Evaluation of bean qualities of indigenous Arabica coffee genotypes across different environments

Evaluation of bean qualities of 30 Arabica coffee genotypes were carried out at four different locations (South-western Ethiopia). The genotypes had high overall yield potential, during a preliminary evaluation carried out at Gera. The differences among genotypes for cherry weight (CW), bean weight, parchment length (PL), bean length (BL), floater beans and outturn percent at each location were highly significant (p < 0.01). Two genotypes: 8143 and 8213 exhibited exceptionally higher mean values for CW, hundred beans weight (HBW) and BLs. However, coffee genotypes with higher CW or HBW did not exhibit higher outturn compared to those genotypes with lower CW or HBW indicating the needs to apply intensive agronomic practices such as mulching to conserve moisture, pruning to adjust optimum fruit to leaf ratio and adequate fertilization to avoid nutrient shortage. Generally, genotypes exhibited higher CW, HBW, outturn, BL and parchment growth at Gera and Metu than Agaro and Jimma which had relatively favorable climate during the season. Irrespective of the prevailing environmental factors and its higher overall yield potential, genotype 8143 consistently exhibited higher CW, HBW and BL and lower percentage of floater coffee beans.


INTRODUCTION
Arabica coffee is grown in about 80 tropical and subtropical countries.The majority of these countries supply the product to world market.Ethiopia is among these countries which heavily depend on coffee exports for foreign exchange earnings.About 40% of its export is coffee (Alemayehu et al., 2008;Nigussie et al., 2008).The involvement of such many countries in the production and trade increased competition for a sustainable market.Such conditions force the market to consider quality as major criterion to prioritize and ensure higher price for desirable coffee beans.
The term quality refers to beans flavor in fragrance, aroma, sweetness, acidity, caffeine content or overall taste felt by consumer after drink as well as physical characteristics such as length, width, thickness or weights, shape or color of coffee beans and so on (Giomo et al., 2012;Agwanda et al., 2003;Fox et al, 2013).Basically, there are two economic species of coffee, Arabica and robusta, which are supplied in the world market (Vander Vossen, 1997) and Ethiopia produce solely Arabica.There is wide difference among varieties for qualities even within Arabica coffee types (Vander Graaf, 1981;Desse, 2008;Behailu et al., 2008).
Despite the role coffee plays in the national economy and in spite of the fact that Ethiopia is origin of Arabica coffee, an in-depth research study to improve its quality has not been yet undertaken, apart from the limited selection work done to develop desirable varieties with fine flavor.Results of these studies illustrated there were peculiar coffee types in Ethiopia which exhibited fine cup taste (Behailu et al., 2008;Desse, 2008).However, in addition to flavor, improving varieties for desirable bean attribute is important to ensure higher prices (Getachew, 1990).Coffee types with larger beans usually fetch higher prices than smaller ones even though the former does not necessarily produce desirable roast or liquor than the latter (Cavaco Bicho et al., 2010).Both genotype and environment affects beans physical as well as organoleptic properties such as caffeine contents (Agwanda et al., 2003;Fox et al., 2013;Yonas, 2005;Tesfaye et al., 2008;Alemseged and Tesfaye, 2012).Moisture amount received during bean growth is very critical to affect growths of coffee beans (Tesfaye et al., 2008;Alemseged and Tesfaye, 2012).Fertility levels of the edaphic factors where coffee bushes grow also affects beans growth (Yonas, 2005).Other than the independent effects of genotypes across environments, there is interaction where genotypes exhibit differential performance across different environments (Mawardi and Hulupi, 1995;Yonas, 2005).But through selection, it was possible to breed coffee genotypes that exhibited minimum interaction for bean quality across wide environments (Yonas and Bayetta, 2008).Since Ethiopia has both wide genetic diversity of Arabica coffee and diverse environments for growing it, conducting adaptation tests across such environments is important to select those genotypes which exhibit consistently superior performance for bean quality traits.
Thus, the objective of this study was designed to assess the bean qualities of the different Arabica coffee genotypes across wide environments and select the superior ones for commercial use.

METHODOLOGY Experimental sites
The trials were conducted at four different locations in Southwestern region of Ethiopia: Jimma, Agaro, Metu and Gera.The first three locations represent medium altitude, Gera represents high land and their description is given in Table 1.

