Effect of pruning on vegetative and flowering patterns of Becium grandiflorum

Haftom Gebremedhn and Tesfay Belay

Tigray Agricultural Research Institute, Mekelle Agricultural Research Center, P O Box 258, Mekelle, Tigray, Ethiopia
E- mail: haftush@yahoo.com

Abstract

Becium grandiflorum is one of the major honey plants in the northern Ethiopia. It has abundant pollen and nectar. The species is also used as fuel wood, broom, roofing, food flavouring, and in traditional medicine.  Natural vegetation is being used for different purposes and there are no significant replantings. However farmers uproot the whole plant when they put it into use.  As a result, the plant is at risk of extinction when combined with deforestation. Hence this study was designed to see the effect of pruning exercise and pruning height on morphological traits of B. grandiflorum and its suitability for honeybees and other cultural uses of the plant without uprooting mother plants. The study was conducted at Mekelle Agricultural Research Centre in two separate experiments. In the first experiment plants were compared with two pruning treatments:  plants  pruned at 0.5 meters and unpruned plants  The second experiment had two treatments: plants pruned at 0.5 meters and plants pruned at ground level. Each treatment was applied on ten plants. Data was analyzed using t-test procedure using Genstat 13^th version statistical software. Correlation test was also done for certain variables using SPSS version 16.

Significant differences in plant height, number of branches, seeds per plant and flowers, and flowering period between pruning treatments at 0.5 meters high and un-pruned ones were noted. The mean numbers of flowers recorded for pruning at 0.5 meters high and un-pruned were 5621 and 3470, respectively. Significantly longer flowering period was observed on plants prunned at ground level than plants pruned at 0.5 meter.  Pruning therefore increased the number of flowers per plant and increased the length of flowering period. Pruning at ground level would also give the opportunity to harvest suitable sized branches for traditional uses so as to avoid uprooting of the mother B. grandiflorum plants.  

Key words: flower number, honeybee

Introduction

Tigray region of northern Ethiopia is generally regarded as the most degraded part of the country (Hailu and Sue 2006). The clearing of forests to expand cultivable land and tree cutting for fuel wood, timber and agricultural implements were the causes for the decline in forest cover of the region (Zenebe 2007). The overall degradation of vegetation resources in the Tigray region had a negative impact on  bee forage availability and had ultimately resulted to low honey and beeswax production (Tesfaye and Tesfaye 2007).  

Becium grandiflorum (Lam.) is one of the major honey plants of Tigray region. It has abundant pollen and nectar. Honeybees produce large quantities of light and white honey from this plant (Fichtl and Admassu 1994; Nigisti and Sebsebe 2009).  It is an indigenous perennial aromatic shrub and grows in highlands and mid altitude areas (Nigisti and Sebsebe 2009; Bein et al 1996; Guinad and Dechassa 2001). It is endemic to Ethiopia and Eretria (Bein et al 1996; Fichtl and Admassu 1994). The honey of this plant is preferred by consumers because of its attractive color and pleasant taste (Haftom and Tesfay 2012).The species is also used for fuel wood, broom, roofing, food flavouring, and traditional medicine (Haftom 2012; Guinad and Dechassa 2001; Nurya 2010). Traditionally, farmers in the Tigray region  use the branches of the plant for making “shintar”  that is used for eating the traditional food made from barley flour called “Tihlo’’( Haftom 2012). Shintar is like a one-fingered fork made out of B. grandiflorum wood. This tradional food is often served in wedding, and other cultural festivals especially in the eastern part of the region. Branches are also used in making torches during New Year festivals (Bein et al 1996).  In both cases,  farmers  are uprooting the whole plant (Haftom and Tesfay 2012). As a result, density of B.grandiflorum in its  natural habitat is declining and the plant is becoming scarce. Natural regeneration of the plant from seed is limitted due to widespread human interference (Haftom and Tesfay 2012). The reduction in population of such useful bee forage species would eventually lead  to a decline in white honey production in the region.Tigrayan white honey of good quality gets premium price but is often limitted in quantity mainly due to shortage of honey plants  (Taddele and Nejdan 2008).  

