SWD-resistant soft fruit varieties could add to armoury of control methods - Fruit & Vine

SWD-resistant soft fruit varieties could add to armoury of control methods

Work has begun to develop strawberry and raspberry varieties resistant to spotted wing drosophila (SWD), a key problem pest in soft and stone fruit, with initial results showing promise that a new milestone in fly control may be within reach.

The project, funded by Innovate UK through the Growing Kent & Medway (GKM) scheme, is a collaboration between NIAB, Kent-based Producer Organisation Asplins and Chambers. Project leader Adam Whitehouse gave an overview of the initial research work and preliminary findings at the NIAB Soft Fruit Day technical webinar on 30th November.

According to Mr Whitehouse, damage to fruit caused by SWD costs the industry around £20-30 million a year when accounting for labour and pesticide expenses. As a result, the development of more cost-effective and sustainable control methods has been gaining increasing prominence in recent years.

While using resistant soft fruit varieties is an exciting prospect, very little work has been done in this space so far, Mr Whitehouse said. There is known variation in ‘resistance’ in some Fragaria species in strawberry, but no UK-relevant varieties have been explored as of yet.

As such, the project has come in at just the right time to fill in this missing gap in fruit research, Mr Whitehouse pointed out. Its primary aim, he said, is to identify UK-relevant strawberry and raspberry germplasm with natural resistance to SWD for future variety development.

In plant research, germplasm refers to the cultures, seeds and other plant material maintained for the purposes of plant breeding, genetic research, and conservation efforts.

If the initial work is successful and resistance is found, further research would be looking at the cause of the resistance, what are some associated characteristics and traits, and whether the genetic components can be identified for breeding new varieties with resistance or reduced susceptibility to SWD, Mr Whitehouse explained.

Although the project was only awarded in May 2022, substantial work has already been completed in strawberry crops, which has been the focus of this year.

More precisely, a total of 76 accessions of the cultivated hybrid Fragaria x Ananassa variety were observed in a 50m standard insect-proof polytunnel and assessed throughout the season. Fruit parameters measured included skin colour, skin strength, flesh firmness, berry size and sugar levels.

The purpose of these observations, Mr Whitehouse added, was to identify correlations between traits and any variation found in SWD emergence in fruit crops.

To measure emergence, fly assessments were carried out for each berry collected at NIAB labs. Following exposure to SWD egg laying for two weeks, emerging adults were counted to determine if there is any variation in susceptibility or resistance between crops.

Promising results point towards future variety development

According to Mr Whitehouse, early results have shown some variation in the number of emerging flies on accessions, suggesting that certain varieties could be more resistant than others.

While these are already encouraging results, further analysis is needed to fully understand the connection between traits, egg count, and emergence to enable to project to proceed to the next stage.

The next steps, Mr Whitehouse said, will involve producing choice tests with strawberry pulp that was collected and frozen from different accessions this winter. The team will also be performing dye tests to see if SWD can be tempted to some accessions and not others.

As for the next year, the project will be looking at re-screening selected strawberry genotypes for validation in different seasons and will begin the preliminary screen of raspberry accessions. Similar to strawberry, 55-75 raspberry accessions including yellow, purple, and black genotypes will be assessed.

The project will continue for another two years was one of the first to be awarded R&D funding through the GKM programme. To meet the other grant winners, visit: https://www.growingkentandmedway.com/news/meet-the-grant-winners/

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