Micrografting for fruit crop improvement

Abstract

Micrografting is an in vitro grafting technique which involves the placement of a meristem or shoot tip explant onto a decapitated rootstock that has been grown aseptically from seed or micropropagated cultures. Following early experiments of micrografting in ivy and chrysanthemum, the technique has been used in woody species, especially fruit trees. Major work was carried out in different Citrus species for the elimination of various viral diseases. In vitro micrografting has been used for improvement and multiplication of fruit trees as the technique has potential to combine the advantages of rapid in vitro multiplication with the increased productivity that results from grafting superior rootstock and scion combinations. Successful micrografting protocols have been developed for various fruit crops including almond, apple, cherry, chestnut, Citrus, grapes, mulberry, olive, peach, pear, pistacio, walnut, etc. Special techniques have been used for increasing the percentage of successful micrografts with the use of growth regulators, etiolation treatments, antioxidants, higher sucrose levels, silicon tubes, etc. The technique has great potential for improvement and large scale multiplication of fruit plants. It has been used on commercial scale for production of virus-free plants in fruit crops and viroid free plants in Citrus. Micrografting has also been used in prediction of incompatibility between the grafting partners, histological studies, disease indexing, production of disease-free plants particularly resistant to soil borne pathogens and multiplication of difficult to root plants.

In vitro micrografting of lucumo (Pouteria lucuma), Sapotaceae

“…The micrografting technique improved the viability of the explant, although the result was not statistically significant. Likewise, the pretreatment of the scion allowed to select the viable apex and helped their development, which greatly improved the micrografting success especially when very small sized shoot apices were used (Hussain et al 2014). In our study, pre-treatment of scion by immersion in 1.5 mg L -1 BAP improved the viability of the explant, although the result was not statistically significant.…”

“…On the other hand, several techniques have been developed to hold grafts together until fusion takes place. Those techniques include translucent silicon tubing, elastic strip, filter paper bridge, and glass tubing, nylon bands, aluminum foil tubes, dual layer apparatus of aluminum foil and absorbent paper (Hussain et al 2014). In our study, a new technique, which uses copper wires, was tested.…”

“…Wedge or cleft grafting had to be performed to prepare rootstock and scion for micrografting (surface placement method), because it had to be ensured that the thickness of rootstock and the scion material were large enough to allow us to make a wedge on the scion material (Hussain et al 2014), and for the reason that a firm contact between rootstock and scion, with the consequent formation of callus, ensured the success of the process, as has been observed in in vitro micrografting of pistachio (Pistacia vera) on wild pistachio rootstocks (Canan et al 2006). On the other hand, several techniques have been developed to hold grafts together until fusion takes place.…”

“…In general, in vitro micrografting has been reported in many plants such as cashew (Anacardium occidentale) (Thimmappaiah et al 2002), pistachio (Pistacia vera) (Onay et al 2007), olive (Olea europaea) (Revilla et al 1996), almond (Amigdalus communis) (Channuntapipat et al 2003) and cherry (Prunus avium) (Amiri 2006). Reviews on micrografting have been published by Jonard et al (1983), Jonard (1986), Roistacher et al (1976), Navarro (1988), Parkinson et al (1990), Monteuuis (2012) and recently by Hussain et al (2014).…”

“…Micrografting was initially used in herbaceous plants, but then was used in particular on woody species and especially on fruit species; it was modified and improved for increasing the graft success by Murashige et al (1972) and Navarro et al (1975). In general, the technique has great potential for fruit plant improvement and large-scale multiplication, production of pest and systemic disease-free (such as virus, viroids, bacteria and fungi) plants, safe international germplasm exchange and multiplication of plants with problems in root system formation (Hussain et al 2014).…”