FRUIT-SET AND DEVELOPMENT IN THE TOMATO (LYCOPERSICON E S C U L E N T U M MILL.) GROWN UNDER PROTECTED CONDITIONS DURING THE COOL SEASON IN THE SOUTH-EASTERN COAST REGION OF SPAIN. THE RESPONSE TO EXOGENOUS GROWTH REGULATORS. M. Abad and J.L. Guardiola Escuela Técnica Superior de Ingenieros Agrónomos Universidad Politécnica 46020-Valencia, Spain Abstract Fruit-set is not adversely affected by the environmental conditions when tomatoes are grown in unheated greenhouses in the south-east of Spain during the winter. However fruit growth is significantly reduced, and this adverse effect may be overcome through the application of exogenous auxins to ovaries at anthesis. The response to these applications depends on the tomato cultivar, and is inversely related to the growth of the untreated ovaries. There is an increase in early yield, but if the cropping period is prolonged total yield is not increased due to a reduction in the number of flowers in the upper trusses, although fruit-set is not affected.gibberel 1 ic acid did not enhance fruit growth; instead a reduction in fruit weight was obtained and its application opposed the stimulation in growth brought about by the auxins. Both gibberellic acid and auxins interfered with seed formation and/or development, reducing the number of seeds per fruit and increasing the number of seedless fruits. Fruit puffiness was increased by the application of auxins. 1. Introduction Tomatoes are grown throughout the cool season in the Mediterranean coast of Spain mainly in unheated polyethylene-covered greenhouses. The total area planted represented in 1982 7,226 Ha, with a crop of 550,520 Tm, about 25% of the total tomato crop in Spain (Ministerio de Agricultura, Pesca y Alimentación, 1982). However, under the prevalent climatic conditions pollination is sometimes poor (Foti & La Malfa, 1979; Picken, 1984), which may reduce fruit set or bring about a crop of parthenocarpic fruits (Philouze, 1983; George et al., 1984). The size of these fruits is smaller than in pollinated ones, which makes them unmarketable, a condition which is overcome with the application of synthetic auxins. However, the fruit obtained in this way is usually of a lower quality (Rylski, 1979a; Abad y Guardiola, 1986). In this paper we have compared in terms of yield and quality the crop thus produced with that obtained without any treatment with two cultivars which differ in their capacity to carry-out pollination and fertilization under the winter growth conditions. In addition, the response to the application of exogenous auxins and gibberellins has been compared in order to gain more understanding on the mechanisms which induce the loss of quality. Acta Horticulturae, 191, 1986 Solana:ea in Mild Winter 123
2. Materials and methods The experiment was performed with two cultivars, Early Pack and Marmande Raf, which differ in their sensitivity to low temperature, Marmade Raf being reported as to have a relatively high pollen viability and to set seeded fruit under moderately low night temperatures (Maisonneuve & Philouze, 1982). Plants at the 4-leaf stage were transplanted to the soil in an unheated polyethylene-covered greenhouse on December 22, and were pruned to 2 branches. Flowering took place between February 8 and March 29. Cropping started on April 18 and the fruits were picked individually when turning into red. All plants were detopped above the 6th inflorescence and the crops were continued until June 27 when all fruit was ripe. The minimum temperature within the greenhouses during the night was in the range 7-10 C, with occasionally lower values (3-6 C) during the winter months, and then rose steadily up to 15 C towards the end of the experiment. The maximum daily temperature was prevented to raise above 25 C during the time of flowering and fruit set by appropiate^ ventilation as needed. Irradiance ranged from 8 to 24 MJ day m, the lower value corresponding to the winter months. As the aim of the experiment was to determine the response of each variety to the application of growth regulators, separate trials were performed on each case. A randomized design was followed with four replications of 10 plants