AGRICULTURE AND BIOLOGY JOURNAL OF NORTH AMERICA ISSN Print: 2151-7517, ISSN Online: 2151-7525, doi:10.5251/abjna.2014.5.6.227.239

© 2014, ScienceHuβ, http://www.scihub.org/ABJNA

Effect of Traditional Storage and Soil depth on Germination Capacity of Sorghum (Sorghum bicolor (L.) Moench.) Seeds.

Kebede Jobir and Masresha Fetene

Addis Ababa University College of Natural Science Department of Plant Biology and Biodiversity Management, Ethiopia

Corresponding author: kebede Jobir, phone number 251911959258, E-mail: butajobir@gmail.com or kbutajobir@yahoo.com

ABSTRACT

The objective of this study was to investigate the germination capacity, field emergence, and soil depth of seeds stored under a variety of storage types and used by farmers in the rain fed sorghum producing areas of Ethiopia as a seed source. Seeds were obtained from farmers of Derashe and Konso district that store sorghum for one year in underground pit, hang panicle of sorghum on smoke at a kitchen house, and newly harvested. Sorghum stored traditionally was used as a source of seed by the farmers of study area. The traditionally stored seed and newly harvested seeds were used for the study. The following tests were carried out: 100-seed weight standard germination test, percentage of seeds in different classes of ungerminated seeds, percentage of field emergence and depth of sowing. Seeds stored traditionally in underground pit for one year showed significantly lower percentage of germination both in the laboratory and field emergency test compared to panicle smoked seeds over the kitchen and newly harvested seeds. The result revealed that, seeds stored in underground pit for one year lost most of their germination ability and their viability. Seeds stored as panicle smoked in the kitchen had significant germination and emergency capacity followed by those of the newly harvested seeds.

Keywords: Sorghum, underground pit, panicle smoked seed quality. INTRODUCTION

Sorghum (Sorghum bicolor L. Moench) is an important crop consumed as a principal food that forms the basis of the diet of the farmers in Derashe and Konso district of Ethiopia. It is also a major source of income to small-scale farmers who are its major growers. In this area depending on the rainfall, several hectares are grown annually. However, productivity is as such not much. In addition to its dependency on the amount of rainfall, poor seed quality is perhaps one of the most important factors contributing to this low productivity. In Ethiopia, as elsewhere in many African countries, the seed industry is not well developed. Similar to previous work stated by Eltayeb & Sana (2010) farmers in Derashe and Konso also usually keep part of their product to be used as seed in the following season. This is usually done by using traditional storage method.

In Konso and Derashe, Ethiopia, Sorghum is traditionally stored in underground pits, smoked over the kitchen (for panicle). Sometimes farmers may not be able to provide their own seed. In this case a

farmer may obtain seeds from the local market or from other farmers. Thus, farmers used to sow the seeds collected from this storage. However, information on the effect of this traditional storage on germination of sorghum seeds in the study area is not known. Therefore, this study attempts to identify the effect of traditional storage as well as soil depth on the germination of Sorghum (Sorghum bicolour (L.) seeds in major Sorghum producing area of Konso and Derashe, Southern Ethiopia.

MATERIALS AND METHODS

The study was carried out in 2012/13 in the Laboratory and green house of Eco-physiology, Addis Ababa University Ethiopia.

Sample collection: In 2012 the mature Sorghum seeds were collected from farmers of Derashe and Konso, Southern Ethiopia. Sorghum seeds were collected for germination, emergence and soil depth study from the following traditional seed storage (appendix Fig. 1).

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Fig.1: Panicle smoked over the kitchen, A; Underground pit, B; Newly harvested, C.

a. Sorghum smoked over the kitchen (for panicle) for one year from Konso and Derashe farmer was collected just before planting, and the panicle was carefully threshed by hand.

b. Seeds stored in underground pit without any lining for one year was collected from Derashe farmer.

c. Newly harvested seeds that stay for three months on the open air and ready to be transferred to other storage types were also collected from both konso and Derashe.

All seeds were washed, sun dried at room temperature and tested for viability by floatation. The seeds were poured into the small bucket, swished them around with hand to remove any air bubbles from the surface of the water, and then leave the seeds undisturbed for about 15 minutes. Those seeds that sank were considered to be the most viable, and those that floated were the least viable and discarded and recorded.