Hence this study was designed to investigate the effect of pruning and pruning height on flower density, flowering period and other related traits on B. grandiflorum in an attempt to use the prunned branches of the plant for different purposes without uprooting the mother stock and without negatively affecting its flower production. As the plant is not cultivated, the pruning experiment itself is being conducted for the first time.

Materials and methods

Area description  

The study was carried out at the Mekelle agricultural research centre (MARC). MARC is located at an altitude of  1970 meters,  25⁰ 51N latitude and 39⁰ 61 N or S longitude. Soil type in the study area is  dominantly vertisol.

Treatments and experimental design 

Before conducting the study, 40 mother plants were established at the experimental site for about 18 months that were later divided into two blocks each containing 20 plants. Seedlings raised from seeds were used for establishing the mother plants.  

These studies had two sets of experiments and were conducted in two blocks. The first block contained the first experiment that consisted of two treatments: prunned at 0.5 meters high and non-prunned plants. The second block housed the second set of experiments that had also two treatments: pruning at 0.5 meters high and pruning plants at ground level or sometimes called basal pruning or radical pruning. Each block had two rows and each row had 10 plants. Spacing between rows and plants within each block were 2 and 1 meters, respectively. For each experiment 20 well established mother plants were used. For each treatment 10 plants were selected using systematic random sampling from the established mother plants following zigzag pattern. For both experiments pruning was done first week of May 2010. After pruning, supplementary irrigation was applied at times of no rain once every week till flowering.   

Data collection and analysis  

Data  collected include canopy cover, number of head flowers per plant, number of flowers per head flower, total number of flowers and branches per plant, height, number of seed pods per plant, seed per pod and seed per plant. Data were collected on all the plants from the respective treatments. 

Canopy cover was calculated by using the formula, 

C.C= (D₁ +D₂)/2 

where D₁ is diameter of the plant towards the larger canopy coverage and D₂ is diameter of the plant towards the small canopy coverage and C.C reprsents  canopy cover of the plant in cm. So the canopy cover of the plant was expressed in terms of the average diameter in cm. Similar formula was used to estaimate canopy cover of Hypoestes forskaolii (Haftom and yaynishet 2012); and Becium grandiflorum (Haftom and Tesfay 2012). 

The total number of flowers per plant was calculated by counting the total number of flower heads per plant and number of flowers per flower head. The total number of flowers per plant was then calculated by the formula: T.F = H.F *N.F.H 

Where T.F refers to the total number of flowers per plant, H.F to the number of flower heads per plant and N.F.H is number of flowers per flower head. To know the number of flowers per flower head, a sample of 10 flower heads per plant was taken randomly. 

Height  was measured from ground level to the tip of the longest branch with the help of a measuring tape. Actual number of branches and seed per plant were determined by direct counting and recording. 

T-tests were used to compare mean values of the different treatments and P-values less than 0.05 were considered significant using Genstat 13^th version statistical software. Correlation test was also done for certain variables using SPSS version 16. 

Results and Discussion

Effect of pruning on features and flowering patterns of B.grandiflorum

Effect of pruning on plant height, number of branches, flowers, and seeds and canopy cover of B.grandiflorum is shown in table 1. Pruning had highly significant effect on number of flowers, seeds and branches per plant, flowering period, canopy cover and plant height. B.grandiflorum plants pruned at 0.5 meters had higher number of flowers, seeds and branches per plant than unprunned plants thus increasing the chances of natural regeneration. Prunned plants also had larger canopy cover and longer flowering period than unprunned ones. Roy (2008) reported that pruning increased branching and flowering in Jatropha spp.  