each. Each^inflorescence was sprayed once with circa 0.5 ml of either 10 mg.l gibberellic acid (GA3 treatment), or the mixturj of synthetic auxins (Auxin treatment) b-naghtoxyacetic acid (5 mg.l ) and 4-chloro-phenoxyacetic acid (17 mg.l ). This mixture and concentration was selected because it proved the most favorable among all the tested in previous trials (Abad & Guardiola, 1984). When a combined application of GA3 + Auxins was performed, a solution having all these substances at the concentrations stated was prepared. The spray treatments were given when there were two open flowers on the inflorescence. Both the number of flowers and fruits were recorded for each inflorescence, and percentage set calculated as a quotient. Fruits were measured, weighted, inspected for the presence of seeds and puffiness determined by measuring the separation of the pericarp from the locule tissue in four positions. No attempt was made to measure the number of seeds per fruit, which were classed as seedy, seedless or with aborted seeds. Seedless fruits and those with aborted seeds are described as parthenocarpic in the text. Those fruits ripened within the first 25 days from the first picking were considered as early crop. 3. Results 3.1. ruit set In both cultivars fruit set was high and identical for all trusses (table 1). All fruits were seeded in the Marmande Raf cultivar, while in Early Pack 52% of the fruits were parthenocarpic. Empty seeds of smaller size but without embryo were present in some of the parthenocarpic fruits. Neither the auxin nor the GA3 applications affected fruit set. The application of auxins increased the number of seedless (parthenocarpic) fruits in both cultivars. The number of seeded fruits was reduced by GA3 in Early Pack but not in Marmande Raf. The effect of GA3 on seed 124
formation was smaller than for the auxin. 3.2. Fruit size In the untreated controls the percentage of marketable fruit (above 47 mm diameter) was higher for Marmande Raf, particularly in the earlier crops. In this cultivar, this paremeter was hardly affected by the application of growth regulators, and remained nearly constant through all the cropping period (table 2). Most of the seedless fruit set in Early Pack failed to reach marketable size. This situation was overcome by the auxin application, which rised the percentage of marketable fruit in the early crop from 49% to more than 87%. Most of the effect of the auxins on fruit weight was due to the growth stimulation of the parthenocarpic fruits, with a small increase in the number of big fruits (diameter larger than 67 mm; figure 1). Moreover, while in the controls the percentage of marketable fruit increased in the late croppings, the opposite trend was observed for the auxin- -treated plants, although this figure was always higher in these plants at any cropping date. In this cultivar, the application of GA3 reduced fruit weight and the percentage of marketable fruit. In addition it opposed the stimulatory effect of the auxin treatment, and the plants treated simultaneously with both hormones presented figures for these parameters intermediate between the untreated controls and the auxin- -treated. 3.3. F1owering The number of flowers per inflorescence decreased for the higher trusses. This effect was more important in the cultivar Marmande Raf, which had a larger number of flowers in the first two inflorescences than Early Pack (table 3). While in the cultivar Marmande Raf the number of flowers was not affected by the treatments, in Early Pack was increased by the GA3 applications and reduced by the auxins. Significant differences were found in the 5th and 6th inflorescences. Inflorescences 2 to 4, which were already differentiated at the time of the first application, had the same number of flowers in control and treated plants. 3.4. Yield and fruit earliness Total yield was not affected by the auxin treatment (table 4), and even a reduction was found in some experiments when a higher number of inflorescences were allowed on the plants (data not shown). In the Marmande Raf cultivar this response could be anticipated from the lack of effect on both flowering and fruit weight. In the Early Pack cultivar, the increase in fruit weight brought about by the auxin application was compensated by the reduction in fruit number in the upper trusses (see above). Neither auxin nor GA3 affected the earliness of the crop in Marmande Raf. In Early Pack, the number of fruits picked during the first 25 days was significantly increased both by auxins and GA3. However, only the auxin treatment increased early yield in weight since GA3 reduced fruit weight, thus compensating for the increase in the number of fruits cropped. 125
