Elisa González-Domínguez

A Mechanistic Model of Botrytis cinerea on Grapevines That Includes Weather, Vine Growth Stage, and the Main Infection Pathways

A mechanistic model for Botrytis cinerea on grapevine was developed. The model, which accounts for conidia production on various inoculum sources and for multiple infection pathways, considers two infection periods. During the first period (“inflorescences clearly visible” to “berries groat-sized”), the model calculates: i) infection severity on inflorescences and young clusters caused by conidia (SEV1). During the second period (“majority of berries touching” to “berries ripe for harvest”), the model calculates: ii) infection severity of ripening berries by conidia (SEV2); and iii) severity of berry-to-berry infection caused by mycelium (SEV3). The model was validated in 21 epidemics (vineyard × year combinations) between 2009 and 2014 in Italy and France. A discriminant function analysis (DFA) was used to: i) evaluate the ability of the model to predict mild, intermediate, and severe epidemics; and ii) assess how SEV1, SEV2, and SEV3 contribute to epidemics. The model correctly classified the severity of 17 of 21 epidemics. Results from DFA were also used to calculate the daily probabilities that an ongoing epidemic would be mild, intermediate, or severe. SEV1 was the most influential variable in discriminating between mild and intermediate epidemics, whereas SEV2 and SEV3 were relevant for discriminating between intermediate and severe epidemics. The model represents an improvement of previous B. cinerea models in viticulture and could be useful for making decisions about Botrytis bunch rot control.

Effect of Environmental Factors on Mycelial Growth and Conidial Germination of Fusicladium eriobotryae, and the Infection of Loquat Leaves.

In Spain, loquat scab, caused by Fusicladium eriobotryae, is usually controlled by fungicides when there are favorable conditions for infection. Lacking specific data on the effect of weather conditions on infection by F. eriobotryae, infection periods are predicted based on the Mills table for apple scab. Experiments were conducted to determine the influence of temperature, wetness duration, relative humidity (RH), and dry periods on mycelial growth, conidial germination, and infection of loquat leaves by F. eriobotryae. F. eriobotryae was able to grow and the conidia to germinate in a wide range of temperatures, whereas no germination occurred at RH < 100%. Maximum conidial germination occurred with 24 h of wetness and germination was strongly reduced by >10 h of dryness interrupting the wetness period. Loquat infection occurred between 10 and 20°C, and disease incidence and severity increased as the duration of wetness period increased. The combined effect of temperature and wetness duration on conidial germination of F. eriobotryae and infection of leaves was described by combining β and Gompertz equations, while the effect of dry periods on reducing the conidial germination was described by a logarithmic equation. The equations developed in this work provided a reasonable fit of the biological processes investigated and could be used for better disease control; they could be further integrated in a disease prediction system for scheduling fungicide sprays against loquat scab.

Characterization of Cylindrodendrum, Dactylonectria and Ilyonectria isolates associated with loquat decline in Spain, with description of Cylindrodendrum alicantinum sp. nov.

Thirty-one loquat orchards (Eriobotrya japonica ‘Algerie’) with plants exhibiting decline symptoms were surveyed between 2004 and 2007 in the province of Alicante, Spain. Twenty-eight representative isolates with Cylindrocarpon-like asexual morphs recovered from affected roots were included in this study, with the objective to characterize them by means of phenotypical characterization, DNA analysis and pathogenicity tests. Dactylonectria alcacerensis, D. torresensis and Ilyonectria robusta were identified based on morphological and cultural characteristics as well as DNA sequence data for part of histone H3, with D. torresensis the most frequent species. All of them are reported for the first time on loquat, and I. robusta is reported for the first time in Spain. In addition, one species is newly described, Cylindrodendrum alicantinum. Pathogenicity tests with representative isolates showed that these species were able to induce typical root rot disease symptoms, affecting plant development or even leading to plant death. This research demonstrates the association of species belonging to the genera Cylindrodendrum, Dactylonectria and Ilyonectria with root rot of loquat and loquat decline in the province of Alicante (eastern Spain). This information should be considered for the improvement of the current management strategies against these soil-borne pathogens when establishing new loquat plantations or introducing new susceptible fruit crops in the region.

Biology and Epidemiology of Venturia Species Affecting Fruit Crops: A Review

The fungal genus Venturia Sacc. (anamorph Fusicladium Bonord.) includes plant pathogens that cause substantial economic damage to fruit crops worldwide. Although Venturia inaequalis is considered a model species in plant pathology, other Venturia spp. also cause scab on other fruit trees. Relative to the substantial research that has been conducted on V. inaequalis and apple scab, little research has been conducted on Venturia spp. affecting other fruit trees. In this review, the main characteristics of plant-pathogenic species of Venturia are discussed with special attention to V. inaequalis affecting apple, V. pyrina affecting European pear, V. nashicola affecting Asian pear, V. carpophila affecting peach and almond, Fusicladium oleagineum affecting olive, F. effusum affecting pecan, and F. eriobotryae affecting loquat. This review has two main objectives: (i) to identify the main gaps in our knowledge regarding the biology and epidemiology of Venturia spp. affecting fruit trees; and (ii) to identify similarities and differences among these Venturia spp. in order to improve disease management. A thorough review has been conducted of studies regarding the phylogenetic relationships, host ranges, biologies, and epidemiologies of Venturia spp. A multiple correspondence analysis (CA) has also been performed on the main epidemiological components of these Venturia spp. CA separated the Venturia spp. into two main groups, according to their epidemiological behavior: the first group included V. inaequalis, V. pyrina, V. nashicola, and V. carpophila, the second F. oleagineum and F. eriobotryae, with F. effusum having an intermediate position. This review shows that Venturia spp. affecting fruit trees are highly host-specific, and that important gaps in understanding the life cycle exist for some species, including V. pyrina; gaps include pseudothecia formation, ascospore and conidia germination, and mycelial growth. Considering the epidemiological information reviewed, this paper shows that the use of Mills tables to predict infection periods should be avoided for Venturia spp. other than V. inaequalis.

Accurate prediction of black rot epidemics in vineyards using a weather-driven disease model.

BACKGROUND Grapevine black rot caused by Guignardia bidwellii is a serious threat in vineyards, especially in areas with cool and humid springs. A mechanistic, weather-driven model was recently developed for the detailed prediction of black rot epidemics. The aim of this work was to evaluate the model by comparison with observed disease development in leaves and clusters in a vineyard in north Italy from 2013 to 2015. RESULTS The model accurately predicted disease onset. The probability of predicting new infections that did not occur (i.e. unjustified alarms) was ≤0.180, while the probability of missing actual infections was 0.175 for leaves and 0.263 for clusters. In 78% of these false negative predictions, the difference between expected and actual disease onset was ±2 days; therefore, only one infection period was actually missed by the model. The model slightly overestimated disease severity (mainly on leaves) when the observed disease severity was >0.6. CONCLUSION The model was highly accurate and robust in predicting the infection periods and dynamics of black rot epidemics. The model can be used for scheduling fungicide sprays in vineyards.

Development and Validation of a Weather-Based Model for Predicting Infection of Loquat Fruit by Fusicladium eriobotryae

A mechanistic, dynamic model was developed to predict infection of loquat fruit by conidia of Fusicladium eriobotryae, the causal agent of loquat scab. The model simulates scab infection periods and their severity through the sub-processes of spore dispersal, infection, and latency (i.e., the state variables); change from one state to the following one depends on environmental conditions and on processes described by mathematical equations. Equations were developed using published data on F. eriobotryae mycelium growth, conidial germination, infection, and conidial dispersion pattern. The model was then validated by comparing model output with three independent data sets. The model accurately predicts the occurrence and severity of infection periods as well as the progress of loquat scab incidence on fruit (with concordance correlation coefficients >0.95). Model output agreed with expert assessment of the disease severity in seven loquat-growing seasons. Use of the model for scheduling fungicide applications in loquat orchards may help optimise scab management and reduce fungicide applications.

A network meta-analysis provides new insight into fungicide scheduling for the control of Botrytis cinerea in vineyards: Meta-analysis Botrytis bunch rot control

BACKGROUND Control of Botrytis bunch rot (BBR) is currently based on the application of fungicides at four timings corresponding to specific growth stages of vines: end of flowering (A), pre-bunch closure (B), veraison (C) and before harvest (D). The current research provides a network meta-analysis of 116 studies conducted between 1963 and 2016 in nine countries, in which 14 strategies (based on combinations of 1, 2, 3, or 4 sprays applied in A, B, C, and/or D) were compared. RESULTS When a one-spray strategy was applied, BBR control was more effective with sprays applied in A, C, or D than B. With a two-spray strategy, strategy AC provided similar control as strategy BC; strategy CD also provided good control. For a 3-spray strategy, the best disease control was consistently obtained with strategy ACD. Four-spray strategy ABCD provided the best control but often involved needless sprays so that the routine application of four sprays is not justified. CONCLUSIONS Spraying at timing A seems to be very important for achieving efficient and flexible disease control. Flexibility is reduced by spraying at timing B rather than A.

Pest categorisation of Apiosporina morbosa

Abstract The Panel on Plant Health performed a pest categorisation of the fungus Apiosporina morbosa, the causal agent of black knot, for the EU. The identity of the pest is well established and reliable methods exist for its detection/identification. The pest is listed in Annex IIAI of Directive 2000/29/EC and is not known to occur in the EU. Apiosporina morbosa is present in Alaska, Canada, Mexico and the continental states of the USA. The major hosts of A. morbosa are Prunus domestica and Prunus cerasus; the host status of other Prunus species and hybrids is uncertain because of contradictory reports or lack of information. The pest could potentially enter the EU on host plants for planting and plant parts originating in infested third countries. Wood of Prunus spp. is also a pathway of entry, but of minor importance. The current pest distribution and climate matching suggest that the pest could establish and spread in the EU wherever the hosts are grown. In the infested areas, the pest causes girdling of twigs and occasionally of larger branches, whereas trees with multiple infections loose vigour, bloom poorly, and become unproductive, stunted and susceptible to winter injury and infection by other pathogens. The presence of black knots makes trees unsuitable for timber production. It is expected that the pest introduction and spread in the EU would impact host production. Uncertainty exists on whether the agricultural practices and chemical control methods applied in the EU could prevent the establishment and spread of A. morbosa. A. morbosa meets all the criteria assessed by EFSA for consideration as potential Union quarantine pest. As the pest is not known to occur in the EU, this criterion to consider it as Union regulated non‐quarantine pest is not met.

Release of Guignardia bidwellii ascospores and conidia from overwintered grape berry mummies in the vineyard

Background and Aims Black rot, caused by Guignardia bidwellii, is a polycyclic grape disease with repeated primary and secondary infections. In this work, the release of primary inoculum (both ascospores and conidia) from overwintered grape mummies was studied over a 3‐year period. Methods and Results A spore sampler was designed consisting of: (i) a funnel for collecting spores washed off from grape mummies by rain; and (ii) microscope slides for spores being airborne in the proximity of mummies. Ascospores and conidia were frequently found in the runoff water; Gompertz equations were developed describing their seasonal cumulative numbers as a function of degree‐days, with R2 ≥ 0.92. The number of both spore types in the runoff water significantly increased as the amount of rain and its duration and intensity increased; >1 and >3 mm of rain were the best cut‐off points for predicting the release of conidia and ascospores, respectively. No ascospores were found on the microscope slides, but conidia were found on rainy days, clustered in circular areas, probably due to droplets splashing from mummies to slides during rainfall. Conclusions This work provides new information on the inoculum dynamics of G. bidwellii in vineyards that can be used in refining disease prediction models for improved disease control. Significance of the Study New equations were developed to describe the dynamics of G. bidwellii spore release as a function of degree‐days, and 1 and 3 mm of rain have been proposed as cut‐off values to predict the release of conidia and ascospores, respectively. This information could be incorporated into the mathematical models supporting the decision‐making for disease control.

Pest categorisation of Venturia nashicola

Abstract The Panel on Plant Health performed a pest categorisation of Venturia nashicola, the causal agent of Asian pear scab, for the European Union (EU). The pathogen is a well‐defined, distinguishable fungal species affecting Pyrus pyrifolia var. culta, P. ussuriensis and P. bretschneideri in Asian countries. P. communis (European pear) is not a host of V. nashicola, but the host status of other Pyrus species is unclear. V. nashicola is not known to occur in the EU. It is listed in Annex IIAI of Directive 2000/29/EC. The pathogen could potentially enter the EU on host plants for planting and fruit originated in infested countries. There are no climatic factors limiting the potential establishment and spread of the pathogen in the EU, as its epidemiology is similar to those of Venturia inaequalis (apple scab) and Venturia pyrina (European pear scab), which are well‐established in the EU. The hosts are present in the EU, but no data were found on their abundance and distribution. In the infested areas, V. nashicola causes premature leaf and fruit drop and fruit distortion resulting in considerable yield/quality losses. The introduction of the pathogen into the EU could cause yield/quality losses and environmental consequences because of the additional fungicide sprays for disease control. Cultural practices and chemical measures applied in the infested areas reduce the inoculum sources but they cannot eliminate the pathogen. Phytosanitary measures are available to mitigate the risk of introduction and spread of the pathogen in the EU. All criteria assessed by EFSA for consideration as a potential Union quarantine pest are met. As V. nashicola is not known to occur in the EU, this criterion assessed by EFSA to consider it as a Union regulated non‐quarantine pest is not met.