Fig. 1. Non-invasive diagnosis of microbial pathogenic infection and diseased plant tissues by volatile analysis. Volatile interpretation can be separated into two phases: 1. Volatile collection and 2. Volatile analysis. Analysis techniques include quantification of relative amounts of different volatiles and real-time analysis to assess ongoing changes. Volatile collection tools include dynamic sampling methods such as closed-loop-stripping-analysis (CLSA) and static headspace sampling methods such as solid phase microextraction (SPME), stir bar sorptive extraction (SBSE), and silicone tubing (ST). Quantification methods involve conventional gas chromatography-mass spectrometry (GC-MS) and portable GC-MS devices. Real-time analysis tools include Proton Transfer Reaction (PTR)-MS, multi-capillary column (MCC)-PTR-MS and E-nose. Two of these technologies, E-nose and portable GCMS, can be used in the field.
Fig. 2. Preparation of biogenic volatile compound formulations. There are three main steps in the preparation of volatiles for application to crop plants: 1. Emulsification, where an emulsion of volatiles, a polymer such as alginate, gelatin, or starch, and an emulsifier is prepared; 2. Processing, where volatiles are coated with polymers by means of spray drying with heat, coacervation with dissolving compounds such as ethanol, or extrusion with cross-linking compounds such as CaCl2; and 3. Microcapsulation, where microcapsules are separated and dried for field applications.
Fig. 3. Uses of biogenic volatiles in plant health applications. Microcapsule and sol-gel formulations of biogenic volatile compounds can be used in a range of situations: 1. Storage application; 2. Greenhouse application; 3. Insect pest control; 4. Open-field application; and 5. Seed priming.