The use of Lycopersicon cheesmanii in breeding for salt-tolerant tomatoes

Costa, J., Nuez, F., Anastasio, G. and Palomares, G.

Breeding for salt tolerant tomatoes is an important goal for certain areas of southern Europe with salinity problems. For this goal, crosses were made between a tomato cultivar (Lycopersicon esculentum cv. DF 24) and the wild accession L. cheesmanii ssp minor LA 1401 (Rick, 1972), described as salt tolerant by Rush and Epstein, (1976). (Table 1). Both the interspecific hybrid and the parental lines were grown in hydroponics with sand as a substrate, and under three salt treatments (T1 = 4 ds/m; T2 = 7 ds/m; T3 = 10 ds/m) and a control (T0 = 2.5 ds/m). The F1 was self pollinated and the F2 (Table 2) was screened outdoors in a salty soil (EC = 10 ds/m) irrigated with the addition of 14 g/1 NaCl: CaCl2. Selected plants out of the F2 were self pollinated and the F3 was screened under the same conditions. The process is now at the level of F5 and selfing of the backcrosses between the hybrid and the cultivated tomato.

Preliminary analyses of both quantitative and qualitative traits (Figure 1,2,3) have shown that surprisingly, the more saline the treatment (T3 = 10 ds/m) the greater the vigour in the hybrid. This could be due to an exacerbated heterosis under stress conditions (Barlow, 1981).

The F2 displayed a wide segregation for all the traits studies (see Table 2). The growth habit was difficult to score as most of the plants had a bushy growth. Nevertheless the rate found suggests a control by a single gene with recesivity for the determinacy (X^2 = 3.24) as it is usual in the tomato. The same was noticed for the fruit color (X^2 = 0.69).

An even larger variability was detected in quantitative traits (Table 3). Seven of the F2 plants were selected based on their similarity to the cultivated tomato. The yielding characteristics were particularly taken into account (Table 4), looking for plants with the biggest fruit size among the progeny, although fruit size was still smaller than that of cultivated tomato.

The seven F3 families were screened with eighty plants per family; only eleven plants were selected. These F4 families looked more similar to the cultivated tomato. Simultaneously the self progeny of the backcross F1 x DF 24 is being selected.

TABLE 1. Qualitative traits in the parental lines and the hybrid F1 (DF 24 x LA 1401).

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          Growth   Leaf     Stem                      Fruit  Green  Fruit
Genotype  habit    division pubescence Inflorescence  size   back   color
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DF 24     Determ.  Pinnate  Weak        Multiparous   Large  Pres.  Red

LA1401    Indet.   Bipinn   Medium      Uniparous     Very   Absent Orange
          Bushy                                       small

F1        Indet.   Bipinn.  Medium      Uniparous     Small  Pres.  Orange
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TABLE 2. Qualitative traits in the F2 from the interspecific cross(percentage of plants).

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Growth habit  Leaf divis.  Infloresc.   Greenback    F. color       F. size
Det.  Indet. Pinn. Bipin. Unip. Multip  Pres. Abs. Red   Orange   <2cm  2-4 cm
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32.8   67.2    38   62    8.38   16.2    13    87  78.6   21.4      58    42
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TABLE 3. Mean, standard deviation and minimum and maximum values for fruit number, average weight and total yield in the F2.

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Fruit              Mean  Std. Deviation  Min.  Max.
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Fruit number        28.0      27.3       1.0   80.0
Average weight (g)   6.3       5.8       1.2   33.6
Total yield (g)    173.0     171.9       2.5  527.5
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TABLE 4. Characteristics of the seven plants selected from the F2.

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Trait                  P7    P10    P3    P5     P16    P20    P1
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Fruit number         20     80     62     79     34     56     11
Average weight (g)    1.25   5.84   5.60   4.81   7.86  2.27   33.63
Total yield (g)      25.0  467.5  347.5  380.0  267.5  127.5  370.0
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Literature cited:

Barlow, R. 1981 Experimental evidence for interaction between heterosis and environment in animals. Animal Breeding Abstracts. 49: 715-737.

Rick, C.M. 1972 Potential genetic resources in tomato species: Clues form observations in native habits. In: Genes, Enzymes and Populations. A.M. Srb (ed). Plenum Press, New York, pp. 255-269.

Rush, D.W. and E. Epstein 1976 Genotypic responses to salinity. Differences between salt-sensitive and salt-tolerant genotypes of the tomato. Plant Physiol. 57: 162-166.