plants as well as to investigate its movement in eucalypt clones CLR172 and CLR371, which exhibit resistant and susceptible phenotypes, respectively. We found that the bacterium translocates acropetally and basipetally in inoculated but symptomless cuttings of the resistant clone, as in cuttings of the susceptible clone displaying symptoms. Nevertheless, a smaller concentration of bacterial DNA was detected in tissues of the resistant clone. Mature biofilms occluding the xylem vessels were present in the susceptible clone whereas only single cells or small aggregates were observed in the resistant clone. This work contributes to improve our knowledge of the colonization process of R. solanacearum in eucalypt clones with different levels of susceptibility and to understand how the defence mechanisms against bacterial wilt in Eucalyptus work. Our findings could aid in the selection of the most resistant eucalypt clones to be used in wilt disease management programmes.     

Biocontrol of potato early blight and suppression of Alternaria grandis sporulation by Clonostachys spp.

Early blight, caused by Alternaria solani and A. grandis, severely affects potato crops around the world, and few management options apart from intensive fungicide use are available. In this work, we tested whether biocontrol treatments with different species of the mycoparasitic fungus Clonostachys could reduce early blight severity on the foliage of pot-grown potatoes of cultivar Ágata, and affect the survival and sporulation of the causal pathogen A. grandis. Twenty isolates from five Clonostachys species were screened in a preliminary biocontrol trial, and nine of them were selected and tested further in two confirmation trials. Treatments with three isolates from three species (C. chloroleuca, C. pseudochroleuca, C. rhizophaga) resulted in a significant reduction in disease severity in both confirmation trials, with control efficacy ranging from 88.7% to 92.9% in the first trial, and from 83.1% to 84.7% in the second trial. All Clonostachys isolates used in the confirmation trials survived on potato leaf tissues for at least 15 days, and resumed growth when subjected to high humidity, resulting in mycoparasitic overgrowth and significant reduction of the pathogen sporulation. Our results provide evidence that different species of Clonostachys, not only the ubiquitous C. rosea, are sources of useful candidates for the biocontrol of potato early blight and possibly other plant diseases caused by fungal pathogens.     

Effects of Low Doses of Glufosinate-Ammonium on Upland Rice Agronomic Traits

The use of herbicides and growth regulators in agricultural crops to reduce vegetative growth is widely studied worldwide. This study aimed to evaluate the agronomic traits of upland rice subjected to low doses of glufosinate-ammonium applied at different development stages. The treatments consisted of five low doses (0; 15; 30; 60; and 100?g a.i. ha^?1; a.i.: active ingredient) of glufosinate-ammonium herbicide: a single low dose between active tillering (AT) and floral differentiation (FD); a single low dose after FD; low dose divided into two applications, the first at the beginning of the AT and the second between AT and FD; low dose divided into three applications, the first at the beginning of the AT, the second between AT and FD and the third after the FD, with four replications. The agronomic traits of upland rice were negatively affected due to the application of low doses of glufosinate-ammonium, with reduction in grain yield, 1000-grain weight, number of panicles, full spikelets and spikelets per panicle. Glufosinate-ammonium has no potential to be used as hormesis effect in rice plants due to loss in grain yield.

     

Soybean drought-stressed plants impair Anticarsia gemmatalis (Lepidoptera: Erebidae) midgut proteolytic activity and survival

Phytoparasitica - Soybean plants are exposed to multiple stresses during development. Co-occurring stresses can activate common defense pathways on plants, increasing end products concentrations,...     

Colletotrichum gloeosporioides sensu lato associated with anthracnose in Bauhinia forficata

European Journal of Plant Pathology - Bauhinia forficata is an important plant commonly used in traditional medicine, and as an ornamental plant in parks and gardens. Its use as an ornamental plant...     

Ophthalmic imaging.

The availability of advanced imaging modalities in veterinary medicine has greatly widened the diagnostic imaging capabilities possible.Ultrasonography provides a rapid noninvasive modality that provides detailed examination and resolution of the intraocular structures and soft tissues surrounding the orbit of opaque eyes.Ultrasonography is cost-effective and widely available to practitioners,referral centers, and academic institutions. In many areas,mobile specialist ultrasonographers are available to supplement the equipment and skills of the practitioner. The added strengths of CT and MRI lie in their cross-sectional capability and better image quality. Unfortunately, the cost of CT and MRI currently limits their availability to referral centers and academic institutions.Primarily because of financial considerations, CT is currently more widely available for evaluation of equine disorders than MRI. A thorough evaluation of the multiple images and an understanding of normal anatomy and abnormal tissue patterns are indicated to maximize the use of each modality. Unlike ultrasonography, which can be performed in awake horses, the costs and contraindications of general anesthesia in some critical patients should also be considered when using CT and MRI. Finally, imaging artifacts are frequently encountered with each of these modalities. Thus, a thorough understanding of the various types of artifacts that occur is important so as to avoid interpretation pitfalls.     

Ground vegetation as an indicator of site quality: effect of non-site factors on the productivity of newly established chestnut plantations in northwestern Spain

The growth of 67 young hybrid (Castanea × coudercii A. Camus) and pure sweet chestnut (Castanea sativa Mill.) plantations was studied in relation to ground vegetation (GV) and non-site factors such as type of site preparation, weed control (WC), disease-related damage and prior land use. The classification and regression trees procedure was used to analyse the data. Ground vegetation communities accounted for a large amount of variability in the site index (SI) and were found to be useful as predictors of chestnut site quality. The presence of broom communities indicated the best site for establishing chestnut plantations, whereas bracken and bramble communities indicated poorer conditions, although those sites can still be considered suitable for growing chestnut. Terrain covered with herbaceous communities also indicated intermediate or even good site conditions. The poorest sites were the heathlands. As regards non-site factors, only weed control was found to be a significant variable. Ground vegetation caused a significant reduction in tree growth, indicating the importance of carrying out regular weeding to improve productivity. The most positive effect of weeding on height growth was detected in terrain covered by gorse and broom, and the least positive effect was observed in heathland. The findings are important for forest management purposes, as evaluation of ground vegetation will enable rapid prediction of site productivity classes in afforested areas and help in selecting the best land for planting this species in reforestation programmes.     

The invasive mealybug Maconellicoccus hirsutus: lessons for its current range expansion in South America and invasive pest management in general

The invasive mealybug Maconellicoccus hirsutus (Green) (Hemiptera: Pseudococcidae) is a plant feeding insect believed to be native to Southern Asia or Australia. This mealybug has become established in many regions throughout the world (including the Caribbean and North America) in the past 100 years and is currently expanding its range in South America. Because this insect is of concern as a potential pest of many plant species, this review is provided to summarize knowledge of M. hirsutus based on past research that may be most useful for addressing the current invasion of South America by the species, and to identify gaps in information that may need to be addressed to inhibit the spread of the insect and improve management methods for this and similar organisms. In most areas into which M. hirsutus has expanded its range it is commonly suppressed by native or introduced natural enemies. Therefore, besides preventing introduction, establishment and spread of this potential pest, efforts should be made to determine if natural enemies of M. hirsutus are present in areas of concern (i.e., where the mealybug may be introduced and become established). Such information will enable determination of the need for introduction or augmentation of biological control agents in response to possible entry and establishment of the mealybug in new areas. Methods developed in response to the recent invasion of the Caribbean and North America by M. hirsutus may serve as models for addressing the threat of this and similar invasive pests in South America and elsewhere.