Tomato breeding Introduction Tomato is one of the

Tomato breeding

Introduction • Tomato is one of the most widely grown vegetables in the world and has become popular within the last six decades.

• The tomato belongs to the Solanaceae family. • The tomato was classified by Miller (1754) as Lycopersicon esculentum and renamed by Child (1990) and Peralta and Spooner (2006) as Solanum lycopersicum. • Tomato is a diploid species with 2 n = 2 x = 24 chromosomes.

• The tomato has passed from uncertain acceptance to its arrival in Europe to occupying first place among horticultural crops at the present.

• Worldwide production of tomatoes reached 122 million tonnes in 2005 (FAOSTAT data, 2005).

• Asia, producing 50% of the total, Europe ranking as the second (17. 5 %), followed by Central and North America (12. 3 %), • China is the main producer of tomato, followed by the US, Turkey, India and Italy.

• It is grown in small home gardens, farm gardens and market gardens for fresh consumption as well as for processing purposes. • It is consumed raw, cooked or processed as puree, ketchup and sauce.

• Although a ripen tomato has 94 per cent water, being a good source of vitamin A and B and an excellent source of vitamin C, it has a good nutritive value. • It is very appetizing, removes constipation ( )ﻳﺒﻮﺳﺖ and has a pleasing taste.

• Tomato was cultivated and consumed in Mexico well before the arrival of the Spanish.

• Its introduction and diffusion in Europe were accompanied by a trans-domestication which developed different types associated with new uses and growing systems.

• As a result, an increase in yield and fruit quality relative to the new uses took place during this period.

• More recently, the exploitation of 1) heterosis, 2) the development of cultivars adapted to processing, and 3) the exploitation of extra-specific variability, especially for resistance to biotic and abiotic stresses, have given rise to the development of current varieties.

• In spite of the considerable improvement obtained to date, the application of new biotechnological tools offers the promise to address new objectives technically unattainable until now.

• One new biotechnology that may prove to have the greatest impact is molecular markers, which allow, among other things, marker-assisted selection.

• The identification, isolation and cloning of specific genes has permitted the development of transgenic crops.

Origin, Domestication and Diffusion • The centre of origin of the genus Solanum section Lycopersicum (formerly genus Lycopersicon) is the Andean region that includes parts of Colombia, Ecuador, Peru, Bolivia and Chile. • All tomato wild relatives are native to this area (Rick, 1973; Taylor, 1986).

• The word tomate, introduced into the Spanish language in 1532, comes from the word tomatl and it was applied in a general manner to plants bearing spherical fruits or berries, with many seeds and juicy flesh.

• When the expression tomatl or tomato was used, it referred to any one of these species or to the most popular at the time, the “milpero”, or husk-tomato (Physalis philadelphica).

• There are some points about which we have a reasonable degree of certainty (Rick, 1976, 1978). 1 -The cultivated tomato had its origin in the New World. It was unknown in Europe and the rest of the Old World before the discovery of the Americas.

2 -The cultivated tomato had reached a certain level of domestication before being taken to Europe and Asia. 3 -The most likely ancestor of tomato is the wild cherry tomato, formerly Lycopersicon esculentum var. cerasiforme (Dun. ) Gray.

• This species is spontaneous throughout tropical and subtropical America and has spread throughout the tropics of the Old World.

• The place where the domestication took place has been a controversial topic. • Some state domestication took place in Peru, as it was introduced in Italy with the names of Mala peruviana or Pomi del Perú (Candolle, 1883; Luckwill, 1943).

• However, it is known that it was consumed only sporadically in the Incan Empire, no remains of tomato have been found in archaeological sites in the Andean region where remains of other crops have been found. • Therefore, no clear evidence supports this hypothesis.

• Most of the evidence supports Central American domestication, with Mexico as the probable region of domestication.

