Simona Giosue

A simulation model for the development of brown rust epidemics in winter wheat

A model simulating the progress of Puccinia recondita severity, expressed as a percentage of rusted leaf area (both as average and its 95% confidence interval) on individual wheat leaves over the course of a growing season, with a time step of one day, was elaborated using laboratory and field data from literature. Data on the stages of each infection cycle (uredospore germination, penetration, latency, uredium eruption and infectiousness) were transformed into model parameters by curve fitting, Montecarlo stochastic procedures, corrections and empirical assumptions. Data on host growth, like the timing of all phenological stages, the dynamic of the green area of each leaf from appearance to complete senescence, and tillering were obtained from a specific sub-model. Model validation was performed on actual data not used in model building and representing a wide range of conditions (several winter wheat cultivars grown at eight locations in northern Italy between 1990 and 1994) by using subjective, non-parametric and parametric tests: it revealed a satisfactory agreement between the data simulated by the model and actual data.

Modelling Plant Diseases for Decision Making in Crop Protection

A plant disease model is a simplification of the relationships (between a patho-gen, a host plant, and the environment) that determine whether and how an epi-demic develops over time and space. This chapter describes an approach for de-veloping mechanistic, weather-driven, dynamic models which are suitable to be applied in precision crop protection. Model building consists of four steps: (I) defi-nition of the model purpose; (II) conceptualization; (III) development of the mathe-matical relationships; and (IV) model evaluation. Conceptualization is based on systems analysis; it assumes that the state of the pathosystem can be quantitatively determined and that changes in the system can be described by mathematical equations. A conceptual model describes the system (both conceptually and mathematically), and a set of driving models accounts for changes caused by the external variables. Two main types of conceptual models are described: plant- and pathogen-focused models. Model evaluation is the judgement of the overall adequacy of the model, which includes: verification, validation, uncertainty analysis, sensitivity analysis, and judgement of utility. Finally, the chapter briefly considers how models can be used as tools for decision making at different scales of time and space: from warning services to precision agriculture.

Growth and sporulation of Stemphylium vesicarium, the causal agent of brown spot of pear, on herb plants of orchard lawns

The inoculum sources of ascospores of Pleospora allii and of conidia of its anamorph Stemphylium vesicarium were investigated in relation to the brown spot disease epidemiology on pear. Dead and living leaves of three pear varieties (Abate Fétel, Conference and William), seven grasses (Poa pratensis, Festuca rubra, Festuca ovina, Lolium perenne, Digitaria sanguinalis and Setaria glauca) and Trifolium repens, which are used in pear orchard lawns, were inoculated with conidia of Stemphylium vesicarium virulent on pear and incubated under controlled-environment. Stemphylium vesicarium was always re-isolated from dead leaves of the considered plants, but not from symptomless green or yellowish living leaves. The fungus was occasionally re-isolated from leaf segments showing unspecific necrosis. Inoculation of pear leaves with isolates from grasses demonstrated that the fungus did not lose pathogenicity. Pseudothecia, ascospores and conidia were produced on all the dead inoculated leaves; differences between specimens were found for phenology of pseudothecia, their density and size, and for the number of conidia produced. Pseudothecia were produced faster in the lawn species than in pear leaves, and their density was higher, especially for S. glauca, L. perenne and P. pratensis. Ascospore maturation and ejection was more concentrated for the pseudothecia developed on pear leaves than for those on F. ovina and S. glauca. All the lawn species produced more conidia than pear leaves.

Influence of Environmental Conditions on Infection of Peach Shoots by Taphrina deformans

ABSTRACT The effect of weather conditions on the infection of peach shoots by Taphrina deformans was investigated both under orchard conditions and in controlled-environment experiments. Leaf curl incidence and severity were related to rainfall, length of wet periods, and temperature during wetness and during the incubation period, as well as to the development stage of shoots. Surface wetness was more important than rainfall for infection to occur. Minimum rainfall for infection was 3 mm, with a wet period of at least 12.5 h; higher amounts of rainfall did not cause infection when the wet period they triggered was shorter. Wet periods initiated by dew or fog were too short for infection to occur. Infection occurred only when air temperature was <16 degrees C during the wet period and <19 degrees C during incubation. Logistic equations relating relative disease incidence and either duration of wetness or temperature were developed under controlled-environment conditions, with asymptotes at >/=48 h of wetness and </=8 degrees C for temperature, respectively. Rate of shoot and leaf development during the season influenced disease development, so that three different periods of susceptibility were defined, maximum susceptibility being between bud break and petal fall due to a low development rate of shoots.

