**3. Rootstock selection and tomato grafting against root-knot nematode**

Grafting a selected crop variety on to another is based on the genetic attributes of both crop varieties. Farmers select rootstocks with desirable genetic properties, for example, resistance to nematodes, flooding, salinity, extreme temperatures, and increased yield production. Tomato and eggplants are the most grafted plants in the Solanaceous family, although crops of the cucurbitaceous family (melon) are also utilized [17].

watermelons [*Citrullus lanatus* (Thunb.) Matsum and Nakai] as scion and squash (*Cucurbita moschata* Duch.) The watermelon grafting technique was then widely introduced to farmers in Japan and Korea between the 1920s and 1930s; later, the technique was extended to grafting of other vegetable crops *Cucumis sativus* L. [2] and *Solanum melongena* L. in the 1950s [2] and

Vegetable grafting is implored to impart resistance to soilborne pathogens, for example, nematodes [1, 3] and increase yields [3] and tolerance to abiotic stress conditions [4–8].

Tolerance to soilborne diseases is one of the main reasons why vegetable grafting is practiced. Rootstocks are selected based on their tolerance to common vegetable production diseases

Vegetable grafting has been shown to increase fruit yields of vegetables such as tomato and eggplants and enhances nutrient uptake together with improved water use efficiency [3, 12]. An improved water use efficiency and nutrient uptake enables grafted plants to withstand short dry spells and also increase photosynthetic activity. Eggplant rootstocks have the ability

There are cost implications in any grafting venture, and these must be properly considered before beginning a grafting project. A positive or negative net return is mainly dependent on the cost of producing the grafted plants and the prevailing market price for the tomato fruits that will be produced [14]. Falling tomato prices coupled with high input cost for raw materials needed for grafting may result in some negative net returns. The net returns are also sensitive to the vigorousness of the rootstock and that the higher the marketable fruits, the higher the net returns. Costs of grafted plants (including seed, labor, and cost of other materials) have been estimated as \$0.78 per grafted plant for 1000 plants per season in a small nursery [15]. Other investigators have also estimated the production costs of grafted and non-grafted seedlings at \$0.67 and \$0.15

per plant, respectively, in the production of fresh market tomato in Florida, USA [14].

**3. Rootstock selection and tomato grafting against root-knot** 

Generally, labor cost represents a small proportion of the total cost of grafting, and the majority of the cost goes into the purchase of root stock seeds that are specially bred and forms 36% of the total cost [16]. However, apart from the cost of seeds, other inputs such as grafting clips

Grafted transplants are more expensive to produce per plant than nongrafted plants. Therefore, a lower cost of rootstock can easily boost the rate at which farmers adopt this technology [15].

Grafting a selected crop variety on to another is based on the genetic attributes of both crop varieties. Farmers select rootstocks with desirable genetic properties, for example, resistance

caused by *Verticillium*, *Phytophthora*, *Fusarium*, and nematodes [3, 9–11].

to withstand flooding conditions for several days [13].

**2. Grafted tomato plants and cost implications**

and building a humidity chamber serve as additional cost.

**nematode**

then to *Lycopersicon esculentum* Mill [1].

4 Recent Advances in Tomato Breeding and Production

The most common rootstocks used for commercial tomato grafting are hybrids (F1) or interspecific hybrids, which have been specifically bred for resistance against pathogens and other diseases such as nematodes, *Verticillium* wilt, and *Fusarium* wilt. Hybrids are produced by crossing selected tomato varieties with other wild *Solanum* species with the genetic ability to offer resistance to specific diseases and pathogen infection [18].

In Europe, tomato hybrids are used as rootstocks compared to other *Solanum* spp., because of their high level of genetic improvements [17]. There are other plants that share the same family with tomato (*Solanum torvum, S. aethiopicum*, and *S. macrocarpon*); these can serve as rootstocks for their tolerance to waterlogged and drought conditions, *Fusarium* wilt, and root knot nematode infestation [13]. Most eggplant lines utilized will graft successfully with tomato lines. Rootstocks selected should be resistant to bacterial wilt (caused by, for example, *Ralstonia solanacearum*) and other soilborne diseases. The Asian Vegetable Research and Development Centre (AVRDC) recommends eggplant accessions EG195 and EG203, which are resistant to flooding, bacterial wilt, root-knot nematode (*Meloidogyne incognita*), tomato *Fusarium* wilt (caused by *Fusarium oxysporum* f.sp. *lycopersici*), and southern blight (caused by *Sclerotium rolfsii*) [13]. Grafting of a tomato variety "Pectomec" onto *S. aethiopicum* and *S. macrocarpon* in the University of Ghana Farm, Legon provided resistance to *Fusarium* wilt caused by *Fusarium oxysporum*; however, nongrafted tomato plants had a disease intensity of 46% (**Table 1**) and were highly diseased [19] (**Figure 1**). Grafting success of the tomato variety "Pectomec" onto *S. aethiopicum*, *S. lycopersicon "*Mongal F1," and *S. macrocarpon* was poor with the rootstock *S. lycopersicon "*Mongal F1" [19] (**Table 2**).

