Evaluation of the activity of aqueous extracts of some organic waste materials on in vitro-cultured shoots of 'M9' apple rootstock

The present work investigated the effects of different aqueous extracts of organic waste compounds on growth, proliferation and photosynthetic activity in ‘M 9’ (Malus x domestica Borkh.) shoot cultures, with the final aim to determine the feasibility of using in-vitro cultures as a tool for a rapid evaluation of organic amendments in agriculture. Aqueous extracts of the following organic waste compounds: cow manure (CM), sugarbeet industrial waste (SB), mixed grape, poultry and municipal solid waste (GPM) and citrus pruning and industrial waste (CPI) were prepared at 1:10 (w/v) compound:distilled water rate. The basal media used in the proliferation phase were: (i) modified Murashige and Skoog (MS) enriched with 4.4 M 6-benzyladenine (BA) (PM1); (ii) reduced cytokinin concentration (1 M BA, PM2, to evaluate possible hormone-like effects); and (iii) 4.4 M BA and reduced salt strength (0.33 x MS salt strength, PM3, to induce nutrient deficiency). Hormone free medium with half-strength MS salt was used for rooting. All the media were enriched with each extracts at 0, 0.2, 2, 20 or 200 ml l-1. Photosynthetic activity was measured on PM3 medium enriched with SB or CM. Standard culture conditions were 22°  2 °C, with 16 h photoperiod, 30 μmol photosynthetically active radiation (PAR) m-2 s-1, but 80 μmol PAR m-2 s-1 to determine photosynthetic activity. Shoot weight increase in PM1 was not affected by GPM and CPI extracts, while growth trends of CM and SB-treated shoots were described by a second degree function with a maximum at 2 ml l-1 and 0.2 ml l-1, respectively. Proliferation for SB was represented by a quadratic curve (maximum at 2 ml l-1), linearly reduced as GPM increased and not affected by CM and CPI. Treatments did not affect significantly rooting percentage and root length, however root number was increased by SB 2 ml l-1. Carbon dioxide fixation linearly increased with both SB and CM, despite of the reduced growth at the highest extract levels.