Role of Embryo Rescue Techniques in Fruit Crops
Authors: Anjali Soni and Sunita Dhakar
Division of Fruits and Horticultural Technology
ICAR-Indian Agricultural Research Institute, New Delhi-12
Corresponding author email: anjali00soni@gmail.com

Embryo rescue is one of the successful forms of in-vitro culture techniques that is used to assist in the development of plant embryos that might not survive to become viable plants. This techniques in fruit crops have played an important role in breeding new, early-maturing seedless triploid types as well as obtaining distant hybrids preventing embryo degeneration at early development stages and shortening breeding cycle .

Embryo Rescue Techniques

  • Embryo Culture
The most commonly used embryo rescue procedure is embryo culture, in which embryos are excised and placed directly onto culture medium. Fruit plants is collected prior to the time at which embryo abortion is thought to occur. Since embryos are located in a sterile environment, disinfestation of the embryo itself is not required and careful excision of the embryo is critical to the success of embryo culture.

  • Ovule Culture
To prevent damaging embryos during the excision process or embryos are difficult to excise when very young or from small-seeded species they are sometimes cultured while still inside the ovule. This technique is referred to as ovule culture. As with embryo culture, ovaries are collected prior to the time at which embryo abortion is thought to occur. The ovary is surface sterilized and the ovules removed and placed into culture.

  • Ovary Culture
In ovary, the entire ovary is placed into culture. Ovaries are collected and any remaining flower parts removed. Disinfestation protocols must remove surface contaminants without damaging the ovary. The ovary is placed into culture so that the cut end of the pedicel is in the medium.

Applications of embryo rescue in Fruit crops

  • Shortening of breeding cycles - Embryo culture has also been used to shorten breeding cycles in various fruit crops where effective germination was reduced from years to months by overcoming dormancy.
  • W ide crosses - Development of intergeneric and interspecific hybrids is possible .
  • Seedlessness - Grape -Many seedless grape cultivars are stenospermocarpic i.e., they are characterized by cessation of embryo development after fertilization and failure of seed development. Embryos have been rescued and grown into plants from stenospermocarpic seedless grapes, allowing growth of progeny resulting from the hybridization of seedless with seedless grapes. (Roy et al.,1985).
  • Disease and pest resistance -Some hybrids obtained through embryo rescue have recombined desirable genes like disease and pest resistance in various crops.
  • Rapid testing of seed viability- Embryo culture allows rapid testing of seed viability where seed dormancy can be circumvented. Removal of pericarp and testa from around the embryo removes the source of hormones that inhibit germination and, if all else is in place, allows the embryo to germinate and grow.
  • Germination- Naturally vegetatively propagated plants like bananas produce seeds that do not germinate in nature, probably due to recalcitrant dormancy. These stand to benefit from embryo culture.
  • Prevention of embryo abortion with early ripening stone fruits - Early-ripening varieties of peach, cherry, apricot and plum produce sterile seeds which do not germinate under natural conditions and, eventually, decay in the soil. Seed-sterility here may be due to incomplete embryo-development, so embryo culture helps in germination of such type of fruits.
  • Embryos for propagation/ conservation/ germplasm exchange : Embryos are excellent material for in vitro preservation and propagation. As per IPGRI, Rome, it is compulsory to exchange germplasm of coconut internationally using embryo cultures (otherwise, shipping of whole nuts is cumbersome besides requiring huge cargo-space on flights or ships).
Reference

Roy, S. P., Sahar, N. and Baron, J. (1985). In vitro culture and plant formation from grape cultivars with abortive ovules and seeds. Journal of the American Society for Horticulture Sciencei 110:109–112.




About Author / Additional Info:
I am a Research Scholar at IARI New Delhi