Importance of Rootstock
The rootstock is the lower portion of the graft, which develops into the root systems of the grafted plant. It may be a seedling, a rooted cutting, or a layered or micro-propagated plant.
Importance of rootstock
1. Size and growth habit
- In apples, rootstocks can be classified as dwarf, semi-dwarf, vigorous, and very vigorous rootstocks based on their effect on a scion cultivar.
- If a scion is grafted on dwarf rootstocks (e.g. M.9), the scion grows less vigorously and remains dwarf only. On the other hand, if the same scion is grafted on a very’ vigorous rootstock (e.g. M2) the scion grows very vigorously.
- In citrus, trifoliate orange is considered to be the most dwarfing rootstock for grapefruit and sweet oranges. On the other hand, in mango, all plants of a given variety are known to have the same characteristic canopy shape of variety despite the rootstocks being of seedling origin.
- But the rootstocks of mangoes like Kalapade, Olour provide dwarfism in scion varieties. Guava varieties grafted on Psidium pumilum are found to be dwarf in stature. The ‘Pusa Srijan’ guava rootstock also imparts dwarfism to the commercial cultivar of guava Allahabad Safeda.
2. Precocity in flowering and fruiting
- The time taken from planting to fruiting i.e., precocity is influenced by rootstocks. Generally, fruit precocity is associated with dwarfing rootstocks and slowness to fruiting with vigorous rootstocks.
- Mandarin, when grafted on Jambhiri rootstock is more precocious than those grafted on sweet orange or orange or acid lime rootstocks.
3. Fruit set and yield
- In oriental persimmon (Diospyros kaki Hachiya), rootstock directly influences flower formation and fruit set. When it is grafted on D. lotus, it produces more flowers but only a few mature into fruits. However, when Diospyros kaki is used as a rootstock, the fruit set is very high.
- The effect of rootstock on the yield performance of many fruit cultivars has been well documented. Acid lime on rough lemon increases the yield by about 70 percent compared to Troyer citrange, Rangpur lime, or budding on its own rootstock. Sweet orange variety Sathuguri grafted on Kichili rootstock gives higher yield as compared to Jambhiri or own rootstock
4. Fruit size and quality
- Sathuguri sweet orange grafted onto Gajanimma rootstock produces larger but poorer quality fruits while those grafted on their own rootstock produce higher juice content and quality fruits.
- Physiological disorder ‘granulation’ is very less in sweet orange on Cleopatra mandarin rootstock, on the other hand, rough lemon rootstock induced maximum granulation.
- Physiological disorder black end is not observed when Pyrus communis rootstock is used in Bartlett pear. When P. pyrifolia is used as rootstock, the appearance of this disorder affects the quality of the fruits.
5. Nutrient status of scion
Rootstocks also affect the nutritional status of the scion. The leaves of Sathuguri sweet lime tree have a better nutrient status of all nutrients when grafted on C. volkarimariana rootstock as compared to its rootstock or Cleopatra mandarin rootstock.
6. Winter hardiness
Grapefruit scion on Rangpur lime rootstocks withstands winter injury better than rough lemons or sour oranges. On trifoliate rootstock, sweet orange, and mandarin are more cold tolerant.
7. Disease resistance
In citrus, considerable variability exists among rootstocks in their response to diseases and nematodes. For example, the rough lemon rhizome is tolerant to ttristeza, xyloporosis and exocortis, but susceptible to gummosis and nematode. On the other hand, Troyer citrange is tolerant to gummosis but susceptible to exocortis virus disease. Similarly, guava varieties grafted on Chinese guava (Psidium friedrichsthalinum) rootstock are resistant to wilt disease and nematodes.
8. Ability to resist soil adverse conditions
In citrus rootstock, trifoliate orange shows poor tolerance, while Sweet orange, Sour orange, and Rangpur lime rootstock show a moderate ability to withstand excess salt in the soil. Similarly, in pome fruits, variation exists between rootstocks to resist excess soil moisture or excess boron in the soil. Myrobalan plum rootstocks generally tolerate more boron and moisture than Mariana plum rootstocks or other rootstocks such as peaches, apricots, or almonds.