Pregerminative treatments of yellow mombin (Spondias mombin L.) seeds/Tratamentos pre-germinativos em sementes de caja (Spondias mombin L.).
Spondias mombin is a tree (Anacardiaceae) native to the tropical Americas. The species has been introduced in parts of Africa, India, Bangladesh, Sri Lanka and Indonesia (SACRAMENTO; SOUZA, 2009). Due to its ecological importance Spondias mombin is the most suitable species to restore the degraded areas in association with secondary forests species, that can be planted in the nearby areas of the Brazilian igapo forests (VALE; COSTA; MIRANDA, 2014). Additionally, yellow mombin fruits have an excellent flavor and aroma in addition to being a good producer of pulp, this being the reason of their use in preparation of refreshments, ice creams, jellies, and liquors (CARVALHO; ALVES, 2008).
One of the production problems to be solved for the commercial production of yellow mombin, is that it is related to the production of plantlets due to the slow and irregular germination of the seeds (AZEVEDO; MENDES; FIGUEIREDO, 2004). Yellow mombin seed germination starts 160 and ends 844 days after sowing (CARVALHO; NASCIMENTO; MULLER, 1998). Fungi development on the pulp remaining on the endocarp is pointed by farmers and researchers as an obstacle to the germination of some fruit species (VIEIRA; GUSMAO, 2006; POLTRONIERI; AZEVEDO; SILVA, 2013) and this may be the case of yellow mombin. On the other hand, another explanation for the distribution of germination along a period of time would be seed dormancy (LOPES et al., 2009; CARVALHO; NAKAGAWA, 2012). Mechanical scarification on the fruit distal region or near the embryo was sufficient to promote seed germination (FIRMINO; ALMEIDA; TORRES, 1997; LOPES et al., 2009). This is a treatment that may be used to overcome seed dormancy (BRASIL, 2013).
The structure known as seed by the agronomists and used for the sexual production of yellow mombin, is a diaspore of the nuculanic type (CAVALCANTE et al., 2009; CARVALHO; NAKAGAWA, 2012) from the botanical point of view. The nuculanium contains the true seeds surrounded by the woody endocarp which makes impossible their extraction without harming the embryo and thus reducing germination. The diaspores contain from zero to five seeds, although in 60% of the fruits only one true seed is found (AZEVEDO; MENDES; FIGUEIREDO, 2004).
Depending on its precedence, the nuculanium may be of different sizes with a length from 25.2 to 34.8 mm and a diameter between 13.2 and 21.2 mm (SOUZA et al., 2000; AZEVEDO; MENDES; FIGUEIREDO, 2004). Nuculanium size may be related to the speed of germination; Azevedo, Mendes and Figueiredo (2004) reported that the largest diaspores bear seeds which primary roots are emitted more promptly than those of the smaller diaspores. It is supposed that the larger nuculania were, during their formation, more well-nourished and thus have more vigorous seeds.
In addition to that, the larger nuculania have a larger number of true seeds (AZEVEDO; MENDES; FIGUEIREDO, 2004) so that the sowing of the larger diaspores may enhance the chances of germination to occur and the development of at least one of those seeds and the production of plantlets.
Classifying fruit seeds as to size or weight is a strategy that may be adopted to make more uniform seedling emergence, seedling size and to get more developed plantlets. Larger or denser tamarinds (ALMEIDA et al., 2010), Brazilian grape tree (WAGNER JUNIOR et al., 2011), and 'pitanga' (ANTUNES et al., 2012) seeds were reported to be more vigorous than the smaller and lighter ones.
Fruit or seed color is also a simple criterion for field verification of stage of maturity viewing to establish the right moment for harvest, that is, when the seeds have reached physiological maturity and consequently maximum germination and vigor. (MARTINS et al., 2004; SILVA et al., 2009; CARVALHO; NAKAGAWA, 2012; LOPES; NOBREGA; MATOS, 2014). Seeds should not be harvested before or after physiological maturity since, before, they have not reached maximum physiological quality and, after, because the deterioration process has already started (SILVA et al., 2009; CARVALHO; NAKAGAWA, 2012). But, for the production of yellow mombin plantlets, the seeds are extracted from mature fruits picked right from the plants or those which have dropped to the ground, where they remain for variable periods of time (COSTA et al., 2001). After the pulp is eliminated, the nuculania are observed to display a clear or a dark surface--the dark surface results from the oxidation processes caused by the time they remained in contact with the fermenting pulp.