Materials
The experimental plots consisted of 30 Arabica coffee genotypes planted out in randomized complete block design (RCBD) of three replications.They represent all the three types of canopy configuration in Arabica coffee: compact, intermediate or open.The genotypes were selected for, cup quality and yield and their higher resistance to RCBD, during a preliminary evaluation at Gera.Primarily, they were collected from farmers' field of different coffee growing parts of the country in South-western Ethiopia.Each plot consisted of 10 bushes in single row.The spacing between rows and bushes within rows were 2 × 2 m, respectively.The materials are presented in Table 2.They were grown in field which had shade of Susbania susban.However, the shades were very sparse and light penetration was high.The plots received uniform application of fertilizer and cultural practices throughout the period of data collection.All the coffee bushes were maintained in single stem pruning system.The coffee fruit were matured and harvested on 2 and 15 September at Agaro and Gera, and on 3 and 7 December at Jimma and Metu, respectively.During harvest all the red cherries from all the 10 bushes in a plot were harvested and thoroughly mixed.Ten (10) sample cherries were taken and weighed using Sartorius sensitive balance (with a precision level of four decimal places) immediately after harvest.The weight of 100-sample coffee beans was weight using sensitive balance at 11% standard moisture level.The outturn percent was determined by dividing the dried clean coffee at the stated moisture level to the corresponding sample fresh cherry weight (CW) from which the clean coffee was prepared and multiplied by 100.The mean bean length (BL) of the different coffee genotypes was determined by measuring the length of 10 sample coffee beans and then the sum was divided to the total numbers of beans.The mean parchment length (PL) was also determined in a similar fashion as for BL.The percent of floater beans was determined by taking 100 sample cherries, pulping it immediately after harvest and the pulped beans were soaked in distilled water.The pulped beans that settled were counted.The floating beans with endosperm filled incompletely were also counted, excluding the empty locoules.Then the settled and floating beans (incompletely filled beans) were added.Later, the number of floating beans was divided to the sum of the total number of settled and floating beans and multiplied by 100.

Statistical analysis
First, analyses of variances of each trait were carried out at the specific environments using Agrobase software.Later combined analyses of variance for all traits were carried out after error variances at the different environments were confirmed to be homogeneous, to calculate environmental, genotypic and genotype by environment interaction effects.Since the error variances of the different traits at each location were homogenous, pooled error mean squares were used to calculate coefficient of variance (CV) and least significant differences (LSD) for the combined means.