All determinations were carried out according to International Rules for Seed Testing (ISTA, 1985).

100-seed weight: 4 x 100 seeds were weighed, for each three treatments separately and the result expressed in gram based on seed weight determination of ISTA (1985) rules.

Germination percentage: 3x25 seeds of each traditionally stored and newly harvested seeds of Sorghum bicolor were placed on standard germination paper on Petri-dishes. Each Petri-dish contained 25 seeds and four Petri-dishes kept close together and incubated at 25°C. The paper was moistened regularly with water using dropper. The seeds were arranged in a regular equidistance pattern on the surface of the paper and covered with the lid. A total of 4 x 100 seeds were germinated for each storage types according to International Rules for Seed Testing (ISTA, 1985).The first count was made 4 days later and the second 10 days from the start following the procedure described by Eltayeb & Sana (2010). On the 10th day of germination, germination of only normal seedlings was recorded, as germinated ones and the coleoptiles and radicles length of 20 germinated seedlings 5 from each Petri dish were measured. The germination was repeated twice. The average data of germination count for each storage was recorded.

Root length (cm): Twenty normal seedlings of each storage types were randomly selected from the germination test for measuring the root length on 10th day of germination. The root length was measured from the collar region to the tip of root. Average root length of twenty seedlings was computed and expressed in centimetres.

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Shoot length (cm): The earlier twenty seedlings used for the root length measurement were used for measuring shoot length also. The shoot length was measured from the collar region to the point of attachment of cotyledons. The average of twenty seedlings was computed and expressed in centimetres.

Types of un germinated seeds: At the end of the germination test, un germinated seeds were counted and classified into hard, fresh, molded and empty based on Eltayeb & Sana (2010) method.

Emergence percentage: 3x20 seeds for three treatments planted, 2 to a container, were germinated in a pot, 10 replication (planting depth was 2cm) using Firew Mekbib (2008) method. A seed was regarded as germinated when the plumule had emerged. Seedling counts were made daily from the seventh to fourteen days from sowing following Eltayeb & Sana (2010) method. The number of emerged seedlings which indicate the initiation of

germination on each day was recorded. The time of development from emergency to four leaf stage was considered as completion of germination followed Martin et al. (1935) method as cited in Evans et al. (1961).

Soil depth treatment: Plastic pots with 12 cm in diameter and 10 cm in height were filled out with garden soil, and seeds of Sorghum bicolor for four soil depth treatments were sown at 3cm, 5cm, 7cm and 9cm depth, 5 replication (3x4x5 =60) (two seeds in each pot) was tested (appendix Fig. 2). The plastic pots were kept moist throughout the trial. During plant growth, pots were irrigated within 3 days by spraying with water until water drained from the bottom of the pot. Germination was measured daily for 28 days following Mohammad (2011) method. The emergence and soil depth experiments were repeated twice and the pooled mean values were separated on the basis of Least Significant Differences (LSD) at a probability level of 0.05.

Fig. 2: Sorghum sown in a pot to test for emergency and depth of sowing

The following was observed:

1. Effect of smoke over the kitchen (for panicle), Underground pit storage, and Newly harvested Sorghum bicolor seeds germination capacity

1.1. Days for initiation of germination 1.2. Days for completion of germination

1.3. Total percentage of germination

2. Effect of depth for sowing in germination of Sorghum bicolor seeds/ depth treatment for the three treatments (Underground pit, Panicle smoked & Newly harvested seeds)

2.1. Days for initiation of germination 2.2. Days for completion of germination 2.3. Total percentage of germination

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Data analysis: Data were statistically analyzed using the analysis of variance (ANOVA) method according to Gomez and Gomez (1984). The mean separation was performed by Duncan's multiple range tests at the level of the significance (LSD at P< 0.05) (Duncan, 1955). Sigma plot 10 was used to present the analyzed data in different graphs.

RESULTS AND DISCUSSIONS

RESULTS: Effects of storage type on the measured parameters are given below:

Seed weight: Panicle smoked seeds had significantly the lowest weight compared to seeds from all other storage facilities, followed by seeds stored in underground pits for one year. New harvested seeds maintained a weight different to that of seeds stored in underground pit and panicle smoked seeds. The result of multiple comparisons showed significant (p< 0.01) difference in seeds weight between newly harvested and panicle smoked seeds. Similarly significant (p< 0.01) difference was found between newly harvested and underground stored seeds. Conversely, no significant (p > 0.05) difference were found between panicle smoked and underground stored seeds (appendix Fig 13).

