Nineteen accessions of Lycopersicon esculentum, three of L. esculentum var. cerasiforme, five of L. pimpinellifolium and one of L. cheesmanii were tested under controlled saline conditions. The trial was carried out in a hydroponic system, in beds of inert substrate (silica sand). Nutrients and concentration of NaCl necessary to reach the required electrical conductivity were added by means of a drip irrigation system.
The experimental design was in random blocks. Two treatments were applied, one of them with a saline concentration of 8 dS/m and the other as a control (3 dS/m). There were two replicates per treatment and three plants per replicate. The final Ca/Na relation was 2.05 in the control treatment (T0) and 0.19 in the saline one (T1). This unbalance was not corrected as the aim of the experiment was to study the plant response under salinity stress with ionic disequilibrium.
The search for salinity tolerance sources has to be based on the ability for setting fruits under stress conditions. Seedling and vegetative characteristics screenings show a low correlation with yield components (Maas and Hoffman, 1977; Norlyn and Epstein, 1984; Shannon, 1984), which are, at last, the ones with agricultural interest. Therefore, it would be advisable to look for materials with a good capacity to develop fruits under saline conditions.
Some accessions with no losses-or even increases regarding to control yield were detected among the group of small-fruited accessions. These could be considered as sources for salinity tolerance. Yield reductions were greater when studying larger-fruited accessions.
It has been noted that the correlation between the T1/T0 ratio on fruit number and on fruit weight was not significant (r = -0.05 0.67) in the small-fruited genotypes (group C). However, the correlation became significantly negative as fruit weight increased. Correlations are -0.34 0.15 and -0.58 0.16 for groups B and A respectively. Breeding for larger fruit weight can produce a fall in the fruit setting number due to the physiological load and/or competition among fruits. Consequently, when introducing a genetic system for salt tolerance into a background with greater fruit weight, a decrease in the fruit number T1/T0 ratio in comparison to the original source, would be expected. The lowering of the T1/T0 ratio would mean concomitant yield losses.
This inter-dependent relationship makes the search for new sources of stress tolerance with any agronomical value rather difficulty.
Literature cited:
Mass, E.V. and G.F. Hoffman. 1977. Current assessment. J. Irrig. Drain. Div. ASCE 103, 115-134.
Norlyn, J.D. and E. Epstein. 1984. Crop Science Vol. 24, Nov-Dec. 1984. 1090-1092.
Shannon, M.C. 1984. In:"Salinity Tolerance in Plants. Strategies for Crop Improvement" Eds. R.C. Staples and G.H. Toenniessen) Wiley-Interscience, New York, pp. 231-254.
Table 1. Fruit weight (FW) of the twenty-eight accessions under control treatment (TO). T1/T0 is the ratio between the control and the saline treatment (T1) for yield (Y) and fruit number (FN) per plant, and for fruit weight.
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T0 T1/T0
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Genotype FW(gr) Y FN FW
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GROUP A
L-S-80 169.83 0.36 0.56 0.65
L-S-65 137.38 0.41 1.03 0.40
L-S-36 134.46 0.61 1.21 0.50
L-S-75 117.68 0.46 0.89 0.51
L-S-18 114.48 0.49 0.78 0.63
L-S-81 114.42 0.62 0.97 0.64
L-S-71 110.81 0.44 0.83 0.53
L-S-74 100.18 0.57 0.90 0.63
GROUP B
L-S-64 95.26 0.48 0.83 0.58
L-S-66 78.79 0.32 0.67 0.47
L-S-60 78.52 0.49 0.91 0.54
L-S-52 65.39 0.60 1.15 0.52
L-S-2 65.29 0.54 0.88 0.63
L-S-29 64.71 0.52 0.78 0.66
L-S-72 57.74 0.62 0.76 0.81
L-S-56 42.50 0.45 0.79 0.56
L-S-63 34.42 0.40 0.57 0.66
L-S-59 29.63 0.54 0.99 0.55
L-S-4 23.57 0.52 0.79 0.65
GROUP C
L-S-70 2.88 0.58 0.88 0.66
L-S-67 1.49 1.00 1.04 0.96
L-S-68 1.36 0.89 1.11 0.81
L-S-77 0.95 0.39 0.35 1.15
L-S-62 0.95 0.69 0.85 0.82
L-S-78 0.93 0.45 0.53 0.85
L-S-79 0.77 0.44 0.64 0.69
L-S-76 0.71 0.58 0.80 0.72
L-S-61 0.39 2.11 2.54 0.88
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