3.5. Fruit quality As reported earlier (Abad & Guardiola, 1986), the auxin application increased hollowness and pointed blossom end in both cultivars, this effect being more prominent in Early Pack. When fruits of a comparable diameter are compared it is shown that puffiness comes from the smaller development of the locule tissue in the treated fruits, the reduction in their development brought about by the treatment being more important in Early Pack (table 5). No significant effect of auxins on pericarp thickness was detectable. GA3 on the contrary reduced puffiness in both varieties. The number of locules was unaffected by the auxin applications in both cultivars. It was decreased by GA3 in Early Pack from 5.7 to 3.2 (P=0.99) but not in Marmande Raf. The number of locules in this cultivar was higher (8.2 + 0.5, n=75) than in Early Pack. 4. Discussion An increase in crop value may come through an increase in total yield, an increase in the percentage of marketable fruits and/or an earlier cropping. None of these parameters was significantly altered in the cultivar Marmande Raf by the application of auxin. This cultivar produced under our experimental conditions a fully seeded crop, and the small-sized fruits found in a variable proportion were formed because they held an unfavorable position in the inflorescence (Bangerth, 1981) rather than from a failure in fertilization. This effect could not be overcome through the application of auxin. Furthermore, as a result of the auxin application a high proportion of fruits became parthenocarpics, and although of a comparable size they had a lower quality than seeded ones. No clear benefit was obtained from the treatment in this cultivar. No increase in total yield was obtained from the auxin treatment in the cultivar Early Pack. The increase in size of the parthenocarpic fruits was compensated by the reduction in the number of fruits cropped, a phenomenon reported earlier and related to a decrease in set in the upper inflorescences (Picken, 1984). Flower formation rather than fruit set appears to be the critical step in our work, and although this process is influenced by exogenous hormones (Kinet et al., 1978; Leonard et al., 1983), a competition for the carbohydrate supply seems the more likely explanation. The effect of the growth regulators on flowering is inversely related to their effect on fruit growth, and thus flowering in the cultivar Early Pack was increased by gibberellins and reduced by auxins, while it was unaffected in the cultivar Marmande Raf. Despite the failure to increase total yield, marketable yield was significantly increased in the cultivar Early Pack by the auxin treatment (from 2.7 to 3.6 kg per plant, P=0.99) due to the reduction in the number of small-sized fruits (figure 1). This effect was more important in the early crop (from 0.4 to 1.7 kg per plant, P=0.99) due both to the higher proportion of underdeveloped parthenocarpic fruits in the lower trusses and to the earliness of parthenocarpic fruit in this cultivar, as shown by the higher number of fruits which ripened in the auxin-treated plants during the first 25 days (table 4). Conflicting reports have been published on the effect of the seeds on fruit ripening. Earliness has been found directly related to the number of seeds (Verkerk, 1957; Varga & Bruinsma, 1976), unrelated 126