Germination: A seed was regarded as germinated when the plumule had emerged. The result of seed germination test in the laboratory showed that, a significant (p< 0.01) difference was observed between the germination percentages taken four and ten days under all storage conditions. Panicle smoked seeds and newly harvested seeds had the highest germination percentage (appendix Table -1). Seeds stored in underground pit had the lowest percentage of germination. The result of this study is supported by Eltayeb & Sana (2010).

The germination percentage obtained in laboratory for some traditionally stored seed in Konso and Derashe, does not met the national sorghum seed standard. According to ICARDA (1985) as cited in Firew (2008), the Ethiopian seed standard for certified sorghum seed is 75% germination and 98% purity. The germination percentage obtained here for panicle smoked seeds (95.5%); newly harvested seeds (80.75%) met the national sorghum seed standard except for underground pit (46%) (appendix Table1). Similarly, mean shoot length (1.0cm) and root length (0.75cm) (appendix Table 1) (appendix Fig. 3) showed least in sorghum stored in underground pit followed by newly harvested seeds, shoot length (2.09cm) and root length (2.71cm).The highest shoot length (3.29cm) and root length (4.92cm) was observed in panicle smoked sorghum seeds (appendix Fig. 3). There was a significant variation for germination among the traditional storage type indicating that, variation of the seed germination capacity depends on the farmer’s seed storage management.

The germinated roots morphology of sorghum seeds stored in underground pit were deformed, short in length and weak compared with panicle smoked over the kitchen and newly harvested which was healthy and vigour’s (appendix Fig3 & 5). In both Konso and Derashe, farmers do undertake continuous intra-varietal seed selection practice to maintain seed quality and rejuvenate seed stocks. Almost all farmers did intra-varietal replacement to maintain and rejuvenate the seed quality. Similar to other areas of the country as stated by Firew (2008) seed selection was routinely done for increasing yield, maintain seed quality and rejuvenate seed stocks. However, storage seems to influence the seed germination capacity and vigorsity of seedlings (appendix Table-1).

Table-1: 100-seed weight (g) and germination (%) of seeds stored in different storage facilities.

Storage type 100-Seed weight (g)

Germination (%) Shoot Length

(cm)

Root Length(cm)

4 days 10 days %

Newly harvested 13.9 39.75 41.0 80.75 2.09 2.71

Panicle smoked 8.9 40.0 45.5 95.5 3.29 4.92

Underground pit 9.3 22.75 23.25 46.0 1.0 0.75

Mean 10.73 34.16 36.58 70.74 2.12 2.79

S.E ± ab.11 .19 .23 - .005 .007

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Table- 2: Percentage of seeds in the different classes of un-germinated seeds from the germination test.

Storage type Hard seed Fresh seed Molded seed

Empty seed

Mean

Newly harvested 1.0 0.4 1.0 1.0 0.85

Panicle smoked 0.4 0.6 1.2 0.4 0.65

Underground pit 0.8 1.4 2.6 0.8 1.4

Mean 0.73 0.80 1.60 0.73 0.96

S.E ± 0.57 0.57 0.57 0.57 -

Ungerminated seeds: The highest mean percentage of ungerminated seeds was recorded for the seeds stored in underground pits, this result is supported by Eltayeb & Sana (2010), followed by newly harvested seeds and least was recorded in panicle smoked seeds(Fig 14). There were significant (P< 0.001) difference in the percentages of ungerminated seeds between seeds stored in the smoke for one year newly fresh seeds, and underground pit storage. The result of multiple comparisons showed significant (P< 0.05) difference in seed germination between newly harvested and panicle smoked seeds. The mean difference between newly harvested and underground pit was also found significant (P< 0.001). Similarly significant (P< 0.001) difference in seed germination was recorded between panicle smoked and underground pit storage (appendix Fig 14)

On the other hand, in all storage types molded seed was observed with high in underground pit followed by newly harvested seeds (appendix Fig-6).This result was supported by Dejene et al. (2004) who observed and identified the greatest incidence of all storage fungi in the soil pits.

