Influence of arbuscular mycorrhizae and phosphate fertilization on shoot apical growth of micropropagated apple and plum rootstocks.

We studied the effects of phosphate fertilization and inoculation with the arbuscular mycorrhizal fungi Glomus mosseae (Nicol. and Gerd.) Gerdmann and Trappe, Glomus intraradices Schenck and Smith or Glomus viscosum Nicolson on shoot apical growth of plantlets that had been micropropagated from MM 106 apple (Malus pumila L.) and Mr.S. 2/5 plum (Prunus cerasifera Ehrh.) rootstocks. Unfertilized and non-mycorrhizal plantlets showed no apical growth during the post in vitro acclimation phase, whereas P fertilization induced early resumption of shoot apical growth. Growth enhancement and percentage of actively growing apices of mycorrhizal-inoculated plantlets were comparable to those obtained in plantlets fertilized with P. Furthermore, tissue P concentrations of mycorrhizal plantlets were similar to those of plantlets fertilized with P. We conclude that mycorrhizal inoculation can be used as a biotechnological tool to overcome blocked apical growth and to reduce chemical inputs, especially P inputs, to micropropagated fruit trees.