Onion storage diseases and their headspace volatiles

Onion, Allium cepa, is one of the world’s most commonly produced and consumed vegetables. In order to be available year round in temperate climates onions must be stored for several months. During this time parts of the harvested weight of bulbs are lost to storage diseases, sprouting and respiration leading to loss of carbohydrates and water. Diseases developing in storage may be difficult to spot at early stages as bulbs are typically stored in large bins. However, storage diseases can change the volatile metabolite profile of the infected onions. Electronic sensors that detect the concentration of specific volatile compounds in the air could be deployed in storage facilities to detect these changes. This would provide an early warning system that could detect diseases developing in storage bins before it becomes obvious to a human observer. In this way, some of the losses that occur during storage of onions could be prevented. This introductory paper discusses some of the available literature on the facets of onion production that are connected to storage disease development and the detection of said storage diseases using headspace sampling and analysis. The focus of the paper is mainly on onion production and storage of long day cultivars in relatively cold, temperate climates, as the use of short day cultivars and warm storage in warmer climates comes with different challenges and diseases

The behavioural response of Drosophila suzukii to fermentation products

Drosophila suzukii, or the Spotted Wing Drosophila (SWD), is an invasive fly that is a pest of soft fruits and berries. Unlike other Drosophila species, the females lay their eggs in ripening and ripe fruits, causing crop losses. In the last decade SWD has invaded North and South America and Europe and since 2014 the fly can also be found in Sweden. Despite preferring to oviposit in ripe fruit, D. suzukii is, like many other drosophilids, dependent on yeasts as a source of important nutrients. An especially strong connection has previously been seen to the yeast Hanseniaspora uvarum. In this work the behavioural effect of this yeast on D. suzukii was investigated. A larval assay was carried out to identify the most attractive single compounds from the headspace of H. uvarum. A blend of two of the more attractive compounds, ethyl acetate and acetoin, produced similar attraction levels as an H. uvarum liquid culture. Oviposition assays were carried out with real and artificial blueberries where mated female flies were given a choice between laying eggs in berries inoculated with undiluted, diluted or no H. uvarum. While no significant differences could be found between the treatments, it was noted that females were more likely to lay eggs if given access to undiluted yeast. Mating observations to investigate where matings where most likely to take place showed that a majority of the flies aggregated and mated on raspberries inoculated with H. uvarum compared to clean raspberries, fresh raspberry shoots and an H. uvarum culture the flies could smell but not feed on. Finally, a monitoring project was carried out in collaboration with hobby growers to investigate the current distribution of D. suzukii in Sweden. The results showed that D. suzukii is now present in most of southern Sweden, up to and including Stockholm, in both populated and rural areas

Correlation between germination and viability in seed tests and field emergence in spinach, Spinacia oleracea L.

För att kunna förutsäga vilken mängd utsäde som krävs för att få en önskad planttäthet i fältet är det viktigt att veta vilken fältuppkomst som kan förväntas. För att förutsäga detta används grobarhetstest. Detta arbete undersöker hur den uppmätta grobarheten korrelerar med den faktiska fältuppkomsten hos Spinacia olereacea L. Fem olika frösorter testades med grobarhetstest och tetrazoliumkloridtest och fältuppkomsten räknades. Resultatet visade att det fanns en signifikant korrelation mellan grobarheten och fältuppkomsten och tetrazoliumkloridtestet gav ett liknande resultat. Korrelationen var dock endast medelstark med ett värde på 0,583. Om den frösort vars resultat avvek kraftigt bortsågs ifrån ficks istället en korrelationskoefficient på 0,734.In order to be able to predict the required amount of seed needed to get the required plant density in the field it is important to know what kind of field emergence that can be expected. This work examines how the germination measured in a germination test correlates with the field emergence of Spinacia olereacea L. Five kinds of seed were tested with germination test and tetrazolium chloride and their field emergence was counted. The result showed a significant correlation between field emergence and germinability, and the results from the tetrazolium chloride test showed similar results. However, the correlation between germinability and field emergence was not overly strong, at a value of 0,583. However, if the values of of the seed type whose results differed greatly from all other types is disregarded a stronger correlation, with a value of 0,734, can be found

