Photograph showing effects on root rot on root system of raspberry

Raspberry root rot is currently the most economically damaging of all pests and diseases that affect raspberries in the UK.

The UK raspberry industry has come under increasing pressure by consumers to produce high quality fruit using a minimal quantity of chemical pesticides. To remain financially viable, commercial producers must achieve high yields of high quality fruit. This can be extremely difficult without the use of pesticides, particularly as the raspberry varieties currently in demand by the market are susceptible to a wide range of insect pests and fungal diseases.

Raspberry root rot, caused by Phytophthora fragariae var. rubi is currently the most economically damaging of all pests and diseases that affect raspberries in the UK. None of the commercially used varieties at present exhibit resistance, although the Canadian variety Cowichan tolerates the disease to some degree.

The industry desperately requires new commercially acceptable varieties that are resistant to Phytophthora. This will allow raspberries to be grown on infected sites that are otherwise ideally suited to raspberry production. It will also avoid the need to use fungicides and improve the viability of raspberry production for many fruit growers.

Breeding for root rot resistance is a major objective of the breeding programme at the James Hutton Institute. However, traditional breeding is a very slow process, particularly with raspberry and other Rubus species and it can take up to nine years to find a seedling that has the necessary traits for a new variety.

New methods of evaluating seedlings for Phytophthora resistance at an early stage in the selection process are required. New techniques have been developed that allow breeders to identify molecular markers on the genetic map of plants which can be used to identify seedlings with specific traits such as disease resistance.

The use of molecular markers linked to root rot resistance are now used in raspberry breeding to quickly and effectively identify selections with likely resistance to raspberry root rot. This technique significantly reduces the time taken to breed new varieties with Phytophthora resistance. Glen Mor has recently been released with root rot resistance.