MATERIALS AND METHODS

Seed preparation: Some seeds of Eucalyptus species (viz., E. citriodora, E. camaldulensis and E. cloeziana) were obtained from Forestry Research Institute of Nigeria/JICA Kaduna house station as shown in Fig. 1-3. The seeds were thoroughly cleaned and screened before conducting the experiment. The seeds were kept under normal room temperature before the experiment. All experiments were carried out under laboratory condition.

Determination of seed bulk density: The bulk densities of the three species of Eucalyptus (i.e., E. citriodora, E. camaldulensis and E. cloeziana) were found by filling a container of specific volume with the seeds after which it was tapped and leveled.

Fig. 1:	Eucalyptus citriodora seeds

Fig. 2:	Eucalyptus camaldulensis seeds

Fig. 3:	Eucalyptus cloeziana seeds

Fig. 4:	Light transmissivity set up

The mass of the seeds inside the container was weighed using a digital weigh balance (Denver Instrument XP-300) reading to 0.01 g as conducted by Aremu and Fadele (2011). The ratio of the seed mass to the volume of the container gives the bulk density of the seed as reported by Sugri et al. (2011) in Eq. 1. This was replicated fourteen times for each of the species while their average values were calculated:

(1)

Determination of light transmissivity: Light transmissivity is used to indicate the quantity of light that can pass through a material. The set up for the experiment included a light source, a Lux meter and a small transparent container as shown in Fig. 4. The light source was focused at a distance of 9.0 cm from the light receptor with the transparent container being placed on it. The container was loaded with the Eucalyptus species (E. citriodora, E. camaldulensis and E. cloeziana) to 11.60 cm³ of its capacity and leveled; after which the light intensity value was read from the Lux meter. This was replicated for six times for each of the Eucalyptus species. Before this, the radius of the container was measured as 2.80 cm and the seed dept was calculated as 0.471 cm. The experiment was carried in a dark environment to prevent light interference from other source.

Determination of germination capacity: Some seeds of the three Eucalyptus species (viz., E. citriodora, E. camaldulensis and E. cloeziana) were collected from the whole bulk and made to fill up a container having a specific volume of 5.80 cm³, after which it was planted in boxes filled with sharp sand (Franks et al., 1995). This was wet periodically until all the seeds have germinated. The seedlings were subsequently harvested and counted after 11 days. The germination capacity of each Eucalyptus species were found on volume basis by calculating the ratio of the seedling harvested to the seed volume planted respectively for each of the species as given in Eq. 2:

(2)

RESULTS AND DISCUSSION

Bulk density of Eucalyptus seeds: The bulk densities mean values of some Eucalyptus seeds namely, E. citriodora, E. camaldulensis and E. cloeziana were found to be 1.18, 1.13 and 1.14 g cm^-3 with ranges of 1.16-1.24, 1.10-1.17 and 1.12-1.16 g cm^-3, respectively. The value obtained for Eucalyptus species indicated that good portion of their seeds would not float in water and this asserts that their true densities are more than that of water. Most researchers have conducted experiment involving both true and bulk densities with the true density having greater value than the bulk density (Aremu and Fadele, 2011; Balasubramanian, 2001; Baryeh, 2001; Isik and Izli, 2007). This shows that water could be used to for the viability of the seed by dropping them in it. The bulk densities values of each of the Eucalyptus species were subjected to paired sample t-test statistics using SPSS 15 version, by comparing them with one another to determine their level of discrepancy. Eucalyptus camaldulensis compares favourably with E. cloeziana with a significance value greater than 0.05; thus indicating that there is a little difference in their bulk densities. However, the significance values obtained when the bulk density of E. citriodora was compared to that of E. camaldulensis and E. cloeziana were much more less than 0.05; indicating a significant difference in their bulk densities. Figure 5 shows the bulk densities of some Eucalyptus species.

Fig. 5:	Bulk densities of some Eucalyptus species

Fig. 6:	Light transmissivity of some Eucalyptus species

Fig. 7:	Germination capacity of some Eucalyptus species

Light transmissivity of Eucalyptus seeds: The light transmissivity of Eucalyptus seeds namely E. citriodora, E. camaldulensis and E. cloeziana were found to have mean values of 12.17, 2.00 and 2.66 lux, respectively as shown in Fig. 6. The light source was also found to have a value of 2380 lux; indicating that the Eucalyptus seeds are opaque in nature and will allow little or no amount of light to pass through it. E. citriodora has the highest value of light transmissivity because of its seed size which creates pore spaces for light to pass. This was also observed in E. cloeziana seed which is larger than E. camaldulensis and also having higher light transmissivity, even though not as high as that of E. citriodora. This property could be applied in developing a device that can be used to identify viable seed of Eucalyptus.

Germination capacity of Eucalyptus seeds: The mean values of germination capacity for some Eucalyptus seeds (viz., E. citriodora, E. camaldulensis and E. cloeziana) were found to be 25, 94 and 64 seedlings cm^-3 with ranges of 23-28, 88-104 and 56-73 seedlings cm^-3, respectively. Eucalyptus camaldulensis obviously has the highest value of germination capacity as shown in Fig. 7. It was observed at germination stage that the seedlings of Eucalyptus camaldulensis densely covered the planting area while seedlings of Eucalyptus citriodora sparsely spread over the planting area. Moreover, germination rate of E. camaldulensis was much higher than that of E. citriodora and E. cloeziana while the stalk of E. citriodora is stronger than that of E. camaldulensis and E. cloeziana; and able to withstand water droplet impact during wetting unlike the other two species. The fewer number of seedlings of E. citriodora that germinated could be due its larger volume occupied by its seeds, when compared to E. camaldulensis and E. cloeziana. The circumscribing radius of E. citriodora seed was found to be more than 2.00 mm greater than the other two species and similar to that obtained by Beltrati (1978).

CONCLUSION

Some physico-viable properties of E. citriodora, E. camaldulensis and E. cloeziana seeds were investigated. The results obtained revealed that the bulk densities and germination capacity of E. citriodora, E. camaldulensis and E. cloeziana seeds have ranges of 1.16-1.24, 1.10-1.17 and 1.12-1.16 g cm^-3 and 23-28, 88-104 and 56-73 seedlings cm^-3 with their light transmissivity having mean values of 12.17, 2.00 and 2.66 lux, respectively. All these data could be useful testing for the viability of these seeds. However, further research should be conducted on non-viable seeds of these eucalypts for comparison.

ACKNOWLEDGMENT

The authors will like to thank the Forestry Research Institute of Nigeria for providing all the seeds used for the conduct of this research and the Department of Agricultural Engineering, Federal College of Forestry Mechanization for making their facilities available. Many thanks to the staffs of Forestry Research Institute of Nigeria/JICA Trial Afforestation Kaduna for the assistance rendered during the conduct of the research.