The process by which a seed is activated from dormancy to an active state of growth and development into a plant is called germination. Many seed psychologists consider seed germination to be a process that begins with water imbibitions and ends with the emergence of the radical [1]. The manifestation of germination is increased water absorption by the seed, followed by the appearance of a radicle (2 mm long). Most legume seeds face difficulty to germinate, and the success of the plant (which can be determined by germination and establishment) depends largely on seed germination. The seeds of some legume species, such as Cassia, Albizia, Acacia and Leucaena, have a hard seed coat [2,3,4,5,6], mainly due to the accumulation of lignin, suberin or cutin on the seed coat as well as on mature endosperm [7,8,9,10]. Seed dormancy is a major problem in tropical forests due to the lack of penetration of the seed coat [11]. Some methods to promote germination in a few tropical plant seeds have been standardized till now [12,13]. Little is known about the mechanisms of breaking seed dormancy in trees such as Acacia, Cassia, and Leucaena[14,15].

Pretreatment, broadly defined, refers to the processes that seeds must go through before being sown. The utility of priming has also been reported for many field crops such as wheat, maize, sugar beet, soyabean, and sunflower [17,18]. We know that light plays a vital role in the regulation of germination [19]. It has been demonstrated that the mechanism of light sensitivity in seeds is related to the phytochrome pigment, which is widely dispersed in plants and photochemically reactive [20].The most popular method of treating legumes is hot water pretreatment, which successfully reduces the hard seededness and improves seed permeability [21,22,34]. As per several studies [23,24,25,26] gibberellins are now widely acknowledged to be strong promoters of seed germination. Applying IAA to Alstonia scholaris [27], Saussurea costus [28], and red sanders [29] was also found to increase the percentage of seed germination. Hormones also have a well-established role in reviving the dormancy of forest tree seeds [30,31]. To disrupt the physiological dormancy of hard seed coat species, exogenous treatments of GA3 have been widely used [32]. Use of GA as a growth promoter has been established in pennycress [35,36]. Potassium nitrate has been reported to enhance seedling growth by improving nutrient uptake and promoting robust root and shoot development [37,40]. Application of thiourea has shown promise in breaking dormancy and speeding up germination, especially for seeds with hard or impermeable seed coats [38]. In legumes, such as chickpea and soybean, thiourea has been found to promote faster germination and higher seedling vigor [39].

Materials and Methods

In the recent study, five plant species (Acacia mangium Willd., Albizia procera (Roxb.) Benth, Bauhinia acuminata Linn., Millettia pinnata (L.) and Peltophorum pterocarpum (DC.) K.Heyne were taken as plant material to determine germination percentage. These plants grow abundantly in and around Purulia, westernmost district of West Bengal, India. Purulia is located between 23.33⁰ North and 86.36 East longitudes. The soil of Purulia is of lateritic type. The temperature ranges from 26-45°C during summer season while from 11-24°C during winter.

Healthy seeds of five plants were taken and they were surface sterilized by using 1% sodium hydrochlorite solution for 5 minutes, washed thoroughly with purified water and dried on tissue paper. Seeds were then sown in covered petridishes on the layers of filter paper soaked with distilled water. Light was provided 8 hours daily for light treatment. While in hot water pretreatment, seeds were immersed in warm water (85 ºC) for 5 min. followed by washing several times with water before incubation. For pretreatment with Phytohormones and nitrogenous substances, seeds were pre-incubated in test solution of phytohormones (250 μg ml^-1 of GA and IAA) or nitrogenous substances (2.5 mM of potassium nitrate and thiourea) for a day before germination. Emergence of radicle by 2 mm was taken as the criterion of germination. In case of each species, the percentage of seed germination was calculated at 24h intervals up to 15 days of incubation period. The values were expressed as seed germination percentage of total number of seeds. Every experiment was repeated three times with three replicates in each time and the mean values were presented.