Hanseniaspora uvarum Attracts Drosophila suzukii (Diptera: Drosophilidae) With High Specificity

Since the early phase of the intercontinental dispersal of Drosophila suzukii (Matsumura) (Diptera: Drosophilidae), fermentation baits have been used for monitoring. Self-made lures and commercial products are often based on wine and vinegar. From an ecological perspective, the formulation of these baits is expected to target especially vinegar flies associated with overripe fruit, such as Drosophila melanogaster (Meigen) (Diptera: Drosophilidae). Hanseniaspora uvarum (Niehaus) (Ascomycota: Saccharomyceta) is a yeast closely associated with D. suzukii and fruit, and furthermore attractive to the flies. Based on this relation, H. uvarum might represent a suitable substrate for the development of lures that are more specific than vinegar and wine. In the field, we therefore, compared H. uvarum to a commercial bait that was based on vinegar and wine with respect to the number of trapped D. suzukii relative to other drosophilids and arthropods. Trap captures were higher with the commercial bait but specificity for D. suzukii was greater with H. uvarum. Moreover, H. uvarum headspace extracts, as well as a synthetic blend of H. uvarum volatiles, were assayed for attraction of D suzukii in a wind tunnel and in the field. Headspace extracts and the synthetic blend induced strong upwind flight in the wind tunnel and confirmed attraction to H. uvarum volatiles. Furthermore, baited with H. uvarum headspace extract and a drowning solution of aqueous acetic acid and ethanol, 74% of field captured arthropods were D. suzukii. Our findings suggest that synthetic yeast headspace formulations might advance the development of more selective monitoring traps with reduced by-catch

Jästbaserat lockbete för prognos och bekämpning av Drosophila suzukii

Den invasiva fruktflugan Drosophila suzukii är en allvarlig skadegörare på mjukskaliga frukter och bär. Bekämpningen av flugan är komplicerad och kräver en kombination av förebyggande och direkta åtgärder. Övervakning är ett nyckelelement i bekämpningen av D. suzukii, men traditionell fällfångst ger problem i form av stor bifångst av fel sorts insekter. Baserat på den mutualistiska relation som finns mellan D. suzukii och jästsvampen Hanseniaspora uvarum undersökte vi möjligheten att använda denna jästart för att utveckla lockbeten för flugan

Detection of the spotted wing drosophila, Drosophila suzukii, in continental sub-Saharan Africa

The spotted wing drosophila, Drosophila suzukii Matsumura, is an insect pest of soft-skinned fruit, native to Eastern Asia. Since 2008, a world-wide dispersal of D. suzukii is seen, characterized by the establishment of the pest in many Asian, American and European countries. While the potential for invasion of continental Africa by D. suzukii has been predicted, its presence has only been shown for Morocco in Northern Africa. Knowledge about a possible establishment in other parts of the continent is needed as a basis for pest management. In 2019, we carried out a first survey in three counties in Kenya to monitor for the presence of D. suzukii using traps baited with a blend of apple cider vinegar and red wine. A total of 389 D. suzukii flies were captured in a fruit farm at Nakuru county, with more female flies being trapped than males. We confirmed the morphological identification of D. suzukii using DNA barcoding. In 2020, we performed a follow-up survey at 14 locations in six counties to delimit the distribution of D. suzukii in the main berry growing zones in Kenya. The survey indicated that so far D. suzukii is restricted to Nakuru county where it was initially detected. This is the first study to provide empirical evidence of D. suzukii in continental sub-Saharan Africa, confirming that the pest is expanding its geographic range intercontinentally. Given the high dispersal potential of D. suzukii, a concerted effort to develop management strategies is a necessity for containment of the pest