Segregation of plum hybrid families bred for resistance to Plum pox virus

The main target of the contemporary plum breeding programmes is obtaining of cultivars, resistant or tolerant to Plum pox virus (PPV). The present article reports the results from a segregation of plum hybrids depending on their reaction to PPV in field conditions. The segregation included 160 plum individuals belonging to six plum (Prunus domestica L.) hybrid families obtained from the following parental combinations: ‘Stenley’ x ‘Serdika 2’, ‘Stenley’ x ‘Pacific’, ‘Pacific’ x ‘Serdika 2’, ‘Pacific’ x ‘Stenley’, ‘Pacific’ x ‘Green gage’ and ‘Green gage’ x ‘Pacific’. During 3 vegetative cycles under natural infection background, the hybrids were observed for Sharka symptoms on the leaves and on the fruits. The sympomless plants were tested by enzyme - linked immunosorbent assay (ELISA) for latent PPV infection. On the base of visual inspections and ELISA results 20 hybrids were selected as follows: 5 numbers from cross ‘Stenley’ x ‘Serdika 2’; 10 from ‘Stenley’ x ‘Pacific’; 3 from ‘Pacific’ x ‘Serdika 2’ and 2 from ’Green gage’ x ‘Pacific’. Representing the results in relative values, PPV infection was not detected in 17 % of individuals from the cross Stenley’ x ‘Pacific’, in 13.8 % from Stenley’ x ‘Serdika 2’, in 13.3 % from ’Green gage’ x ‘Pacific’ and in 11.5 % from Pacific’ x ‘Serdika 2’. All observed individuals from the families ‘Pacific’ x ‘Stenley’ and ‘Pacific’ x ‘Green gage’ showed medium or severe PPV symptoms and by reason of that they were discarded of survey. Most of individuals without PPV symptoms originated from combination ‘Stenley’ x ‘Pacific ’in contrast to the reverse cross ‘Pacific’ x ‘Stenley’. In all observed hybrid populations prevailed the individuals reacting with medium symptoms on the leaves and mild symptoms on the fruits. Some of chosen hybrids are under course of artificial inoculation by PPV isolates to resolve of their real reaction to PPV.