Graziella Marcolini

Response of Potted Pear Trees to Increasing Copper Concentration in Sandy and Clay-Loam Soils

ABSTRACT The response of potted pear trees grafted on quince (Cydonia oblonga Mill.) Sydo stock to increasing concentrations (0, 50, 100, 200, 400, 600, 800, and 1000 mg kg−1) of copper (Cu) in sandy and clay-loam soils were evaluated and crop toxicity thresholds and symptoms were determined. Reductions of shoot growth and leaf area were observed only for pear grown in sandy soil with more than 400 mg Cu/kg. During the growing season, carbon assimilation and soil microbial biomass were reduced as concentration of soil Cu increased. However, the effect was always stronger in sandy than clay-loam soil. Copper accumulated in roots, with response to soil Cu additions described by a linear and a quadratic function for sandy and clay-loam soil, respectively. A possible antagonism was observed between Cu and zinc (Zn) in the roots. Root Zn concentration decreased as soil Cu concentration increased.

Adventitious shoot formation in cultured leaf explants of quince and pear is accompanied by different patterns of ethylene and polyamine production, and responses to aminoethoxyvinylglycine

Summary The gaseous environment inside culture vessels is an important factor affecting the growth and differentiation of plant cell and tissue cultures. Carbon dioxide (CO2) and ethylene (C2H4), in particular, play important roles. The effect of reduced gas exchange in sealed Petri dishes has previously been shown to strongly inhibit adventitious shoot formation in cultured leaf explants of quince ‘BA29’, but has not been investigated in pear. In the present work, the accumulation of CO2 and C2H4 in Petri dishes was quantified during the shoot induction and development phases in quince (Cydonia oblonga Mill.) ‘BA29’ and in ‘Conference’ pear (Pyrus communis L.) that have higher and lower regeneration capacities, respectively, on medium supplemented with 4.5 µM thidiazuron (TDZ) and 5.4 µM naphthaleneacetic acid (NAA). In order to evaluate the specific role of C2H4 on the shoot-forming process, the effect of treatment with an inhibitor of C2H4 biosynthesis, aminoethoxyvinylglycine (AVG), was also evaluated during the shoot induction phase. The results showed that AVG strongly reduced both C2H4 accumulation and the rate of production of C2H4, without affecting CO2 accumulation, in both species; whereas it differentially affected the regeneration capacity, enhancing it in quince and reducing it in pear. A time-course analysis of free and soluble conjugated polyamine (PA) titres was also performed in control vs. AVG-treated quince and pear explants during the induction phase. Quince explants exhibited a marked peak in free and conjugated spermidine on day-7 in culture, while pear explants did not. AVG did not alter PA levels, or the PA profile in either species. The addition of AVG to the induction medium is recommended to improve shoot regeneration in quince ‘BA 29’ leaf explants in culture systems that prevent optimal gas exchange. In contrast, the low genotype-specific regeneration capacity of pear prevailed over the effect of AVG treatment in our experimental conditions.

USE OF SOIL-AND FOLIAR-APPLIED CALCIUM CHLORIDE TO REDUCE PEAR SUSCEPTIBILITY TO BROWN SPOT (STEMPHYLIUM VESICARIUM)

We evaluated the effectiveness of soil and foliar applications of calcium chloride (CaCl2) on reducing pear susceptibility of brown spot (Stemphylium vesicarium). Two experiments were done using pear trees of the variety Abbé Fetel grafted on quince (Cydonia oblonga) rootstock. Potted trees were treated with soil and foliar application of CaCl2, while commercial trees were subjected only to soil application of 5.6 g CaCl2 L−1, and 11.2 g CaCl2 L−1. In a controlled environment, leaf and fruit brown spot incidence decreased with the increase of residual calcium (Ca) concentration in the tissue, according to a second degree function. In fruits from field experiment, disease symptoms were decreased by soil application of CaCl2 that increased Ca fruit concentration above 1000 mg kg−1 dw; however, no clear correlation between fruit Ca and brown spot incidence was found. Leaf water and osmotic potential were not related to brown spot incidence.

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

Summary The present work investigated the effects of different aqueous extracts of organic waste compounds on growth, proliferation and photosynthetic activity in ‘M9’ (Malus domestica Borkh.) shoot cultures, with the aim of determining the feasibility of using in vitro cultures as a tool for the 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 a rate of 1:10 (w/v) compound:distilled water. The basal media used in the proliferation phase were: (i) PM1, modified Murashige and Skoog (MS) enriched with 4.4 µM 6-benzyladenine (BA); (ii) PM2, as PM1 but with a reduced cytokinin concentration (1 µM BA) to evaluate possible hormone effects; and (iii) PM3, 4.4 µM BA with reduced salt strength (0.33 MS) to induce nutrient deficiency. Hormone-free medium with half-strength MS salts was used for rooting. All media were enriched with each extract 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 a 16 h photoperiod at 30 µmoles photosynthetically active radiation (PAR) m–2 s–1, but at 80 µmoles PAR m–2 s–1 to determine photosynthetic activity. Shoot weight increase in PM1 was not affected by the GPM and CPI extracts, while the growth trends of CM- and SB-treated shoots were described by a second-degree function with maxima at 2 ml l–1 and 0.2 ml l–1, respectively. Shoot proliferation for SB was represented by a quadratic curve (maximum at 2 ml l–1), was linearly reduced as GPM increased, but was not affected by CM or CPI. Treatments did not significantly affect rooting percentage and root length; however root number was increased by SB at 2 ml l–1.CO2 fixation increased linearly with both SB and CM, despite reduced growth at the highest levels of extract.