Assessments of Resistances of Indigenous Arabica Coffee Genotypes for Multiple Diseases

An evaluation of resistances of thirty Arabica coffee genotypes for coffee berry disease (CBD) and coffee leaf rust (CLR) infections were carried out across different locations in south-western Ethiopia. The genotypes were first screened against the diseases at Gera which is high land. Eighteen out of thirty genotypes were found to be highly resistant to CBD. However, the earlier screening against CLR at Gera did not favor selection of genotypes which exhibited high resistance levels to it except 75187B, 8136, 8143 and 7803B showing high land is not an optimum environment to discriminate among genotypes for rust resistances. The resistances of these genotypes for rust at multi-locations with different races of rust indicate that they are resistant at least to the two prevalently localized races of II and III in southwestern Ethiopia. The identification of Arabica coffee types resistant to coffee leaf rust at multilocations shows the possibility of improving genotypes for CLR resistances. Genotype 75187B and 8143 apart from exhibiting multiple resistances for coffee berry disease and coffee leaf rust; they also exhibited high performance for yield at the stated locations. This indicates that it is possible to improve the indigenous Arabica coffee types in Ethiopia for multiple traits simultaneously.


INTRODUCTION
Arabica coffee is an important crop in the national economy of Ethiopia.Twenty five percent of the people in the country one way or the other earn their livelihood from coffee.The country used to fetch up to 65% of its foreign exchange earnings from coffee export until very recently (Vander, 1997;Bayetta, 2001).Even now after the incoming of many other exportable commodities the share that comes from coffee still represents 40% of the national export (Behailu et al., 2008;Nigussie et al., 2008).Furthermore the land covered with coffee in the country currently is very substantial and is estimated to range from 400,000 to 650,000 the average being 550,000 hectares.
Despite Arabica coffee is important to the national economy and in spite of the fact that the country is home of Arabica coffee, the coffee industry is threatened of low level of productivity and poor quality associated to diseases mainly coffee berry disease (CBD), coffee wilt disease (CWD) and coffee leaf rust (CLR).CBD is an anthracnose of green coffee berries caused by the fungus Colletotrichum kahawae Waller (Sy.) Colletotrichum coffeanum (Noak) has been the most serious disease that poses considerable losses on arabica coffee in Ethiopia and East Africa (Vander, 1981;Vander, 1997;Eshetu, 1997).It causes direct yield loss as it attacks the fruits at green stages.It also deteriorates quality by infecting the fruits during ripening stages.The national average yield loss due to CBD in Ethiopia is estimated to range from 18-30% (Eshetu, 1997), which amounts to well over 600 million Ethiopian Birr per annum.CLR is the third important disease threatening coffee production in Ethiopian preceded by CBD and CWD.It causes direct yield reduction and deteriorates quality as the active part of the leaves which is engaged in photosynthesis is affected by the disease.In Brazil, leading coffee producer and where CLR is studied intensively, the national average yield loss due to CLR is estimated not to be less than 30% (Messert, 1996).Similar study conducted in Ethiopia shows that from the total coffee growing districts surveyed 70% of the coffee orchards had light or moderate rust and 20% of the orchards had high rust severity.In Srilanka, which used to produce coffee once using limited varieties, complete abandonment of coffee orchards were encountered associated to severity of the disease and replaced by Tea (Cliford and Wilson, 1985).Both CBD and CLR can be controlled using resistant varieties, spraying recommended fungicides and applying cultural practices.However, development of resistant varieties is the safest method among the control measures as it saves money spent on fungicide , fuel and sprays machinery.It also avoids hazardous effect of pesticide on the environment.Therefore the objective of this study was designed to evaluate the indigenous Arabica coffee genotypes for coffee berry disease and leaf rust resistances across different environments and identify resistant types for commercial purposes.

