3 minute read
Identifying strawberries and raspberries with resistance to SWD
NIAB’s Michelle Fountain, Adam Whitehouse and Feli Fernandez outline some promising results emerging from a Growing Kent & Medway funded research project.
Since the arrival of spotted wing drosophila (SWD) in the UK in 2012, NIAB’s entomologists at East Malling have led a host of industry research projects to learn more about its biology and behaviour in UK conditions and how best to manage and control it. Most recently exciting progress has been made through the use of precision monitoring in the winter months, use of bait sprays, and the development of Sterile Insect Technique (SIT) in collaboration with commercial company BigSis.
However, one approach to control that hasn’t been fully explored is variety resistance to the pest. Ripening soft and stone fruits are highly attractive to adult SWD, with the female making an incision in the skin of the fruit and laying eggs under the surface. The resulting larvae feed on the flesh of the fruit, leading to fruit collapse and an unmarketable product. If any accessions (varieties, selections, or species) of soft fruits are found to have berries that are less attractive to SWD or that inhibit egg laying or larval emergence, we could then investigate the fruit traits that are associated with this and utilise such traits in the NIAB breeding programmes.
In this Growing Kent & Medway funded project, NIAB scientists are collaborating with Asplins PO and WB Chambers to screen many accessions (varieties, selections, or species) of strawberry and raspberry, initially to identify if any show resistance to SWD and then find out what such resistance might be caused by.
In 2022, the focus was on strawberry and a wide range of strawberry genotypes were chosen based on their origin and pedigree. The material tested was diverse, ranging from old English bred June-bearer variety ‘Cambridge Favourite’, to the large, firm Californian variety day-neutral type ‘Diamante’. The range included differing traits like skin colour, skin firmness, flesh firmness, size, and sugar levels (Brix).
The aim was to identify any correlations between fruit traits and emergence of adult SWD from the fruit.
A total of 76 accessions were planted in replicated plots hosted by WB Chambers. Fruit was picked throughout the season, brought back to NIAB laboratories where fruit traits were assessed, and the fruit exposed in containers to adult female SWD. The number of eggs laid in each variety was recorded and the adult females then removed. Following 14 days, the number of emerging adults was counted from each of the original berries.
The results so far on strawberry have been very promising, as there was found to be statistically significant variation in the numbers of adults emerging from berries between the 76 accessions included. The genotypes used were grouped together based on the level of emergence. For those genotypes where a lack of emergence was found, several fruit quality traits were found to be correlated. In particular, the levels of Brix and the skin colour appeared to influence the level of emergence.
In 2023, the results from 2022 are being validated by re-screening those genotypes which showed either high levels of emergence or low levels of emergence. A similar exercise will also be undertaken for raspberries, looking at a wide range of accessions, including red, purple, and black coloured raspberry.
