Chapter One General Introduction

This chapter aims at introducing our study of the control of the tomato yellow leaf curl disease. It includes an overview of the historical of tomato cultivation and Tomato yellow leaf curl disease in Somalia. It presents the research problem and hypothesis and set objectives as well as the limitations of the study and its significance to the academic writers and to the university.

Chapter One
General Introduction
1.1Origin of Tomato Cultivation in Somalia
All basic cultivated plants were probably derived from wild species. Cultivated plants have undergone extensive modifications from their wild prototypes as a result of the continuous efforts to improve them. The difference between cultivated and wild types are largely in their increased usefulness to humans, due to such factors as yield, quality and reduced shattering of seeds. Through the centuries, people selected from many thousands of plant species the few were most satisfactory to their needs and which, at the same time, were amenable to culture. Primitive people were masters in making these selections, and modern times have added little of basic importance.
There is a scientific hypothesis that in order to find where a food crop originated in the world, you should look for the area where there is the most diversity of that crop growing in the wild. Applying this idea to the tomato, scientists conclude the mountains of Peru in North America were the birth place of tomato.
Keep in mind that there are wild types of tomato, very resemble to the current cherry type (Yaanyo miroodle), and still grown in our country, Somalia, but the above mentioned rule restricts North America to be the ancestral home of our cultivated local cherry type. Our wild tomatoes have leaves and stems much similar to the cherry type except in that they have very, very small and numerous red fruits similar to the neck-beads and are inedible to the humans (Sultan Bube, 2011).The penetration of Portuguese, the conqueror of Mexico, around the 17th century to the coastal areas of east Africa supported to the introduction and distribution of cherry tomato to the east African countries, including Kenya and parts of the northern regions of Somalia, especially those are very close to Kenya.
Locals strongly believe that the migratory birds introduced the tomato seeds from their cultivated zones in Kenya and the peoples at that time saw growing tomato plants under trees in their fields.
Linguistic evidence suggests that the tomato cultivation in Somalia is started by African slaves around the end of the 17th century. The Somali word “Yaanyo” is a modification of the word “Nyanyo”, which is a Kiswahili word used by the Kenyans and most east African clans for tomato.
Unlike the Europeans which considered the tomatoes as poisonous, Somali people urgently took the fruit as a diet, unless very small families considered them as food items for poor people and slaves, and proud from eating them.
In the colonial times, Arabs, Italians and Indians introduced vegetables including tomatoes into Somalia for their daily needs and to a lesser extent for commercial purposes. Improved production practices and crop handling extensively grew among the casual laborers utilized by Italians and Asians in Somalia during the colonial era. Thereafter, the trained laborers were attracted to the tomato cultivation by their profitability. This led to the deletion of the above-mentioned mistaken idea and considered the tomato to be the best vegetable crop used with different starch-containing foods, and used a sauce in many locations in the country. Tomato was not only a welcome food but also became an important source of income for many households living in most regions of Somali country.
The establishment the tomato processing plant (ITOP) around 1970s in Afgoi was the master agent that led to the introduction of productive varieties such as San Marzano and Roma VF in the country, and the mass cultivation of tomato in water-sourced regions in Somalia. Studies conducted on tomatoes at CARS (Central Agricultural Research Station) in the 1980s revealed that the production of tomato has increased at that time and this was due to the selection of high yielding cultivars, such as Roma VF (Abukar, 2004). Prior to the civil strife in Somalia, there were several tomato varieties under cultivation including the following ones:
I. Local Cherry: Small, with tough skin, these are tolerant to drought condition and are mainly grown under flooded land or rain fed cropping systems. They are very tasty and good in making soup. The small-fruited cherry tomato is the pioneer of all the tomato varieties and has been cultivated in Somalia at least in the late of the 18th century in our beloved country, Somalia. Due to their higher seed content, cherry tomatoes has not being used for processing tomatoes, and because of this Somalis named as Yaanyo miroodle. Other Somali descriptions has been found for the cherry type such as Yaanyo shalambod, as it was and still is largely cultivated and adopted in Shalambod and Jennaale areas. Indeed, cherry tomato was resistant to leaf curl disease, but it had been seen that they became affected and susceptible to the infection as their friends. ii. Roma VF and San Marzano: These varieties are exotic, developed originally in Italy. They were introduced in Somalia by U.N Agencies. They are large with good fruit-flesh and good for processing purposes, but susceptible to leaf curl virus. iii. Money-maker: They were introduced for research purposes in Somalia and are characterized with larger and fleshy fruit. They are also susceptible to the Tomato yellow Leaf Curl Virus (TYLCV).
After the collapsing the central government, the tomato factory was looted and its metals were sold as scrap metals. The processing tomato varieties leading Roma VF and San Marzano were lost behind the factory, and the cherry tomato had its role, which is still in extensive use and its cultivation became wide spread in almost all arable lands in our beloved country, Somalia. Currently, it seems that everything goes back in its origin and let us start where we are at the moment and do what we can do to go head and reach the passed by world trip.

