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BREEDING THE TOMATO MICRO-TOM MODEL SYSTEM FOR ORNAMENTAL VALUE

2009; International Society for Horticultural Science; Issue: 836 Linguagem: Inglês

10.17660/actahortic.2009.836.30

2406-6168

Tatiana Bistaco Farinha, Agustín Zsögön, Lázaro Eustáquio Pereira Peres,

Plant tissue culture and regeneration

Taking advantage of its small size (8 cm tall) and short life cycle (70 days), the ornamental tomato cv. Micro-Tom (MT) was proposed as a model system for tomato genetics. Ever since, MT has been used for large scale mutagenesis and the introgression of allelic variation already known in other cultivars and tomato wild species. Such new genotypes could also be used to improve its value as an ornamental. Here we report the introgression, through successive backcrosses, of various mutations affecting fruit color and morphology into the MT background. Various true type genotypes combining reduced plant size and fruit color variation were obtained upon introgression of the mutations Del, old gold (og), Beta (B), green stripe (gs), pink fruit (y), yellow flesh (r), tangerine (t), apricot (at) and green flesh (gf). Four mutations affecting fruit format, i.e. ovate (o), fasciated (f), sun and fs8.1, were also introgressed into MT. These mutations and the combination of them greatly extends the value of MT as an ornamental and introduces the possibility of exploring the large diversity of induced and natural mutations in tomato for this purpose. INTRODUCTION Micro-Tom (MT) is a miniature dwarf determinate cultivar of tomato (Solanum lycopersicum L. Syn. Lycopersicon esculentum Mill.), originally bred for home gardening purposes (Scott and Harbaugh, 1989). It differs from standard tomato cultivars primarily by two recessive genes: dwarf, and probably, miniature (Meissner et al., 1997; Lima et al., 2004; Marti et al., 2006). The determinate phenotype of MT is caused by a mutation in the SP gene (Marti et al., 2006). MT has been put forward as a model system for tomato genetics (Meissner et al., 1997) being amenable for large scale mutagenesis (Meissner et al., 1997; Watanabe et al., 2007; Matsukura et al., 2007) and introgression of alleles present in other cultivars and wild species (Lima et al., 2004). Thus, MT is now being used to address research topics from fleshy fruit development (Serrani et al., 2007), and mycorrhyzae formation (Zsogon et al., 2008) to stress tolerance (Malacrida et al., 2006; Gratao et al., 2008a, b). Since novelty is highly valuable for ornamentals, some of the new mutations and allelic variation in MT may also be useful for this propose. Here we report the introgression, through successive backcrosses, of various mutations affecting tomato fruit shape and color (Stevens and Rick, 1986) into the MT background. These mutations and the combination of them greatly extend the ornamental value of MT. MATERIALS AND METHODS The genotypes harboring the mutations described in Table 1 were used as pollen donors for crosses with MT. The F1 plants were selfed to obtain a recombinant F2 population which was selected for small size, as described in Lima et al. (2004), and the mutation of interest. The selected plants were backcrossed with MT up to the sixth generation (BC6), with selfing every second generation to screen for homozygous recessive alleles (Fig. 1). Plants were grown in a greenhouse under automatic irrigation (four times/day to field capacity), mean temperature of 28°C, 11.5 h/13 h (winter/ summer) photoperiod, and 250 to 350 μmol photons m s PAR irradiance obtained by reduction of natural radiation with a reflecting mesh (Aluminet, Polysack Industrias Ltda, Itapolis, Brazil). Mutant seed was sown in trays containing a 1:1 mixture of commercial mix (Plantmax HT, Eucatex, Brazil) and expanded vermiculite, supplemented with 1 g L Proc. 