わい性台木を用いたリンゴ1年生苗木における堀り上げ前の摘葉処理の時期が苗木の耐凍性とデンプン含量ならびに定植後の生育に及ぼす影響(繁殖・育苗)  [in Japanese] Freezing Tolerance, Starch Content and Growth after Replanting of 1-year-old Apple Nursery Trees on Dwarfing Rootstock Affected by Hand-Defoliation Date before Digging(Propagation & Transplant Production)  [in Japanese]

リンゴ1年生わい性台木苗木における,掘り上げ前の摘葉処理時期が,貯蔵後の苗木の耐凍性,定植後の生育およびデンプン含量に及ぼす影響について検討した.その結果,摘葉処理時期が早いほど,耐凍性が低いことが明らかとなった.また,摘葉処理時期が最も早い条件(10月15日摘葉)においては,翌年の定植後の苗木生育が極度に劣り,発芽,展葉したものの途中で枯死する苗木か40%認められた.さらに,慣行的に行われている時期(11月14日)の摘葉処理であっても,最晩期(12月3日)の摘葉処理に比べるとデンプン含量が低下し,苗木の耐凍性が弱まることか認められた.したがって,耐凍性の向上およびデンプン含量の増加を考慮した場合,なるべく遅い時期の摘葉処理か望ましいと考えられた.

'Shinano-sweet' apple nursery trees (Mains 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℃ 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℃ 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.