Bean qualities and outturn percent
The differences among coffee genotypes for ten cherries weight (TCW), hundred beans weight (HBW), BL, PL, outturn and floater beans percent (FBP) at the specific locations were highly significant (p < 0.01) (Tables 3, 4  and 5).This shows that the indigenous Arabica coffee types in Ethiopia exhibited genetic variability for traits related to determine bean qualities.It also showed that the possibility of these traits could be improved through selection.This enables the country to produce and supply high standard coffee beans to the world coffee market.However, the interactions of genotype by environment of  the different traits were highly significant (p < 0.01) (Table 6).This may indicate the fact that a genotype which is superior in performance at one set of environments for one agronomic trait may not be superior at a different set and therefore its performance at the different environments must be inspected before it is recommended for commercial use.Generally, there are four major stages of bean growth in Arabica coffee (Tesfaye et al., 2008).The first stage is pin head and it starts immediately after fertilization.During this stage, the fertilized flower undergoes internal cellular activities such as cell division and does not exhibit much change in size.The second is the berry expansion stage where exocarp and endocarp, that encloses the parchment and beans, respectively, are grown to their full genetic limit unless restricted by external environmental factors such as age of bearing bush, moisture availability, presence of pruning practices, crop load, plant population density, shade level and availability of nutrients in adequate amounts (Tesfaye et al., 2008).The third is bean filling stage during which the parchment is filled with photosynthetic assimilates.The fourth or the last is the maturity stage during which much change in the size of the berry as well as bean is not noticed except internal processes that facilitate maturity.Each stage stays for nearly 2 months at medium altitude and may be longer at higher elevation areas where the climate is cooler.
From the genotypes evaluated: 8213, 7803A, and 8143 exhibited higher mean value for CWs (Table 3).The weight of coffee cherries across the distinct locations ranged from 14 to 19 g, the least and the highest being observed at Jimma and Metu, respectively.This was a very pronounced difference and showed that environment plays an important role in determining berry size apart from genetic factors.The moisture received from June to September at Jimma during 2009/10 was adequate, however; the restricted berry growth at the particular site could be attributed to shortage of moisture in May which was critical for berry expansion (Figure 1).On the other hand, the highest CW observed at Metu could be attributed to the optimum rainfall received throughout all stages of berry growth at the particular location as shown in Figure 1.Similar justification was stated by Tesfaye et al. (2008) and Tesfaye and Ismail (2008) that moisture amount received during fruit growths has a significant influence on bean quality.The range among genotypes for HBW was 13.37 to 19.89 g.This is also a very pronounced difference.On average three genotypes: 7803A, 8143 and 8213 exhibited the three highest mean values for HBW as shown in the work.They also exhibited higher mean value for overall mean yields (Yonas and Bayetta, 2008).The range for HBW across the distinctive locations was 12.56 to 16.97 g the least and the highest being observed at Agaro and Metu, respectively.The highest mean values observed for HBW at Metu was attributed to the favorable environmental factor (climatic condition) mentioned earlier.On the other hand, the lowest mean value of the genotypes for HBW at Agaro might be attributed to lack of adequate moisture in May which was critical for bean filling at the particular location as there was no rain in the same month at Jimma.Similar justification was reported by Tesfaye et al. (2013a, b) that the amount of moisture available during the critical period of fruit growth has significant influence on physical quality of coffee beans.The existence of genotypes combining large bean size along with high yield potential and fine cup taste is preferable as it fulfills both productivity and all aspects of qualities.Coffee beans with larger sizes usually achieve higher grading and fetch higher price than smaller ones.However, currently, high demand and premium prices are ensured for those coffee types which combine high bean and cup qualities.
The parchment that grows inside the exocarp determines the ultimate bean sizes: bean weight as well as length.It is in turn determined by the size of the exocarp.The overall range among genotypes and locations for PL was 1.053 to 1.279 cm and 1.117 to 1.213 cm, respectively (Table 4).The highest was observed at Gera followed by Metu and Agaro, respectively and the least was observed at Jimma.However, HBWs and BLs at the distinct locations were not in the same order with their corresponding PLs noticed at the respective locations.The absence of correlation between PL and BL or HBW at the different locations could be attributed to absence of correspondence in the amount of moisture received during berry expansion and bean filling stages at the distinct locations as the latter two processes take place at different times and this illustrates that larger berry volume does not necessarily ensure larger bean size (Figure 1).
The range among genotypes for outturn was 13.22 to 15.73% (Table 5).The range across the distinct locations for outturn was 13.32 to 16.23% the least the highest being observed at Jimma and Gera, respectively.Genotypes 8010, 7512 and 74191 exhibited the three top outturn percent as shown in the work.However, these genotypes were not among the top for overall yield (Yonas and Bayetta, 2008), HBW or BL.On the other hand, genotypes: 8143, 8019 and 8133 which were top for overall yield, HBW or BL exhibited the three least values for outturn.This shows that genotypes with higher CW or HBW do not necessarily exhibit higher outturn.The overall range among genotypes for FBP was 3.28 to 24.84% (Table 5).The range across the distinct locations was 3.11 to 26.07%, the highest and the lowest being observed at Agaro and Metu, respectively.The floater bean percent of genotypes at Agaro was much higher and it ranged from 9.77 to 57.52%.Three genotypes: 808 (3.28), 8010 (4.24), and 8143 (4.84) however exhibited the three least floater percent.The higher floater beans noticed at Agaro compared to the other locations is attributed to the fact that high proportion of the parchments was not filled by an endosperm during the critical stage of grain filling for reason mentioned earlier.However, irrespective of the prevailing environmental conditions genotype 8143 consistently exhibited minimum floaters in addition to its relative Yonas B, Bayetta B (2008).Genotype by environment interaction and Stability analysis of Arabica genotypes.Proceedings of Coffee Diversity and Genotype Knowledge Workshop EIAR, Addis Ababa, pp.58-63.

Table 1 .
Characteristics of test locations.

Table 2 .
Thirty Arabica coffee genotypes evaluated at four different locations.

Table 3 .
Ten cherries weight and hundred beans weight (g) of 30 Arabica coffee genotypes at four different locations during 2009/2010.
LSD, Least significant differences.

Table 4 .
Parchment and beans lengths of 30 Arabica coffee genotypes at four different locations during 2009/2010.

Table 5 .
Outturn and floater bean percent of 30 Arabica coffee genotypes at four different locations during 2009/2010.
LSD, Least significant differences.