23rd Intl. Eucarpia Symp. (Sec. Ornamentals) on “Colourful Breeding and Genetics” Eds.: J.M. van Tuyl and D.P. de Vries Acta Hort. 836, ISHS 2009 216 10:10:10 NPK and 4 g L lime. Ten days after germinations, plants were transferred to 150 ml (MT) or 10 L (donor cultivars) pots containing the aforementioned soil mix. After each crossing, mature fruit was harvested and the seed was cleaned of the pulp by fermenting for 12 h with bread yeast (Saccharomyces cerevisae, Fermix, Brazil). Seeds were then washed and air-dried in the shade. RESULTS AND DISCUSSION Here, successive backcrosses were made using MT as a recurrent parental (Fig. 1) in order to introgress mutations affecting fruit shape and color (Table 1). This is a less labor-intensive approach than mutagenesis, which would require a large structure and the screening of a large amount of plants to create an equivalent mutant collection. Further, for some loci, particularly those which are probably already knocked-out in MT (e.g. Del and B), introgression may be the only way to produce the desired allelic variation. Hence, 14 new mutants were obtained in the MT background in a short period of time and within limited growth facilities. The ornamental value of the genotypes created stands on their reduced plant size and diversity of fruit shape and color (Fig. 2). The collection presented here could be also used as a founder of new fruit shapes and colors, through the combination of mutations such as y + r, which creates white fruits, and ovate + sun, which produces extreme elongated fruits as in the cv. Long John. Since some of the mutations now near isogenic to MT are also the subject of intense research (Ronen et al., 2000; Isaacson et al., 2002; Liu et al., 2002), their availability in a plant with reduced size and short life cycle will greatly facilitate such studies. Moreover, the ornamental MT collection presented here may also be helpful as a tool for preliminary genetic mapping of new mutations, since the mutations introgressed are easy to score and cover almost all tomato chromosomes (Table 1). ACKNOWLEDGMENTS We thank the Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP) for financial support (grant 02/00329-8 and 07/07175-0). Literature Cited Gratao, P.L., Monteiro, C.C., Peres, L.E.P. and Azevedo, R.A. 2008a. The Isolation of antioxidant enzymes from mature tomato (cv. Micro-Tom) plants HortScience 43:1608-1610. Gratao, P.L., Monteiro, C.C., Antunes, A.M., Peres L.E.P. and Azevedo, R.A. 2008b. Acquired tolerance of tomato (Lycopersicon esculentum cv. Micro-Tom) plants to cadmium-induced stress. Ann. Appl. Biol. 153:321-333. Isaacson, T., Ronen, G., Zamir, D. and Hirschberg, J. 2002. Cloning of tangerine from tomato reveals a carotenoid isomerase essential for the production of beta-carotene and xanthophylls in plants. Plant Cell 14:333-342. Lima, J.E., Carvalho, R.F., Tulmann Neto, A., Figueira, A. and Peres, L.E.P. 2004. MicroMsK: a tomato genotype with miniature size, short life cycle and improved in vitro shoot regeneration. Plant Sci. 167:753-757. Liu, J., Van Eck, J., Cong, B. and Tanksley, S.D. 2002. A new class of regulatory genes underlying the cause of pear-shaped tomato fruit. Proc. Natl. Acad. Sci. USA 99:13302-13306. Malacrida, C., Valle, E.M. and Boggio, S.B. 2006. Postharvest chilling induces oxidative stress response in the dwarf tomato cultivar Micro-Tom. Phys. Plant. 127:10-18. Marti, E., Gisbert, C., Bishop, G.J., Dixon, M.S. and Garcia-Martinez, J.L. 2006. Genetic and physiological characterization of tomato cv. Micro-Tom. J. Exp. Bot. 57:20372047. Matsukura, C., Yamaguchi, I., Inamura, M., Ban, Y., Kobayashi, Y., Yin, Y., Saito, T., Kuwata, C., Imanishi, S. and Nishimura, S. 2007. Generation of gamma irradiationinduced mutant lines of the miniature tomato (Solanum lycopersium L.) Micro-Tom. Plant Biotech. 24:39-44.