4 Use of Airborne Inoculum Detection for Disease Management Decisions

Transcript

Hello!! Welcome to the fourth talk of this week that is “Use of Airborne Inoculum Detection for Plant Disease Management Decisions”. We all know that the vast amount of plant pathogens they produce spores and these spores are mostly airborne in nature. So, detection of airborne inoculum of a particular pathogen can help us to take a decision that whether a disease is going to occur in a shortly or not. So, let us see how it is helping us to take a decision. Knowledge of inoculum presence has been used for decades to help guide disease management decisions. However, its implementation on a broad scale has been limited due to the capital cost and requirement of technical skill for effective monitoring of plant pathogen presence across large areas. Recent advances in nucleic acid detection technologies are showing promise in enabling field level implementation of inoculum detection and quantification to aid in disease management decisions. And, this is the typical inoculum trapping device and that is put in field situations and the spores it collects then transferred for detection and diagnosis at molecular level.

There have been several success in monitoring airborne inoculum to aid in disease management systems for example presence of airborne inoculum was used to initiate fungicide application to manage potato early blight caused by Alternaria solani so, this was a successful example. Similarly, the hop downy mildew disease forecaster system is used to in the area of Hallertau regions in Germany to timely application of fungicides. This system relies on a combination of weather based disease forecasting and the visual identification and quantification of Pseudoperonospora humuli sporangia to guide timing of fungicide application; thus, it demonstrate that the monitoring airborne inoculum can be commercially implemented. So, this successful examples has enough to say that this technology needs to be deployed for inoculum detection so that timely application of fungicides can be taken place. While inoculum monitoring can be useful for aiding the disease management decision it has always been difficult to implement on a broad scale due to the difficulty in and cost of sample collection and visual identification of infective propagules. So it has some challenges and these has to be managed accordingly to reduce the time required for assessing samples and increase confidence in inoculum identification various amino logical and nucleic acid-based technologies have been developed that are suitable for detecting and quantifying airborne inoculum.

Epidemiological concepts for monitoring airborne inoculum

So, epidemiological concepts for monitoring airborne inoculum – disease management strategies of airborne plant pathogens are based on the assumption that inoculum will always be present and often failed to predict that the severity of the epidemics because they do not account for quantity of initial inoculum present at the location. So, the assumption are that there will be always in the presence of the inoculum and the inoculum presence will be normally in a higher level for causing a disease in the nearby plants. There are numerous regions for differences in initial inoculum: it may be due to the microclimate, or it may be due to the management practices that impact inoculum survival and the amount formed by the previous season inoculum. So, different factors may be associated and these factors may play a significant role in determining the inoculum level but at times this is also a challenge for the diagnosticians to accurately assess the environmental implications and presence of inoculum load. For example, the grape powdery mildew cleistothecia are considered the predominant overwintering structure and are formed in late summer to early fall. The amount form is considered to be the function of the disease severity and influenced by canopy density and microclimate, which result in the aggregation of overwintering inoculum. So in case of grape downy mildew it is the cleistothecia that is responsible for causing the disease and it is not only the cleistothecia that is present in the canopy but it is the structure of the plant micro environment, it is the pranker canopy and all these factors come into play a role in governing the disease severity by the pathogen.

Methods for Monitoring Airborne Pathogen Inoculum

So, methods for monitoring airborne pathogen inoculum includes the practical assessment of airborne inoculum presence requires a means of collecting airborne propagules that is both easily processed and inexpensive .There are two main approaches for sampling airborne inoculum that is passive sampling and volumetric sampling. In passive sampling it relies on either gravitational forces to cause settling of airborne propagules to horizontal surfaces that is coated with glass slides or agar plates in the area of interest or inertia to impinge particles onto a vertical surface. Although quite cheap and easy to implement the highly variable sample volume associated with passive sampling strategies limits their utility in monitoring for pathogen presence. This approach also tends to utilize a large sampling surface which can be advantageous for visual detection but poses problems for other detection methods. The volumetric samples utilizes three main approaches that is inertia, filtration and cyclonic or centrifugal separation to collect propagules by moving either volumes of air over the sampling surface or by moving the sampling surface at a known rate through the air to cause impaction of airborne propagules onto a or in sampling matrices. Thus, achieving a standard air sample volume electrostatic charge has also been used to collect airborne propagules onto a sampling matrix. So, these are the two basic approach that are used for monitoring airborne pathogen inoculum that is the passive sampling as well as the volumetric sampling.

Methods for Pathogen Identifications

The methods for pathogen identification after sampling involves immunological testing nucleic acid testing and isothermal amplification. All these techniques are capable of delivering and appropriate answer to the questions like what type of pathogens inoculum is available at a current location, at the current season, and what threat it is going to cause in the coming weeks or month on the crop that is being cultivated in and around the area. So airborne inoculum monitoring is a very specific method of detection of plant pathogens and once the spores are trapped either through passive or volumetric methods they are then subjected to immunological nucleic acid or isothermal amplification process for its accurate diagnosis and then to recommend appropriate recommendations for control of that particular disease to occur in that particular locality. So with this we have come to an end of the topic that airborne inoculum monitoring how it helped us in detection of the threat of the pathogen that may cause certain disease in that particular locality. And in the last talk of this week we will be talking about plant disease diagnostic capabilities and networks and how it is helping us to manage plant disease in a greater way. Till then have a good time.

Thank you very much.