Asian Pear Pollination Compatibility

Q. Hi Peter, I have two Asian pear trees. One is a Shinseiki and the other is a Hosui. Both have been in the ground in full sun for going on 5 years. They are 8-9′ tall now and healthy but the Hosui has never set more than a few fruit although it blooms profusely. The Shinseiki is loaded every year. I’ve read the Hosui is the best-flavored Asian pear and the Shinseiki is a good pollinator. What’s wrong with the Hosui? Is there something I can do to get better fruit set? Thanks, Henry Raynor – Puyallup, WA
                                                                                                        
A.  Hello Henry. Nice to hear from one of my “regulars”.  Pollination in fruit trees can be one of the most confounding of concepts for home orchardists.  This is because fruit trees are not always self-pollinating.  On our most common orchard trees (peaches, pears, cherries, apples et. al) the flowers are “complete” which means that both the male and female parts are on one flower. In a self-pollinating tree the pollen with fertilize any flower on the same tree.  Self-infertile trees on the other hand have a built in mechanism that blocks pollen from the same tree from germinating and thereby fertilizing themselves. This is likely an evolutionary strategy to promote out-crossing.  Out-crossing often promotes more vigorous offspring.  There are also shades of gray in between the two extremes and these are usually called “partially self-pollinating”.  When trees are self-infertile they require another cultivar be planted nearby to provide pollen for fertilization. This is because cultivars (from: cultivated varieties) are actually clones.  Therefore self-infertile varieties cannot pollinate each other even if they are physically two separate trees since they are genetically identical.  When selecting two varieties to compliment each other the pollen must be compatible and they must also have overlapping bloom period.  So you were on the right track planting two different cultivars but they are not helping each other to pollinate.  The Shinseiki Asian pear is considered nearly completely self-pollinating whereas Hosui is only partially self-pollinating.  I referenced what is called a pollination chart and found that these two varieties are not listed as pollinators for each other.  This explains why your self-pollinating variety is more fruitful than you partially self-pollinating variety.  The cultivars Chojuro, Yoinashi, Shinko and Korean Giant are all good pollinators for both the trees you have. Adding one of them should bring balance to your orchard. 

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