Determination of the germination temperature of Moringa oleifera seeds with support of vigor tests

Determinación de la temperatura de germinación de las semillas de Moringa oleifera con apoyo de las pruebas de vigor

Marlen Navarro,^I S. M. Cicero,^II F. G. Gomes-Junior,^II

^IEstación Experimental de pastos y Forrajes “Indio Hatuey”. Universidad de Matanzas. Central España Republicana. CP44280. Matanzas, Cuba.
^IIEscola Superior de Agricultura “Luiz de Queiroz”. Universidade de São Paulo. Brasil.

ABSTRACT

Samples from six seeds lots of Moringa oleifera cv. Supergenius were used with the objective of determing the optimum temperature for the germination test of this species. The temperatures 25°C; 30°C and 20-30°C were evaluated. The used vigor tests were: germination test (G), germination rate index (GRI), electric conductivity test (EC) and the plantlet computerize analysis through the SVIS software and the indexes that are automatically generated. All variables were subjected to analysis of variance, differences were declared significant according to Tukey test (P≤0.05) with the help of the statistical package SPSS 22.0.The EC values showed better seed quality in the lots two and four. For G and FGC, the lot four showed the highest value for the evaluated temperatures. Although for FGC the lot four at 30°C did not differ from lots one, two and six. The best GRI performances were for the  lots one, two, four, five and six at 30°C.For the indexes generated by the SVIS, the vigor index (VI) in lot four at 30°C was higher, as for the growth index (GI).The analysis of the uniformity index (UI) for temperatures showed differences for the lots two, four and five; always with the highest values for 30°C.For plantlets length (PL) lots one, five and six showed the best performance at 30°C without differ from 25°C. Neither differ lot one for25 and 30°C. While lot four showed higher performance for PL at 30°C in relation to other temperatures. In a general way, the study results showed the best performance of moringa seeds at 30°C.

Key words: moringa, germination, SVIS®, vigor.

RESUMEN

Se utilizaron muestras de seis lotes de semillas de Moringa oleifera cv. Supergenius con el objetivo de determinar la temperatura óptima para el test de germinación de esta especie. Se evaluaron las temperaturas: 25°C; 30°C y 20-30°C. Las pruebas de vigor empleadas fueron: test de germinación (G), índice de velocidad de germinación (IVG), test de conductividad eléctrica (CE) y análisis computadorizado de plántulas a través del software SVIS y los índices que se generan automáticamente. Todas las variables se sometieron a análisis de varianzas, las diferencias se declararon significativas según el test de Tukey (P ≤ 0.05) con auxilio del paquete estadístico SPSS 22.0. Los valores de CE indicaron mejor calidad de las semillas en los lotes 2 y 4. Para G y PCG, el lote 4 exhibió el valor más alto para las temperaturas evaluadas, aunque para PCG el lote 4 a 30 °C no difirió de los lotes 1, 2 y 6. Los mejores comportamientos de IVG fueron para los lotes 1, 2, 4, 5 y 6 a los 30 °C. Para los índices generados por el SVIS, el índice de vigor (IV) en el lote 4 a 30°C fue superior, al igual que para el índice de crecimiento (IC). El análisis del índice de uniformidad (IU) para las temperaturas mostró diferencias para los lotes 2, 4 y 5, siempre con los valores más altos para 30 °C. Para la longitud de las plántulas (LP), los lotes 1, 5 y 6 exhibieron el mejor desempeño en 30 °C, sin diferir de 25°C. Tampoco difirió el lote 1 para 25 y 30°C. Mientras que el lote 4 mostró desempeño superior para LP a 30 °C con relación a las demás temperaturas. De manera general, los resultados del estudio indicaron el mejor desempeño de las semillas de moringa a 30°C.

Palabras clave: moringa, germinación, SVIS®, vigor .

Under controlled conditions, when humidity does not limit, the rate and germination percentage are controlled by temperature (Bewley and Black, 1984).For each species there is a temperature range within which the germination process can be completed in a reasonable time.

The process of seeds germination involves a series of metabolic activities, during which a sequence of chemical reactions occur with own demands in terms of temperature (Marcos Filho, 2005). Similarly, the temperature is essential for germination, because it acts on the water absorption rate and in biochemical reactions that determine the whole process (Bewley and Black, 1984); in consequence, it affects the rate and the uniformity of the total germination (Carvalho and Nakagawa, 2012).Therefore, temperature is a factor of vital importance in the germination, emergence and vigor expression.

For the analysis of moringa seeds, the germination test is not still standardized. There are few studies related with the optimal conditions of light, temperature and substrate for germination. From the growing interest in this species, the objective of this research was to determine the optimal germination temperature of Moringa oleifera seeds, with the purpose of contributing to the analysis of seeds of this species and the standardization of the germination test.

MATERIALS AND METHODS

Seeds from six lots of Moringa oleifera cv. Supergenius were used and three options of temperature were evaluated:  25°C; 30°C and 20-30°C.

Germination test. Four repetitions of 25 seeds from each lot were used for each temperature. The test was performed in substrate of paper towel humidified with distilled water in the ratio 1:2. 5 (paper: water).The rolls were kept in the germinator according to the evaluation temperature until 14 days after sowing.

Germination rate index. It was calculated during the germination test and the counts were performed daily at the same time, from the sowing. For the calculation the formula proposed by Maguire (1962) was used.

