REJUVENATING OLDER APPLE TREES BY ROOT PRUNING COMBINED WITH ARBUSCULAR MYCORRHIZAL FUNGI

Older apple trees often demonstrate physiologically unreasonable shoot distribution due to root system aging, which results in lower fruit yield and poor fruit quality. Therefore this study was conducted to test whether root pruning combined with arbuscular mycorrhizal fungi could restore growth potential of fortyyear-old Red Fuji apple trees (Malus × domestica Borkh.) in a commercial orchard in 2013, by root pruning along both sides of rows, 80 cm from the trunk, to a depth of 30 cm and application of 100 ml arbuscular mycorrhizal inoculum per plant. Results showed that the percentage of root colonized by mycorrhizal fungi increased as root pruning was combined with arbuscular mycorrhizal fungi, however mycorrhizal colonization was not seen in the control roots and roots only by root pruning. For control tree total number of shoots decreased by 28.22% in 2015 than in 2013 and shoots mainly distributed in the outer canopy accounting for 58.10% of the total, which caused the lower light intensity inside the canopy, followed by lower fruit yield and poor fruit quality. Compared to control plant, shoot reduced by 33.96 and 38.51% in the outer canopy but increased by 97.99 and 123.69% in the inner canopy in 2015, as well as 390.20 and 478.43% in the verticalheight of 1.5 to 2.5 m canopy, respectively treated by root pruning alone and combined with arbuscular mycorrhizal fungi. Root pruning alone and combined with arbuscular mycorrhizal fungi also raised the relative light intensity by 38.71 and 60.26% in the inner canopy in 2015, subsequent fruit yield by 315.79 and 373.68% respectively, in comparison to control plant. Shoot re-distribution improved fruit quality such as increase in firmness and soluble solid. Data indicated that the effect of root pruning combined with arbuscularmycorrhizal fungi on the rejuvenation of older apple trees was stronger than root pruning alone. It is therefore concluded that root pruning combined with arbuscular mycorrhizal fungi can think of as a measure to renew the older apple trees.