Articles
STUDY OF SHARKA SPREAD PATTERN IN SOME PLUM ORCHARDS
Three orchards (1,2,3) were planted in a heavily infected district and two (4,5) in a district with slight infection.
All orchards were planted with sharka-free trees of Pozegaca, which is known to be the most susceptible cultivar to sharka virus.
The pattern of sharka spread in the first three orchards, established in the severely infected district, was similar.
In the first two years of investigation the infected trees were scattered in different parts of orchards without any regularity, which showed that they were infected from external sources of infection.
In the following years the majority of newly infected trees were concentrated in the vicinity of the trees infected in the previous years.
So, in the third year of investigation the average per cent of infected trees adjacent to previously infected trees was about 50, in the fourth year 73 and in the fifth 66 average.
Considering the orchards located in the slightly infected district it was difficult to estimate the sharka spread pattern, because of very slow spread of virus.
But results obtained in one of these orchards, in which some infected trees were planted, showed that the pattern of spread is very similar to those planted in severely infected districts.
The evidence obtained in these studies showed that sharka virus was spread in nature by aerial vectors only.
In the first years of spread the infected trees were distributed in different parts of orchards.
Later, new infected trees were mostly situated close to the trees infected in previous years, which indicate that the main sources of virus infection were trees infected in the orchard.