Effect of native arbuscular mycorrhizal fungi and Glomus mosseae on acclimatization and development of micropropagated Citrus limon (L.) Burm

Arbuscular mycorrhizal fungi (AMF) have been successfully used to improve acclimatization, survival and growth of many micropropagated fruit species. In this work we tested the influence of the AM fungus Glomus mosseae (BEG 116) and that of a Sicilian native mixture of Glomus species, on the survival and growth of micropropagated lemon plants (Citrus limon (L.) Burm. 'Zagara Bianca') during the weaning phase to a final age of 16 months. Plantlets were obtained from embryogenic callus derived from style and stigma cultures. The native AM fungal mixture was obtained from the rhizosphere soil of a citrus grove (Sicily, Italy) and was found to be more infective than G. mosseae alone. It significantly increased plant height, root and shoot weight, leaf area, P content and shoot/root ratio at the end of the weaning phase, i.e: 17 weeks after in vivo transferring and inoculation. A severe growth depression was observed in plants inoculated with G. mosseae. During the early weaning phase, plant survival was reduced only by the native AMF mix inoculum that may still have been too rich in soil-borne pathogens; at the end of the experiment (69 weeks) plant survival was reduced by all the treatments except for the native AMF mix inoculum. A rhizosphere effect other than mycorrhizal was detected in the rhizosphere control inoculated with the sievate of the native AMF inoculum, in particular on root development. To our knowledge, this is the first report on mycorrhization of micropropagated citrus plants.