Forecasting infections of the leaf curl disease on peaches caused by Taphrina deformans.

An Israeli model forecasting leaf curl disease on peaches caused by Taphrina deformans was validated in the Emilia-Romagna region of northern Italy, during a three-year period (1996–1998), in 13 cases (year × location × cultivar). When the peach trees are susceptible to infection, the model uses mathematical functions to calculate the risk of infection on the basis of weather conditions (daily rainfall greater than 10 mm, and maximum air temperature greater than 5°C), and it forecasts periods of possible symptom appearance based on the length of incubation. Peach trees became susceptible to infection between the end of January and mid March, when the first leaf buds attained phenological stage C, i.e. appearance of leaf apex. The trees remained susceptible for at least 9 weeks: the last infection occurred in mid-May.Since most of the leaf curl onsets observed in the orchards fell within the range of model forecasts, the model proved to be accurate in signalling both the first seasonal infection and repeated infections during the primary inoculum season. Few errors occurred, caused either by conditions of rainfall and temperature lower than the thresholds fixed in the model, or by discrepancies between forecast and actual length of incubation. Infection occurred also at 3.1–3.5°C, and with 9.6 mm rainfall. Thus, thresholds should not be accepted too rigorously, and perhaps temperature should not be considered as a limiting factor for infection under the conditions of the present work. The length of incubation showed high variability: it was 23 days long on average, with a 95% confidence interval ranging from 20 to 27 days, and extreme values of 9 and 33 days.

Predicting the dynamics of ascospore maturation of Venturia pirina based on environmental factors.

Airborne ascospores of Venturia pirina were trapped at two sites in northern Italy in 2002 to 2008. The cumulative proportion of ascospores trapped at each discharge was regressed against the physiological time. The best fit (R(2) = 0.90, standard error of estimates [SEest] = 0.11) was obtained using a Gompertz equation and the degree-days (>0 degrees C) accumulated after the day on which the first ascospore of the season was trapped (biofix day), but only for the days with > or =0.2 mm rain or < or =4 hPa vapor pressure deficit (DDwet). This Italian model performed better than the models developed in Oregon, United States (R(2) = 0.69, SEest = 0.16) or Victoria, Australia (R(2) = 0.74, SEest = 0.18), which consider only the effect of temperature. When the Italian model was evaluated against data not used in its elaboration, it accurately predicted ascospore maturation (R(2) = 0.92, SEest = 0.10). A logistic regression model was also developed to estimate the biofix for initiating the accumulation of degree-days (biofix model). The probability of the first ascospore discharge of the season increased as DDwet (calculated from 1 January) increased. Based on this model, there is low probability of the first ascospore discharge when DDwet < or =268.5 (P = 0.03) and high probability (P = 0.83) of discharge on the first day with >0.2 mm rain after such a DDwet threshold.

