Tree growth and fruit production of various organic Asian pear (Pyrus pyrifolia Nakai) cultivars grown under a rain- shelter system

摘要

A study was conducted to compare the effects of an open-field or rain-shelter system on the physiological responses of four Asian pear (Pyrus pyrifolia Nakai) cultivars ('Hanareum', 'Wonhwang', 'Manpungbae', and 'Niitaka') in an organic orchard in 2013 and in 2014. The rain shelter was covered with polyethylene film between 31 March - 4 July each season, then uncovered during the remainder of each growing season. The incidences of fruit disease and insect pests, and fruit quality were measured in 2013. The rain-shelter system increased leaf chlorophyll contents to a SPAD value of 44.0 and rates of CO2 assimilation to 17.0 mu mol m(-2) s(-1) in all four cultivars. It also increased leaf total nitrogen concentrations and dry weights in 'Wonhwang' and 'Niitaka' trees compared to the open field. Freezing temperatures were observed in the open field during flowering. The rain-shelter system resulted in a 10.3% delay in completion of current year shoot extension in all cultivars on 7 August 2014. It also significantly increased fruit yields (22,900 kg ha(-1)), mean fruit fresh weights (582 g), fruit size (94 mm in length and 105 mm in diameter), and total soluble solids contents (12.7 degrees Brix) in 2013 and 2014. The incidence of scab on fruit was reduced by 3.3% in the rain-shelter system in 2013, but scab and rust on leaves and fruit were not completely prevented by this system in September 2014. The incidence of green chafers on leaves was significantly reduced from 23.3% to 51.0% by the rain-shelter system on 15 July 2014. The average income from fruit production in both seasons increased by approx. 138%, 167%, 326%, and 215% for rain-sheltered 'Hanareum', 'Wonhwang', 'Manpungbae', and 'Niitaka' trees, respectively, compared to open-field production.