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Trifoliate Scientific name: Poncirus trifoliata Origen: China Last update: August 2008
Trifoliate is a citrus relative with distinct characteristics. The main one is the leaf blade divided into 3 folioles hence the name trifoliate. There are records of its utilization as a citrus rootstocks from the beginning of the first millennium in China, where it originated. As opposed to common commercial citrus varieties, Trifoliate trees become dormant during the winter, lose their leaves, and become significantly more cold resistant. Trifoliate's habitat, therefore, extends to higher latitudes than that of oranges, tangerines, and lemons. As a citrus rootstock, trifoliate typically induces slower growth to the scion. Vegetative cycles are well defined, plants entering a resting condition earlier in the fall and starting to grow later in the spring. Final tree size is normal but can with time easily exceed that of more vigorously growing rootstocks. There are trifoliate variants, however, that induce smaller tree sizes. Flying Dragon trifoliate, for instance, is considered a dwarf rootstock, typically reducing canopy size by 50% or more. As a result of the slow growth and the dwarfing variants, trees on trifoliate are planted at higher densities. Trees on trifoliate are considerably susceptible to drought. Its international use typically occurs with irrigation. In southern Brasil, however, trifoliate is the most common rootstock and it is cultivated without irrigation. Drought susceptibility can help when continuous flushing is not desirable for attracting more pests and disease vectors. In addition, trees are less susceptible to late freezes and fruit maturity is delayed. Productivity of trees on trifoliate is proportional to their size. It is common practice to increase tree density in an area in order to obtain higher productivity in the early years of the orchard on trifoliate. Severe drought during the spring bloom, however, may reduce crops in certain years. Trees on trifoliate begin to bear fruit at 2 to 3 years of age and have their first commercial crop usually when 4 years old, similarly to what happens with more vigorous rootstocks. Fruit quality is excellent on citrus scions over trifoliate. Sugar levels are high and their combination with slightly higher acids give excellent flavor to the fruit. Sugar yields per fruit or box of fruit is typically higher than those of more vigorous rootstocks. Fruit size can be somewhat smaller in heavy crop years, causing problems in the fresh fruit market for small fruit size varieties like Natal. Fruit rind is smooth, well colored and of good resistance to harvesting and shipping. Pera sweet orante is not compatible with trifoliate-type rootstocks. There are other varieties with some record of incompatibility with trifoliate as Murcott, Seleta, and true lemons. As a result, trifoliate use must be carefully analyzed for local conditions and varieties. No problems have been reported in Brasil for Valencia, Hamlin, Natal, Folha Murcha, Westin, Rubi, Americana, Ponkan, Bahia, Lima or Tahiti. One of the most important characteristics of trifoliates are their resistance to foot and root rot. This makes them viable alternatives for heavy and humid soils. As a result, it is common to say that they are rootstocks for low and humid areas. However, their tolerance to water accumulation in the soil is similar to that of other rootstocks. They only withstand a few days with free water at the surface. After the terrain dries out, however, they usually have a better survival due to their resistance to soil diseases. They are also resistant to citrus nematode, Tristeza and sudden death. Trifoliates are susceptible to exocortis and citrus blight. Exocortis is avoided by using disease free budwood. Trifoliate is frequently used in genetic breeding to obtain new citrus rootstocks . This occurs due to its resistance to foot rot and nematodes, and the fact that hybrid seedlings can be easily distinguished by the trifoliated leaves, which is a dominant genetic characteristic. Trifoliate and some of its hybrids like Swingle citrumelo and the citranges Carrizo and Troyer are the most utilized rootstocks world wide. Their alternatives, Sour orange, Rangpur lime, and Rough lemon are being replaced due to disease susceptibility. Trifoliates can be grouped into the large flowered and the small flowered types, both utilized commercially. The large flowered types have a more upright growth with less lateral branching, and are more vigorous. Flying Dragon trifoliate distinguish itself as a dwarfing rootstock. Its numerous curved thorns and curved branches are vey characteristic. Its use as rootstock has increased recently for Tahiti lime as a scion. It also holds potential as a rootstock for tangerines whereas it induces too small plants for oranges. Among oranges, Pera sweet orange is the mosto vigorous when grown on Flying Dragon. Even though Pera's incompatibility with trifoliates is not so pronounced with Flying Dragon, more research is needed for larger scale utilization. |
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