A survey of Rosellinia in apple orchards and nurseries in South Africa

White root rot of apple is caused by Rosellinia necatrix and causes the decline and death of trees. It occurs on many woody hosts commonly cultivated in Mediterranean climates such as grapevines, olives, pears and peaches. In this survey it was isolated from infected apple trees collected in the Western Cape and characterised with species-specific primers (R2 and R7) and sequencing of the ITS region. This is the first time Rosellinia necatrix collected from orchards in South Africa was identified by this means. The 40 isolates were all identified as Rosellinia necatrix and it is suspected that there is low diversity in the population associated with apple in South Africa. The typical symptoms included sparse foliage and small fruit, rotten roots, discolouration of the wood below the bark at soil level and in some instances white mycelial networks on the root surfaces. This disease has the potential to be a serious threat to the apple industry.