Effect of Replant Disease on Growth of Malus x domestica ‘Ligol’ Cultivated on P-series Apple Rootstocks

The study was conducted in 2009 and repeated in 2010. Its aim was to determine the effect of replant disease on the growth vigour of Malus x domestica ‘Ligol’ grafted on P-series rootstocks (P 2, P 14, P 16, P 22, P 59, P 60, P 66, P 67 and P 68) and rootstocks M.7, M.9, M.26, MM.106, CG 16. Plant material for the study was produced by winter grafting the scions of ‘Ligol’ on the above rootstocks. In mid-April, mineral soil was collected from a field where for the previous 25 years an apple orchard had been cultivated. The soil was collected from two soil layers- the arable layer (0-20 cm) and the sub-arable layer (20-40 cm), and mixed at a ratio of 1-1 by volume. The mixed soil was divided into two parts- one part was pasteurized with steam (95°C for 30 minutes), the other part was not pasteurized. Plastic containers (5 litre) were filled with both types of soil and the grafts were planted. Each treatment involved 20 trees. Two weeks after planting, a slow-release fertilizer was added (20 g per container) and a drip irrigation system installed. The containers were placed outdoors and the trees were grown until late October when stem height and fresh weight of the root system were recorded. Regardless of the rootstock, ‘Ligol’ trees in sterilized soil grew less vigorously than the trees in ‘sick’ soil; however, those trees produced a significantly larger root system.