Effects of in vivo mycorrhization on micropropagated fruit tree rootstocks

In order to establish an endomycorrhizal symbiosis on micropropagated plants and to evaluate its effect on plant growth and survival, three rootstocks belonging to the Prunus genus were used: M51 (P. dulcis), GF677 (P. persica x P. dulcis) and cv Citation (P. domestica x P. persica). The plants were micropropagated and in vitro rooted. Spores of Glomus mosseae (LMSS) and Scutellospora calospora (SCLS) and root fragments of clover or corn mycorrhized by them were used as inocula. Plants were inoculated in: (1) the early acclimatization phase; (2) the transplant phase; (3) in both phases. Two similar experiments were conducted for each plant genotype, differing only in the type of inoculum. One month after transplanting, plant survival indexes, mycorrhization percentages and growth parameters for each plant were recorded. No significant effects were observed on survival. In M51 no mycorrhizae were found and no significant growth effects were recorded in either experiments. LMSS infected GF677 in the second experiment, but not in the first, when inoculated in the transplant phase, with a better establishment when a second inoculation was done. Citation was not colonized by LMSS in either experiment. SCLS was able to establish mycorrhizal infection of Citation and GF677 only in the first experiment, and only when inoculated in the acclimatization phase. There were significant positive effects of the inoculation phase, the inoculum strain and the plant genotype on growth parameters, regardless of whether symbiosis was established or not. In conclusion, M51 did not seem to be dependent on the establishment of an endomycorrhizal symbiosis, at least with the fungal strains used in our experiments. On the contrary, Citation and GF677 seemed positively influenced by inoculation, even when there was no infection by the mycorrhizas. This fact is probably due to growth promoter components of the inocula - possibly microflora. (C) 2000 Elsevier Science B.V. All rights reserved.