Performance of advanced generation from a hybrid Japanese cucumber 553 Sci. Agric. (Piracicaba, Braz.), v.65, n.5, p.553-556, September/October 2008 Note PERFORMANCE OF ADVANCED GENERATION FROM A HYBRID JAPANESE CUCUMBER Victoria Rossmary Santacruz Oviedo1; Amanda Regina Godoy2; Antonio Ismael Inácio Cardoso3* 1 USP/ESALQ - Programa de Pós-Graduação em Fitotecnia. 2 UNESP/FCA - Programa de Pós-Graduação em Horticultura. 3 UNESP/FCA - Depto. de Produção Vegetal, C.P. 237 - 18603-970 - Botucatu, SP - Brasil. *Corresponding author ABSTRACT: Inbreeding reduces the vigor in plants as a result of a decrease in the proportion of heterozygous loci. However, the influence of inbreeding is different among the species. The objective of this work was to evaluate the inbreeding depression in a cucumber Japanese population. An F 2 population was obtained from a commercial hybrid (Natsu suzumi), which was considered as S 0 population. S 1, S 2 , S 3 , S 4 and S 5 progenies were obtained by the ‘Single Seed Descent’ methodology. A complete blocks design with seven treatments (different generations of self pollination - S 0 to S 5 and the hybrid Natsu suzumi), and six replications of five plants per plot was used in protected cultivation from Aug. 21 to Nov. 29, 2002. Number of leaves, length of the main stem, number and weight of fruits (total and commercial) number of nodes and vines percentage were evaluated. For most of the traits appraised differences were not observed among populations showing that there was no loss of vigor due to inbreeding in this population. Key words: Cucumis sativus L., breeding, heterosis COMPORTAMENTO DE GERAÇÕES AVANÇADAS DE UM HÍBRIDO DE PEPINO JAPONÊS RESUMO: A endogamia reduz o vigor em plantas pela diminuição da proporção de loci heterozigotos. Entretanto, a influência da endogamia é diferente entre as espécies. O objetivo deste trabalho foi avaliar a depressão causada por endogamia em uma população de pepino do tipo japonês. A partir do intercruzamento entre plantas do híbrido Natsu suzumi foi obtida a geração F 2 , considerada como população S 0 . Obtiveram-se progênies S 1 , S 2 , S 3 , S 4 e S 5 , através de autofecundações sucessivas pelo método do SSD (‘Single Seed Descent’). Foram sete tratamentos (híbrido Natsu suzumi, populações S 0 a S 5 ) e o delineamento experimental foi em blocos ao acaso, com seis repetições e cinco plantas por parcela cultivadas em ambiente protegido de 21/08/2002 à 29/11/2002. Foram avaliados o número de folhas, semanalmente, o número e a massa de frutos, total e comercial, número de nós e porcentagem de nós com brotações laterais. Na comparação entre as populações S 0 a S 5 não foram observadas diferenças para todas as características avaliadas demonstrando não haver perda de vigor por endogamia nesta população. Palavras-chave: Cucumis sativus L., melhoramento, heterose INTRODUCTION Inbreeding reduces the vigor in plants as a re- sult of a decrease in the proportion of heterozygous loci (Hayes et al., 2004). Although the inbreeding de- pression is a consequence of an increase of the ho- mozygous, its magnitude depends on number and types of deleterious genes, exposed to conditions of homozygosis (Charlesworth & Charlesworth, 1979). The influence of inbreeding is thoroughly different among species (Byers & Waller, 1999; Husband & Schemske, 1996). Most of the superior plants, mainly cross-pollinated, show a depression in larger or smaller degree as a consequence of the inbreeding. However, some species that are naturally self-polli- nated do not show this depression. Cucurbits are cross-pollinated, but they are examples of species in which some lines seem to lose little vigor due to inbreeding (Allard, 1978; Withaker & Robinson, 1986). Inbred lines have been developed in cucumber, pumpkin, melon and watermelon without loss of vigor Oviedo et al.554 Sci. Agric. (Piracicaba, Braz.), v.65, n.5, p.553-556, September/October 2008 (Robinson, 1999). Inbreeding depression is not an im- portant factor for hybrid seed production in cucurb- its. Nowadays, the use of hybrid seeds in veg- etables is common in developed and in some develop- ing countries. However, most of Japanese cucumber hybrids used in Brazil are matter of concern since rep- resent high annual expenses in seed importation (Lopes, 1991). In spite of the absence of loss of vigor, the use of cucumber hybrid is very common due to heterosis. But lines can produce as well as hybrids and they can be used directly, because lack of inbreeding depression (Cramer & Whenner, 1999; Robinson, 1999). Researches are contradictory in relation to loss of vigor in cucumber due to inbreeding depression. The objective of this study was to evaluate the possible existence of inbreeding depression in a Japa- nese cucumber population. MATERIAL AND METHODS The experiment was carried out in São Manuel, State of São Paulo, Brazil (48°34‘W, 22°44‘S; mean altitude 750 m) at protected cultivation. Populations were obtained from the F1 commercial hybrid Natsu suzumi (Takki company) a Japanese type tolerant to powdery mildew recommended to protected cultiva- tion. After randomly crossing F1 plants, the F2 genera- tion was obtained. This was considered as the initial population, called the S0 population. About 80 plants of this F2 population were self-pollinated in order to obtain the S1, S2, S3, S4 and S5 progenies, through suc- cessive self-pollination using the SSD method ("Single Seed Descent"), proposed by Brim (1966). Population S1 was obtained by mixing seeds of progenies S1, in other words, the S1 population was a random sample of all S1 progenies, and each progeny participated with the same number of seeds. The same procedure was performed for the other generations to obtain popula- tions S2, S3, S4 and S5. Self pollinations were controlled according to Lower & Edwards (1986). Seeds were stored in a chamber with 40% relative humidity and temperature of 20ºC. The commercial hybrid Natsu suzumi was used as a control for fruit type and potential yield. Seven treatments (hybrid Natsu suzumi and the six derived populations: F2 = S0, S1, S2, S3, S4, S5) were planted according a randomized block designed with six rep- lications of five plants per plot. Soil analysis was performed and fertilization was in agreement to the recommendation by Raij et al. (1996) and drip irrigation was used. Seedlings were produced in trays of expanded polystyrene of 128 cells, for subsequent transplantation to the definitive place. The spacing was 1.0 m between rows and 0.5 m be- tween plants. Seeding was made on 21/august/02 and the transplantation on 12/september/02. Plants were grown in a vertical position and the stems and flowers were removed until the fifth node of the main stem. The apical meristem of the plant was removed when reaching an approximate height of 1.80 m. Harvesting started 34 days after the transplant and lasted for 43 days, with two-day inter- vals; all fruits with approximately 20 cm length were harvested. The total cycle was 97 days, starting from the sowing. In each harvest, the fruits were classified into commercial (fruits without apparent and straight defects) and non commercial. In this way, the total production of fruits was obtained, in number and weight, per plant, as well as the production of com- mercial fruits, number and weight, the rate of com- mercial fruits and the average weight of commercial fruit. The number of days from sowing to harvest was also recorded. Determination of number of leaves per plant was recorded weekly, and at the end of the cycle the number and the percentage of nodes with lateral stems were also determined. Variance analysis was accomplished and the means were compared by the Tukey test (PL 0.05). RESULTS AND DISCUSSION Differences were not observed among the treatments for number of leaves per plant in all evalu- ations along the cycle. The plants showed a slow de- velopment until the third week after the transplant, when a fast vegetative development occurred. Between the 26th and 34th days, after transplant, a medium in- crease of approximately 1.0 new leaf a day was ob- tained. Therefore, the successive self-pollination did not affect the vegetative development of the plants com- paratively to the original F1 hybrid. Differences were also not observed among the treatments from the beginning of the crop harvesting, with an average of 58 days after the sowing for all lev- els of inbreeding studied (F2-S5) and the commercial hybrid (Table 1). An average of 35.5 days was obtained after the transplant for the crop, a value similar to the 33 days obtained by Blanco et al. (2002). On the other hand, Cardoso & Silva (2003), studying a different japanese hybrid, obtained 72 days after the sowing in autumn - winter cultivation. However, for the summer cultivation the harvest began 47 days after the sowing. In this way, the inbred populations were as precocious as the original hybrid, what have not been reported in the several heterosis papers for precocity in cucum- ber (Wehner & Miller, 1985; Filgueira et al., 