**4. Grafting techniques**

method, of choice with *S. torvum, S. macrocarpon,* and *S. aethiopicum* being the most selected eggplants [21]. In rootstock selection, the eggplants are exposed to the biotic agent in pot or field evaluations, and tolerant or resistant rootstocks are selected for grafting experiments.

P/M = Pectomech grafted onto *Solanum lycopersicon "*Mongal F1"; P/SA = Pectomech grafted onto *Solanum aethiopicum*;

**Figure 1.** Symptoms of fusarium wilt disease of tomato variety "Pectomech". (A) Advanced symptoms (browning and

**Rootstocks Number of grafted plants Graft success Percentage (%) graft success**

P/M 196 2 1 P/SM 196 184 94 P/SA 196 185 94

wilting of leaves—red arrow), (B) Browning of tomato vascular tissues (red arrow).

P/SM = Pectomech grafted onto *Solanum macrocarpon*. Agyeman [19].

6 Recent Advances in Tomato Breeding and Production

**Table 2.** Grafting success of Pectomech onto three *Solanum* rootstocks.

In a grafting study by Owusu et al. [22], against root-knot nematodes, five tomato cultivars were selected with "Big Beef," "Celebrity," and "Jetsetter" being resistant to *Verticillium* wilt, *Fusarium* wilt, nematodes, and tobacco mosaic virus (VFNT), which served as the nematoderesistant rootstocks, and "Tropimech" (VF) and "Power" (locally grown nematode-susceptible cultivar) served as scions. Grafted plants had the least nematode populations in the plant house. In field experiments, nematode population levels were lower in "Power" that had been grafted on Celebrity, Jetsetter, and Big Beef rootstocks, compared to self-grafted or ungrafted "Power". Fruit yields were also higher in the grafted plants utilizing resistant rootstocks than

In another study, grafting for root-knot nematode management in heirloom tomato production was undertaken. Susceptible heirloom tomato cultivars (*S. lycopersicum* "Brandywine" and *S. lycopersicum* "Flamme") were grafted onto two hybrid rootstocks (*S. lycopersicum* "Multifort" and *S. lycopersicum* "Survivor"); the non-grafted and self-grafted plants served

nongrafted plants.

A successful grafting technique is one that would unite the scion and rootstock and enable both sections to grow together as a composite plant. The scion could be a small piece of shoot with several buds or a single bud that has been removed from an existing plant. The rootstock on the other hand forms the lower portion of the graft that forms the plant's root system.

Several grafting techniques are used by farmers for various tree crops and vegetable production generally. In grafting of vegetables, methods such as the splice, whip and tongue, hole insertion, and pin and cleft grafting methods can be used. However, the splice/tube grafting and cleft/wedge grafting are most commonly used because of the relative ease and strong vascular connection formed between scion and rootstock. It can also be used on seedlings with age ranging from 3 to 4 weeks [26].

With the splice grafting method, slanting cuts are made on both the scion and the rootstock at an angle of 45°, and the cut surfaces are then joined together to ensure the cambium layers of the scion and the rootstock, which are properly aligned. The joined surfaces are held firmly in place with the help of a grafting clip or tube.

The cleft graft method on the other hand, involves making a clean horizontal cut on the rootstock 5 mm below the cotyledon; a 4-mm vertical incision is then made in the middle of the root stock. The scion is then sharpened in the form of a wedge and gently inserted into the incision made in the rootstock.

The selection of a particular grafting method or technique depends on the skill of the person carrying-out the grafting and the ease with which the technique can be carried out. Other factors such as the type of vegetable crop and the sowing period of the rootstock and the scion are also considered. For instance, some farmers prefer using the whip and tongue technique when grafting cucumbers because the seedlings of cucumber are large (hypocotyl length and diameter), making the grafting process easy [27].

The tube grafting method also has a high percent graft rate. The grafting of two tomato cultivars ("PG3" and "Beaufort") using the tube and the cleft graft methods resulted in a high-percentage graft rate (79–100%), an indication of the suitability of both methods for tomato grafting [28].
