Fruit and seed development in aubergine cv. Tsakoniki in relation to the fruit load on the plant

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1 Fruit and seed development in aubergine cv. Tsakoniki in relation to the fruit load on the plant E.M. Khah 1, S.A. Petropoulos 2, L. Myzithras 2, H.C. Passam 2 1 Laboratory of Genetics and Plant Breeding, University of Thessaly, School of Agricultural Sciences, Department of Agriculture, Crop Production and Rural environment, Fytokou Street, N.Ionia, Volos Contact: ekhah@agr.uth.gr 2 Laboratory of Vegetable Production, Agricultural University of Athens, Iera Odos 75-77, Votanikos 11855, Athens. Abstract Aubergines of a local Greek cv. Tsakoniki (elongate fruit) were cultivated for seed production under cover during the period July-November and fruit and seed quality parameters were recorded during fruit development (35-75 days from flowering) in the absence (one fruit per plant) or the presence (2 or 3 fruit per plant) of competition. It was found that fruit size (length and diameter) increased until days from flowering irrespective of the number of fruits on the plant. Fruit size was similar for the first and second set fruit but decreased significantly for the third fruit. Although the number of seeds per fruit was not affected by inter-fruit competition, seed weight per fruit was lower in the third fruit than in the first or second fruit due to a decrease in seed size (mean 1000 seed weight). Seeds in the first fruit matured within 55 days after flowering, compared to 65 and 75 days for the second and third fruit, respectively. At maturity, seed germination was 100% in all cases. We conclude that inter-fruit competition affects fruit and seed development and causes a delay in the maturation process of the later set fruit. Consequently, under the conditions of the present experiment (autumn crop under cover) the third fruit should be retained longer on the plant (75 days from flowering) than the first fruit (55 days from flowering) prior to harvest. Keywords: Eggplant, Solanum melongena L., inter-fruit competition, seed maturity, seed weight, germination. Introduction Aubergine (Solanum melongena L.) is an important vegetable crop of countries bordering the Mediterranean Basin, particularly Egypt, Turkey and Italy, where annual production is estimated to be 1.16, 0.86 and 0.33 million tonnes, respectively (FAO, 2007). In Greece, annual production amounts to 77,000 tonnes of which approximately 20% is cultivated in greenhouses and 80% in the field. In addition to its use as a fresh vegetable, aubergine is a potentially important source of antioxidants (Passam and Karapanos, 2008). Although most of the aubergine cultivars grown in Greece are imported F 1 hybrids, local varieties, such as Tsakoniki, are also widely grown. It is estimated that the annual seed requirement for aubergine in Greece is 260 kg, valued at 546,000 Euros (Vasileiou, 2004). The advantages of using local cultivars are that they are adapted to the climate of the region and are favoured on the market. Moreover they may be of value to aubergine breeders for the development of improved hybrids (Munoz-Falcon et al., 2008) and reduce the dependence on foreign imports and the loss of foreign exchange. For seed production the aubergine fruit must ripen fully on the plant (Chen, 2001; Demir et al., 2002). During this period there is competition between fruits on the plant,