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

Materials and Methods
The trials consisted of thirty Arabica coffee genotypes.They were selected for their high potential for resistance to diseases, yield and cup quality during a preliminary evaluation at Gera.Primarily they were collected from different farmers' field of south-western region of the country along with quite large numbers of coffee accessions.The seeds (beans) were prepared from representative bushes of each genotype.The beans were sown and raised in polythene bags for ten months.Holes were dug and filled with topsoil before planting.The seedlings were field planted in July when they are approximately ten months old in randomized complete block design of three replications.They were mulched in September two months later after planted.Each seedling was also protected from direct sunlight by small grass shelters starting from October until the normal rain in 2006 commenced.The shelters were removed when the normal rain after the dry months started.Sesbaniasesban (temporary shade bush) were planted to provide regular shade over the plots.Each plot consisted of ten bushes in single row.The spacing between rows and bushes within row were 2m by 2m, respectively.All coffee bushes were maintained on single stem pruning system.The orchards were three and four years old when the disease evaluations were carried out in 2008/ 9 and 2009/10.From the ten trees established in a plot per genotype, only five sample trees were used for disease evaluations.Three pairs of branches one from bottom, one from middle and the other from top for all the five sample bushes were marked in advance before symptom of the disease was observed (June in this case).The number of berries on each branch were counted and recorded in same month when the marking was done.The number of berries infected with CBD after disease occurrence (August in this case) were counted and recorded.The proportion of the berries infected by CBD was finally calculated by dividing total number of infected berries to total number of berries recorded originally before disease occurrence and multiplied by hundred.Similarly same bushes, which were used to evaluate CBD, were used to estimate CLR severity.From each random bushes three pairs of branches one from bottom, one from middle and the other from top for all the five sample bushes were marked in advance before the disease symptom was observed (July in this case).Each branch having eight to ten leaves was marked by tying thread between intervals in advance before the critical time of disease occurrence.Severity of the disease (CLR) was estimated by estimating overall percent leaf area infected at the critical time of disease occurrence (November in this case).Furthermore yield data of each genotype was recorded at each season to associate disease severity with yield level.Yield was recorded in kilograms of fresh cherry per bearing bushes from those sample bushes which used to record disease evaluations and converted to clean coffee bean yield in kilogram per hectare.The test materials are presented in Table 2

Statistical Analysis
Percentage values of CBD and rust were transformed using arc-sine transformation before the statistical analysis was carried out and the analysis of variance was employed for each location using Agrobase software package.3).The mean CBD infection range across locations was 0.02 to 4.2 percent at Metu and Gera, respectively.Higher CBD infection was observed during 2008/9 than 2009/10.There was also higher crop load at the first than the second year (Fig1, 2).This was partly one reason for the moderately high disease occurrence observed in the former than the latter as high yield is a favorable condition for disease development.This is in agreement with the work of Vander (1987) who stated that CBD infection is aggravated in seasons which have heavy crops than light.When the individual genotypes were inspected at each individual environment for CBD severity, twelve genotypes exhibited higher or above the tolerable threshold level of 5% at Gera (hotspot).Using such genotypes for production purposes at higher elevation areas exposes them for higher infection and this deteriorates quality even though the reduction that could result in yield might not be much significant.This implies that the genotypes need to be used at lower and medium altitude areas only.On the other hand eight genotypes: 808, 8019, 75187B, 8104, 8143, 8219, 8211 and 8213 exhibited lower CBD infection which is below the threshold level of 5% at all locations irrespective of altitude difference indicating that they can be used for commercial production as they had been confirmed to have high potential for yield and quality attributes during the preliminary as well as the present study.The infection was much lower in the mid altitude areas of Jimma, Agaro and Metu than it was at Gera.The relatively lower level of CBD infections of the genotypes at these locations clearly confirms the truth that CBD pressure is generally low at mid altitude areas, not favorable for CBD fungus development.This is in line with earlier findings of Vander (1978;1981).The severity of the disease was generally very low even at Gera which is hot spot and conducive for CBD pathogen development.This is also what is expected as the genotypes had already been selected for resistance to CBD at this hot spot area during the first phase of the screening.

Table1: Characteristics of the test locations
The lower level of CBD infection observed by the three top yielders (8213, 8143 and 75187B) even at the hot spot area suggests that they can be recommended for commercial purpose across all environments regardless of the disease pressure.This result clearly shows that majority of the genotypes tested were CBD resistant and also in agreement with the previous conclusion that CBD resistant selections proved to be resistant for CBD at Gera remains resistant anywhere in the country be it higher, lower or medium attitude areas (Eshetu and Girma, 1992;Mesfin, 1982;Mesfin and Bayetta, 1983).