Various workers had explained the effect of pruning on physiological and morphological traits of plants. James et al (2004) for instance revealed that pruning promotes growth by releasing a plant’s internal chemical controls that allow new branches to grow. He further mentioned that pruning out all older wood on many shrubs will stimulate the growth of new wood and the newer wood will have more flowers. David et al (2011) too indicated that pruning has a major influence on shrub flowering and unpruned shrub becomes woody, with little new growth to support flower bud development.

Regarding the flowering period, there was a variation in the onset and ending of the blooming period. Unprunned plants bloomed earlier and also finished their flowering period earlier than plants prunned at 0.5 meters high. Prunned plants bloomed late but had a longer flowering period and that meant a lot to honey bees as it leads to increased availability of pollen and nectar.  Possible reason might be the fact that unprunned plants had matured leaves and branches that can support early flowering. Flowering period too had showed a positive correlation with number of branches (Table 3). According to  John et al (1987) a plant with more vegetative growth develops more flowers. Arthur and Kossler (2004) working on Brassica rapa and Haftom and Yaynishet (2012) on Hypoestes forskaolii also demonstrated that flowering time was correlated positively with flower production.

Effect of pruning height on features and flowering patterns of B. grandiflorum

Effect of pruning heights on plant height, number of branches, flowers, and seeds and canopy width of B.grandiflorum is shown in table 2. There was highly significant differences between plants pruned at zero and 0.5 meters in length of the flowering period and number of seeds per plant (P< 0.001), while there was no significant differences in number of flowers, branches, canopy cover, and plant height (P> 0.05) between the treatments. Even there was no significant difference between the treatments regarding these characters; plants pruned at ground level had a numerical advanatage over pruning at 0.5 meters high in number of branches, flowers, and seeds and canopy cover. Significant differences were obtained in number of seeds per plant between the pruning treatments while there was no significant  diference in number of flowers per plant. This observation might be interesting and may deserve attention in future investigations.   

Regarding the flowering period, plants pruned at ground level had significantly long flowering period than plants pruned at 0.5 meters high. Plants pruned at 0.5 meters started flowering 10 days earlier and finished flowering 18 days earlier than plants prunned at ground level. The variation between the treatments in the length of the flowering period might be due to a variation in the number of branches. Besides, flowering period had significant positive correlation with number of branches (r = 0.85, P<0.01). Similar trend was reported on Hypoestes forskaolii (Haftom and Yaynishet 2012).

Correlation analysis 

The correlation matrix among the variables considered is presented in table 3. In both experiments number of flowers per plant had significant and positive association with number of head flowers, branches, and seeds and flowering period. Haftom and Yaynishet (2012) also reported positive correlation between number of flowers and and number of branches on Hypoestes forskaoli. On Matricaria chamomilla L., Rasoul et al (2012) reported significant and positive correlation between number of flowers and branches. In this study strong association between number of seeds per plant and number of seed pods per plant was also observed (r ₌ 0.79).  

In the experiment plant height had negative correlation with number of flowers (r ₌ -0.90) and branches (r ₌ -0.89) and flowering period (r ₌ -0.60). Bal (2005) reported negative and significant correlation between plant height and number of flowers per plant in Tartary buckwheat. Similar relationships were earlier reported in Becium grandiflorum by Haftom and Tesfay (2012).  

Conclusions and recommendation

• From this study, we came to understand that pruning of B.grandiflorum improves its performance as prunned plants had more number of branches, flowers and had larger canopy cover compared to unpruned ones. On the pruning height, we also found out that pruning at ground level to have produced more flowers and seeds than plants pruned at 0.5 meters high. Hence to have flowers for honeybees, to use the branches for other traditional uses and to increase its regeneration (through production of more seeds), it is recommended to prune B.grandiflorum at ground level.

Acknowledgments

We are grateful and acknowledge the technical assistance provided by Mr. Kinfe Mezgebe and staff of Apiculture and sericulture case team of Mekelle Agricultural Research Center, Ethiopia. 

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Received 25 July 2012; Accepted 31 October 2012; Published 2 December 2012

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