Diversity of Guizotia abyssinica pollinators and their effect on seed quality in Mekelle, Northern Ethiopia

Haftom Gebremedhn and Alemayehu Tadesse¹

Apiculture and Sericulture Case Team, Mekelle Agricultural Research Center, Tigray Agricultural Research Institute,
P.O.Box 492, Mekelle, Tigray, Ethiopia.
haftush@yahoo.com
¹Mekelle University, Department of Animal, Rangeland and Wildlife Sciences,
P.O Box 231, Mekelle, Tigray, Ethiopia

Abstract

Guizotia abyssinica (L.f.) is one of the indigenous oil crops to Ethiopia. A flower of G.abyssinica opens and liberates pollen early in the morning, while the style emerges about midday and the plant is thus basically self-sterile, although self-pollination has been recorded. G. abyssinica is a cross pollinated crop with cross pollination percentage ranging from 0 to 100%. However, pollination studies on G.abyssinica are very limited and the role of honeybees for pollination of the local farming systems is still poorly understood. Hence, this study was designed to determine the effect of honeybee and other insect pollination on seed quality of G.abyssinica and to raise the awareness about honeybee pollination services among the G.abyssinica seed growers. The study was conducted at Mekelle Agricultural Research Center. It was conducted in a complete randomized block design (RCBD) with three treatments and four replications in an experimental plot size of 3m×3m. The treatments were crops caged with honeybee, caged without honeybee and open pollinated.

The highest germination rate was found in plants caged with honeybees (86.2%) followed by open pollinated (79%), while the lowest germination rate was found in plants excluded from insects (60.5%). The mode of pollination had no effect on 1000 seed weight, oil and moisture content of G.abyssinica seeds.

Key words: germination, farming system, honeybee, insects, oilseed

Introduction

Guizotia abyssinica is one of the indigenous and important oil crops both for domestic and commercial uses to Ethiopia (Ethiopian Ministry of Agriculture 2011). It is commonly known as Ramtil, Kalatil, Gurellu, Tilangi, Neuk, Noog and Nug (Weiss 2000; Dhurve 2008). G.abyssinica is one of the major oil crops and contributes up to 50% of the Ethiopian oil seed crop production (Weiss 2000; Ethiopian Ministry of Agriculture 2011).

Honeybees visit the flowers of the plant for collection of both pollen and nectar, which in turn results in florets getting cross-pollinated (Dhurve 2008). A flower of G.abyssinica opens and liberates pollen early in the morning, while the style emerges about midday and the plant is thus basically self-sterile, although self-pollination has been recorded (Weiss 2000). G. abyssinica is a cross-pollinated crop with cross-pollination percentage ranging from 0 to 100% depending on the genotype and other environmental factors (Subhas 2005). Pollination studies on G.abyssinica are very limited. Despite its great importance, little attention has been given to improve its quality and production.

Honeybees and flowering plants are dependent upon each other for their existence (Mattu and Hem 2013). Honeybees have great economic importance in terms of increased yield and quality of commercially grown insect pollinated crops (Abd El-Wahab and Ebadah 2011). Utilization of bees in pollination not only increases the yield of various crops but also improves their quality (Sattigi et al 2004). However, the role of honeybees for pollination in the local farming systems is still poorly understood and up to now not sufficiently appreciated (Jacobs et al 2006). Hence, this study was designed to determine the effect of honeybee pollination on G. abyssinica seed quality and also to raise the awareness about the pollination services among the G.abyssinica seed growers.

Materials and methods

The study was conducted during the 2013 cropping season at Mekelle Agricultural Research Center, Illala site. The Center is located North East of Mekelle at an elevation of 2012 m and at N13031’21. 2” latitude and E39030’14. 7” longitude.

Experimental setup

For this experiment, plants were established with a seed rate of 10kg/ha, 40cm distance spacing between rows and 10cm distance between plants. DAP and Urea were applied immediately after sowing and thinning of seedlings at a rate of 100kg/ha, respectively. Thinning of seedlings was done two weeks after sowing. The study was conducted in a complete randomized block design (RCBD) with three treatments and four replications in an experimental plot size of 3m×3m. The treatments were crops caged with honeybee (one colony of five combs), caged without honeybee and open pollinated (exposed to all insects including honeybees). The cages were put immediately before the beginning of blossom and colony transferring was done at 5-10% flowering stage of the plant.

Quality determination

The improvement in the quality of the crop due to honeybees and other insect pollination was assessed in terms of increase in 1000 seed weight, oil content, protein and moisture content and germination rate of seeds.