Emergence percentage: Germination capacity of seeds under different storage types were sown in a pot at a depth of 2cm to assesses days for initiation and completion of germination using Rajesh and Amit (2010) method. The initiation and completion of germination for three storage types vary and the morphological appearance of young coleoptiles differs among the three storage types. The initiations of germination of panicle smoked seeds are vigour’s followed by less developed newly harvested fresh seeds. In underground pit storage types, germination of one weak seed with poor green color was observed (appendix Fig- 7).

According to the result of multiple comparisons there was significant (P< 0.001) difference in initiation of germination between panicle smoked and newly

harvested seeds. Similar significant (P< 0.001) difference was recorded for panicle smoked and underground pit and also newly harvested and underground pit storage. The completion of germination was also significantly different between the storage types. The result showed that, there was significant (P< 0.001) difference in completion of germination between panicle smoked and newly harvested seeds. Similar significant (p < 0.001) difference was recorded between panicle smoked and underground pit and also newly harvested and underground pit storage. The study showed that, the significance difference in the level of initiation and completion of embryo seed germination indicated the effect of storage on the germination capacity of sorghum seeds stored in different traditional storage types used as a seed source in Konso and Derashe, Southern Ethiopia.

The result of all traditionally stored seeds sown at soil depth of 2cm for emergency test showed that, germination capacity was higher in panicle smoked seeds (86.5%) (appendix Fig 8). The germination had started after 4 days of sowing and was completed in 6days (appendix Fig-9). In newly harvested seeds, germination capacity was 80.5%; the germination had started after 5 days of sowing and completed in 8 days. Minimum capacity of germination was observed in underground pit. In contrast to others, germination capacity was 66.0% in underground pit storage, the seed had germinated after 7 days of sowing and germination was completed in 10 days.

Soil depth treatment: The result on the effect of soil depth on germination capacity of Sorghum seeds showed that, after the first week, maximum germination of seeds was observed in 3.0cm depth of sowing, panicle smoked over the kitchen (81.7%), followed by newly harvested (80.3 %,), and the least percentage of germination was observed in underground pit storage (46.7%) (appendix Fig.10,11and 12 respectively). On the other hand,

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among the traditionally stored sorghum seeds at planting depth of 5 cm germination percentage of Sorghum seeds stored in underground pit (33.3 %) were affected by depth of sowing largely compared to other types of storage (appendix Fig.12). Minimum germination capacity was observed in 7.0cm depth of

sowing for all storage types and least germination was observed at 9cm depth of sowing with no germination in underground pit (appendix Fig. 12). Similar result was also reported by Rajesh and Amit (2010), in castor seeds.

Fig.3: Shoot and root length germination differs between storage types; Panicle smoked over the

kitchen, A; Newly harvested, B; Underground pit, C.

Fig. 4: Effect of storage types on shoots and root length of sorghum seeds germinated in the laboratory

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Fig. 5: Short and deformed root germination was observed in underground pit storage types; Panicle

smoked over the kitchen A; Underground pit storage B.

Fig.6: Molded seed was observed more on underground pit storage followed by newly harvested seeds

types; Panicle smoked over the kitchen, A; Newly harvested, B; Underground pit, C.

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Fig. 7: Initiation of germination differs in storage types; Panicle smoked over the kitchen, A; newly harvested, B; underground pit, C.

Storage types

Panicle smoked Newly harvested Underground pit

Ge

rmin

atio

n (

%)

0

20

40

60

80

100

Fig. 8: Emergency germination (%) of traditionally stored sorghum seeds, ± SE

Fig. 9: Completion of germination (four leaf stage) days differs in storage types; Panicle smoked over

the kitchen, A; Newly harvested, B; Underground pit, C.

