Plant tissue culture is a relatively new propagation technique started about 50 years ago. It has become a major propagation tool for many plant species, especially for fruit tree rootstocks: apple, pear, cherry, peach, almond, etc. In Europe, the majority of peach and cherry rootstocks are propagated through tissue culture. About 15 to 20 million peach rootstocks are propagated by tissue culture annually. More and more pear, cherry, peach, almond, walnut, and pistachio rootstocks have been propagated by tissue culture in the United States. Even many fruit or nut crops are directly propagated by tissue culture, such as berry crops and hazelnut.
|Apple rootstock in tissue culture. Photo: Yongjian Chang, North American Plants Inc.|
Tissue culture propagation has several advantages:
- Can provide pathogen-free plants.
- Can provide plants with better root systems and uniformity compared to plants propagated from conventional methods.
- Can significantly improve the rooting ability for most rootstocks.
- Can be used to rapidly propagate new selections or cultivars from breeding programs for use in experimental trials and for large-scale production of rootstocks for commercial production.
- Can offer year-round propagation for rootstocks without many seasonal restrictions.
|Apple rootstocks in acclimation tunnel. Photo: Yongjian Chang, North American Plants Inc.|
Tissue culture has played an important role in apple rootstock propagation. During the last few decades, apple tissue culture propagation has been used in many countries, especially on new rootstock development. Rooting ability improvement through tissue culture propagation has been widely used for establishing apple rootstock stool beds for getting high-quality (more roots per shoot) and more productive (more shoots per foot) beds. However, high cost of apple tissue culture was the limiting factor for the extended application of this technology on apple rootstock propagation because most apple rootstocks can be propagated by stool beds or layer beds with much lower cost.
Some of the apple rootstocks with excellent horticultural characteristics are difficult to propagate with conventional methods, that is, SH series apple rootstocks in China. These rootstocks have been propagated by tissue culture for years because they perform poorly in stool beds. Geneva® 41 is another example in the United States. Geneva® 41 may be a good rootstock for replant sites, size control, and cold hardiness, but it is hard to propagate by conventional methods, so tissue culture propagation has been used.
|Tissue cultured apple rootstocks growing in greenhouse. Photo: Yongjian Chang, North American Plants Inc.|
High cost is the major factor limiting the use of tissue culture application on apples. Recently, commercial labs have significantly improved their techniques and reduced the cost of tissue culture propagation, so it is similar to the layer bed production. Tissue culture propagation will play a more important role in rapidly propagating new rootstocks for growers' trials or commercial production.
Yongjian Chang, North American Plants Inc.