The 2012 ASHS Annual Conference

The pear cultivar ‘Red Sensation’ is showing popularity in the industry because of the highly-colored, sweet and juicy fruit.  The effects of shading on fruit and leaf characteristics of 'Red Sensation' pear trees were evaluated at the Experimental Farm of the Universidad Nacional del Comahue, in the High Valley region, Río Negro, Argentina (38°56' S, 67°59' W).   A crop of pear trees grafted on Pyrus communis L. rootstock, planted in 1993 at 4.0 x 2.3 m spacing, trained to palmette leader and grown in sandy loam were studied. Row orientation was north-south. The orchard was kept weed-free, fertilized, thinned, pruned and sprayed for pest and disease control according to the local standard program for pears.  The experimental site was located in an arid region; trees were surface irrigated at weekly intervals to match the crop evapotranspiration requirements throughout the season.  An automated meteorological station collected air temperature, relative humidity and sunshine duration data. Two comparable branches on each of six uniform trees were selected for good exposure and one branch of each pair was shaded. Treatments were: a) control and b) application of shade, by covering branches with a 20% transmission (i.e. 80% reduction in irradiance) black saran neutral density shade net, from 30 to 50 days after full bloom (DFB). Full bloom occurred on 29 September 2011. Fruit diameter (FD), shoot length (SL), leaf area (LA), specific leaf weight (SLW) and SPAD value were determined at 50 DFB. LA was measured with a Cid – 202 leaf area meter. SPAD value was assessed with a Minolta SPAD – 502 portable apparatus. Discs were excised between the midrib and leaf margin, using a cork borer of 11 mm diameter. They were subsequently dried at 80 ºC for 48 h and weighed to obtain SLW. FD was the maximum width perpendicular to the main axis and it was recorded with a Vernier caliper. Means were compared using Student's t-test to determine significant differences (P ≤ 0.05). Low light level significantly reduced FD and SL and compared to the controls: 28.1 vs. 26.6 mm and 42.7 vs. 32.4 cm for treatments a) and b), respectively. LA, SLW and SPAD values were not affected:  18.8 cm², 4.23 mg·cm^-2 and 42.2 SPAD value for the control samples, respectively. Further studies are needed to study the relative effects of reductions in light levels during different periods on ‘Red Sensation’ fruit and shoot growth.