2 leading to changes in flower development and a reduction in seed size (Lenz, 1970; Petrov et al., 1981; Passam et al., 2001; Karapanos et al., 2008; Leonardia and Giuffrida, 2009). To maximize seed quality it would be an advantage to the seed producer to know the optimum harvest time of fruit relative to the degree of inter-fruit competition upon the plant. In the present paper, therefore, we examine the size and germination ability of seeds produced from aubergines relative to the number of fruit developing on the mother plant. Materials and methods The experiment was carried out in an unheated plastic-covered greenhouse at the Agricultural University of Athens between July and November. Seeds of aubergine cv. Tsakoniki were sown on May 25, in seed trays containing commercial peat-based compost (Vitamix, Lambert, Canada) and maintained in the dark at 25 C. On emergence the trays were transferred to light in a greenhouse (15-30 o C) and 21 days after sowing the seedlings were transplanted to pots (8x8x8 cm) containing the same substrate. The plants were watered every second day and from 15 days after transplantation were fertilized weekly with 15 ml l -1 Complesal Fluid Green (12N-4P- 6K, GreenAgro S.A., Thessaloniki, Greece). On 19 July (55 days after sowing) the plants were transplanted to 10 l plastic pots containing peat and soil (1:1 v/v) with a base dressing of 600 g marble dust, 150 g 0N-48P-0K and 90 g KNO 3 per m 3. The pots were spaced to provide a plant density of plants per hectare and the plants were pruned on a regular basis so as to maintain one stem. Irrigation and fertilizer was provided through a drip system in accordance with recommended procedures for aubergines (Smith, 1979). Flowers were tagged as soon as they formed in order to record flowering date, flower number and flower position on the stem. Flowers were defined as first, second and third in order of appearance and subsequent flowers were excised. Fruit length and diameter was measured over 75 days and fruit were harvested at 35, 45, 55, 65 or 75 days after flowering. Three fruit were harvested from each plant (one from each order) and immediately weighed. The seeds were extracted by cutting the fruit and exerting pressure under water. The seeds were then washed and dried until constant weight at 25+3 o C room temperature. After drying, the number of seed per fruit and the mean 1000 seed weight were recorded. Germination was assessed by placing 4 replicates of 50 seeds from each replicate and harvest stage on moist paper in Petri dishes at 25±1 C and recording radicle emergence (minimum length 0.2 cm) over 1 month. The statistical design employed completely randomized blocks of ten plants, each block being replicated three times. Statistical analysis was carried out with the use of the Statgraphics 5.1.plus (Statistical Graphics Corporation) and Microsoft Excel 2007 (Microsoft Corporation) programmes. Data were evaluated by analysis of variance for the main effects, whereas the means of values were compared by the Duncan Multiple Range Test and Least Significant Difference test (p=0.05). Results and discussion Fruit growth in terms of length and diameter increased from the time of fruit set until days after flowering in the first-set fruit (Figure 1).

3 Figure 1. Fruit length and diameter of the first-formed fruit in relation to the number of days after flowering. Bars = standard deviation. A similar pattern of fruit development was observed in the second and third formed fruit (data not shown), with fruits attaining the same mean size in the first and second set fruit, but decreasing in the third-formed fruit (20+2 cm length and cm diameter). In consequence, by the completion of its development, the mean fruit weight of the first and second-formed fruits did not differ significantly ( g), but that of the third-formed fruit was lower (200 g). The number of seeds per fruit varied between 1400 and 2100 but did not differ to a statistically significant level between the three fruit levels. However, seed size decreased progressively between the first, second and third-formed fruit with the mean 1000 seed weight of the third-formed fruit being less than 3.5 g even at full fruit maturity (65-75 days after flowering) compared with 4.5 and 4.2 g in the first and second-formed fruits (Figure 2). This led to a decrease in the total weight of seeds per fruit particularly in the third-formed fruit. It is also clear from Figure 2 that while the seeds of both the first and second-formed fruits attained their maximum size by 55 days after flowering, those of the third-formed fruit continued to develop (fill) until 65 days after flowering. Seed germination was first observed at 45 days after flowering, but only to a low percentage: <10% in the first-formed fruit and 2% in the second-formed fruit. At 55 days after flowering, seeds of the first-formed fruit attained maximum germination but those of the second and third-formed fruit germinated to levels of 37% and 2% respectively (Figure 3). Although the germination of seeds from the second-formed fruit increased significantly at 65 days after flowering (90%), that of the third formed fruit was still very low (<5%) and only increased to a maximum (100%) at 75 days after flowering.

4 Figure 2. The 1000 seed weight of seeds from the first, second and thirdformed fruit in relation to the number of days after flowering. Bars = standard deviation. Figure 3. The percent (%) seed germination for the first, second and thirdformed fruit in relation to the number of days after flowering. Bars = standard deviation. The results of the present experiment clearly show that inter-fruit competition affects fruit and seed development in aubergine cv. Tsakoniki. This brings about a reduction in seed size (1000 seed weight) and a delay in seed maturation particularly in the third-formed fruit, as shown by the delay in attaining a high percent germination.

