Plant Propogation and Nursery Management

Stock -Scion Relationships

A grafted or budded plant can produce unusual growth patterns which may be different from what would have occurred if each component part of a graftage viz., rootstock and scion was grown separately or when it is grafted or budded in other types of rootstocks. Some of these have major horticultural value. This varying aspect of rootstocks will influence the performance of a scion cultivar or vice versa is known as stock-scion relationship.

A. Effect of stocks on scion cultivars

1. Size and growth habit:

• In apple, 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 remain 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 grape 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 mango rootstocks like Kalapade, Olour have been found to impart dwarfness in the scion cultivars. Guava cultivars grafted on Psidium pumilum are found to be dwarf in stature. ‘Pusa Srijan’ guava rootstock also imparts dwarfness in Allahabad Safeda, a commercial cultivar of guava.
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 Citrus jambhiri rootstock is precocious than those grafted on sweet orange or orange or acid lime rootstocks.
3. Fruit set and yield

• The rootstocks directly influence on the production of flower and setting fruits in oriental Persimmon (Diospyrous kaki cv. Hachiya). When it is grafted on D. lotus, it produces more flowers but only few mature into fruits. However, when D. kaki is used as the rootstock, the fruit set is very high.
• The influence of rootstock on the yield performance of cultivar has been well documented in many fruit crops. Acid limes budded on rough lemon register nearly 70 per cent increased yield than those budded on troyer citrange, Rangpur lime or its own rootstock. Sweet orange var. Sathugudi budded on Kichili rootstock gave higher yield than on Jambhiri or on its own seedling.
4. Fruit size and quality

• Sathugudi sweet oranges grafted on Gajanimma rootstocks produced large but poor quality fruits while on its own roots they produced fruits with high juice content and quality.
• The physiological disorder 'granulation' in sweet orange is very low if on Cleopatra mandarin seedlings, on the other hand, rough lemon seedling stocks induced maximum granulation.
• The physiological disorder black end in Bartlett Pear did not appear if Pyrus communis was used as the rootstock. When Pyrus pyrifolia was used as the rootstock this disorder appeared, affecting fruit quality.
5. Nutrient status of scion

Rootstocks do influence the nutrient status of scion also. Sathugudi orange trees have a better nutrient status of all nutrients in the leaves when it is budded on C. volkarimariana root stock than on its own rootstock or Cleopatra mandarin stocks.

6. Winter hardiness

Young grapefruit trees on Rangpur lime withstand winter injury better than on rough lemon or sour orange. Sweet oranges and mandarins on trifoliate stocks were more cold hardy.

7. Disease resistance

In citrus, considerable variability exists among the rootstocks in their response to diseases and nematodes. For instance, rough lemon rootstock is tolerant to tristeza, xyloporosis and exocortis but is 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 frie-drichsthalianum) resist wilt diseases and nematodes.

8. Ability to resist soil adverse conditions

Among the citrus rootstocks, foliate orange exhibits poor ability, while sweet oranges, sour orange, rangpur lime rootstocks exhibit moderate ability to resist excess salts in the soil. Similarly, in pome fruits, variation exists among rootstocks to resist excess soil moisture or excess boron in the soil. Myrobalan plum rootstocks generally tolerate excess boron and moisture than Marianna plum root or other rootstocks' viz., peach, apricot or almond.

B. Effect of scion on rootstock

1. Vigour of the rootstocks:

In apple, it has been found that if apple seedlings were budded with the 'Red Astrachan' apple, the rootstock produced a very fibrous root system with few tap roots. On the other hand if scion 'Goldenburg' was budded on the seedlings, they produced two or three pronged deep roots without fibrous root system. In citrus, if the scion cultivar is less vigorous than the rootstock, the rate of growth and the ultimate size of the tree is more determined by the scion rather than the rootstocks.

2. Cold hardiness of the rootstock

Cold hardiness of citrus roots is affected by the scion cultivar. Sour orange seedlings budded to 'Eureka' suffered much more from winter injury than the unbudded seedlings.

3. Precocity in flowering

Young mango rootstock seedlings (6 months to one year old) were found to putforth inflorescence when the branches from old trees are inarched which can be attributed to the influence of scion on the rootstock.