Taking in consideration the commercial potential of this fruit, the present research work viewed the establishment of techniques and strategies for the selection of yellow mombin seeds capable of a germinating within shorter periods of time.
Material and Methods
Yellow mombin fruits were harvested during the months of April and May of 2012 from ten matrix plants in the College of Agrarian and Veterinarian Sciences in Jaboticabal, state of Sao Paulo, Brazil, or from small rural properties in the same state. The fruits were submitted to depulping by washing and friction on screens and running water after which they were dried for 24 hours in a shaded and ventilated place. The nuculania containing the true seeds were named seeds, according to definition found in the Rules for Testing Seeds (BRASIL, 2013). These seeds were used to carry two experiments: in the first one, they were classified as to color--beige and brown and as to size: small, medium-small, medium-large, and large. Those classes were base on 100 seed samples (Table 1).
Immediately after the seeds were extracted from the fruits, they were submitted to drying on a table in the laboratory; the superficial water remaining in the seeds was removed with the help of paper towel and then the seed water content was determined by the oven method under a temperature of 105 [+ or -] 3 [degrees]C for 24 hours (BRASIL, 2009), two replications of 4 seeds each. Seed length and width were measured with the help of a digital caliper and their weight determined with the help of a 0.001 g precision scale.
In the second experiment, the seeds were classified as to color in beige and brown. These seeds were either treated or not with a fungicide and, with the help of an emery, submitted or not to mechanical scarification in the base, apex, and lateral. Immediately before sowing, the seeds were treated with the fungicide Maxim[C] XL (metalaxil-M+fludioxonil) solution at a concentration of 100 mL of the commercial product/100 kg of seeds.
In both experiments, the following seed attributes were evaluated:
Seedling emergence in sand--it was conducted with four 20 seed replications in sterilized sand which was moistened to 60% of its water holding capacity (BRASIL, 2013). The sand was placed in plastic boxes (30.2 x 20.8 x 6.3 cm) which were kept on a workbench for 730 days (temperature 26 [+ or -] 3 [degrees]C). Normal seedlings emerging from the substratum were weekly counted and removed. When two seedlings emerged from the same seed, they were counted as one for the calculation of the emergence percentage.
First count of emergence and mean time for emergence--both counts were made concomitantly with the seedling emergence in sand test. In the first count test, normal seedlings emerging at 180 days after sowing, a date established with basis on the moment when 50% of the final evaluation took place (NAKAGAWA, 1999).
The mean time for emergence (TME)--was calculated based on the seedling count at each week up to the final evaluation date. The data so obtained were used to calculate the TME by means of the formula proposed by Labouriau and Valadares (1976).
The means were compared by the Tukey's test at the level of 5% of probability. The replications were distributed according to a completely random design the treatments arranged according to the following factorial combinations: 4 x 2 (size and color) in the first experiment and 4 x 2 x 2 (scarification x color x fungicide) in the second one. For the analysis of variances the data expressed in percentage were previously transformed in arc sen of the square root of x + 0.05. The means shown in the tables are nontransformed values.
Results and Discussion
The water content of recently harvested yellow mombin seeds, beige and brown, was not influenced by color or size--it was between 45.2 and 46.0%, respectively, independently of treatment. These moisture values are different from those reported by Gama et al. (2012), that is, 61.8%, probably because the seeds of this experiment were previously submitted to a 24-hour period of drying in a shaded room.
In the first experiment it was verified a significant interaction between color and size in the results of seedling emergence in sand. The speed of seedling emergence as evaluated by the first count and mean time for emergence tests were influenced only by the color of the seeds (Table 2).
The brown seeds were verified to be superior to the beige ones (Table 3). The faster emergence of the brown seeds is probably due to their oxidation since, according to Sampaio et al. (2007), yellow mombin fruits undergo high oxidation soon after the fruits are harvested. Such a process may have caused a reduction in the level of seed dormancy and a softening of the endocarp mechanical barrier. This barrier is thought to be the cause of Spondias mombin seed dormancy (CARVALHO; ALVES, 2008).
It is important to emphasize these results of the mean time for seedling emergence test since this is a relevant characteristic for the production of commercial plantlets (COSTA et al., 2001).
In Table 4, data of seedling emergence in sand as influenced by seed color and size are found. It is verified that medium-large seeds result in a larger number of seedlings independently of their color although, when the seeds were beige, the medium-large and the medium small resulted in statistically similar results. When the seeds were brown, the medium-large seeds did not differ from the large ones.
