CONTROL OF SHARKA BY BREEDING

Abstract

PPV is the most dangerous virus in stone fruit growing and is spread worldwide. In infected areas it is recommended that only tolerant or resistant cultivars are cultivated. From the plum breeding programme at Hohenheim 6 tolerant or resistant cultivars have been produced, which are successful in production in Germany. Some promising clones will be introduced. Tolerant or resistant cultivars can be infected by PPV and will continue to be a source of infection. The first absolute virus resistant cultivar worldwide is 'Jojo' introduced in 1999. 'Jojo' reacts hypersensitivly to PPV and has continued to grow healthily for more than 20 years in totally infected orchards. In the breeding programme quantitative and hypersensitive resistance were combined. The heredity of hypersensitivity depends upon the chosen parents. Using donors from Hohenheim the hypersensitivity index has been much higher than that achieved by using the K 4 hybrid or its progenies. Forty-three promising clones with different size and ripening times have been selected for tests in different regions. By pyramiding of the genes responsible for quantitative and hypersensitive PPV resistance we hope to get cultivars with a durable absolute PPV resistance and high fruit quality.