(Rylski, 1979b; Scott & George, 1983) and enhanced in isogenic parthenocarpic cultivars (Mapelli et al., 1978; George et al., 1984). Varietal differences may account for their opposite observations as in our work. Earliness in parthenocarpic Early Pack fruits is unrelated to the fruit growth rate as was enhanced both by auxins, which increased it, and by GA3, which reduced it. In agreement with previous reports (Asahira et al., 1968; Monteiro, 1983; Shawney, 1984) GA3 failed to increase fruit size in parthenocarpic fruits. Further, it antagonized the growth enhancing effect of the auxin mixture in the cultivar Early Pack. As GA3 enhanced the development of the locule tissue, it opens the possibility to prevent or reduce the hollowness caused by the auxin treatments, which comes from a differentiated growth effect on the pericarp and the locule tissue. However, this effect may depend on the cultivar since an inhibition of the locule tissue by GA3 has been reported by Asahira et al.(1968). The relationship of this effect to its influence on seed development has not been studied; although GA3 induced parthenocarpy in the cultivar Early Pack, at the same time prevented the ovule and/or seed abortion caused by the auxin, so the number of seedless fruits was lower when the auxin applied alone than when together with GA3. References Abad, M., and Guardiola, J.L., 1984. Respuesta del tomate cultivado en invernadero a baja temperatura a la aplicación de auxinas de síntesis. Comunicaciones I Congr. Nal. Soc. Esp. Cieñe. Hortic., Valencia, 1983, Vol. I: 151-159. Abad, M., and Guardiola, J.L., 1986. Influencia de las auxinas de sínte sis en la calidad del fruto del tomate (Lycopersicon e s c u l e n t u m Mili.) cultivado en invernadero a baja temperatura. An. INIA. Ser. Prod. Veg. (In press). Asahira, T., Takagi, H., Takeda, Y., and Tsukamoto, Y., 1968. Studies on fruit development in tomato. II. Cytokinin activity in extracts from pollinated, auxin- and gibberellin-induced parthenocarpic tomato fruits and its effect on the histology of the fruit. Mem. Res. Inst. Food Sci., Kyoto Uni., 29: 24-54. Bangerth, F., 1981. Some effects of endogenous and exogenous hormones and growth regulators on growth and development of tomato fruits. In Aspects and Prospects of Plant Growth Regulators. (B. Jeffcoat ed.). Monograph 6: 141-150. British Plant Growth Regulator Group. Wantage. Foti, S., and La Malfa, G., 1979. Basi fisiologiche e condizioni ambientali nel processo di fruttificazione di L y c o p e r s i c o n e s c u l e n t u m Mill. Riv. Ortoflorofrutt. It. 63: 170-187. George, W.L., Scott, J.W., and Splittstoesser, W.E., 1984. Parthenocarpy in Tomato. In Horticultural Reviews. (J. Janick ed.). Vol.6: 65-84. The AVI Publishing Co., Inc. Westport. Connecticut. Kinet, J.M., Hurdebise, D., Parmentier, A., and Stainier, R., 1978. Promotion of inflorescence development by gowth substance treatments to tomato plants grown in insufficient light conditions. J. Amer. Soc. Hort. Sci. 103: 724-729. Leonard, M., Kinet, J.M., Bodson, M., and Bernier, G., 1983. Enhanced inflorescence tjîgvelopment in tomato by growth substance treatments in relation to C-assimilate distribution. Physiol. Plant. 57: 85-89. Maisonneuve, B., and Philouze, J., 1982. Action des basses températures nocturnes sur une collection variétale de tomate (Lycopersi- 127
con e s c u l e n t u m Mill.). II. Etude de la quantité et de la qualité du pollen. Agronomie 2: 453-458. Mapelli, S., Frova, C., Torti, G., and Soressi, G.P., 1978. Relationship between set, development and activities of growth regulators in tomato fruits. Plant & Cell Physiol. 19: 1281-1288. Ministerio de Agricultura, Pesca y Alimentación. Secretarla Gral. Técnica.1982. Anuario de Estadística Agraria 1982. Madrid. Monteiro, A.A., 1983. Tomato fruit growth in relation to methods of improving fruit-setting. Acta Hortic. 137: 307-314. Philouze, J., 1983. Parthénocarpie naturelle chez la tomate. I. Revue bibliographique. Agronomie 3: 611-620. Picken, A.J.F., 1984. A review of pollination and fruit set in the tomato (Lycopersicon e s c u l e n t u m Mill.). J. Hort. Sci. 59: 1-13. Rylski, I., 1979a. Effect of temperatures and growth regulators on fruit malformation in tomato. Scientia Hortic. 10: 27-35. Rylski, I., 1979b. Fruit set and development of seeded and seedless tomato fruits under diverse regimes of temperature and pollination. J. Amer. Soc. Hort. Sci. 104: 835-838. Sawhney, V.K., 1984. Gibberellins and fruit formation in the tomato: a review. Scientia Hortic. 22: 1-8. Scott, J.W., and George, W.L., 1983. Influence of pollination stimulation and/or prevention on tomato parthenocarpic fruit set and development. HortScience 18: 599. Varga, A., and Bruinsma, J., 1976. Roles of seeds and auxins in tomato fruit growth. Z. Pflanzenphysiol. 80: 95-104. Verkerk, K., 1957. The pollination of tomatoes. Neth. J. Agrie. Sci. 5: 37-54. 128
