Cover crops can mitigate effects on grape pathogen dispersal

Different kind of ground covers has been indicated as an efficient way to limit rain-splashed dispersal of disease-causing spores in several crops, but not in vineyards. In the CORE Organic Cofund project BIOVINE cover crops are tested to reduce both splash- and air-borne diseases

Chile y Bolivia en cuatro obras

Reseña de las obras: Maira, Luis y Javier Murillo de la Rocha, "El largo conflicto entre Chile y Bolivia", Santiago : Aguilar Chilena de Ediciones, 2004 ; Pérez Yoma, Edmundo,"Una misión: las trampas de la relación chileno-boliviana", Santiago : Random House Mondadori, 2004 ; Pinochet de la Barra, Oscar, "Chile y Bolivia : ¡Hasta cuándo!" Santiago : LOM, 2004 ; Bustos, Carlos, "Chile y Bolivia : un largo camino : de la Independencia a Monterrey", Santiago : ADICA, RIL Editores, 200

On The Coefficient Of Restitution Of Tennis Rackets

The evolution of research on tennis equipment has recently introduced some parameters for the evaluation of the racket's efficiency. Among them, the most used in current practice is the coefficient of restitution of the racket (COR), that is simply defined as "the ratio of the rebound speed to the incident speed of the ball for orthogonal impact". Remarkable differences between values of COR reported in the tennis literature are mainly due to the various test conditions adopted. In order to compare different results, some important test parameters must be imposed for a better COR definition. Our recent laboratory tests show that the COR of the same racket is mainly affected by: - kind and conditions of balls kind and tension of strings impact velocity. Moreover, they show that the largest portion of energy is lost because of ball's deformation. Figure 1 shows the coefficient of restitution of a ball, at different impact velocities and on a rigid wall. Furthermore, in a tennis shot, ball deformation for a given velocity is affected by the other test parameters listed above. The augments of string's tension, for instance, increases the ball deformation and consequently decreases COR. This highlights that the traditional coefficient of restitution is not a direct measure of the racket frame efficiency, but it involves the behaviour of ball, strings, frame and grip restraint together. Therefore, in order to be compared by means of COR, rackets must be tested with the same kind of balls and the same kind of strings at equivalent string tension (i.e. tension that gives the same stiffness to the string plane). We suggest to test the racket at four different ball velocities in order to analyse different play conditions; thus we propose a new COR which should contain four values. Moreover, the knowledge of the influence of balls and strings allows to evaluate the portion of COR that is related only to the racket's frame characteristics

Epidemiology and modelling of grapevine downy mildey primary infections caused by Plasmopara viticola (Berk et Curt). Berlese et de Toni

La peronospora della vite è causata dall’Oomicete eterotallico Plasmopara viticola ed è ampiamente diffusa in tutte le aree caratterizzate da primavere miti e piovose. Gli organi svernanti di questo patogeno sono le oospore, che rappresentano l’unica fonte di inoculo per le infezioni primarie. Recenti studi molecolari hanno evidenziato l’importanza delle infezioni primarie e suggerito una revisione dell’epidemiologia di P. viticola. Questa tesi è costituita dagli studi epidemiologici realizzati per indagare il processo di maturazione e germinazione delle oospore mirati all’elaborazione di un modello dinamico per la simulazione delle infezioni primarie di P. viticola. Il modello è stato successivamente validato in diverse aree viticole italiane e, inoltre, utilizzato come base per un warning system in tempo reale per la gestione dei trattamenti in vigneto.The heterothallic Oomycete Plasmopara viticola represents the causal agent of downy mildew of grapevine (Vitis spp.). The unique source of inoculum is represented by the overwintering sexual spores, originated by the fusion between anteridium and oogonium, so called oospores. Despite their critical impact on the epidemiology of this disease, knowledge about oospores presents some inconsistencies that are engaged in the present dissertation. Initially, the effect of water moistening the grape leaf litter holding overwintering P. viticola oospores was investigated. A close relationship was found between vapour pressure deficit (VPD in hPa) and aW (water activity) of the leaf litter, so that when VPD is lower than 2.13 hPa there is sufficient water for oospores to develop. Results showed that moisture of the leaf litter due to the water flow from the atmosphere makes the oospore development possible also during non rainy periods. Then, the effects of environmental conditions on the variability in germination dynamics of Plasmopara viticola oospores were studied over five years. The germination course was determined indirectly as the relative infection incidence (RII) occurring on grape leaf discs kept in contact with oospores sampled from a vineyard between March and July. The time elapsed between the 1st of January and the infection occurrence was expressed as physiological time, using sums of hourly rates from a temperature-dependent function only in hours when VPD was not a limiting factor (hydro-thermal time, HT). The Gompertz equation calculated over hydro-thermal time produced a consistent modelling of the general relationships between the germination dynamics of a population of P. viticola oospores and weather conditions. It represents the relative density of the seasonal oospores that should have produced sporangia when they have experienced favourable conditions for germination. Finally, a dynamic model for Plasmopara viticola primary infections on grapevine was elaborated according to a mechanistic approach. Development of the sexual stage of the pathogen was split into different state variables, in which changes from one state to another were regulated by rates depending on environmental conditions. The conceptual model was based on the definition of a primary inoculum season, a seasonal oospore (inoculum) dose, and its division into many coeval cohorts. Each cohort progresses along the primary infection cycle (production and survival of sporangia, release, survival and dispersal of zoospores, infection, appearance of disease symptoms) simultaneously, with a time step of one hour. The model was evaluated by comparing model predictions with disease onset in: i) 100 vineyards of Northern, Southern and Insular Italy (1995 to 2007); ii) 42 groups of potted grapevine plants exposed to inoculum (2006 to 2008). Most of the wrong positive predictions occurred in early season, when the host was in the earlier growth stages, or when the oospore germination was triggered by isolated weak rain events. Considering that neither calibration nor empirical adjustment of model parameters were necessary to obtain accurate simulation, it was concluded that this model produces a reasonable approximation of the primary infection processes underlying oospore development. A warning system based on such a model and on short-term weather forecasts was developed and its use was evaluated in experimental vineyards over a 3-year period in North Italy. An unsprayed control was compared with a “warning” treatment (fungicides were applied when the warning system predicted an infection), a “threshold” treatment (fungicides were applied as in the warning treatment, but only for the oospore cohorts higher than a fixed threshold), and the grower’s schedule. Average efficacy in decreasing disease incidence on leaves compared to the unsprayed control was > 90% for all treatments. On the average, 6.8 sprays were applied following the grower’s schedule; use of the warning system reduced applications by about one half (warning treatment) or two third (threshold treatment). The grower’s schedule was the most expensive control strategy, with average of 337 €/ha; the average saving was 174 and 224 €/ha for the warning and the threshold treatments, respectively. The value of this dissertation consists in two relevant and connected aspects. From one side the studies performed on the oospore maturation and germination allowed to better understand and clarify a key point of the downy mildew epidemics still wrapped by a lack of information. From the other side the model elaborated during this thesis represents a practical and efficient tool that leads to the reduction both of growers’ costs and chemical input in the environment