1.2 Historical Review of the Control of the Tomato Yellow Leaf Curl
“There is a war going on that began millions of years ago. Although the many generations of soldiers have not changed a great deal in appearance during this time, the tactics and weapons have grown more sophisticated. Each army has won a share of the battles, but the consummate victory has eluded both. Neither side can afford to give up for nothing less than the sustenance of life at stake. The war I refer to is, of course, the war between humankind and certain species of insects, weeds, pathogens, nematodes, rodents, and other pests that daily compete for our crops, gnaw our dwellings, infest our domestic animals or destroy our health” (Kuhr, 1978).
The above statement clearly describes the problem mankind had always to produce sufficient and well-balanced foods. The loss caused by the Tomato Yellow leaf curl Virus (TYLCV) with its vector whitely is not new. It has always a problem of mankind since it is recovered and identified in the eastern Mediterranean more than 70 years ago.
TYLCV causes yellow leaf curl disease in processing and fresh market tomatoes, causing severely stunted plants, premature flower drop, and severely reduced or no fruit set. If plants are infected at an early growth stage, 100% yield loss can occur. TYLCV has devastated tomato production in many parts of the world, eliminating or curtailing tomato production in many areas.
The virus is spread by the sweet potato whitefly (B. tabaci), which can remain viruliferous throughout their entire lifecycle. Since the virus can be acquired and transmitted by whiteflies in minutes, the whitefly vector can rapidly spread the virus over broad geographical areas. Fortunately, the virus is not seed transmitted nor can it be spread by physical contact. Long-distance spread is primarily through movement of infected plants (e.g., tomato transplants) or virus-carrying whiteflies moved in association with plants.
Over the years, it was found that the privileged mode of spreading of the disease was via international trade of tomato and tomato vegetative parts, but it was demonstrated that the green tissue attached to the fruit is very efficient virus reservoir for the local whiteflies.
In Somalia, the virus i.e. TYLCV entered the country with the introduction of the exotic commercial types of tomatoes, such as Roma VF and San Marzano, in 1970s. It was infecting all the tomato varieties cultivated in the country, Somalia, except the local cherry type, Yaanyo miroodle, as it was resistant to the virus attack.
In several instances, the TYLCV became prevalent virus displacing the local related viruses in his family that had previously infecting tomatoes and develop new strains or races adopting to the available conditions. For example, the local cherry type, which was resistant to the Tomato Yellow Leaf Curl virus as mentioned above, became very susceptible to this virus and its disease (A.H.Hirabe 2010). This could be due to the fact that TYLCV is very aggressive and could become prevalent because of better fitness to the host. In addition to the trade impact, the explosion of different biotypes of B.tabaci can explain the worldwide spread of the TYLCV.
Currently, it is known that new strains of the TYLCV and different vector (B.tabaci) biotypes are emerging in the world as well in African countries, like Tanzania and Egypt. In Somalia, there is lack of information on prevailing tomato viruses and their vectors. However, the occurrence of some tomato viruses and their vectors in neighboring countries, together with the lack quarantine measures, and the ability of vectors to move across borders, implies a high probability of Somalia having similar tomato viruses and vectors. The actual information gap on tomato viruses and pests occurring in Somalia is basically due to attribution of tomato crop losses caused by pests and diseases to other production constraints.
Thus, the TYLCV and its whitefly vector became the most limiting factor of the tomato production in Somalia as well in many other tropical and sub-tropical countries throughout the world which often leads to100% yield loss. The management of the disease in tomato production areas is difficult and expensive and the control measurements are focused mainly on the whitefly control and are based mainly on insecticide treatments which have, in turn their limitations to the environment and have been a little help to control the vector as it develops resistance to the chemicals.
One of the best ways to reduce TYLCV damage is to breed plants resistant to both the virus and the vector. Breeding programs for TYLCV-resistant cultivars are based on the transfer of TYLCV resistance genes from wild tomato species into cultivated tomato. However, the progress in the breeding program has been slow, primarily due to the complexity of TYLCV-resistance genetics and the virus-vector-host interactions.
So far and before 1990s, only limited studies have been carried out with the objective of identifying resistance to viruses in Somalia. Most of these studies have been conducted on curly-top virus, which is much resembled to the TYLCV in symptom appearance, but these efforts destructed by moving wind currents that rooted the central government from the Somali environment.
An alternative strategy could be the introduction of new promising varieties which are resistant to TYLCV to the growing region, but this may not available and affordable to the farmers. Instead, they are controlling the disease and the vector with chemical insecticides, which in turn, are not reliable and secure to their effectiveness or may have not the ability to control the insect-pest and the disease.
In general, TYLCV and its whitefly vector made cried by all most all the tomato farmers in the world in various and different manners. Somalia is not an exception. The management and controlling of the disease needs a concentrated action at the international level and Somalia will do its best if Allah wills.

