FLOWERING OF TOMATO IN RELATION TO PRE-PLANTING LOW TEMPERATURES G. Noto; G. La Malfa Istituto di Orticoltura e Floricoltura Università' degli Studi Catania - Italy Abstract The results of two trials carried out to evaluate the advantages of the use of tomato seedlings cooled following the cotyledon expansion, and after transplanting grown in the variable thermal conditions of the cold house, are reported. The trials concerned three tomato varieties, three night temperatures (7 - lu - 21 C) and various periods of cooling of the seedlings - from one to three weeks after cotyledon expansion -. With regard to the effects, the lower- the temperature and the longer the cooling period then the younger the plant at flowering and the lower the number of leaves before the first truss. 1. Introduction It is known that during the two to three weeks after the cotyledon expansion the tomato seedlings are rather sensitive to cold conditions as far as the flowering habit is concerned. The exposure of seedlings during this period to low temperatures (10-13 C) in comparison with high ones (l8-21 C) in particular promotes an earlier initiation of flowers as shown by the lower number of leaves up to the first and, sometimes, the second truss (Calvert, 1957;Lewis, 1953;Wittwer & Teubner, 1956). Furthermore, a. somewhat longer exposure to cold temperatures could increase, depending on the light conditions,the number of flowers on these trusses (Calvert, 1959: Hurd & Cooper, 1967). All these effects are shown variably according to the varieties and the environmental conditions that follow the cold treatment (Aung, 1976; Wittwer & Teubner, 1957). For this reason it is not easy, also due to the lack of experimental data,to define precisely the advantages of the use of cooled tomato seedlings when these are transplanted and grown under variable thermal conditions, such as those found in a cold greenhouse. Acta Horticulturae, 191, 1986 Solanacea in Mild Winter 275
Our research - carried out thanks to the aid grants of the Italian Ministry of Education - concerned these last points, i.e.: the flowering of tomato seedlings cooled after the cotyledon expansion and subsequently grown in a cold greenhouse. Two experiments were carried out and concerned three night temperatures and different cooling periods of seedlings from three cultivars. 2. Methodology In the two experiments low night temperature exposure took place from U p.m. to 8 a.m.; during the hours of daylight a constant temperature of 21 C and natural light conditions were imposed on the seedlings. For experiment 1 the treatments - began on 28th March,18 days after sowing - lasted two weeks. Three levels of night temperature were studied: 21 C; 111 and 7 C. For experiment 2 the treatments - began 21st September, 17 days after sowing - lasted three weeks, during which the seedlings were grown in the four following night temperature levels: constant 21 C; 7-21-21 C and 7-7-21 C respectively in the first, second and third weeks; constant 7 C. The varieties studied in both the experiments were Fl Precodor, F1 Vemone and Marmande Raf. After the thermic treatments the plants were transferred to the cold house where the temperatures were as reported i n figure 1. Standard measurements taken from each of the 10 plants in every treatment, were: - number of leaves up to first inflorescence - time of flowering of first and second inflorescence (days from seeding to anthesis of three flowers on every truss) - number of flowers in first and second inflorescence. 3. Results Number leaves. Cooling, as a rule, produced a reduction in the number of leaves below the first truss (fig.2) and, consequently, in the stem length. In the first experiment the lower the temperature the more pronounced the reduction in the number» of leaves, at least In the two hybrids F1, Pr-ecodor and Vemone. In comparison with 21 C the seedlings exposed during the night to 7 C and reduced their number of leaves below the first truss by 30 and 16% in Precodor and by and -15% in Vemone. In Marmande the chilling had no significant effect. 276
In the second experiment the leaf nodes formed between the cotyledons and the first inflorescence were reduced for all the cultivars when the exposure to 7 C at night lasted two weeks, and were reduced even more after three weeks exposure. One week's exposure to this temperature level was ineffective for the hybrids Precodor and Vemone, but was efficacious for Marmande. This last is the only different result from those achieved in the first experiment. In short chilling was generally effective in provoking advanced inflorescence differentiation. Tim :- of flowering. The results followed those concerning the number of leaves. In fact, the shortest number of days from sowing to anthesis was recorded when the tomato seedlings were grown at the lowest temperatures and exposed to the longest periods of chilling (fig.3). In the two experiments the variations in the time of flowering caused by chilling have appeared less pronounced in comparison with the variations in the number of leaves before the first inflorescence. This is true for the first and second cluster, but particularly for the second. This fact means that the growth rate of the plants and therefore the rate of leaf formation is quicker at higher temperatures. This allows the plants grown in these conditions to reduce, at least partly, the gap in the time of inflorescence differentiation with respect to the chilled plants. In fact,owing to the different ' growth rate, just after the thermic treatment the number of leaves of seedlings exposed to 21 C was higher than that of the seedlings exposed to lower night temperatures. The maximum difference was recorded in the second experiment between seedlings exposed constantly throughout three weeks to 21 C, and those exposed for the same period to 7 C (5.0 and 3.6 leaves respectively). of. Was virtually unaffected on the first and second trusses by chilling; the effects recorded seem incidental (fig. /I). This appears to be at odds with the positive results reported in some papers regarding the effects of chilling on the flower number. The results of our experiments, on the basis of results reported in numerous other papers, could be explained as follows: firstly, chilling in the early stages, when low temperatures are not always effective; secondly, the low light availability in the period following treatment, at least in the second experiment. 277
In conclusion the transplanting into a. cold greenhouse of tomato seedlings exposed after the cotyledon expansion to low temperatures generally could be useful only for the following purposes: a) to lower the stem length through the reduction of the number of leaves below the first truss. b) to anticipate the time of flowering in the first in florescence. These ends can be achieved to a greater or to a lesser extent according to the level of the temper.9t1.1re and the duration of the cooling period, at least within the treatments investigated. References Aung, L.H., 1976. Effects of photoperiod and temperature on vegetative and reproductive responses of Lycopersicon esculentum Mill. J. Am. Soc. Hort. Sei., 101:358-360 Calvert, A., 1957. Effect of the early environment on the development of flowering in the tom-ato. T. Temperature.7. Hort. Sei., 32:9-17 Calvert, A., 1959. Effect of the early environment on the development of flowering In tomato. II. light and temperature interactions..7. Hort. Sei., 3ft: 151-16? Hurd, R.G. and Cooper, A.J., 1967. Increasing flower number in single-truss tomatoes..7. Hort. Sei., UP: 1.9.1-1 P.K Lewis, D, 1953. Some factors affecting flower production in the tomato..7. Hort. Sei.?3:?0?-??0 Witt wer, S.H., and Tsuhner, F.O., 19 56. C-.3 <j exposure of tomato seedlings and flower formation. Free. Artier. Soc. Hort, Sei., 67:369-376 Wit t wer, S.H., and Teubr r, F. G.,.1957- The effects of temper a ture and ni trogen nutrition on f 1 ower formatier? in the tomato. Am..7. Bot., ü Ii: 1 P 5-1 pa 278
- DAY NIGHT 21- IV 5-V 19-V 2-VI 19- X 2-XI 16-XI 30-XI 14 XII Figure 1. Weekly mean of air temperatures in the cold house. MEAN PRECODOR F, VEMONE MARMANDE RAF Figure 2. Number of leaves to first inflorescence. * Values differ significantly (P=0,05) from those for plants grown continuously at 21 C. 279
Figure 3. Time of flowering (days from seeding) of first ( ) and second ( Cj ) inflorescence. Figure 4. Number of flowers on first ( ) and first + second ( Ij ) inflorescence. * Values differ significantly (P=0,05) from those for plants grown continuously at 21 C. 280