5 Demir et al. (2002) measured the seed mass accumulation and germination of fieldgrown aubergines during two consecutive summers in S.E. Turkey and concluded that seed quality was maximum at the end of the filling phase, which was 50 and 60 days after flowering for the two years of their experiments. Similarly, days after flowering has been recommended as a suitable harvest time for aubergine seed production in S.E. Asia (Rashid and Singh, 2000; Chen, 2001; Yogeesha et al., 2008). In Greece, summer production of aubergine seed also requires a fruit maturation period on the mother plant of at least 55 days, but the results of the present experiments indicate that in the autumn this should be extended to 75 days to promote the filling and maturation of seeds from later-formed fruit under conditions of inter-fruit competition. Demir et al. (2002) pointed out that the rather slow and non-uniform germination frequently seen in aubergine seeds is due to the lack of uniformity of maturity in seed lots harvested by once-over mechanical methods. Aubergine flowers are initiated sequentially either singly or in clusters (Nothmann et al., 1983) and inter-fruit competition increases with increasing flower set (Passam and Khah, 1992; Karapanos et al., 2008). This may be seen not only by the progressive decrease in mean 1000 seed weight and the delay in seed filling of the later-formed fruit (Figure 3), but also by changes in floral structure leading to flower abortion (Lenz, 1970; Passam and Khah, 1992; Passam et al., 2001). Such problems are likely to be exacerbated by the decreasing light conditions of autumn which lead to even greater competition for essential nutrients. References Chen, N.C Eggplant seed production. AVRDC, International Cooperators Guide. Asian Vegetable Research and Development Center, Shanhua, Taiwan. Daunay, M.; Janick, J History and iconography of eggplant. Chronica Horticulturae 47 (3): Demir, I.; Mavi, K.; Sermenli, T.; Ozcoban, M Seed development and maturation in aubergine (Solanum melongena L.). Gartenbauwissenschaft 67 (4): Karapanos, I.C.; Mahmood, S.; Thanopoulos, C Fruit set in Solanaceous crops as affected by floral and environmental factors. European Journal of Plant Science and Biotechnology 2 (Special issue 1): Lenz, F Effect of fruit on sex expression in eggplant (Solanum melongena L.). Horticultural Research 10: Leonardia, C.; Giuffrida, F Growth rate and carpometric characteristics during eggplant fruit growth. Acta Horticulturae 807: Munoz-Falcon, J.E.; Prohens, J.; Vilanova, S.; Nuez, F Characterization, diversity and relationships of the Spanish striped (Listada) eggplants: a model for the enhancement and protection of heirlooms. Euphytica 164: Nothmann, J.; Rylski, I.; Spigelman, M Floral morphology and position, cluster size seasonal fruit set in different eggplant cultivars. Journal of Horticultural Science 58: Passam, H.C.; Baltas, C.; Boyiatzoglou, A.; Khah, E.M Flower morphology and number of aubergine (Solanum melongena L.). in relation to fruit load and auxin application. Scientia Horticulturae 89: Passam, H.C.; Karapanos, I.C Eggplants, peppers and tomatoes: factors affecting the quality and storage life of fresh and fresh-cut (minimally-processed) produce. European Journal of Plant Science and Biotechnology 2 (Special issue 1):

6 Passam, H.C.; Khah, E.M Flowering, fruit set and fruit and seed development in two cultivars of aubergine (Solanum melongena L. ) grown under plastic cover. Scientia Horticulturae 51: Petrov, Hr.; Doikova, M.; Popova, D Studies on the quality of eggplant seed. Acta Horticulturae 111: Rashid, M.A.; Singh, D.P A manual on vegetable seed production in Bangladesh. AVRDC-USAID-Bangladesh Project, Horticulture Research Centre, Bangladesh Agricultural Research Institute, Joydebpur, Bangladesh, pp Smith, D Peppers and Aubergines. Grower Books, London, pp. 91. Vasileiou, Z.K Vegetable propagation material. Stamoulis A.E., Athens, pp Yogeesha, H.S.; Singh, T.H.; Naik, L.B Seed germination in relation to seed development in eggplant (Solanum melongena). Indian Journal of Agricultural Science 78: