In Japan, mango (Mangifera indica L.) is generally cultivated in small greenhouses in which the height of the ridge is relatively low. Therefore, pot cultivation has been introduced for the purpose of lowering tree height and suppressing tree vigor (Yonemoto, 2008). However, pot cultivation in a greenhouse poses a problem in that the bearing fruit position tends to be higher than with conventional planting in the ground due to the height of the pot (40–60 cm). In addition, grafting in mango occurs at a high position of 30 to 50 cm above the ground (Yonemoto, 2008), which makes the rootstock longer and the fruit position higher.
In ‘Irwin’, the leading mango cultivar in Japan, because whole fruit colored red has high commercial value, lifting of the flower cluster and fruit is performed to improve coloring via exposure to light. Furthermore, to harvest a fully ripened fruit on a tree, the fruit is covered with a bag-shaped net and hung with a string before harvest, so that the fruits do not fall as they mature. Thus, cultivating low tree heights, which bear fruit at low positions, is desirable.
The Aikou cultivar used in this study is a cross-breed between ‘Chiin Hwang No. 1’ as the seed parent and ‘Irwin’ as the pollen parent (Kindai University, 2008), and it is the first mango cultivar bred in Japan. It is characterized by its red skin color, large fruit, and soft, juicy flesh. The introduction of ‘Aikou’ should lead to the expansion of production areas and increased consumption of mango fruit. However, ‘Aikou’ has strong tree vigor, so it is likely to be higher than ‘Irwin’. Furthermore, this cultivar needs more exposure to light for coloring the peel than does ‘Irwin’.
Another problem with pot cultivation is that the rootstock of mango rapidly enlarges, so the interior of the pot tends to become clogged with age. The rootstocks that have been used in Japan are a vigorous Taiwan native strain, and trees grafted onto these rootstocks have strong vigor (Yonemoto, 2008). The underground part also has strong vigor, and enlargement of the underground part proceeds rapidly, such that the pots clog. Tree vigor declines when the roots become clogged, which decreases yield and fruit quality and can lead to death.
Because own-rooted trees have no rootstocks, the primary scaffold branches can be trained at a position closer to the ground, and lower tree height is thus expected. In addition, as own-rooted trees do not have an underground rootstock part to enlarge, it is possible to delay the decline in tree vigor caused by root clogging, and the life span of the tree is thus expected to be prolonged.
This study compared tree height, growth, yield, and fruit quality of own-rooted ‘Aikou’ mango trees propagated using an air layering with trees propagated using a conventional grafting method for 8 years after planting, to assess the practicality of using own-rooted trees for pot cultivation.
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