1986; Cui et al., 1992; Viggiano, 1994; Li et al., 1995). Performance of advanced generation from a hybrid Japanese cucumber 555 Sci. Agric. (Piracicaba, Braz.), v.65, n.5, p.553-556, September/October 2008 Differences were also not observed for num- ber of commercial fruits, total weight and commer- cial weight per plant (Table 1). For number of total fruits, the commercial hybrid was superior to genera- tion S5. However, no differences were obtained for this characteristic among the inbred populations (S0-S5), demonstrating the absence of loss of vigor with the successive inbreeding generations. It is pointed out, however, that the means of populations with different degrees of inbreeding were evaluated and that the lines obtained after a certain number of generations of self- pollination can present results with different relation- ship to the loss of vigor (Maluf, 2001). The evaluated populations representing a mix- ture of progenies, on average, presented reduction in the total fruit number per plant after five generations of self-pollination in comparison with the commercial hybrid. However, progenies can be found where there is no loss in comparison to the original population with- out inbreeding. Besides, progenies with low vigor can generate populations or hybrids with high vigor after recombination to obtain heterozygosity (Maluf, 2001). The values obtained (Table 1) are not similar to those reported in the literature. Cardoso & Silva (2003) obtained 33 and 20 fruits/plant in the evalua- tion of hybrids of Japanese cucumber in winter and summer cultivation, respectively. Fernandes et al. (2002) obtained 920 g per plant in nutrient solution. On the other hand, Blanco et al. (2002) obtained a to- tal production of 33.0 fruits per plant and 29.1 com- mercial fruits in cucumber grafted under protected cultivation irrigated with saline water. There was no difference in the commercial fruit rates (Table 1), so, the successive self-pollinations did not affect fruit qual- ity. For average fruit weight, no differences were ob- tained, probably because the harvesting point was ap- proximately the same for all the materials (fruits with about 20 cm of length). Furthermore, differences were not observed among the treatments when the number of nodes (20.0 in average) and its percentage with lateral stems (17.3% in average) are considered. Cardoso & Silva (2003) obtained, on average, larger production in the hybrid (Tsuyataro, from Takii company) with larger percentage of lateral stems. On average, the absence of loss of vigor with the successive self-pollinations was noticed, in several reports in cucumber (Jenkins Jr., 1942; Rubino & Wehner, 1986; Cramer & Wehner, 1999) as in other cucurbits (Allard, 1978; Withaker & Robinson, 1986; Robinson, 1999; Cardoso, 2004) in spite of other sev- eral reports of significant heterosis in hybrid F1 in cu- cumber (Wehner & Miller, 1985; Filgueira et al., 1986; Cui et al., 1992; Viggiano, 1994; Li et al., 1995). In- breeding depression depends on the allelic frequency and on the dominance effects (Falconer, 1989). There- fore, there is not loss of vigor for F1 hybrid with large heterozigosis in absence of dominance effects. There- fore, in this population, lines can be used like open pol- linated cultivars as productive as the hybrids and with the same uniformity level (S5 lines) being less expen- sive for the producer, in agreement with Robinson (1999). The absence of loss of vigor for inbreeding in this population can be due to: i) the original popula- tion is not a hybrid as mentioned by the company or Treatments NDH NTF NCF TMP CMP CF MCF ---------------- days ---------------- - - - - - - - - - - - g - - - - - - - - - - - % g per fruit Natsu suzumi 58.2 a 21.6 a 13.6 a 2298.8 a 1625.1 a 63.1 a 117.6 a F2 = S0 58.8 a 20.2 ab 14.0 a 2237.0 a 1679.3 a 67.4 a 121.4 a S1 57.5 a 15.6 ab 10.7 a 1676.6 a 1256.7 a 68.9 a 117.9 a S2 57.2 a 17.2 ab 10.9a 1878.4 a 1324.4 a 62.6 a 122.2 a S3 57.9 a 15.6 ab 9.9 a 1691.1 a 1178.3 a 62.9 a 117.5 a S4 57.3 a 19.9 ab 12.9 a 2408.4 a 1556.9 a 64.9 a 120.9 a S5 58.5 a 14.3 b 8.9 a 1551.5 a 1066.9 a 61.9 a 118.9 a Means (S0-S5) 57.9 17.1 11.2 1907.2 1343.8 64.8 119.8 C.V (%) 2.12 9.8 14.2 29.9 30.8 6.2 10.2 TSM1 0.01ns 0.60* 0.45ns 718727ns 337883ns 0.16ns 23.1ns Means followed by the same letter, in the columns, do not differ by the Tukey test (5%). 1TSM - treatment square mean: ns, *, ** = not significant at 5% and 1%, respectively, by F test. 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