Articles
CHERRY LEAF ROLL VIRUS IN HUNGARIAN WALNUT ORCHARDS
To survey the spread of the disease within fruit bearing orchards, a plantation established in 1959–1961 was used.
An equal proportion of trees was on Juglans regia and J.nigra rootstocks.
Extent of virus infection of the orchard was visually observed and tested with ELISA in 1981,1982 and 1989.
The initial infection in 1981 was 24,2 %, in 1982 48,4 %, and by 1989 it has increased to 96,8 %. On the one hand, there was no difference in the extent of infection between the trees of the two rootstocks, there was a great one, on the other hand, in the ratio of the died trees.
Trees on J.nigra died in 1981: 6,7 %, in 1982: 13,3 % and 1989: 50 %. Death of trees on J.regia rootstock started in 1982 with 3,3 %, and in 1989 only 10 % of the trees died in spite of the fact that the condition of the infected trees was very bad.
As the CLRV spreads by pollen, it is important to regularly check the mother trees, with ELISA and with patch budding onto hypersensitive rootstocks.
It is recommended to graft the nuclear stock onto hypersensitive rootstocks, because the infected bud will not take.
It is desirable to choose variety with separated blooming period of pistillate and staminate flowers for planting commercial orchards, because in this case only the pollenizer varieties should ‘be regularly checked.