Effect of spore density, cultivar resistance and Phytophthora infestans isolate on tuber blight under field conditions

Survival of P. infestans in soil was limited to 5 weeks at high inoculum density. With a ten fold dilution of the infection pressure survival of P. infestans in soil was limited to two weeks. Differences between isolates concerning survival in the soil were small. From these experiments we conclude that survival of P. infestans in soil depended on spore density rather than P. infestans isolate used. Tuber blight infection rate depends on density of the sporangia in the soil, tuber blight resistance of the cultivar and to a lesser extent the P. infestans isolate used. Isolate of type EU 13 A2 was not more aggressive to tubers than IPO 428-2, regardless of the resistance level of the cultivar used. A mixture of isolates was found to be more aggressive than two single isolates tested on cultivar Bintje only. Thus measures to avoid infection of the soil with P. infestans sporangia lower the tuber blight infection risk, especially on the susceptible cultivar Bintj

Sensitivity analysis of leaf wetness duration within a potato canopy

A description and analysis is given of a wetness duration experiment, carried out in a potato field in the centre of the Netherlands in September 2005. The observations are used to design and evaluate a within-canopy dew model which provides the leaf wetness distribution within the canopy caused by dew processes and by precipitation. This withincanopy dew model consists of three layers (bottom, centre, top) each with equal contribution to the leaf area index. The model results compared favourably with experimental evidence. The sensitivity of the dew and precipitation interception on the amount of free water and the duration of the leaf wetness was analysed by varying the leaf area index and some important weather variables. The findings suggest that the leaf area index affects the amount of free water, but is barely sensitive to leaf wetness duration. Wind speed has hardly any effect on the amount of free water collection as well as on leaf wetness duration. The net radiation, however, appears to be sensitive to the amount of collected free water as well as the leaf wetness duratio

New Phytophthora populations: A shift from indirect to direct sporangial germination?

Phytophthora infestans, the causal agent of potato- and tomato late blight, remains a serious threat for (commercial) potato and tomato production. In North Western Europe, frequent fungicide applications, mostly aimed to prevent infection, form the back bone of potato late blight control. Modern protectants such as Shirlan (a.i. fluazinam) are highly effective against (germinating) P. infestans sporangia and zoospores. Zoospores in particular are so sensitive to low concentrations that the many applications over the past two decades may well have exerted sufficient selection to pressure against the formation of zoospores. Thus, over the years the balance between direct and indirect germination may have shifted towards direct germination. This hypothesis was investigated at Bayer Crop Science and Plant Research Internationa

Report of subgroup epidemiology and decision support systems

Developments Decision Support Models. In France, the DSS’s Mildi-LIS and MilPV merged to form a new DSS for advisors and potato growers: Mileos. Furthermore, DSS’s for organic production in France (Fredon) and Germany (Oko-SIMPHYT) were developed to help scheduling copper applications within the national and local regulations for application of copper. The EuroBlight platform saw the birth of an application which allows comparison of the performance of core algorithms for potato late blight DSS for a range of years and locations (weather). EuroBlight now also provides a list of DSS’s, contact persons etc. available in Europe

Invasion of a Virulent Phytophthora infestans Genotype at the Landscape Level; Does Spatial Heterogeneity Matter?

Proper landscape-scale deployment of disease resistant genotypes of agricultural crop species could make those crops less vulnerable to invasion by resistance breaking genotypes. Here we develop a multi-scale, spatiotemporal model of the potato late blight pathosystem to investigate spatial strategies for the deployment of host resistance. This model comprises a landscape generator, a potato late blight model, and a suite of aerobiological models, including an atmospheric dispersion model. Within individual growing regions, increasing the number of host genotypes caused the greatest reduction in epidemic extent, followed by reduction of the proportion of potato in the landscape, lowering the clustering of host fields, and reducing the size of host fields. Deployment of host resistance in genotype mixtures had a large effect on disease invasion. The use of space as an isolation barrier was effective in scenarios involving two distinct potato growing regions. It was possible to completely eliminate the risk of epidemic spread from one region to another using inter-regional separation distances ranging from 8 to 32 km. The overall efficacy of this strategy was highly dependent, however, on the degree of spatial mixing of potato genotypes within each region. Deployment of host resistance in genotype mixtures in both regions served to reduce the overall level of incidence in the landscape and the inter-regional separation distance required to eliminate relevant levels of between-region spread of diseas

Regional spore dispersal as a factor in disease risk warnings for potato late blight: a proof of concept

This study develops and tests novel approaches that significantly reduce the fungicide input necessary for potato late blight control while maintaining the required high level of disease control. The central premise is that fungicide inputs can be reduced by reducing dose rates on more resistant cultivars, by omitting applications on days when conditions are unsuitable for atmospheric transport of viable sporangia and by adapting the dose rate to the length of the predicted critical period. These concepts were implemented and tested in field experiments in 2007 and 2008 in the North Eastern potato growing region in the Netherlands which is known for its high potato late blight disease pressure. Field experiments contained three starch potato cultivars, representing a range in resistance to potato late blight from susceptible to highly resistant, and a series of decision rules determining spray timing and incorporating an increasing number of variables such as: remaining fungicide protection level, critical weather, atmospheric capacity for viable transport of sporangia and the length of the predicted critical period. The level of cultivar resistance was used to reduce the dose rate of the preventive fungicide Shirlan (a.i. fluazinam) by default. A 50% – 75% reduction of the fungicide input proved possible in both years without adverse consequences to the crop or yield. The principles can be used in many decision contexts, but further work is needed to test and refine the methods before it can be used in practic