1.3 Statement of the Study Problem
In Somalia, tomato is both a high-value cash crop and an important subsistence vegetable grown mainly by small scale farmers. The ongoing global spread of Tomato yellow leaf curl virus represents a serious looming threat to tomato production in all tropical and temperate parts of the world. It causes a dramatic yield loss to the crop and poses a great threat to commercial tomato cultivation in all most all the countries in the world including Somalia.
The negative effect from the loss of the many important tomato varieties resulted from the demise of the tomato industry, ITOP; farmers in Somalia had another significant problem with their exceptional cherry tomato type threatening its existence and cultivation in the country. Within few years after the collapsing g of the central government in 1991, the local cherry type lost its ability to resist with the tomato leaf curl virus and this became and additional headache to the natural perishability of the tomato crop which the farmers were crying on previously. The disease and its vector may lead to 100% yield loss of the tomato production in Somalia as well as in most tropical and temperate regions of the world.
As you see from above, the problem of the tomato leaf curl disease is not an exceptional one to the stateless Somali country only, but this is a cosmopolitan factor suffering in varying degrees in all most all the developed countries as well. There is no a rule of thumb in the control of this disease and its vector whitefly except the use of virus resistant varieties and the availability of such types of varieties is a limiting factor within the country, Somalia, and therefore, most or the entire tomato fields are extremely susceptible. Another limiting factor is the adoptability of such exotic varieties which may not fit the environmental conditions prevailing in the country, Somalia, and encourage the use of susceptible ones.
Widespread infection of tomato fields with TYLCV would severely impact yields, threatening the livelihood of tomato growers statewide and its control is expensive which increases the production costs of the tomato crop.
Losses from plant diseases can have a significant economic impact, causing a reduction in income for crop producers, distributors, and higher prices for consumers. In response to the demand of the solution of this problem, affordable technologies and management practices must be developed to target the whitefly vector and this research can provide the information needed to deal with the problem. 1.4 Purpose and Objective of the Study
The aim of this study was to improve both the quality and quantity of Somali tomato production through cost-effective management of two-principle researchable constraints Tomato Yellow Leaf Curl Virus (TYLCV) and its whitefly vector, B. tabaci.
The specific objectives designed for this study were: * To assess the effect of the chemical insecticides on the management of Tomato Yellow Leaf curl disease and on the tomato yield. * To compare the yields of the tomato fruits of the treated tomato plants to the untreated ones.

1.5 Research Hypotheses
The following hypotheses were tested in this study: * There is a significance difference in average tomato fruit production per plant between the sprayed tomato and non-sprayed tomato plants. * The chemical insecticides can only minimize the severity and incidence of the disease via lowering the number of the whitefly vectors instead of totally sweeping out the tomato yellow leaf curl disease and its whitefly vector, Bemisia tabaci.

1.6 Significance of the Study
A study that would look at Tomato Yellow Leaf Curl disease in Somalia from a critical vantage point has been lacking so far or did not exist. The existing thesis on the subject matter were written from the angle of the importance of tomatoes have to Afgoi communities, which are usually assumed to be poor farmers lacking applicable recommendations on the control or minimizing the effect of Tomato Yellow Leaf Curl disease at about one quarter of century.
This study, therefore, served as a document of the existing situation among the small tomato producing farmers in Lower Shebelle region, particularly those residing in Afgoi district and its surrounding villages. In addition, since the study was conducted in Afgoi district, where farmers are crying from the loss gained on Tomato Leaf Curl disease, the study could serve as a lesson and the recommendations given could be applicable to other local tomato farmers, based on the experiences of the Afgoi farmers. Lastly, it could also serve as a stepping point for further study of the same problem by some researchers who wish to continue a similar study in the future.
1.7 Assumptions of the Study
Due to the absence of efficient government which may secure and restrict or regulate the efficiency of the chemical insecticides imported from outside the country Somalia, it was not reliable and sure the affectivity of the chemicals to kill the insect pest, whitefly. Therefore, it is assumed that the insecticides in the different markets or those used in the experiment are similar in quality to those used by the farmers in developed countries. However, the chemicals are used experimentally in the appropriate methods & the suitable dosage and on the time suggested by most of the pathological scientists.
In addition to the above, the chemicals in the market mostly are exposed to inappropriate conditions, such as higher temperature and direct sunlight, which indeed lower the efficiency and capacity of the chemicals to kill the insect vector. This was another issue ignored during the research implementation and seems to be uncontrollable.
1.8 Limitations of the study
Although the research was carefully conducted, we are still aware of its limitations.
First of all, the scope of time in which the research is conducted was not enough for us to monitor as we were busy with the class lectures. It would be better if it was done in a longer and efficient time.
Second, lack of available and\or reliable records about the issue of the research in the country, Somalia.
Third, less experience of us about conducting a research like this, as it was the first time according to us doing this project of its kind.
In addition to the above conditions, the state of the country, especially the Mogadishu city which is in a risky and anarchy condition and we could not have access to the frequent movement, if it was possible, between the two regions, the experimental center in Afgoi area and Mogadishu city.