The nightshade family

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Introduction

The nightshade family (Solanaceae) has provided many plants to humankind. The genus Solanum has been very particularly important due to provision of our basic food plants, the Irish potato (S. tuberosum), and the commonly used eggplant (S. melongena). The family Solanaceae consists of 96 genra and about 2800 species in the three subfamilies Solanoideae, Cestroideae, and Solanineae (Nee et al., 1991). The genus has recently become even more important with the addition of two other food plants-both because of recent changes in their names. The tomato, which has previously known as Lycopersicon esculentum, is now familiar as S. lycopersicum and the tree tomato, Cyphomandra betacea, has now become S. betaceum. Three other Solanums-the pepino (S. muricatum) the cocona (S. sessiliflorum) and the naranjilla (S. quitoense), long valued for their fruits in South America, deserve greater attention (Heiser, C et al.1999).

Tomato (Lycopessicon esculentum) is an imperative and most well-liked vegetable produce. This crop occupies an area of 520 thousand hectares with a production of 7420 thousand metric tons (FAO, 2002). It is perennial, repeatedly grown in moderate climates as an annual. According to FAOSTAT, China is on top in production of tomato of about 38 million tones followed by US with 25 million tones and then Turkey, India and Itlay, (FAOSTAT, 2008). The tomato is the most popular vegetable in today's home gardens, but it was not always so popular. Native to South America, the tomato was introduced by early explorers to Europe, where it became known as the "Apple of Love'' in France and Italy. Thomas Jefferson raised tomatoes for his guests in 1781. On the other hand, it was not usually cultivated in the United States until 1835 because, until then, it was thought to be poisonous. Tomatoes are healthful and low in calories. One medium sized tomato provides 57% of the recommended daily allotment (RDA) of vitamin C, 25% RDA vitamin A, and 8% RDA iron, thus far it has only 35 calories. Moreover being eaten fresh, the multipurpose tomato can be baked, fried, juiced, or pickled and can be used in soups, salads, and sauces. New cultivars appear on the market each year, expanding selection and improving disease resistance.

Tomatoes can grow in many different soil types, but deep, loamy, well-drained soil is ideal. Tomatoes grow best in a to some extent acid soil with a pH of 6.2-6.8. Tomatoes are warm-season plants which do not tolerate chill or cold temperatures. Transfer to the garden after danger of frost is past and the soil has warmed: mid-late April in southern Indiana and mid-late May in northern Indiana. Cover plants if late frosts are forecast after tomatoes have been planted (B. Rosie Lerner).

Tomato is attacked by a large number of insect pests and diseases from seedling stage to harvest.

Tomato yellow leaf curl virus (TYLCV) is one of the major and serious diseases of tomato which causes considerable loss in potato production (Abdel-Salam, 1999) One hundred twenty five million tons of tomatoes were produced in the world in 2007. China, the largest producer, accounted for about one quarter of the global output, followed by the United States, Turkey, India and Egypt. (http://www.fas.usda.gov/htp/2009%20Tomato%20Article.pdf) .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 1959, the Israeli Ministry of Agriculture urged farmers in the Jordan Valley to replace the tasty but soft tomato "Marmande" with the long-shelf life variety "Money Maker," which was more suitable for export. A month after transplanting (August), most of the tomato plants in the region were affected by a disease of unknown etiology. Symptoms included severe stunting of plant growth, erect shoots, and markedly smaller and misshaped leaflets. The leaflets that appeared immediately after infection were cupped down and inward and subsequently developing leaves were strikingly chlorotic and showed an upward curling of the leaflet margins. When young plants were infected, they barely produced any marketable fruits (Cohen & Nitzany, 1960).

The growers' first reaction was to blame the change in tomato variety and they demanded compensation from the Ministry of Agriculture. Dr. F. E. Nitzany, head of the Virology Laboratory at the Volcani Center, Agricultural Research Organization (ARO), Israel, was asked to determine the causal agent of the disease and find solutions to the problem. A field survey revealed that most of the tomato plots in the area had been completely destroyed, and that the disease was accompanied by large populations of whiteflies. The whitefly population had built up in the nearby cotton fields, a crop which was being grown on a commercial scale for the first time in Israel. Soon enough, the suspicion that the whiteflies were the vector of the disease was confirmed, following controlled transmission experiments in the laboratory. Moreover, the "Marmande" tomato was found to be as susceptible as "Money Maker" to the disease, which was found to be viral in nature (Cohen & Nitzany, 1960). The virus was named Tomato yellow leaf curl virus (TYLCV) by the late Professor I. Harpaz of the Hebrew University (Cohen & Harpaz, 1964). Interestingly, similar disease symptoms had first been observed on tomatoes grown in the Jordan Valley as early as 1929, as well as in subsequent years (Avidov, 1944). The outbreaks of TYLCV disease were always accompanied by large populations of whiteflies (Cohen & Berlinger, 1986). However, the geminate shape of the viral capsid was first observed in 1980 (Russo et al., 1980), and it was only in 1988 that the virus was isolated (Czosnek et al., 1988). It took another 3 years to clone and sequence the virus, and to demonstrate that the genome of TYLCV is composed of only one single stranded (ss) DNA molecule (Navot et al., 1991).

Tomato yellow leaf curl was ?rst described in Israel around 1940 and was known only in Old World locations until the early 1990s, when it was introduced into the Dominican Republic. It has since spread to other Caribbean islands, is now established in Florida, and has been found in Georgia, Louisiana, and North Carolina. A severe outbreak of TYLCV occurred in northern Mexico during the 2005-2006 seasons. In fall 2006 TYLCV was found in Texas and Arizona. The virus was ?rst identi?ed in California in March 2007, in diseased tomato plants from a non- commercial greenhouse in Brawley, California. Researchers think these greenhouse plants were infected by white?ies that acquired the virus from host plants outside the greenhouse, and that the virus most likely came from northern Mexico. (Robert L. Gilbertson, http://www.ipm.ucdavis.edu/PDF/PMG/TomBrochure04NoTriFold.pdf)

The first evidence of economic damage to vegetable crops caused by the whitefly Bemisia tabaci (Gennadius) in Israel was recorded in 1931 (Avidov, 1944). Since 1935, it has been a permanent pest, mainly in the Jordan Valley. Avidov concluded that the Bemisia whitefly can raise as many as 15 generations per year in the Jordan Valley, due to the favorable climate in the area (Avidov, 1944). The silvering of squashes caused by Bemisia, which was observed as early as 1963 (Baery & Kapoller, 1963), and the very wide host range of this insect indicate that the B (or silverleaf) biotype has been present in this region for a long time.

FAO, 2002, Quarterly bulletin of statistics, food and agricultural organization of the united nations, Rome.

  1. Abdel-Salam AM: Isolation and characterization of a whitefly-transmitted geminivirus associated with the leaf curl and mosaic symptoms on cotton in.

Egypt Arab J Biotech 1999, 2:193-218.

FAOSTAT, Crop statistics, 2008.

B. Rosie Lerner, tomatoes. http://www.hort.purdue.edu/ext/HO-26.pdf

Heiser, C. and G. Anderson. 1999. "New" solanums. p. 379-384. In: J. Janick (ed.), Perspectives on new crops and new uses. ASHS Press, Alexandria, VA.

Nee, M., J.G.Hawkes, R.N.Lester, and N.Estrada (1991). Solanaceae III: Taxonomy, Chemistry, Evolution, Kew, UK: The Royal botanic Gardens.

http://www.ipm.ucdavis.edu/PDF/PMG/TomBrochure04NoTriFold.pdf

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