Freezing tolerance, starch content and growth after replanting of 1-year-old apple [Malus domestica] nursery trees on dwarfing rootstock affected by hand-defoliation date before digging
2007
Ono, T.(Nagano-ken. Fruit Tree Experiment Station, Suzaka (Japan)) | Ito, T. | Ogawa, H. | Usuda, A.
'Shinano-sweet' apple nursery trees (Malus domestica Borkh.), that were grafted on Pajam 1 rootstocks in February 2004, were hand-defoliated on 15 October, 14 November, or 3 December 2004, to investigate the effects of defoliation on freezing tolerance, starch content and growth after replanting. The nursery trees were dug on 3 December 2004, and stored in a cold room at 2 deg C with humidification. Freezing tolerance was tested in March 2005. It was clear that freezing tolerance decreased as the date of hand-defoliation advanced. The rootstocks of the nursery trees were kept at -17 deg C for 16 h.; subsequently the degree of freezing injury was evaluated on an index from 0: without injury to 1: complete injury. The rootstock of trees that had been defoliated on 15 October had an index of 1.00, while that of the nursery trees that were defoliated on 3 December was 0.41. The earliest defoliation (15 October) resulted in 40% tree mortality after replanting, and lower shoot growth in the remaining trees. In addition, early defoliation reduced the starch content; the earliest defoliation produced an 84% reduction in the starch content of the roots. In conclusion, it is desirable to delay hand-defoliation of nursery trees until as late in the season as possible in order to preserve cold tolerance, starch reserves, and tree vigor after replanting.
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