A Web-based Decision Support System for Managing Durum Wheat Crops

One important goal in agricultural crop production is to develop less intensive and integrated farming systems with lower inputs of fertilizers and pesticides, and with restricted use of the natural resources (water, soil, energy, etc.). The main objectives of these systems are to maintain crop production in both quantitative and qualitative terms, maintain or preferably improve farm income, and at the same time reduce negative environmental impacts as much as possible. Achieving all of these objectives is a prerequisite for sustainable agriculture (Geng et al., 1990; Jordan & Hutcheon, 1996). Integrated Production (IP) (Boller et al., 2004) and Integrated Farming (IF) (EISA, 2001) have been developed as holistic concepts that involve all crop and farming activities and that shape these activities according to the individual site and farm. The Thematic Strategy on the Sustainable Use of Pesticides adopted in 2006 by the European Commission aims to establish minimum rules for the use of pesticides in the Community so as to reduce risks to human health and the environment from the use of pesticides. A key component of this Strategy is implementation of Integrated Pest Management (IPM), which will become mandatory as of 2014. In the context of IPM, the EU will develop crop-specific standards, the implementation of which would be voluntary. According to ENDURE (2009), IPM creates synergies by integrating complementary methods drawing from a diverse array of approaches that include biocontrol agents, plant genetics, cultural and mechanical methods, biotechnologies, and information technologies, together with some pesticides that are still needed to control the most problematic pests and to manage critical situations. Concepts of IPM, IP, and IF are based on dynamic processes and require careful and detailed organisation and management of farm activities at both strategic and tactical levels. This means that time must be invested in management, business planning, data collection and detailed record keeping, and identification of required skills and provision for appropriate training to ensure safe farm operation. In IPM, IP, and IF, farm managers must also know where to obtain expert advice, and they must be willing to accept scientific and technical advances that benefit the environment, food quality, and economic performance, and that therefore can be integrated into the crop management as soon as they are reliable (EISA, 2001).

Influence of weather conditions on infection of peach fruit by Taphrina deformans

ABSTRACT The effect of environment on the infection of peach fruit by Taphrina deformans was investigated using orchard observations under natural conditions (in 2001 to 2004) or in trees managed in such a way to exclude rainfall. These conditions were then validated using pot-grown peach plants exposed to single infection events and independent orchard observations. Leaf curl incidence was related to rainfall, length of wet periods, and the temperature during wetness and during the incubation period, as well as to the developmental stage of flowers and fruit. Weather conditions before petal fall did not influence fruit infection. After petal fall, rainfall and the duration of the wet period triggered by rainfall played a key role in infection occurrence. The minimum rainfall required for infection was 12 mm, with at least 24 h of wetness interrupted by no more than 4 h. No infection occurred when temperature was >/=17 degrees C during the wet period or >19 degrees C during incubation. Disease symptoms appeared on fruit after approximately 3 weeks of incubation, which is equivalent to 240- to 290-degree-days (base 0 degrees C). The period for fruit infection was relatively short being from petal fall until air temperature remained greater than 16 degrees C. During this period, the incidence of fruit that developed symptoms was closely related to the number of favorable events and the total wetness duration during such events.

Seasonal Dynamics of Taphrina deformans Inoculum in Peach Orchards

ABSTRACT The dynamics of the inoculum of Taphrina deformans were studied during a 4-year period by (i) inspecting curled leaves for the presence of asci, (ii) placing deposition spore samplers within the tree canopies, and (iii) exposing potted peach plants (trap plants). These three approaches produced consistent results. Four main periods characterized the dynamics of the inoculum: the first period coincides with the parasitic stage of the pathogens life cycle and the other periods with the saprophytic stage. Mid- to late spring (first period) was characterized by the presence of asci on infected leaves which produced and ejected large quantities of ascospores in 96% of the samplings. Rainfall was not necessary for ascospore dispersal, which was favored by air temperature <20 degrees C and relative humidity >/=80% or wetness duration >8 h. In summer and autumn (second period), blastospores were trapped in 54 and 24% of samplings, respectively, with low spore numbers. In the winter (third period), blasto-spores were trapped in the lowest numbers and in only 6% of samplings. In late winter to early spring (fourth period), blastospores were found in 56% of samples, with increasing numbers. Rainfall significantly influenced blastospore dispersal and temperature was correlated with the seasonality found during the saprophytic stage.

An Advisory System for the Control of Brown Rust on Winter Wheat in Northern Italy

The aim of this work is to develop an advisory system for the control of brown rust (caused by Puccinia recondita Rob. & Desm. f. sp. tritici Eriks. & Henn.) on winter wheat by combining three simulation models previously elaborated and validated with the networks of weather station, spore collection and field monitoring which act in the Emilia Romagna region (Bugiani et al., 1996). It is a part of research promoted and supported by the Emilia-Romagna region by means of the co-ordination of CERAS.