SCREENING OF TOMATO ACCESSIONS FOR RESISTANCE TO ...

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1.2 Botanical description Tomato belongs to the nightshade family Solanaceae, which is in division Magnoliophyta, class Magnoliopsida, subclass Asteridae, order Solanales, and suborder Solanineae (Knapp et al., 2004; Nee et al., 1991.). The extremely diverse and large Solanaceae family is believed to consist of 96 genera and over 2800 species in three subfamilies, Solanoideae (in which Lycopersicon belongs), Cestroideae, and Solanineae. Solanaceae is one of the most economically important families of angiosperms and contains many of the commonly ~ultivated plants, including potato, tomato, pepper, eggplant, petunia, and tobacco. This family is the most variable of all crop species in terms of agricultural utility, the 3rd most economically important crop family, exceeded only by the grasses and legumes, and the most valuable in terms of vegetable crops (Vander Hoeven, et al., 2002). Among all plant families, members of the Solanaceae are extremely diverse in terms of growth habit (from trees to small annual herbs), habitat (from deserts to the wettest tropical rain forest), and morphology (Knapp et al., 2004). Many Solanaceous species have played important roles as model plants, including tomato, potato, pepper, tobacco, and petunia. The tomato genus Lycopersicon is one of the smallest genera in Solanaceae, though the centerpiece in the family for genetic and molecular research. It is the closest to the genus Solanum (nightshade), an association which originally led people to believe tomato was poisonous (Rick, 1978). The cultivated tomato was originally named Solanum Iycopersicum by Linnaeus.(Linnaeus, 1953). Tomato is susceptible to over 200 diseases caused by pathogenic fungi, bacteria, viruses, or nematodes (Lukyanenko, 1991). Without question, the greatest contribution of modem plant breeding to tomato improvement has been through development of cultivars with improved disease resistance. Resistance has been identified, and in many cases characterized, for more than 30
of the major tomato diseases. Most commercial cultivars possess up to 6 (in true breeding lines) or 10 (in hybrids) disease-resistance attributes. These mainly include diseases for which major resistance genes have been identified, including fusarium wilt, verticillium wilt, root-knot nematode, alternaria stem canker, gray leaf spot, and some bacterial and viral diseases. However, horizontal (a.k.a. field or polygenic) resistance has also been reported for several tomato diseases, where major genes for resistance to a particular pathogen or race are not found, such as early blight, powdery mildew, bacterial canker, and bacterial wilt. Except in a few cases, tomato wild species have been utilized as the source of resistance for all tomato diseases. Resistance resources have been identified in most related wild species of tomato, in particular 1. pimpinellifolium, 1. peruvianum, and 1. hirsutum. For some tomato diseases, such as late blight (caused by oomycete Phytophthora infestans) and powdery mildew (caused by fungus Oidium lycopersicum), both vertical and horizontal resistances have been identified. Although the cultivated tomato is widely adapted to different climates, its growth and development is rather sensitive to different environmental stresses, including salinity, drought, excessive moisture, extreme temperatures, mineral toxicity and deficiency, and environmental pollution. There is limited genetic variation for abiotic stress tolerance within the cultivated species and most commercial cultivars are considered moderately to highly sensitive to different stresses. Fortunately, sources of genetic tolerance (or resistance) to different abiotic stresses are found within the related wild species, including 1. chilense, 1. peruvianum, 1. pennellii, 1. pimpinellifolium, 1. hirsutum,1. cheesmanii, 1. chmielewskii, and 1. parviflorum (Foolad, 2005). In addition, there are a few species within Solanum that exhibit tolerance to environmental stresses and which may be utilized in tomato breeding for stress tolerance. Several tomato wild species have been utilized for
Page 1: SCREENING OF TOMATO ACCESSIONS FOR
Page 4 and 5: My gratitude goes to our Lord Jesus
Page 6: 1.0 Introduction 1.1 Tomato 1.2 Bot
Page 9: Tomato (Lycopersicon escuientum Mil
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Page 15 and 16: most frequently produced within the
Page 17 and 18: from Chaetomium globusum that have
Page 19 and 20: Dextrose Agar (PDA) and incubated a
Page 21 and 22: % range scale Value 1-20.0 1 Resist
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Page 25 and 26: TABLE 3: Growth performance of toma
Page 27 and 28: The tomato accessions were found to
Page 29 and 30: · different disease suppressive me
Page 32 and 33: Olivain C. And Alabouvette C. (1999
Page 34: Sood, S.G. (2003). Chemotactic resp

SCREENING OF TOMATO ACCESSIONS FOR RESISTANCE TO ...

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