New Zealand Journal of Crop and Horticultural Science abstracts
Chemical thinning of Asian and European pear
with ethephon and NAA
STEVEN J. McARTNEY
The Horticulture and Food Research
Institute of New Zealand
Canterbury Research Centre
P.O. Box 51
Lincoln, New Zealand
GILBERT H. WELLS
Plant Science Department
P.O. Box 84
Lincoln University
Canterbury, New Zealand
Abstract In the 1989/90 season 6-year-old Lincoln-canopy
trained `Nijisseiki' and `Hosui' Asian pear (Pyrus pyrifolia Nakai)
trees were part-tree sprayed with 400 ppm ethephon ((2-chloroethyl)phosphonic
acid), applied 15 days after full bloom (DAFB) or hand thinned (leaving one
fruitlet at each fruiting site 56 DAFB) in a split-plot design with ethephon
applied to main plots and hand thinning to subplots. Ethephon reduced fruit set
of `Nijisseiki' and `Hosui' by 37 and 15%, respectively, removing on average
one `Nijisseiki' fruitlet per cluster. Independently of hand thinning, ethephon
reduced mean fruit weight of `Hosui' at harvest by 34 g (21%), but `Nijisseiki'
was unaffected. Hand thinning increased fruit weight of `Nijisseiki' and
`Hosui' at harvest by 19 g each (25 and 13%, respectively), only in the absence
of ethephon application. Ethephon and hand thinning each increased return bloom
of `Nijisseiki' whereas only hand thinning increased return bloom of `Hosui'.
In the same season, a whole-tree spray of ethephon (400 ppm applied 15 DAFB)
increased fruit set of `Doyenne du Comice' European pears (Pyrus
communis L.) by 51%. In the 1990/91 season, ethephon applied at 400 ppm 15
DAFB reduced fruit set and fruit weight at harvest, and increased the incidence
and severity of flesh spot decay of `Nijisseiki' fruit, when assessed after 12
weeks of storage at 2deg.C. Ethephon also increased return bloom. In contrast
naphthaleneacetic acid (NAA) (7.5 ppm, 15 DAFB) had no effect on fruit set or
fruit weight, but reduced flesh firmness at harvest by 1.96 N (6%). In a second
experiment in 1990/91 ethephon was foliage applied to Lincoln-canopy trained
`Nijisseiki' trees 15 DAFB at 0, 200, 400, 600, or 800 ppm a.i. Fruit set was
significantly reduced in proportion to the ethephon concentration with 800 ppm
reducing fruit set by 62% compared to the nil treatment. Increasing ethephon
concentrations significantly decreased mean fruit weight and flesh firmness at
harvest, and significantly increased fruit soluble solids concentration and
seed number. The incidence and severity of the fruit disorder, flesh spot
decay, increased significantly in proportion to the concentration of ethephon
when assessed after 12 weeks of storage at 2deg.C. Ethephon at both 600 and 800
ppm increased the area of individual spur leaves whereas neither shoot leaf nor
spur leaf number were affected. Specific leaf weight (mg/cm2) was
increased irrespective of ethephon concentration. Ethephon significantly
increased return bloom the year after treatment by an average of 52%.
Keywords ethephon; NAA; chemical thinning; pear; Asian pear;
nashi; Pyrus pyrifolia; European pear; Pyrus communis; Lincoln
canopy; fruit set; fruit weight; flesh spot decay; soluble solids; return
bloom
New Zealand Journal of Crop and Horticultural Science, 1995, Vol. 23:
73-84
0114-0671/95/2301-0073 $2.50/0 (c) The Royal Society of New Zealand
1995
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