Fruit Growth and Quality as Influenced by Low Irradiance Levels In the Pear Cultivar ‘Red Sensation'

Shading frequently occurs in the interior of pear tree canopies. Therefore, it has become increasingly important to study the effects low irradiance on final yield. This work was undertaken to measure the influence of light reduction on ‘Red Sensation’ pear fruit growth and quality in the environmental conditions of the High Valley region, Río Negro, Argentina, during the 2007-08 growing season. Fifteen-year-old trees grafted on Pyrus communis L. rootstock, planted in a single row from north to south with spacing of 2.3 m × 4.0 m and trained to palmette leader were used. The orchard was fertilised and sprayed for pest and disease control according to the local standard programme. The experimental site was located in an arid region, with average annual rainfall of 250 mm. An automated meteorological station, situated close to the experimental orchard at the Comahue National University (38°56'S, 67°59'W), continuously monitored high, mean and low air temperature, air relative humidity and solar radiation. Full bloom occurred on 30 September 2007. Treatments were: a) application of shade, by cloth-covering individual whole branches with an 80 % saran shade cloth, from 19 to 113 days after full bloom (DAFB) and b) control. Analysis of variance was used to evaluate the effect of shade on fruit growth and maturity indices; mean separations were computed with Student’s t-test and equations were developed with SYSTAT procedure. From 19 October to 16 November 2007, fruit diameter was measured at two-day intervals. Lineal models best fit fruit growth and significant differences (P≤0.05) were found between shaded and sun-exposed treatments: FD = 0.5024 DAFB + 0.8630, R² = 0.82 and FD = 0.6255 DAFB – 1.7188, R² = 0.83, respectively. At commercial harvest, light reduction decreased fruit diameter by 14.7 % and fruit weight by 35.8 %, as compared to the control; it also affected fruit color, firmness and soluble solids concentration: 40.0 vs. 81.1 %, 22.8 vs. 21.4 N and 8.93 vs. 12.0 ºBrix for treatments a) and b), respectively. It was concluded that shading reduced ‘Red Sensation’ pear quality and diminished fruit size. These results suggest some goals of pruning and training for optimizing yield, by efficiently converting captured sunlight into fruit.