Next generation apple breeding for resilient UK production

Access to new apple varieties is crucial for the future sustainability of the UK apple industry, as new varieties tend to have a significantly higher retail value and therefore offer larger margins for apple growers. However, many of the new cultivars introduced to the UK market are susceptible to apple scab (_Venturia inequalis_), powdery mildew (_Podosphaera leucotricha_) or European canker (_Neonectria ditissima_), three apple diseases that are highly prevalent in the UK. This has led to a heavy reliance on chemical disease control.

Monogenic resistance to powdery mildew and scab are well-documented and the use of the scab resistance gene _Rvi6_ has successfully been incorporated in breeding programmes worldwide. In contrast, the documented resistances to European canker are polygenic and have been poorly deployed in apple breeding. There is thus a lack of cultivars with combined resistance to all three diseases and a heavy reliance on a single resistance gene against scab in commercial cultivars. Breeding apples with improved resistance is a long process, traditionally taking 20-25 years. Such timescales leaves the apple industry vulnerable to the emergence of new biotic and abiotic threats and to the availability of effective plant protection products.

This project aims to develop modern breeding methods to enable a shorter breeding cycle of apple and ensure a faster route to market for new, more resistant cultivars. The project will research three breeding methods and their potential to shorten the breeding cycle: genomic selection, molecular marker-trait associations and speed breeding.

Genomic selection is a form of marker-assisted selection in which markers covering the whole genome are utilised for selection. This breeding method has revolutionised animal and plant breeding and is particularly useful for highly polygenic traits. Nevertheless, genomic selection has not been widely adopted in apple breeding and there are no reports of it's efficacy as a selection tool for polygenic disease resistance in apple. Within this project we will evaluate genomic prediction models for resistance to European canker, an essential trait for UK production.

Speed breeding is a tool in which environmental growth conditions are manipulated to accelerate plant development, thereby allowing for rapid generation cycling. Integrated with marker-based selection methods, this methodology has great potential to produce multi-resistant apple cultivars which meet industry and consumer demand in a significantly reduced time-frame. We will use a combination of photoperiod regime, plant hormones and growth regulators to manipulate the plant development and seed dormancy in apple.