|ISHS Acta Horticulturae 1220: VI International Chestnut Symposium
Studies to determine phenology and pollination in the European × Japanese hybrid 'Colossal' in Michigan orchards
|Authors: ||C. Medina Mora, A.M. Jarosz, D.W. Fulbright|
|Keywords: ||anthesis, female flowers, pollen, pollen timing, pollen application|
Little is known about the phenology of chestnut and the timing of pollination in Michigan-grown chestnuts.
The purpose of this study was to improve our understanding of chestnut phenology, pollination, and its relation to nut set (yield) by conducting both wind pollination (natural), and hand-pollination experiments.
In these experiments, Castanea sativa × C. crenata ‘Colossal’ was selected as the mother tree due to its popularity in Michigan orchards.
Wind pollination of the cultivar ‘Colossal’ was monitored for three years at two orchard sites located in mid-Michigan.
Two cultivars were used as pollinizers of ‘Colossal’, a C. crenata × C. pumila var. pumila ‘Okei’ and C. mollissima ‘Benton Harbor’. Wind pollination was permitted or inhibited by placing bags over flowers or by removing bags from flowers at predetermined times.
Wind pollination of ‘Colossal’ female flowers was initiated on July 2 (2008), June 25 (2009), and June 18 (2010). The highest number of nuts resulted when ‘Colossal’ flowers were continuously exposed to pollen until July 22 (2008), July 5 (2009), and July 2 (2010). To perform hand pollination experiments with ‘Benton Harbor’ or ‘Okei’ pollen, a single catkin was removed from the paternal trees and gently rubbed onto the stigmata of ‘Colossal’ female flowers.
Prior to and after hand pollination, flowers were protected from unwanted pollen by placing bags over the flowers.
In 2009 and 2010, hand pollination experiments were conducted in two orchards. ‘Colossal’ female flowers were pollinated once, twice or three times at pre-anthesis, anthesis and post-anthesis flower development stages.
Results suggested that pollen applied at pre-anthesis and at anthesis produced more nuts than when pollen was applied after anthesis.
Results from the wind-pollination and hand-pollination experiments strongly suggest that the highest ‘Colossal’ nut production is achieved when pollen is available at anthesis.
Anthesis in mid-Michigan is generally between late-June (June 26) and early-July, regardless of the year, and the specific date for optimal pollination fluctuates slightly from year to year.
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