Varietal Groups • Tomato Varieties for Fresh consumption • Tomato Varieties for Processing

Tomato Varieties for Fresh consumption • Tomatoes for fresh consumption obtain high prices in the market and the new hybrid varieties are high yielding. • The varietal types are adapted, in many cases, to greenhouses and long periods of cultivation and harvest, which allows a monetary return to growers

Breeding objectives • In the case of tomato for fresh consumption, seed producer, grower, carrier from the field, storekeeper, and carrier to the retailer, retailer and consumer has specific requirements demanding specific characteristics of the varieties.

• The characteristics required for a variety for fresh consumption are: • open growth habit, • high yield, • earliness, • external quality of fruits (shape, colour, homogeneity), • internal quality of fruits (flavour, sweetness, juiciness), • long shelf life, • adaptation to growing systems and • resistance to biotic and abiotic stresses.

• For greenhouse cultivation, other characteristics are required, such as: • adaptation to long harvesting periods, • not excessively compact plants and • adaptation to low temperature and light intensity.

• Recently, the cultivation of cluster tomato types, also called truss tomatoes or on-thevine tomatoes, has increased. • Cluster types require some additional attributes such as uniformity of size and ripening within the cluster and maintaining a fresh green calyx and vine after harvest.

A) Cherry, B) Cocktail pear-shaped, C) Canary for cluster harvesting,

D) Beefsteak, E) Marmande,

Beefsteak

F) Pepper, G) tomato for processing, long pear shaped and H) tomato for processing, square shaped

MONEYMAKER

Cocktail tomatoes

Tomato Varieties for Processing • Tomatoes for processing differ from tomatoes for fresh consumption in many aspects. • The processing product is bought by the industrial and does not obtain the prices that tomatoes for fresh consumption do.

• To be profitable, the production costs must be drastically reduced, turning the tomato from a horticultural crop into an industrial crop with mechanized harvesting.

• This requires the plant and fruit to be adapted to this type of harvest and therefore the fruits possess some specific characteristics to facilitate a high profit in the industrial process.

• The producer-consumer chain includes industrial processing in this case. • Some requirements are common to all the agents of the chain, but many are specific.

The characteristics needed in the tomato for processing are : • compact growth habit of the plant, • grouped flowering and ripening, • presence of the recessive jointless gene which facilitates the detachment of the fruit without the peduncle, • homogeneity of fruit shape and size,

compact growth habit of the plant

grouped flowering and ripening

Jointless gene

• high consistence, • resistance to cracking, • lack of scar at the point of insertion with the calyx, • lack of puffiness, • flexible skin to facilitate peeling, • thick and firm pericarp, • round, smooth plumb- or pear-shaped fruits and red, uniform colour.

Thick pericarp

Tomato color forming

• The fruits must also have certain other characteristics related to processing quality: • high viscosity and dry extract, • p. H values between 4. 2 and 4. 4 and • high values of total soluble acids.

• There are two main types of processed products: • tomato concentrate and • whole peeled tomato

• Shape requirements are stricter for whole peeled. • pear-elongated, pear-oval or cylindricshaped fruits being more suitable, as these tomato, small-sized, pear, more stylized shapes facilitate peeling.

• For processing two main varietal types can be found, depending on the requirements are mainly in shape and size of the fruit.

• The size can vary between 60 and 100 g. or even smaller for whole canned. • Varieties for paste are less restrictive if shape and size of fruits. • Squared, oval and round fruits are admitted and the size can vary between 60 and 130 g.

Necessities of the processor, growers and consumers and some associated breeding objectives for processing

Genetic Resources • The first source of variability used for tomato breeding was intraspecific variability. • Genes such as the sp (self pruning) gene, which endows the determinate plant growth habit, and the nor (non-ripening) and rin (ripening inhibitor) genes, which determine dramatic alterations in the ripening process, come from S. lycopersicum.

• But this variability was not sufficient to solve diseases nor to improve some aspects of the organoleptic and nutritional quality of the fruits.