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Depth of sowing

3cm 5cm 7cm 9cm

Ge

rmin

atio

n (

%)

0

20

40

60

80

100

Fig. 10: Effect of depth of sowing on germination capacity of Panicle smoked sorghum seeds, ± SE

Depth of sowing

3cm 5cm 7cm 9cm

Germ

ination (

%)

0

20

40

60

80

100

Fig. 11: Effect of depth of sowing on germination capacity of newly harvested sorghum seeds, ± SE

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Depth of sowing

3cm 5cm 7cm 9cm

Ge

rmin

atio

n (

%)

0

10

20

30

40

50

60

Fig. 12: Effect of depth of sowing on germination capacity of underground pit stored sorghum seeds, ± SE

Traditional stored seeds

Me

an

se

ed

s w

eig

ht

(g)

0

2

4

6

8

10

12

14

16

Newly harvested Panicle smoked Underground pit

a

bc

Fig. 13: Effect of traditional storage on weight of stored seeds, ± SE

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Traditional storage types

Mean

un

germ

inate

d s

eed

s

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

Newly harvested Panicle smoked Underground pit

a

b

c

Fig. 14: Effect of traditional storage on germination of stored seeds, ± SE

DISCUSSION

The two most prevalent types of sorghum seeds storage in sorghum-growing areas of Konso and Derashe/Southern Ethiopia are the panicle hanged on smoke and underground pits. Many farmers of the area rely on those sources for their seed supply. Both farmers depend particularly on smoked seeds over the kitchen (for panicle). However those seeds of underground pits were also used as source of seed and for marketing. Some of the farmers of the area used to buy from markets for their seeds. The result of this study revealed that, seeds from underground pit sources had the lowest germination capacity, viability and field emergence compared to other storage facilities and may have thus, contributed to the poor stands and low yield characteristic of the rain-fed sorghum producing areas of Konso and Derashe and perhaps other parts of Ethiopia.

In the laboratory seed germination test, more abnormal, deformed and short weak roots were observed for underground pit seeds (appendix Fig 3 & 5). The low percentage of germination (appendix Table 1) and more ungerminated seeds (appendix Table 2) collected from underground pit showed that,

it may be the result of suffocation occurred due to oxygen depletion, and/or the embryo damage during threshing of seeds from panicle using sticks, to thrash hard. This result is in conformity with the findings of Eltayeb & Sana (2010) in Sorghum (Sorghum bicolor (L.) Moench.). In Derashe, before they collect seeds from underground pit, farmers first used to drop fresh shoots of leaves after opening the hard stone coverage of the pit. If the dropped shoot leaves get wilted they do not enter to collect the seeds and thus, leave open the underground pit and repeatedly drop the leaf shoots until they observe no change occurred on the leaves. They used this to avoid suffocation which may cause death when entered due to oxygen depletion. Sorghum seeds stored in underground pit thus face the shortage of oxygen. This is supported by Krishnamurthy et al. (1990) as cited in Eltayeb & Sana (2010) who stated that, seeds stored in underground pits, may seem likely face oxygen depletion which may led to embryo death and hence loss of viability and germ inability and poor seedling emergence and establishment.

In addition to this, Sorghum seed production in Konso and Derashe is constrained by poor post-harvest handling of seeds. The majority of farmers threshed

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their seed from panicles by beating with sticks or rubbing the panicle on a hard surface like a rough stone. This contributes to high mechanical damage due to the breaking of seeds into small pieces hence reducing the seed quality (NFCI, 2002). When seeds within a seed lot are broken into pieces, the embryos are damaged hence reducing the germination capacity of the seeds. Moreover, the practice of drying sorghum panicles in direct sunlight before storage by farmers in Konso and Derashe might lead to reduced seed quality. It was found that, when seeds were dried at high temperatures, loss of vigour and viability was very rapid (Harrison and Perry, 1976).

In storage, viability and vigour of seeds are greatly influenced by initial seed quality, where it plays a vital role in maintaining the seed quality during the entire storage period (Eltayeb & Sana, 2010). In the present investigation, the viability test using floatation and the germination percentage was reduced significantly in seeds stored in underground pits followed by newly harvested seeds (appendix Table 2 & 1 respectively).

Among all storage types sown in 2cm depth high quality seeds recorded highest (86.5%) mean germination percentage in panicle smoked seeds and significantly lower (66.0) germination percentage was noticed in underground pit storage seeds (appendix Fig-8). Both initiation and completion of germination differs in all storage types (appendix Fig-9). The findings demonstrate not only the extent of emergency, but also the time required for emergences are the major importance. In panicle smoked seeds emergency was essentially completed in 6 days whereas, the delayed initiation and completion of emergency 7 to 10 days respectively was observed in underground pit seeds storage (appendix Fig 9). The longer viable sorghum seeds remain in the soil without emerging, the more vulnerable it becomes to all the factors that contribute to poor emergence (Evans et al., 1961).

