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In Northern Europe, potatoes are harvested at the end of the summer period and kept in large storage facilities for many months. Depending on the agreed delivery time, the demand of the market and/or the quality during storage, potatoes are sold. Higher quality potatoes, delivered at agreed delivery time, or at a time of high market demand, will lead to a higher price and thus more profit for the potato grower. One of the important quality issues during storage is the development of rot, often caused by infection with bacteria belonging to the family of Pectobacteriaceae, causing soft rot (Pectobacterium and Dickeya species). Initial infection can spread to neighboring tubers and therefore trigger a wide infection. Such infections can start anywhere in a potato pile and are thus not always immediately visible, leading to extensive product losses. Respiration and volatile production of healthy, wounded and soft rot-infected potatoes were measured over time using GC and PTR-ToF-MS. We observed that both the respiration, as well as the production of specific volatiles increases significantly in potatoes infected by Pectobacterium polaris. This indicates that there is a potential to use the respiration and volatile-profile as biomarkers for early and remote detection of rot in potato. This would allow growers to take action by adjusting the storage regime to prevent further spread of infection and extend the storage of the healthy potatoes. Depending on the demand on the market, growers could also decide to bring batches showing no signs of infection to the market while the quality is still acceptable, thereby increasing profit for the grower.

The Dutch Ministry of Agriculture, Nature and Food Quality has financially supported the research programme named “Total use of unrefined and unprocessed food(crops)”. The programme consisted of a number of projects and one of the projects was entitled “Control of Restrictive Supply Chains; biomarkers as indicator for shelf life” ( KB 33 002 011). The aim of the project is to build up knowledge needed to optimize and re-design restrictive supply chains of fruit, vegetables and flowers to avoid postharvest losses, maintain high resource use efficiency and connect consumer demands to production and supply chain restrictions. The objective of this project is to measure the production of volatiles in healthy and rotten (infected) potatoes and as such identify volatiles that may be used as a biomarker for rot development. A key aspect of the envisaged experimental design is to measure the development of these volatiles over time. This will give insight in the potential of this idea as an early detection method to avoid the further expansion of a rot infection during storage of potatoes. An experimental set up was built to allow the production of volatiles and respective sampling. The potatoes were placed in a glass jar and an air flow was applied. The volatiles were sampled and measured in the air flow. Three treatments were applied: potatoes wounded and infected with the bacteria Pectobacterium polaris, wounded potatoes (without infection) and healthy potatoes. Each treatment was applied in duplicate. The six glass jars with the potatoes were kept at room temperature for maximal 17 days and the production of volatiles was daily monitored. The volatiles in the out coming air were measured with a thermo-desorption GC, a PTR-ToF-MS and a GC-MS (via a SPME). In addition, the amount of oxygen consumed and carbon dioxide produced was also measured in the air flow with a CompactGC. The amount of infection was visually quantified (through the glass jar). The following has been concluded: - Clear differences in volatile production between infected and non- infected potatoes were found. - Those differences are measurable very early upon the infection. Even when the infection is not yet visible. This indicates that the production of volatiles is a suitable biomarker for bacterial infection in potatoes. - Next to the volatile production, the effect of bacterial infection on the production of CO2 and the consumption of O2 (respiration rate) was studied. The respiration rate of infected potatoes is much higher than that of healthy or wounded potatoes. The tubers react prompt to the infection by increasing the production of CO2 and consumption of O2. Also this change in metabolism may be used as biomarker. - Several methods have been explored for the measurement of the volatile production. The measurements were done with a Thermo-Desorption GC, a PTR-ToF-MS and a GC-MS. Despite the differences in the type of gas analysis the results of the different methods show a good agreement with each other and seem to be suitable for measurement of produced volatiles. - Another important result of the project is the development of a suitable inoculation protocol for the bacteria Pectobacterium polaris (an Erwinia infection has been chosen for this project because this is an aggressive type of microorganism and commonly found in potatoes). The developed protocol makes it possible to successfully infect the tubers in a controlled manner and create a suitable model system. The results are directly relevant for the industry as this kind of micro-organism is responsible for a large amount of infections during storage hence contributing for product waste. The volatiles measured with the Thermo-Desorption GC and the PTR-ToF- MS have not yet been identified. The GC-MS results do not allow to identify all the volatile compounds as the column and the sampling methods differ too much from the ones used with the GC with desorption unit. Only 10 of the 45 volatiles were identified with their chemical names via GC-MS analysis. At this time, not all compounds have been identified with certainty.

Gravistimulation induced differential ethylene production in Antirrhinum majus L. cut flower stems with highest levels in the lower halves of the gravistimulated stems. Expression levels of three different 1-aminocyclopropane-1-carboxylate (ACC) synthase (ACS) genes, an ACC oxidase (ACO) and an ethylene receptor (ETR/ERS homolog) gene were studied in the bending zone after 9 h of gravistimulation. One of the ACS genes (Am-ACS3) was abundantly expressed in the lower halves but not in the upper halves of gravistimulated stems. This strongly suggests that Am-ACS3 is responsible for the observed differential ethylene production in gravistimulated stems. Am-ACO and Am-ETR/ERS gene expression was increased in both the lower and upper halves of gravistimulated stems, suggesting that they play no role in differential ethylene production. When gravistimulation was performed in an environment enriched with either 20 µL/L ethylene or 100 nL/L 1-methylcyclopropene (1-MCP), a slight stimulation of bending by 1-MCP and a slight inhibition of bending by ethylene were observed. The regulation and role of ethylene in gravitropism of cut snapdragon flowering stems is discussed.

Genomics technologies can be applied for unravelling the biological processes that are important for pre- and post-harvest quality. Such knowledge will allow precise monitoring of physiological condition and can be used as a tool for optimising production chains. A combination with quality change models will allow prediction of future product quality with much more precision and certainty than is currently possible. To demonstrate the validity of this approach we set up a project to identify, via cDNA microarray analysis, gene expression patterns that are correlated to the development of mealiness during storage of Cox apples (Malus x domestica `Cox?s Orange Pippin?). The experimental set-up encompassed, next to mRNA profiling, both instrumental and sensory analyses of apples at various time points before and during storage. We were able to select a subset of genes the expression of which is indicative of reduced sensory quality (mealiness and off-flavour). Moreover we detected batch differences in initial profiles that could be related to storage quality. Such indicators can be used as decision support tools for growers and traders.