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).
___________________________________________________________________________ Growth Leaf Stem Fruit Green Fruit Genotype habit division pubescence Inflorescence size back color ___________________________________________________________________________ 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 ____________ ______________________________________________________________TABLE 2. Qualitative traits in the F2 from the interspecific cross(percentage of plants).
_______________________________________________________________________________ Growth habit Leaf divis. Infloresc. Greenback F. color F. size Det. Indet. Pinn. Bipin. Unip. Multip Pres. Abs. Red Orange <2cm 2-4 cm _______________________________________________________________________________ 32.8 67.2 38 62 8.38 16.2 13 87 78.6 21.4 58 42 _______________________________________________________________________________TABLE 3. Mean, standard deviation and minimum and maximum values for fruit number, average weight and total yield in the F2.
____________________________________________________ Fruit Mean Std. Deviation Min. Max. ____________________________________________________ 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 ____________________________________________________TABLE 4. Characteristics of the seven plants selected from the F2.
____________________________________________________________________ Trait P7 P10 P3 P5 P16 P20 P1 ____________________________________________________________________ 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 ____________________________________________________________________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.