The percentage value of seedling emergence displayed by medium-large seeds (between 47 and 68%) may be considered similar to the value of 60% reported by Firmino, Almeida and Torres (1997) also with yellow mombin seeds after treating them for dormancy breaking. These results suggest that seed selection with basis on visual characteristics may be enough to get seeds with improved germination performance.
According to Carvalho and Nakagawa (2012), larger seeds, usually, result from better nourished seeds during their maturation, which result in well-formed embryos with larger amounts of reserve substances. In the case of yellow mombin seeds, the higher seedling emergence could also be ascribed to the fact that the nuculanium has a larger number of true seeds (AZEVEDO; MENDES; FIGUEIREDO, 2004) which increases the chance that at least one of those seeds is successful in germinating. Brito Neto et al. (2009) also reported to have observed that medium and large size Spondias tuberosa Arr. Cam seeds displayed germination and vigor higher than the small ones.
In the second experiment, none of the examined factors had any significant influence on speed of emergence as determined by the first count test (Table 5). But, on the other hand, the mean time for seedling emergence was significantly affected by the interaction between color and scarification as well as fungicide and scarification. As to the percentage of emerged seedlings, it was reduced from 33 to 24% by the treatment of the seeds with the fungicide.
This negative effect of the fungicide may be due to toxicity resulting from the excess to which the product is absorbed and retained by the spongeous fibers covering the nuculanium (seed) as shown by Azevedo, Mendes and Figueiredo (2004). These fibers form a tissue capable of absorbing water and this is the reason why the genus name is spondias, a Latin word meaning sponge. Franca Neto, Henning and Yorinori (2000) reported germination reduction and increment in abnormal seedlings in soybean seeds treated with Rhodiauram 500 SC.
When the effect of the interaction between scarification and color was examined, it was verified that the fastest germination (336 days) took place when brown seeds scarified on their lateral side were used
(Table 6). This result was significantly higher than that of the check treatment seeds of the same color which mean germination time was of 489 days. In a similar way, the interaction between scarification x fungicide also resulted in the shortest mean time of emergence (392 days) for the seeds scarified in the lateral and without the application of fungicide, mainly when compared to the check treatment treated with fungicide (472 days). On the other hand, the fungicide treated and scarified in the basal area of the seed also caused a reduction in the mean time for emergence. But, this treatment should not be used since, as shown in Table 5, the treatment of the seeds with the fungicide brought about a significant reduction in the final emergence percentage.
Firmino, Almeida and Torres (1997) and Lopes et al. (2009) reported results that differed from those of this experiment--according to their data, seeds which had been mechanically scarified both at the base and the top of the seed germinated faster and to a higher proportion whereas our results indicated that scarifying the seeds as indicated by those authors did not result in faster germination (Tables 5 and 6).
The efficiency of the scarification procedure depends on ability and practice of the technician; if the scarification is too deep, it may result in damage to the embryonic axis or, if too superficial, it may be not enough to overcome the mechanical barriers that block seed germination (MARTINS et al., 2012).
Choosing brown and medium-large seeds is an efficient strategy to accelerate seedling emergence.
Treating the seeds with fungicide was harmful to the germination process.
The lateral scarification of brown seeds permitted a reduction in the period necessary for the completion of germination from 489 to 336 days.