• This led to the search for new sources of variation in wild species. • Wild relatives of tomato have been a valuable source of genes of interest for tomato breeding.

solanum habrochaites solanum chillense solanum cheesmanii solanum hispidum

Characteristics of interest of wild tomato relatives in tomato breeding

Major Breeding Achievements • 1) Breeding for Yield • Yield increases have been obtained directly, by increasing the harvest index, • and also indirectly, by improving the potential production through the resistance or tolerance to biotic or abiotic stresses.

• The harvest index has been increasing until reaching, in some cultivars for processing, values of ½ and even up to 3/5 (fruits/vegetative part), which are considered optimal.

• In tomato for fresh consumption, these values are lower, but they tend to come near to those of industry.

• This is due to the correct combination of the different components of yield: • truss number, • number of flowers per truss, • number of fruit set and • fruit weight. • Thus, varieties that produce up to 15 kg/m 2 and with a high percentage of commercial yields have been developed.

2) Breeding of Tomato for Processing • Breeding for mechanized harvesting was started almost in 1943. • The first objectives set by breeders for mechanical harvest were greater firmness, to protect the fruit from machine damage, and a plant type with a very short fruit set period to simultaneously produce a high percentage of ripe fruits.

• VR 145 (resistant to verticillium wilt and fusarium wilt) was the first cultivar for machine harvest to achieve widespread use, reaching a record in harvested area in California in 1962. • Selections made from this cultivar were the most cultivated during more than 10 years.

3) Exploitation of Wild relatives in Tomato Breeding: Introgression of Genes of Resistance • In vitro culture techniques facilitated the hybridization of tomato and facilitated the introgression of genes of resistance. • This allowed the exploitation of all the potential of the wild relatives of tomato.

Genes of resistance to the most important diseases of tomato.

Gray Leaf Spot on Tomato

Early blight on tomato

Tomato Spotted Wilt Virus on Tomato

4) Development of Cultivars Adapted to Abiotic Stresses • 4. 1 Salinity • The cultivated tomato is classified as being “moderately sensitive” to salinity. • It tolerates an EC (electric conductivity) of the saturated soil extract up to about 2. 5 d. S m-1 without any yield reduction.

• Salinity affects different processes of plant life, mainly the percentage and speed of germination. • Salinity also slows tomato shoot growth, and both stem and leaf dry weights are diminished in saline conditions.

• At low ECs, yield reduction is caused mainly by a reduction in the average fruit weight, • while at high ECs the declining number of fruits explains the main portion of yield reduction.

• Variability has been found within : • S. lycopersicum or in closely related wild species, such as • S. cheesmanniae, S. chilense, S. pennellii, S. peruvianum and S. pimpinellifolium.

• 4. 2 Extending the Thermal Range • 4. 3 Long Shelf Life • • Current Goals of Breeding 5. 1 Resistance to Insects in Tomato 5. 2 Resistance to Diseases 5. 3 Breeding for Quality

Breeding Methods and Techniques • Several breeding methods and techniques are required for the development of a new commercial variety.

• to obtain a commercial hybrid, the following methods and techniques can be applied: 1) crosses between different lines or hybrids with complementary characteristics in order to generate a segregant population, • 2) the pedigree method to develop inbred lines from this segregating population with the required characteristics,

3) the backcross method to introgress a specific characteristic in a line as well as others.

• In the development of inbred lines, embryo rescue and in vitro culture can be used to accelerate the process. • Alternatively, anther culture can be employed in order to obtain inbred lines in a shorter period of time.

• The method used for introgressing characters controlled by a single major gene, both from wild species and from a different tomato cultivar, has generally been the backcross. • Backcross combined with selfing generations has been employed in introgressing multigenic characters such as tolerance to salinity or other abiotic stresses.

• Recurrent selection has been employed in the development of many cultivars for processing but not generally with hybrids • Recurrent selection has also been employed in the development of populations with enhanced resistance to pathogens when monogenic resistance is not available

• Doubled haploid technology is a powerful alternative to classic plant breeding strategies, mostly due to the significant time and resource savings that can be achieved through its application.