Result

Seed germination behaviors of Acacia mangium representedin the figure 1. In present study,germination percentage of A. mangium was only 55% under control condition. Slight increase in rate of germination (60%) indicates light may have a positive effect. Hot water pretreatment greatly enhance seed germination (84%). IAA pretreatment has a positive but moderate effect on rate of germination (62%). GA slightly increases germination rate upto to 64%. KNO₃ appears to be slightly more effective than IAA and GA and it is 65%. Thiourea shows 64% germination like that of GA.

Figure 2 – shows germination behavior of A. procera. In A. procera, seed germination percentage was 60% and that is second highest among the plants studied, under control condition. Minor improvement with light treatment leads to 64%. Substantial increase to 82% indicates hot water is highly effective. Pretreatment with IAA and GA are as effective as light treatment and they shows 62% and 64% germination respectively. Potassium nitrate appears to be slightly better (66%), suggesting a beneficial effect. Thiourea shows the best result among chemical treatments with 70% germination.

In all cases B. acuminate shows 100% germination, pretreatments reduced the number of days to achieve final percentage. B. acuminata seed shows 100 percent seed germination in 12 days under control condition while in hot water pretreatment it takes only 9 days. In case of pretreatment with IAA it took only 11 days for complete germination. Pretreatment with nitrogenous substances (both potassium nitrate and thiourea) 100% germination achieved on day 10. Seed germination behaviors of B. acuminata have been shown in the figure 3.

Seed germination behaviours of M. pinnata, have been shown in the figure 4. Under control condition germination was only 43% in M. pinnata. Seeds under daily light cycle increased germination rate up to 49%. Light pretreatment helps marginal increase of seed germination and it is 49%. Hot water pretreatment is extremely effective in this species and germination rate get increased up-to 98%. Improvement of seed germination up to 52% with IAA and in case of GA it is 56%. Potassium nitrate also shows 56% germination like that of GA. Thiourea shows highest germination (61%) among all other chemical pretreatments.

Seed germination behaviors of P. pterocarpum was represented in the figure 5. In P. pterocarpum, germination percentage was only 40% under control condition. Hot water pretreatment shows a remarkable increase in seed germination (84%), showing hot water’s effectiveness in this plant. Pretreatment with phytohormones like indole-3-acetic acid and gibberellic acid showed an increase in final germination percentage (52% with indole-3-acetic acid and 48% with gibberellic acid). While, pretreatment with both potassium nitrate and thiourea showed an increase in final germination percentage (58% with potassium nitrate and 55% with thiourea).

Discussion

In summary, hot water treatment significantly enhances germination for most species. Chemical treatments like indole-3-acetic acid, gibberellic acid, potassium nitrate, and thiourea generally show positive effects on germination compared to the control, with varying degrees of effectiveness across different species. B. acuminata seeds are notably good, in which 100% germination was observed under control conditions. The data suggests that species-specific responses to pre-treatments are crucial to consider in seed germination studies. Germination rates were counted at 24-hour intervals up to 15 days, providing a comprehensive view of the germination process over time. This detailed analysis can help in understanding the optimal conditions for seed germination of these species.

Conclusion

            Finally considering the effects of different pre-treatments to improve seed germination percentage of five plants, it can be concluded that hot water pre-treatment might have increased water permeability of the seed coat and thus the rate of germination. Pre-treatments with phytohormones and nitrogenous substances also increased the germination rate which indicates that some metabolic barrier may be present which limiting germination potential. The outcome of the experiment will be beneficial for improvement of seed germination of the above mentioned tree species. Large scale plantation of these multipurpose legume trees for environmental and commercial purpose can be possible with the insight of this research. The outcome of the present investigation will help plantation of tree legumes in dry lateritic wastelands as a part of agroforestry as well as afforestation and reforestation programme.

Acknowledgement

The authors are highly obliged to the Principals of Bankura Christian College, Nistarini College, Purulia and Achhruram Memorial College, Jhalda, Purulia, for constant helps and encouragement.

Conflict of Interest

The authors declare that there is no conflict of interest.

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