Germination rate, oil, protein and moisture content

To determine the germination rate of G.abyssinica seeds, 50 seeds from each plot were taken and placed on germination paper and kept in a petri dish at room temperature. The germination count was made after 6 days and then the obtained data were converted to a percentage. The oil and protein content of G.abyssinica seeds were analyzed using Soxhlet (AOAC official method 920.39) and Kjeldhal method (AOAC official method 920.87), respectively. The moisture content of G.abyssinica seeds was analyzed using AOAC Official Method 925.10. For this purpose a sample of 100g of seeds was taken from each plot and the obtained oil content was converted to a percentage.

Figure 1: Germination test of Guizotia abyssinica seed in laboratory of Mekelle Agricultural Research Center

 Thousand seed weight

The evaluation of average weight of seeds was made by determining the weight of 1000 seeds (Dhurve 2008). To know the total number of seeds per plant, the seeds were separated and counted manually.

Diversity and abundance of flower visitors

To identify insect visitors to the plant,s mixed methods were used. These were collecting insect samples using a trap made from mesh, using insect guide book and through consulting experienced entomologists from Tigray Agricultural Research Institute. To identify insect pollinators, observations were made during the peak blooming period of G.abyssinica starting from 8:30am to 17:30pm at two hour intervals (8:30-3:30am, 10:30-11:30am, 12:30-13:30pm , 14:30-15:30pm and 16:30-17:30pm) five times per day. For identification purposes, all the non-Apis bees were treated as a single population to compare their population across hours of the day. Recording of visits was done for 15 consecutive days. The numbers of bees and other pollinators foraging in the open treatment were observed in a quadrant holding five plants for five minutes (Figure 2) in each observation time during its flowering period (as for Dhurve 2008). During recording of insects, the crop was kept free from any spray during the flowering period.

Figure 2: A quadrant holding five plants

Result and discussion

Effect of honeybee and insect pollination on seed quality of G.abyssinica seeds

The highest germination rate was found in plants caged with honeybees followed by open pollinated, while the lowest germination rate was found in plants excluded from insects (Table 1). The seeds in covered area with honeybees had 29.4%  increase in  germination rate compared with crops covered without honeybees. Dhurve (2008) revealed that G.abyssinica crop caged with bees had a 19.8% increase in germination rate over the crop caged without bees. In onion seed, open-pollinated crops showed a higher germination rate than those isolated from insect pollinators (Adel et al 2013). In Coriander also the maximum germination was observed in a system open to all insect pollinators while lowest percent was recorded in a self-pollinated crop (Manoj and Kumar 2012).

The mode of pollination had no effect on the oil content of G.abyssinica seeds (Table 1). The oil content of the plant was in line with the finding of Naraja (2009), who reported a range of 35-40%. Dhurve (2008) also reported that mode of pollination had no significant effect on the oil content of G.abyssinicas seed.

There was no difference among the treatments for 1000 seed weight. In G.abyssinica, Dhurve ( 2008) also recorded  no difference among the three modes of pollination for 1000 seed weight. According to Chiari et al (2005) the larger weight of seeds originating from auto-pollination could be the consequence of a larger amount of nutrients available for their development.

Moisture and protein content of G.abyssinica seeds

The moisture content did not show differences among the treatments (Table 1).  The seeds from crops caged without honeybees had the highest protein content, while crops exposed to insects had the lowest protein content. In soybean,  crops enclosed without honeybee had the highest protein content (Chiari et al 2005). This might be due to the larger seed size of crops enclosed without honeybees. Other studies on G.abyssinica and Gossypium hirsutum seeds also reported that 1000 seed weight or seed size had positive correlation with protein content (Getinet and Sharma 1996; Snider et al 2014).

Diversity and abundance of flower visitors

Insect visitors belonging to more than 11 species (4 Orders and 7 Families) were observed visiting flowers of G.abyssinica at the study site (Table 2). The species belonged to the orders of Hymenoptera, Diptera, Coleoptera and Lepidoptera. Among the insects, Order Hymenoptera had the highest abundance (81.6%) followed by Diptera (12%). From the species recorded in this site honeybee had the highest abundance of 5067 or 79% of the total insect visitors (Table 2).

The timely activity density of honeybees and wild bees on G.abyssinica flowers was significantly different from 8:30-9:30AM to 16:30-17:30 (P=0.00, Fig. 3). Honeybees were the most frequent visitors, compared with other insect visitors. The trend of the timely density of the honeybees and wild bees was similar. The foraging density of both honeybees and other insects on G.abyssinica flowers peaked at 10:30-11:30AM.

Figure 3: Number of honeybees and other insects across different hours of the day

Conclusions

• Honeybees and other insect pollinators improved the germination rate of G.abyssinica seeds by 29%.
• The mode of pollination had no effect on 1000 seed weight, oil and moisture content of G.abyssinica seeds.

Acknowledgements

We are grateful for the financial and material support provided by the Mekelle Agricultural Research Center of the Tigray Agricultural Research institute.

References

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Received 11 August 2014; Accepted 16 September 2014; Published 3 November 2014

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