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Plum pox virus as a stress factor in the vegetative growth, fruit growth and yield of plum (Prunus domestica) cv. 'Cacanska Rodna' Abstract During 2005, under the environmental conditions of Cacak (43°53'N; 20°21'E), western Serbia, the effect of Plum pox virus (PPV) on the phenology of vegetative shoot and fruit growth was investigated in a plum orchard of cv. 'Cacanska Rodna' including trees non-infected with PPV and those with infection and clearly visible symptoms, as verified by RT-PCR. The results showed that PPV did not affect the growth phenology of the vegetative shoot (length and thickness) and the fruit growth. However, it caused negative effects on the average length (22.31±0.28 cm in non-infected trees, 18.35± 0.07 cm in infected trees) and thickness (4.21± 0.03 mm in non-infected trees, 4.01±0.02 mm in infected trees) of vegetative shoots as well as on the average fruit weight (20.43±0.16 g in non-infected fruits, 17.58±0.18 g in infected fruits) and fruit dimensions. The greatest effect of PPV during the trial was the induction of a massive premature fruit drop and, consequently, a 52.94% decrease in total yields per tree (18.0±1.10 kg) and unit area (12.0± 0.89 t ha -1 ) in infected vs non-infected trees.

Soils with unfavourable characteristics (pronounced acidity, disturbed structure, compaction, exhaustion, tiredness, etc.) cover a considerable area of Serbia. Specific crops, the fruit ones in particular, are being grown on these soils, yielding, however, considerably lower yields. The paper presents results of two-year studies on the effect of natural zeolites, organic fertilisercattle manure and mineral NPK fertiliser (15:15:15) on soil properties and fruit yield and fruit properties of strawberry and blackberry plants grown on shallow eroded vertisol.The results have shown that the chemical properties of the soil improved with the natural zeolite 'Agrozel' (1 kg m À2 ) þ Manure (1 kg m À2 ) treatment-resulting in a 0Á94-unit acidity decrease and a 0Á58% humus content increase at a 0-20 cm soil depth. Positive but less pronounced changes were also detected at greater soil depths. The strawberry and blackberry cultivation in these soils using the above substances gave rise to a yield increase. In the second year of study, strawberry and blackberry yields increased by 13Á15% and 6Á27%, respectively. Basic chemical properties of strawberry and blackberry fruits (soluble solids and total acid contents) were not significantly affected by zeolite and organic fertiliser additions to the soil.

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