Table 1 - The influence of auxin and GA3 applications on fruit set and parthenocarpic fruit formation. Values for fuit set are mean from 20 plants (240 inflorescences). % of seeded fruits determined on a randomized sample of 75 fruits per treatment. CULTIVAR AND FRUIT SEEDED TREATMENT SET {%) FRUITS (%) EARLY PACK Untreated 90..4 47.,8 GA3 88..3 28.,9 Auxin 87..8 4..4 GA3 + Auxin 86.,5 20..3 MARMANDE RAF Untreated 88..1 100..0 GA3 86..6 96..9 Untreated 87..9 100..0 Auxin 87..7 25..2 Table 2 - The influence of auxin and GA3 applications on fruit size and percentage of marketable fruits. Data calculated for early harvest (EH), late harvest (LH) and all harvest (AH). Each value is the mean from 40 plants. CULTIVAR AND MEAN FRUIT liei^ililil MARKETABLE TREATMENT EH LH AH EH LH AH EARLY PACK Untreated 66 61 64 49 56 56 GA3 50 59 53 31 52 44 Auxin 117 70 89 87 70 76 GA3 + Auxin 80 71 72 59 70 64 Significance * * * * # * # * * * * SE (n=4) 5 2 3 6 3 3 MARMANDE RAF Untreated 68 66 68 67 65 65 GA3 75 59 64 68 56 57 Significance NS NS NS NS NS NS SE (n=4) 2 2 1 2 2 2 Untreated 85 70 74 72 69 69 Auxin 89 82 85 78 80 79 Significance NS * * NS * * SE (n=4) 1 3 3 2 3 3 2 NS, non-significant; *, ** indicate statistically significant differences at P 0.95 and 0.99 respectively. 129
Table 3 - Effect of fruit setting treatments on flowering. Values calculated from 240 inflorescences, 40 on each flower-level. CULTIVAR AND TREATMENT FLOWERS IN T, IT, T FLOWERS PER J-INI LUIlEi OV^EilNVyJZiO INFLORESCENCE INF1+2 INF3+4 INF5+6 (MEAN) EARLY PACK Untreated 12.4 9.4 8.8 5.1 GA3 11.9 10.1 11.9 5.7 Auxin 12.0 8.7 5.4 4.4 GA3 + Auxin 12.7 9.8 8.2 5.1 Significance NS NS * * * SE(n=4) 0.6 0.8 0.3 0.4 MARMANDE RAF Untreated 20.8 11.6 10.0 7.1 GA3 20.6 12.3 10.8 7.3 Significance NS NS NS NS SE (n=4) 0.8 0.5 0.7 0.5 Untreated 12.5 15.5 9.1 6.2 Auxin 11.4 13.1 7.5 5.3 Significance NS NS NS NS SE (n=4) 0.7 0.8 1.0 0.8 Table 4 - Effect of fruit setting treatments on yield and fruit earliness. Data calculated for early harvest (EH), late harvest (LH) and all harvest (AH). Each value is the mean from 40 plants. CULTIVAR AND 1 R_OF_FRUITS TREATMENT EH LH AH EH LH AH EARLY PACK Untreated 0.5 3.1 3.6 8 48 56 GA3 0.7 2.7 3.4 14 46 60 Auxin 1.8 2.2 4.0 16 30 46 GA3 + Auxin 1.1 2.8 3.9 13 40 53 Significance # * * * * * * * * SE (n=4) 0.1 0.1 0.1 1 3 2 1ARMANDE RAF Untreated 1.4 3.6 5.0 21 54 75 GA3 1.7 3.0 4.7 23 53 76 Significance NS NS NS NS NS NS SE (n=4) 0.1 0.1 0.1 1 1 1 Untreated 1.2 3.6 4.8 14 51 65 Auxin 1.5 3.6 5.1 17 44 61 Significance NS NS NS NS NS NS SE (n=4) 0.1 0.1 0.1 1 2 1 130
Table 5 - The influence of fruit setting treatments on the incidence of puffiness and the development of the fruits parts. Values are mean from 75 fruits of a similar diameter. THICKNESS IN CROSS,., FRUIT PUFFY SECTION (mm) CULTIVAR AND DIAMETER FRUITS LOCULE EMPTY TREATMENT (mm) (%) PERICARP TISSUE SPACE EARLY PACK Untreated 67.0 13.8c 5.9 53.8 0.7 GA3 65.9 0.4d 5.7 54.3 0.1 Auxin 71.4 84.8a 5.8 45.6 7.1 GA3 + Auxin 70.8 51.3b 5.8 51.2 4.0 Significance NS * * NS * * * SE (n=75) 2.2 0.1 0.2 0.3 iarmande RAF Untreated 65.3 10.5 4.7 55.1 0.4 GA3 64.6 0.3 4.7 55.0 0.1 Significance NS * NS NS * SE (n=75) 2.5 0.1 0.1 0.1 Untreated 67.1 13.4 4.9 56.3 0.5 Auxin 68.4 83.0 4.8 51.4 ' 3.7 Significance NS * * NS * * * SE (n=75) 2.8 0.1 0.1 0.1 Z Mean separation (P=0.95) carried out on log transformed data. 131
40 30 > o z w o- W «20 10 -L. <40 40-47 47-57 57-67 67-77 =-77 FRUIT DIAMETER (mm) Figure 1 - Fruit size distribution in the cultivar Early Pack for untreated (T), GA3-treated ( ), auxin-treated (O ) and GA3 + Auxin-treated (3) plants.the distribution for all treatments differ significantly^from that for the controluntreated plants (X test). 132