Carbohydrate reserves and CO2 balance of hybrid walnut (Juglans nigra no 23 x Juglans regia) plantlets during acclimatisation

Morphological and physiological characteristics of hybrid walnut plantlets were studied during acclimatisation in growth chambers. The study was conducted on two clones, M41 and D152. At the end of the in vitro phase, D152 had produced more adventitious roots but less leaves than M41, M41 accumulated more soluble sugars and starch than D152, During acclimatisation, the greatest increase in growth occurred in root length, regardless of the clone studied, However, the dry matter and carbon contents were always higher in M41 than in D152. The morphology of rooted plantlets differed markedly from that of young seedlings, During the first 7 days of acclimatisation, the balance of CO2 exchange on a daily basis was negative (respiration was dominant), During this period, the carbohydrates which accumulated chiefly in the roots and callus during the root development phase were used for growth and maintenance processes, The balance of CO2 exchange (on a daily basis) became positive after this heterotrophic phase, The new leaves formed during the acclimatisation phase appeared to be actively involved in the acquisition of autotrophy, At the end of the acclimatisation phase, the carbohydrate content of all organs was very low and the plantlet was dependent on photosynthesis. The capacity of hybrid walnut clones to survive the acclimatisation phase is discussed. (C) Elsevier Science B.V.