Temperature Dependent Seed Germination of Dalbergia nigra Allem (Leguminosae)

Temperature Dependent Seed Germination of Dalbergia nigra Allem (Leguminosae)

Fernanda G. A. Ferraz-Grande and Massanori Takaki^*

Departamento de Botânica - UNESP CP 199 Rio Claro - SP, Brazil

ABSTRACT

The germination of endangered species Dalbergia nigra was studied and 30.5° C was found as optimum temperature, although the species presented a broad temperature range where germination occurs and light had no effect. The analysis of kinetics of seed germination confirmed the asynchronized germination below and above the optimum temperature. The light insensitive seed and germination also at high temperatures indicated that D. nigra could occur both in understories and gaps where the mean temperature was high.

Key words:Dalbergia nigra, endangered species, seed germination, temperature

INTRODUCTION

Dalbergia nigra commonly known as jacarandá-da-Bahia, caviúna, jacarandá is an endangered species found in Atlantic Forest from Bahia to São Paulo States (Lorenzi, 1992). The species is considered as endangered specially due to its use as timber source and use of fire for agricultural pratices. It is also recommended in the reforestation programs of degraded areas (Crestana et al., 1993). In spite of its importance, the seed germination of this species was not studied. Determination of cardinal temperatures is important for the understanding of the ocurrence of this species in natural environment (Laboriau, 1983). The temperature of the soil always is different of the air and in a forest the occurrence of gap of canopy results in broad range of temperature variation during the day (Bazzaz & Pickett, 1980). In accordance with germination behaviour the species can be classified as pioneer, secondary and climax (Budowski, 1965). Mostly the pioneer species present light sensitive seeds or germination at high temperatures and in some cases the pioneer species can germinate under both high temperature in darkness or under white light at 25° C (Vazquez-Yanes & Sada, 1985).

In the present paper, we describe the temperature dependent germination behaviour of D. nigra.

MATERIAL AND METHODS

Seeds of D. nigra were harvested at university campus. For each germination test 20 seeds on imbibed filter paper for each of four 90 mm diameter Petri dishes were used throughout. Isothermic incubations were carried out in B.O.D. incubators in the range of 10 to 45° C. Seeds with 2 mm long roots were considered as germinated. Day-light fluorescent light at 320mW.cm^-2 were used when indicated. The germinability was analysed according to Labouriau and Agudo (1987). Mean time of germination was obtained as follows: Velocity of germination as 1/t where t=Sni.ti/Sni, and ni=number of germinated seeds at time ti; relative frequency of germination as ni/Sni. The entalpy of activation of germination DH_n^# (Kcal.mol^-1) was calculated as: [R.T(q-T).(Tm+TM)/(T-Tm).(TM-T)], where R = universal gas constant (1.987 Kcal.mol^-1), T= actual temperature (° K), TM= maximum temperature of germination (° K), Tm= minimum temperature of germination (° K) and q = mean temperature of TM and Tm. The mean arc sin Ö % were analysed by Tukey test (Sokal & Rolph, 1981). The data of velocity of germination were submitted to logistic regression according to Hsu et al. (1984).

RESULTS AND DISCUSSION

Figure 1 shows the temperature range where seeds of D. nigra germinated. Between 20 and 30° C, seeds germinated without statistical differences indicating a broad range as optimum temperature. The germination of seeds incubated at continuous white light and continuous darkness were similar and here we are presenting only the data obtained under continuous white light. These results confirmed the broad distribution of the species in Brazil (Lorenzi, 1992).

The logistic regression of data of velocity of germination indicated that the highest velocity was found at 30.59° C with correlation coeficient of 0.999 and standard error of curve fitting of 0.00047 (Figure 2). This meant that the calculated optimum temperature was 30.59° C where seeds germinated fast and that almost all seeds germinated (98%). The optimum temperature for tropical plant species was between 20 and 35° C (Brasil, 1992) although Vazquez-Yanes and Orozco-Segovia (1974) reported near 40° C as optimum temperature for Ochroma lagopus.

Figure 3 shows the relative frequency of germination and it was observed that below and above optimum temperature the distribution of germination was spread in time but at optimum temperature there was a synchronization of germination with tendency of unimodal distribution of germination frequency. For crops the synchronization of seed germination is important for homogeneous growth of plants and some pratices are recommended such as priming (Heydecker & Coolbear, 1977) but in the nature the asynchronised seed germination is more important than synchronised germination for the maintainance of delayed-transient seed bank in the soil (Garwood, 1989) and when conditions are adequate, the germination process is induced for the establishment of successional events.

The enthalpy of activation of germination was calculated and according to Laboriau and Agudo (1987), between +12Kcal and -12Kcal the velocity of germination is dependent on the oxygen and water difusion processes (figure 4). This meant that below 22.5 (+12Kcal) and above 31.6° C (-12Kcal) the germination process was dependent on other processes such as phase transition at low temperatures and thermodenaturation of protein at high temperatures (Taylorson and Hendricks, 1972).

Our results indicated that the species was light insensitive and only the temperature was responsible for the control of germination. Because the seeds of D. nigra could also germinate at high temperature, although the kinectics of seed germination indicated that the process was limited, probably by denaturation of proteins the possibility was that the species occurs in both understories and gaps where the mean temperature usually was high (Van Der Meer et al., 1999)

RESUMO

A germinação de sementes de Dalbergia nigra Allem, comumente conhecida como jacarandá-da-Bahia, caviúna, jacarandá, uma espécie em extinção, foi estudada e determinamos a temperatura ótima de 30,5° C. A espécie apresenta uma ampla faixa de temperatura onde a germinação ocorre e a luz branca não influenciou o processo. A análise da cinética da germinação de sementes confirma a germinação não sincronizada acima e abaixo da temperatura ótima de germinação. A semente insensível à luz e a germinação também em altas temperaturas indicam que D. nigra pode ocorrer tanto na sombra da vegetação bem como em clareiras.

ACKNOWLEDGEMENTS

F.G.A.F.G had CAPES studentship and M.T. was CNPq Research fellow. This work was aided by grants from FAPESP, CNPq and FUNDUNESP.

Received: January 14, 2000;

Revised: March 02, 2000;

Accepted: April 23, 2001.

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*

Author for correspondence

Publication Dates

• Publication in this collection
  24 Apr 2002
• Date of issue
  Dec 2001

History

• Accepted
  23 Apr 2001
• Reviewed
  02 Mar 2000
• Received
  14 Jan 2000