An ideal rootstock for tomato grafting should not only be resistant to pathogens, but also have high compatibility with the scion of tomato, with the ability to express a high level of vigorousness and resistance to pest and diseases. Rootstocks with very high levels of vigorousness compared to the scion may result in the tomato grafts being more vegetative with less fruit yield and quality [20]. Rootstocks selected should be resistant to bacterial wilt and other soilborne diseases. The tomato line (Hawaii 7996) has a high level of resistance to bacterial wilt and *Fusarium* wilt and is a recommended variety by AVRDC [13].

In developing countries, the use of tomato hybrids as rootstocks is limited because of the costs of imported hybrid seeds. Therefore, the use of eggplants as rootstocks is the most common


NRP = Number of recording plants; NDRP = Number of diseased recorded plants; DI = Disease intensity (%); P/SA = Pectomech grafted onto *Solanum aethiopicum*; P/SM = Pectomech grafted *Solanum macrocarpon.* Agyeman [19].

**Table 1.** *Fusarium* wilt disease intensity of grafted and nongrafted tomato plants onto solanum rootstocks.

as controls. Results revealed that root damage or galling significantly reduced by 81% in the hybrid rootstocks, compared to the controls. There were, however, no clear correlations

Grafting: An Effective Strategy for Nematode Management in Tomato Genotypes

http://dx.doi.org/10.5772/intechopen.82774

7

Tomato grafting onto a resistant rootstock of wild brinjal (*S. sisymbriifolium*) under farmers' field conditions at Hemza of Kaski district against root-knot nematodes was undertaken. The root system of the grafted plants was free from gall formations; however, nongrafted plants had an average of 7.5 gall index (GI). Fruit yields significantly (P > 0.05) increased by 37% in the grafted plants compared with the nongrafted plants [23]. Eight wild *Solanum* rootstocks and two tomato hybrids were screened against root-knot nematode infection. Results revealed that the *S*. *sisymbriifolium*, *Physalis peruviana,* and *S. torvum* had the least galls per 10 g root (6, 5, 5) and females per g root (2, 2, 2), respectively, and showed the highest level of expression of phenolics and defense-related enzymes viz., peroxidases, polyphenol oxidases, phenylalanine ammonia lyase, and acid phosphatase from leaf samples, compared to the susceptible tomato scion (US-618) [24]. In a previous study, two garden egg rootstocks *S. torvum*

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 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

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

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

between root galling and total tomato yields [15].

**4. Grafting techniques**

with age ranging from 3 to 4 weeks [26].

place with the help of a grafting clip or tube.

incision made in the rootstock.

and *S. aethiopicum* were poor hosts of *M. javanica* and *M. incognita* [25].

**Figure 1.** Symptoms of fusarium wilt disease of tomato variety "Pectomech". (A) Advanced symptoms (browning and wilting of leaves—red arrow), (B) Browning of tomato vascular tissues (red arrow).


P/M = Pectomech grafted onto *Solanum lycopersicon "*Mongal F1"; P/SA = Pectomech grafted onto *Solanum aethiopicum*; P/SM = Pectomech grafted onto *Solanum macrocarpon*. Agyeman [19].

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

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.

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 nongrafted plants.

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 as controls. Results revealed that root damage or galling significantly reduced by 81% in the hybrid rootstocks, compared to the controls. There were, however, no clear correlations between root galling and total tomato yields [15].

Tomato grafting onto a resistant rootstock of wild brinjal (*S. sisymbriifolium*) under farmers' field conditions at Hemza of Kaski district against root-knot nematodes was undertaken. The root system of the grafted plants was free from gall formations; however, nongrafted plants had an average of 7.5 gall index (GI). Fruit yields significantly (P > 0.05) increased by 37% in the grafted plants compared with the nongrafted plants [23]. Eight wild *Solanum* rootstocks and two tomato hybrids were screened against root-knot nematode infection. Results revealed that the *S*. *sisymbriifolium*, *Physalis peruviana,* and *S. torvum* had the least galls per 10 g root (6, 5, 5) and females per g root (2, 2, 2), respectively, and showed the highest level of expression of phenolics and defense-related enzymes viz., peroxidases, polyphenol oxidases, phenylalanine ammonia lyase, and acid phosphatase from leaf samples, compared to the susceptible tomato scion (US-618) [24]. In a previous study, two garden egg rootstocks *S. torvum* and *S. aethiopicum* were poor hosts of *M. javanica* and *M. incognita* [25].