At the end of the experiment (after 4 weeks), the highest germination percentage observed at a depth of 3 cm, 5 cm, and 7cm, were next in rank for all three storage types. The germination capacity gradually decreased as sowing depth increased uniformly for all three storage types (appendix Fig 10, 11, 12). In the fourth week, germination at a depth of 9 cm was least for other storage types and zero for sorghum seeds stored in underground pit. The pots were regularly kept moist, so that the seeds in depth of 3 cm had favoured to absorb water and then seeds immediately began to germinate in all storage types.

On the other hand, the plumule emerged from the small sorghum seeds may be weaker to pull itself out of the increased soil depth. This seems to increase the days of initiation and completion with an increase in sowing depth for all storage types. In addition to this, the dry soil in the pot seems to absorb more water and hence minimize the water to penetrate deeply to the depth where the seeds were sown, and may delay seed water absorption and hence minimize percentage of germination. The result of this study showed that, as soil depth increases the percentage germination of all storage types decreases. Similar result was reported by Mohammad (2011) for Bindweed (Convolvulus arvensis L.) who observed that germination percentage reduced with increasing depth of planting. It is evident from this result that, for better germination sorghum seeds stored in underground pit types should be sown at 3cm depth of study area.

Sorghum has a small seed and should be planted shallow. In this study, a planting depth of 3cm is satisfactory with sufficient water. In contrast to this, emergence is reduced with increasing depth of planting. Among the three types of traditionally Sorghum seed storage in Konso and Derashe, seeds stored in underground pit are highly affected and showed least percentage of germination and emergence both in laboratory and in the green house. This showed that, soil depth affect the embryo of underground pit stored seeds more than the other storage types. Mohammad (2011) reported that, the main reason for the lack of germination in greater depth is secondary dormancy induction in the seeds. Seed dormancy was due to hardening of the gas exchange with increasing depth of sowing. Moreover, low germination with increasing depth of seed may be related to the energy stored in the seed (Mohammad, 2011).

The result of this study showed that, the germination percentage of sorghum seeds stored in underground pits was affected by depth of sowing seeds largely. The germination gradually decreased as sowing depth increased. Maximum germination of seeds was observed in 3.0cm depth of sowing (81.7%) followed by 5.0cm depth of sowing (74.6%) for panicle smoked seeds (appendix Fig 10). Similarly the mean days for initiation vs. completion of germination in panicle smoked seeds comparing to other storage types was less (appendix Fig 7&9). Longer days of initiation vs. completion were observed in underground pit storage (appendix Fig7&9). The newly harvested seeds in 3cm depth of sowing

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(80.3%), and (72.6%) at 5cm depth of sowing, showed lower germination capacity than panicle smoked seeds (appendix Fig11). This showed that, panicle smoked seeds may not be affected at 5cm depth of sowing as other storage types. Least germination was observed in underground pit (46.7 %) in 3.0cm depth and (33.3%) in 5.0cm depth of sowing (appendix Fig12). This revealed that, the embryo germination capacity seems to be deteriorated signifying that, the seed storage type does not favour the strength of embryo germination. Minimum germination capacity was observed in 7.0cm depth of sowing treatment for all storage types and least germination was at soil depth of 9cm for newly harvested and panicle smoked seeds with no germination for underground pit storage (appendix Fig.12). Similar results were also reported by Rajesh and Amit (2010), for castor seeds.

CONCLUSION

In conclusion, the current study showed that from the three types of traditionally storage used as a seed source, the germination percentage and field emergence is low in sorghum seeds stored in underground pit. Field emergency with sowing depth of 3cm was high for all storage types, but reduced with increasing depth of planting and no germination was observed as soil depth increases to 9cm for underground pit storage. The main reason for this is that, seeds stored in underground pit face high suffocation due to oxygen depletion which affects the vigoresity and viability of the embryo. On the other hand, panicle smoked seeds over the kitchen and newly harvested seeds next in rank has high percentage of germination both in laboratory seed germination test and field emergency. However, the emergence of seeds in field was decreased as soil depth increases for all storage types.

ACKNOWLEDGEMENTS

The authors would like to thank Firew Tesfaye and Addis Ababa University Eco-Physiology Laboratory and green house assistants for their invaluable contributions to this research.

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