Coffee Leaf Rust(CLR)
Differences among genotypes for CLR infection were highly significant at all locations in both seasons except at Jimma and Gera during (2009/10) for which it was only significant and non-significant at the respective locations, respectively (Table 4).Similar results were reported earlier that the indigenous arabica coffee types found in Ethiopia show wide genetic variability for CLR resistances (Mesert and Rodrigues, 1984;Mesert, 1996).The disease was found to be higher during the first bearing season than the second and it ranged from 1.60 to 35.40 percent the lowest and highest being observed at Agaro and Gera at the stated seasons, respectively.However, the yield was also higher during the first than the second indicating rust infection is aggravated associated to crop load .Severity of the disease was much lower during the second season and it ranged from 0.36 (Metu) to 2.00 (Agaro) percent.It also indicates that true genetic differences among genotypes for coffee leaf resistances could be confirmed well in the former than the latter.This is in line with earlier findings of Monaco (1977), Vander (1981), Eskes (1983) and Eshetu et al. (1999).The author also observed adjacent non -experimental coffee orchards which had heavy bearing being infected heavily by CLR at Agaro during 2009/2010 whereas the infection level of the experimental materials was extremely low further strengthening the fact that regardless of inoculum's source, CLR severity remains lower in seasons where the crop load is light.Genotypes exhibited lower CLR severity at Gera (highland altitude) than Jimma, Agaro and Metu (mid altitude areas) showing the fact that elevation has much to do in conditioning pathogen development of the disease.This might be one and main reason for the inability of the earlier screening work done against CLR at Gera during the preliminary evaluation, not to favor genotypes with better resistance levels as the environment that is conducive for CLR fungus development rarely occurs at Gera to discriminate genotypes for resistance levels.In addition, the races of rust available at Gera could be different from other locations.Thus any screening works to identify CLR resistant genotypes should be done in mid and low altitude areas where the climate is conducive for the development of the disease and discriminate among genotypes for resistance levels.Furthermore screening of genotypes for CLR resistances should be done in seasons where the crop load is adequate.Earlier study by Eshetu et al. (1999) illustrates that there are five races of rusts (I, II,III, X and XV) that cause considerable losses in Arabica coffee in Ethiopia of which race III was the most dominant in southwest forest coffee regions followed by race II which is distributed in all the areas where rust exists.However, irrespective of the available rust races two genotypes: 75187B and 8136 exhibited consistently high level of resistances at all locations.The identification of such resistant coffee types hints a clue that it is possible to identify resistant coffee types to multiple races of coffee leaf rust from the indigenous arabica coffee populations found at the different parts of the country even though the available rust races at the distinct locations have not been characterized clearly.Genotypes: 7803B and 8143, which had top performance for yield, exhibited moderate level of resistance for CLR at the medium altitude areas of Agaro, Jimma and Metu.These genotypes could be recommended at high elevation areas where the environment is less conducive for pathogen development of the disease.

SUMMARY AND CONCLUSIONS
Even though the variation among genotypes for severity of coffee berry disease at all locations was significant, the infections were generally low.This shows the general truth that any materials that had been screened and approved to be resistant to CBD at Gera (hot spot for CBD infection) remains resistant anywhere in the country be it low, mid or high land area.In this regard eight genotypes: 808, 8019, 75187B, 8144, 8143, 8219, 8211 and 8213arehighly resistant and can be used across all location if they are superior in yield and exhibit minimum interaction across different environments.The other genotypes can also be used at mid and low land areas where the disease pressure is low.
Though the screening for CLR resistances was carried out at high land of Gera which is unfavorable for fungus development of the disease, four genotypes (75187B, 8136, 8143 and 7803B) were identified which exhibited high resistance levels.The identification of resistant coffee types for CLR at multi-locations may also indicate the presence of genotypes with resistant genes for multiple races of rust.
The identification of resistant coffee types to multiple diseases of CBD and CLR also shows the possibility of improving the resistances of the indigenous Arabica coffee types in Ethiopian for multiple diseases.However, to ensure such possibility the genotypes should be evaluated at multi-locations that comprise all agro ecologies to enable presence of all environments which are optimum for pathogen developments of the various diseases.

Fig1:Fig2:
Fig1: Characteristic mean clean coffee yield in kilogram per hectare of thirty Arabica coffee genotypes at four different locations plotted on vertical axis during 2008/9

Table 2 :The thirty arabica coffee genotypes evaluated across four locations
Differences among genotypes for CBD infection percent were highly significant at Agaro and Gera both in 2008/9 and 2009/10seasons and at Metu during 2008/9only.On the other hand it was non-significant at Jimma in both seasons (2008/9 and 2009/10) and at Metu during 2009/10 season (Table