Viability of pollen produced at low temperatures in Lycopersicon F1 hybrids

Fernandez-Munoz, R. and Cuartero, J. E.E. La Mayora (CSIC), 29750 Algarrabo-Costa, Malaga, Spain

Tomato species differ in their ability to produce viable pollen at minimum daily temperatures below 10 deg. C. In a previous varietal screening study we observed that L. peruvianum, L. hirsutum, and L. pennellii were the most tolerant species for this character, and that L. esculentum showed variability in that many cultivars were cold-sensitive and several cultivars were partially tolerant (Fernandez-Munoz and Cuartero, in press).

F1 hybrids between four tomato cultivars (Red Top, Moneymaker, Marroqui, and E-15) and five lines of cross-compatible wild species were made. These wild lines were PE-13 (one of the most sensitive accessions found in L. pimpinellifolium), L. parviflorum PE-52 (with a similar cold-sensitivity to most of the tomato cultivars), and the tolerant lines L. pennellii PE-47, L. hirsutum PE-37, and L. hirsutum PE-41. Cultivars of L. esculentum acted as pistillate parents in the crosses because the incompatibility barriers existing between tomato pollen and pistilles of most of its cross-compatible species. Intra-specific F1 hybrids (red Top, Moneymaker, and Marroqui) x E-15 were also included in the experiment. Six plants of each parent and F1 were cultivated in a greenhouse during winter, and pollen viability for each plant was assessed by acetocarmine staining on three different dates. The average minimum temperatures for the thermo-sensitive periods (Mutton et al., 1987) corresponding to the three dates ranged from 5 to 6 deg. C, so ensuring a negative effect on pollen of the sensitive genotypes.

Table 1 shows the means of the percentage of pollen staining for the parents and the F1's. Those of the parents were in accordance with the results of the above mentioned varietal screening. Higher pollen viability was dominant in L. esculentum F1's, as was also reported by Maisonneuve and Philouze (1982). An outstanding positive heterosis was shown by L. esculentum x L. pimpinellifolium hybrids, in all the cases, excepting for E-15 x PE-13, the F1 mean was significantly higher than the L. esculentum parent mean. No statistical differences were observed between the parents for the L. esculentum x L. parviflorum crosses. L. esculentum x L. pennellii F1's were clearly intermediate between their parents, and the L. esculentum x L. hirsutum F1's were either intermediate, as also found by Patterson and Paull (1987), or closer to the L. esculentum parent. The different heredity patterns observed can be explained by complementary effects of genes from the two species involved. So, in the crosses between two species with reduced expression of character, for instance the L. esculentum x L. pimpinellifolium F1's, the genes can complement each other resulting in heterosis. However, L. esculentum genes would be unlikely to complement those of L. pennellii or L. hirsutim, and intermediate expression in these F1's would emerge. Another explanation for intermediate rather than dominant expression may be pollen abortion due to reasons other than cold effect, i.e. disturbance sin chromosome pairing during pollen meiosis.

Table 1. Means of % stained grains in parents and F1's, and comparisons between the means of, respectively, parents/pistillate parent-F1/staminate parent-F1/F1-intermediate value between parents (t test).

_______________________________________________________________________________
                                        Pistallate parents
             __________________________________________________________________
Staminate       esc Red Top     esc Moneymaker    esc Marroqui     esc E-15
parents         37.1 +/- 9.0     39.3 +/- 15.1    61.6 +/- 7.3    65.1 +/- 6.9 
_______________________________________________________________________________
esc E-15        65.4 +/- 8.3    69.8 +/- 4.6     65.7 +/- 9.8    
65.1 +/- 6.9     **/**/ns/ns      **/**/ns/*      ns/ns/ns/ns 

pim PE-13       57.7 +/- 9.1    81.6 +/- 4.0     86.0 +/- 3.6     71.1 +/- 20.4
28.2 +/- 15.2     ns/**/**/*     ns/**/**/**      **/**/**/**       **/ns/**/ns

par PE-52       48.6 +/- 4.1    53.7 +/- 2.8     54.0 +/- 1.8     53.0 +/- 2.6
48.1 +/- 19.7     ns/*/ns/ns      ns/ns/ns/*      ns/ns/ns/ns      ns/**/ns/ns

pen PE-47       76.0 +/- 6.6    68.4 +/- 7.1     75.6 +/- 7.1     73.7 +/- 10.9
88.0 +/- 3.5     **/**/**/ns     **/**/**/ns      **/**/**/ns        **/ns/*/ns

hir PE\37       62.8 +/- 8.4    60.2 +/- 9.6     66.8 +/- 16.1    53.4 +/- 12.7
89.7 +/- 4.6     **/**/**/ns      **/*/**/ns        **/ns/*/ns      **/ns/**.ns

hir PE-41       68.8 +/- 12.3   63.9 +/- 17.1    63.3 +/- 6.5     66.7 +/- 7.6
97.1 +/- 1.2       **/**/*/ns      **/*/**/ns     **/ns/**/ns      **/ns/**/ns

______________________________________________________________________________
esc: L. esculentum; hir: L. hirsutum; par: L. parviflorum; pen: L. pennellii; 
pim: L.  pimpinellifolium 
**, *, ns: significant with p>=0.99, p>=0.95, not significant

Literature cited

Fernandez-Munoz, R. and J. Cuartero. Variability of pollen tolerance to low temperature in tomato and related wild species. J. Amer. Sci. Hort. Sci. (in press).
Maisonneuve, B. et J. Philouze. 1982. Action des passes temperatures nocturnes sur une collection varietale de tomate (Lycopersicon esculentum Mill.). II. Etude de la quantite et de la qualite du pollen. Agronomie, 2:453-458.
Mutton, L., B.D. Patterson, and V.O. Nguyen. 19987. Two stages of pollen development are particularly sensitive to low temperature. TGC Report. 37:56-57.
Patterson, B.D. and R.E. Paull, 1987. Hawaii as a natural phytotron for the introgression of cold resistance. TGC Report, 37:58-59.