In vitro treatments with low molecular weight humic acid can improve growth and mineral uptake of pear plantlets during acclimatization

Pear (Pyrus communis L.) micropropagation still shows problems in the various phases; acclimatization is especially critical. Humic substances (HS) can influence plant metabolism and morphology, with a stimulating effect on shoot and root growth and nutrient uptake. Low molecular weight (LMW) components of HS are particularly active. The direct and carryover effects of a LMW humic acid (HA) extracted from peat Sphagnum are investigated in in-vitro rooting of shoots of pear, cv. Conference and Abbè Fetel, and on acclimatization of plantlets. Variable HA supplements, corresponding to 0 (control), 0.5, 1 and 2 mg C L-1 were added to the rooting medium (IBA 1 mg L-1). Plants were acclimatized in peat, at 24±2 °C, 16-h photoperiod (70 micromoles PAR m-2 s-1). The number of rooted shoots was increased by HA at 0.5 and 1 mg C l-1 in ‘Abbè Fetel’. Catalase (CAT) activity and malondialdehyde (MDA) content of shoots were slightly reduced by HA at 0.5 and 1 mg C l-1. During acclimatization, HA at 2 mg C L-1 did not show satisfactory results. Lower HA supplements, instead, increased plant height, shoot weight and leaf chlorophyll content, and enhanced nutrient uptake.