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Submissao: 17/02/2016 Aprovacao: 20/02/2018 Publicacao: 29/03/2019
Cibele Chalita Martins (I), Givanildo Zildo da Silva (II), Lais Dezen Durigan (III), Roberval Daiton Vieira (I)
(I) Engenheiro(a) Agronomo(a), Dr(a)., Professor(a) da Faculdade de Ciencias Agrarias e Veterinarias, Universidade Estadual Paulista, Campus de Jaboticabal, Via de Acesso Prof. Paulo Donato Castellane, s/n, CEP 14884-900, Jaboticabal (SP), Brasil. Bolsista PQ-1D do CNPq. cibele@ fca.unesp.br (ORCID: 0000-0002-1720-9252) / firstname.lastname@example.org (ORCID: 0000-0002-7157-3223)
(II) Engenheiro Agronomo, Dr., Pos-doutorando pela Universidade Federal de Goias, Campus Jatai, Rod. BR 364 KM 192--Setor Parque Industrial, 3800, CEP 75801-615, Jatai (GO), Brasil. Bolsista PNPD. email@example.com (ORCID: 0000-0002-6380-1599)
(III) Engenheira Agronoma, Pesquisadora Autonoma, Cooperativa de Trabalho dos Profssionais de Agronomia Ltda., Av. Carneiro Leao, 65, CEP 87014-010, Maringa (PR), Brasil. firstname.lastname@example.org (ORCID: 0000-0002-3343-9816)
Table 1--Yellow mombin seeds classification as to size and weight. Tabela 1--Classificacao das sementes de caja quanto ao tamanho e peso. Size Length (mm) Width (mm) Weight (g) Small 25 14 1.093 Medium-small 29 16 1.623 Medium-large 31 18 2.159 Large 33 19 2.341 Table 2--Summary of the analysis of variance of yellow mombin seeds results as influenced by seed color and size. Tabela 2--Resumo da analise de variancia em sementes de caja classificadas quanto a cor e ao tamanho. Mean square Source of variation GL Emergence First count TEM Color (C) 1 5.281 * 8.000* 50.562 * Size (S) 3 8.531 ** 0.125 (ns) 8.123 (ns) C x S 3 2.948 * 3.000 (ns) 6.828 (ns) Residue 24 0.865 1.479 3.946 CV (%) 14.80 25.96 26.94 Where in: MTE = mean time for emergence; CV = coefficient of variation; GL = degrees of freedom; ** = significant at the level of 1% of probability; * = significant at the level of 5% of probability; (ns) = non significant. Table 3--Effects of seed color on the results of the first count (FC) and the mean time for seedling emergence (MTE) tests of yellow mombin seeds. Tabela 3--Primeira contagem (PC) e tempo medio de emergencia (TME) de plantulas em areia de sementes de caja (Spondias mombin L.), classificadas quanto a cor. Color Tests Beige Brown FC (%) 18 B 28 A MTE (days) 273 B 194 A Means, in the same line, followed by the same large case letter, are not statistically different according the Tukey's test at the 5% level of probability. Table 4--Effects of yellow mombin seed color and size on seedlings emergence in sand length x width; weight. Tabela 4--Emergencia de plantulas em areia de caja (Spondias mombin L.), classificadas quanto a cor (bege e marrom) e ao tamanho. Color Size (1) Beige Brown Small (25x14 mm; 1,1 g) 39 bA 20 bB Medium-small (29x16 mm; 1,6 g) 40 abA 26 bB Medium-large (31x18 mm; 2,2 g) 68 aA 47 aA Large (33x19 mm; 2,3 g) 37 bA 50 aA Means followed by the same lower case letter in the column and capital in line, are not statistically different according the Tukey's test at the 5% level of probability. Table 5--Summary of the analysis of variance of tests results of Spondias mombin seeds submitted or not to fungicide treatment and mechanical scarification. Tabela 5--Resumo da analise de variancia em sementes de caja (Spondias mombin L.), classificadas quanto a cor e submetidas ou nao ao tratamento fungicida e escarificacao mecanica. Mean square Source of variation GL Emergence First count TEM Color (C) 1 1.562 (ns) 1.891 (ns) 54.347 ** Fungicide (F) 1 10.562 ** 1.891 (ns) 5.568 (ns) Scarification (S) 3 0.562 (ns) 1.016 (ns) 12.211 * C x F 1 0.062 (ns) 0.016 (ns) 3.122 (ns) C x S 3 1.562 (ns) 0.682 (ns) 11.749 * F x S 3 0.562 (ns) 0.432 (ns) 14.771 ** C x F x S 3 0.396 (ns) 0.057 (ns) 7.572 (ns) Residuo 48 0.750 0.693 3.475 CV (%) 16.02 52.74 13.72 Where in: MTE = mean time for emergence; CV = coefficient of variation; GL = degrees of freedom; ** = significant at the level of 1% of probability; * = significant at the level of 5% of probability; (ns) = non significant. Table 6--Mean time for the seedling emergence in sand of yellow mombin seeds classified as to color and submitted to mechanical scarification as well as when submitted or not to mechanical scarification and fungicide treatment. Tabela 6--Tempo medio de emergencia de plantulas em areia de sementes de caja (Spondias mombin L.), classificadas quanto a cor e submetidas a escarificacao mecanica, bem como quando submetidas ou nao ao tratamento fungicida e escarificacao mecanica. Color Fungicide Scarification Beige Brown With Without Check treatment 460 bB 489 bB 472 bB 432 bB Basis 432 bB 383 abA 366 aA 449 bB Apex 471 bB 441 bB 427 bB 485 bB Lateral 473 bB 336 aA 418 bB 392 aA Means, in the same line, followed by the same large case letter, are not statistically different according the Tukey's test at the 5% level of probability.