Electric conductivity test. Four repetitions of 25 seeds for each lot were used, which were weighed and placed in a container with 75mL of deionized water and kept in the germinator at 25 ± 1°C, for 24 h in dark (ISTA 2009).The electrical conductivity readings were performed in a DIGIMED equipment DM-31.The readings values were divided between the seeds weight and the results expressed in μS.cm^-1.g^-1.

RESULTS AND DISCUSSION

The germination test is not sufficient to detect differences in the physiological potential of seeds, especially when these are exposed to different temperatures. Therefore the vigor tests are considered important tools in seed testing laboratories.

The conductivity values expressed in μS.cm^-1.g^-1 (table 1) showed better quality in lots two and four, while lots five and six were those of lower vigor.

The principle of the electric conductivity test states that the less vigorous seeds (more deteriorate) have lower rate of restoring the integrity of cell membranes during the imbibitions and therefore release higher amounts of solutes for the external environment (Hepburn et al., 1984).

For germination, the lot four showed the highest value for the evaluated temperatures (table 1).This performance was associated to the results obtained in the electric conductivity test and shows that vigor is directly related  to the cell membranes integrity (Marcos Filho, 2005). For 30°C,the lot four did not statistically differ from lots one, two and six. The worst performance of germination was for lot three.

According to the data of table 1, the germination process was markedly affected in lot six when seeds germinated at 25°C.This could be associated to high values of electric conductivity that were recorded in this lot. According to Carvalho and Nakagawa (2012), in the low vigor seeds are high disorganization in the cell membranes structure and thus prevent the reconstitution of metabolic functions for the star and completion of germination stage.

For the first germination count (table 1) the lot four showed the highest values for the temperatures 20°C, 30°C and 20-30°C. It is important to highlight that for 30°C lot four did not differ from lots one, two and six. Similar performance was verified for the germination test. The analysis of temperature for lots showed the highest value at 30°C in lots one, two and six while the FGC value in lot five was similar for 25°C and 30°C, also 30°C did not show differences at 20-30°C.

Lot four showed the highest values for the germination rate index (table 1), although the same lot did not differ from lot two at 30°C. For lots according to the evaluated temperatures, the best performances were for lots one, two, four, five and six at 30°C.The germination rate in lot three was the lowest in the three evaluated temperatures, which is attributed to the low vigor shown by the seeds through the electric conductivity readings. As shown in table 1, the GRI was significantly higher at 30°C in relation to the other temperatures.

 The integration of automated systems with the vigor tests considered traditional in the evaluation of seeds quality may contribute to the development of methodologies that allow the standardization of vigor tests (Marcos Filho, 2010).

The results of the evaluation of physiological potential of moringa seeds are showed on table 2, evaluated in different germination temperatures through computer analysis of plantlets with seven days of age, analyzed by the SVIS® software.

For vigor index (VI), it was verified that the lot four was higher for 25°C and 30°C, while at 20-30°C lot four did not show differences with lots one and two. In lot four, the VI value for 30°C was higher in high degree relative to 25°C and 20-30°C.While lot five was statistically similar at 25°C and 30°C, and higher for 20-30°C.

For the plantlets length index (GI), the results for 25 and 30°C showed better performance of lot four. For 30°C, the highest GI values were for lots one, two and four. Lot two was highlighted, although without significant differences with lots one and four. Among the evaluated temperatures, the Tukey test reported differences in lots four and five. For lot four, the highest value was at 30°C. Otherwise ,the GI of lot five for 25 and 30°C was statistically similar and differed from the performance for 20-30°C.The same performance for the vigor index (VI) was identified.

The uniformity index (UI) identified the best performance for 25°C (without statistical differences) of lots one, two and four. For 30°C were the lots two and four, and for 20-30°C were the lots one, two, four, five and six. The analysis for temperatures showed differences for lots two, four and five. Always with the highest values for 30°C, althought lots two and five did not differ for 25 and 30°C.

For the individual plantlets length (PL) at 25°C and 30°C temperatures, the highest values were for lot four. While for 20-30°C, there were not significant differences for lots one, two, four and five. In the temperatures analysis, lots one, five and six showed the best performance at 30°C, without differing from 25°C.Nor it differed lot one for 25 and 30°C.Lot four showed higher performance in plantlets length at 30°C, in relation to the other temperatures.

The use of SVIS® allowed to evaluate the seeds vigor and to determine the contribution of plantlets performance in the different evaluated temperatures. Marcos Filho (2010) stated that as added value the SVIS® make possible to reduce subjectivity, human interference and the necessary period for conducing the vigor tests.

For the parameters related with vigor and those generated by the SVIS®, the results showed higher performance for 30°C, intermediate performance for 25°C and the worst performance for 20-30°C.So it is recommended to use  30°C as optimal temperature for the assembly of the germination standard test of moringa seeds.

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Carvalho, N. M. & Nakagawa, J. 2012. Sementes: ciência, tecnologia e produção. 5th ed., Jaboticabal: FUNEP, 590 p.

ISTA 2009. International Rules for Seed Testing. Seed Science and Technology, 333 p.

Maguire, J. D. 1962. “Speed of germination—aid in selection and evaluation for seedling emergence and vigor”. Crop science, 2 (2): 176–177.

Marcos Filho, J. 2005. Fisiologia de sementes de plantas cultivadas. FEALQ, 495 p.

Received: November 24, 2015
Accepted: February 5, 2016

Marlen Navarro, Estación Experimental de pastos y Forrajes “Indio Hatuey”. Universidad de Matanzas. Central España Republicana. CP44280. Matanzas, Cuba. Email: boulandier@ihatuey.cu