The Effect of Different Temperatures and Durations on the Dormancy Breaking of Black Locust ( Robinia pseudoacacia L . ) and Honey Locust ( Gleditsia triacanthos L . ) Seeds

In order to break seed dormancy, different temperatures (20, 30, 40, 50, 60, 70, 80 and 90o C) and durations (10, 20 and 30 minutes) were applied to black locust (Robinia pseudoacacia L.) and honey locust (Gleditsia triacanthos L.) seeds, in the Seed Laboratory of Dicle University Faculty of Agriculture in 2009. According to the research results, the highest germination rate for black locust seeds was obtained in the case of 90o C for 30 minutes pre-treatment (94.5%), whilst the lowest value was obtained for the 40o C for 10 minutes pretreatment (7.5.0%). For honey locust the highest value was obtained at 50o C for 30 minutes (25.5%) and the lowest value was obtained in the case of control sample (6.8%).


Introduction
Black locust (Robinia pseudoacacia L.) and honey locust (Gleditsia triacanthos L.) originated from North America and were spread to large areas throughout the world for various purposes (Cronk and Fuller, 1995;Singh et al., 1991).These species are legume trees which are drought resistant, light lover, thorny and show moderate to fast growth speed (Danso et al., 1995;Burner et al., 2005).The wood of these species has various utilizations: firewood, sawn timber, poles for fences, wind-breaking, erosion control, forage crops and the species are important in beekeeping (Burner et al., 2005;Singh et al., 1991;Sefik, 1995).
In general, the production of black locust (R. pseudoacacia L.) and honey locust (G.triacanthos L.) is from seeds.Without pre-treatments seed germination rate is low because of the physiological dormancy induced by the hard seed coats (Geneve, 2008, Singh et al., 1991).In order to increase germination rate, various heating pre-treatments are applied: Masaka and Yamada (2009) obtained the highest germination rates (45.3%) for their heat shock application to black locust seeds by keeping them at 60 o C for 3 hours.Bolin (2009) in his heat applications to Galactia regularis (Fabaceae), Lupinus perennis (Fabaceae) and Rhus copallinum seeds, obtained the highest germination values by keeping the seeds at 80 o C (G. regularis and L. perennis) and 90 o C (R. copallinum) for 10 minutes.Khadduri et al. (2002), by soaking black locust (R. pseudoacacia) seeds in hot water (98 o C) for 24 hours, achieved 41% germination rate.Basbag et al. (2009) have obtained seed germination rates between 8.39 and 29.52% for caper (Capparis ovata) seeds by applying different temperatures and durations.
The aim of this study is to assess the increase in the germination rates of black locust and honey locust seeds by applying pre-germination treatments of different durations and temperatures.

Materials and methods
The study was performed in 2009 in Dicle University -Faculty of Agriculture Seed Laboratory.Black locust (R. pseudoacacia) and honey locust (G.triacanthos) seeds were collected from trees within the campus of Dicle University (elevation: 700 m, latitude: N37 o 55´27.3˝and longitude: E40 o 17´05.1˝), on the 21 st of November 2009.Seeds separated from pods were washed in water and empty, puny ones were removed.The weight of 1000 seeds was 15.6 g for black locust and 165.7 g for honey locust.
In order to break dormancy, seeds were kept within the drying cabinet (ULM-800) in different temperature environments (20,30,40,50,60,70,80 and 90 o C) and for different durations (10, 20 and 30 min.).Germination experiments were performed in Petri dishes (using paper towels and distilled water) and for each treatment 50 seeds were used with 4 replications.The Petri dishes were placed in a germination cabinet (Growth Chamber, GC 400), at 25 o C temperature and 70% humidity, and the cabinet was programmed to be under light for 12 hours (flourescent, 1500 Lux) and 12 hours under darkness.The 4 replications of the no-pretreatment control sample were placed in the germination cabinet, under the same conditions.The ger-minated seeds were counted periodically starting from the 7 th day until the 30 th day.Germination percentage (%) was calculated according to the below formula (Pieper, 1952); GR: Germination (%) ni: Number of count days ti: Number of germinated seeds at each count T: Total number of germinated seeds The germination values for each pre-treatment were compared, after angle transformation (Zar, 1999) with MSTATC statistical package software (Michigan State University, East Lansing, MI) according to the Randomised Blocks Design.

Results and discussion
Different temperatures and different durations of the pre-germination treatments applied to black locust (Robinia pseudoacacia L.) and honey locust (Gleditsia triacanthos L.) seeds had a statistically different effect on seed germination (Tab. 1 and 2).For black locust seeds, the average germination values varied between 7.5% and71.8%,according to the different temperatures applied during the pre-germination treatment.The highest rate of germination was obtained at 90 o C and the lowest rate was obtained for the control sample (no treatment).Considering the dual effect of temperature and duration the germination values varied between 7.5% and 94.5%.The highest germination value was obtained at 90 o C and 20 minutes duration, whilst the lowest germination value was obtained for the control sample (7.5%).
For honey locust seeds, the average germination values varied between 6.8% and 19.3%, according to the different temperatures applied.The highest percentage of germina- 12.0 h-l 13.0 g-j 13.5 e-h 12.8 30 14.0 g-j 14.

Fig. 1 .
Fig. 1.The effect of different temperatures and durations on germination rates of black locust (Robinia pseudoacacia L.) seeds

Fig. 2 .
Fig. 2. The effect of different temperatures and durations on germination rates of honey locust (Gleditsia triacanthos L.) seeds Tab. 1.The effect of different temperatures and durations on germination rates of black locust (Robinia pseudoacacia L.) seeds