Grafts of crops on wild relatives as base of an integrated pest management: the tomato Solanum lycopersicum as example. Integrated Pest Management and Pest Control–Current and Future Tactics.

Grafts have been used for a long time to induce pests and diseases resistance on plants. The
first record, related to the vine phylloxera (Daktulosphaira vitifoliae), includes the
European vine grafted on scions of the wild American vine, inducing a permanent
resistance to this pest. After that, several cases of grafts have been carried out on woody
plants; however, the use of grafts in herbaceous plants has been less known, particularly in
American countries.
It is known that the main resistance source becomes from wild plants, particularly wild
relatives. Mexico represents the origin of different crops, such as beans, chayote, pumpkin
and chili. Although the tomato is native from South America, Mexico is considered the
domestication center.
After corn, tomato is the plant with greater genetic manipulation to increase productivity.
There is a general agreement that the most domestication grade of the crops, more
susceptibility presents to pests and diseases. Then, it is not casual that tomato became one
of the most problematic crops in relation to insect pests. Unfortunately, the main control
strategy is based on the use of organ-synthetic compound with the collateral broadly wellknown
problems. According to the current agricultural and environmental contamination
circumstances, it is important to develop less innocuous strategies for pest control, and
vegetal resistance is one of them.
Grafting is one strategy to transfer resistance on crops; however, this strategy should be
more studied with regard to insect pests’ resistance. The wild tomato Solanum
lycopersicum var. Cerasiforme is the nearest relative of tomato crop. It grows at different
regions of México and particularly in the state of Michoacan. The wild tomato is locally
named "tinguaraque", name that we will use in the present manuscript. It is recognized that
tinguaraque presents resistance to whitefly, liriomyza and different hemipteran species.
However, the influence of grafting on the incidence of insect pests has not been precisely
studied as yet, particularly knowing that tinguaraque grow in regions with different climatic
conditions.
Since 2005 we have developed different studies about the tolerance of tinguaraque to
phytophagous insects and its potential as scion in grafts with tomato. The research
questions include:
- Which is the incidence of phytophagous insects on tinguaraque?
- Which is the preference of Bactericera cockerelli for tomato, tinguaraque and grafts
from both?
- How is the incidence of insects’ pest on tomato, tinguaraque and grafts from both
under field conditions?
- Which characteristics present tomato fruits grafted on tinguaraque?
- Which is the response of tomato grafts on tinguaraque at different nutrimental
handling systems?
In field conditions we evaluated the incidence of phytophagous insects on S. lycopersicum
var. Cerasiforme, ecotype Jiquilpan. Results showed low incidence of tomato’s insect pests
on tinguaraque and, particularly B. cockerelli was one of the species with lower incidence.
In order to confirm this observation, we established an experiment including tomato,
tinguaraque and graft from both. Consistently, the insect preferred tomato, graft and
tinguaraque in that order. In field conditions, results were similar and, additionally, lower
numbers of eggs, nymphs and adults were observed in tinguaraque and grafts with regard to
tomato. Complementary observations indicated that tinguaraque and grafts had also lower
incidence of others insect pests, such as liriomyza, aphids and whitefly.
Given the wide variability of conditions where the tinguaraque grows in Mexico, we
considered convenient to evaluate different ecotypes, from temperate regions to warm
places. Results showed a wide variability of responses from the tinguaraque and its grafts
ecotypes, generally with lower incidence of pests, compared to those registered on tomato.
Again, tolerance of tinguaraque and grafts toward diverse insect pests was registered (B.
cockerelli and whitefly). In general, the quality of fruits obtained from tinguaraque was
similar to those produced by tomato ungrafted.
Recent unpublished studies (2010) about fruit yield from tomato grafts under different
conditions of nutritious handling, confirmed that the grafts were less susceptible to the
whitefly, both Bemisia tabaci and Trialeurodes vaporariorum. It is interesting to mention
that unfertilized grafts showed higher production than those chemically fertilized.
Additionally, such grafts presented a production similar to control plants (tomato ungrafted
chemically fertilized). It´s necessary, however to repeat this experiment.
The principal use of horticultural grafts has focused on reducing incidence of soils pests
and diseases, and few have been made with pests on the foliar area. We have found that
grafts with wild relatives of crops can be also useful in the management of important foliar
area pests, such as B. cockerelli and whitefly. Of course, we understand the use of grafting
as part of an integrated pest management. At this moment, we recommend the use of
tomato grafted on tinguaraque in small areas, such as hothouses, orchards of backyard and
organic production.
In agreement with the results obtained at this moment, the grafts of tomatoes from wild
relatives have a high potential as part of integrated pest management programs. Although
little is known about the grafts tolerance to tomato diseases, some observations suggest that
grafts can be tolerant to Rhyzoctonia solani; however, more studies must be implemented.
Given the high variability of ecotypes of tinguaraque in Mexico, presumably with different
levels of tolerance to insect pests and diseases, there is a high motivation to develop more
studies about grafters on tomato. Additionally, considering that Mexico is the origin of
diverse crops, the potential is enormous. Many populations of these wild plants are being
decimated by the growth of the agricultural frontier, but fundamentally from the
indiscriminate use of herbicides. The implementation of grafters will increase the
importance of wild plants species and the relevancy of their conservation will be mostly
valued.