Genotype x environment interaction and stability analysis of advanced limmu coffee (Coffea arabica L.) Genotypes in southwestern Ethiopia

Coffee (Coffea arabica L.) is the major agricultural export crop, providing 20 to 25% of Ethiopia’s foreign exchange earnings. Lack of suitable varieties that exhibit stable performance across wide ranges of environments due to genotype x environment interaction (GEI) is the major factors among the several production constraints attributing to low productivity of Arabica coffee in Ethiopia. The objectives of this study were to evaluate the performances and determine the magnitude of GEI and stability of coffee genotypes for bean yield and organoleptic quality. Eleven advanced Limmu coffee genotypes were evaluated at different agro-ecologies of southwestern Ethiopia, four locations for two years (2014/15 and 2015/16), in a total of eight environments. The experimental design was randomized complete block design with two replications. Different stability parameters, namely; Additive Main Effects and Multiplicative Interactions (AMMI), AMMI stability value (ASV), Genotype main effect and Genotype x Environment Interaction (GGE), Cultivar Superiority Index (Pi), Wricke’s ecovalence (W2 i), Static Stability Coefficient (SSC) and Yield Stability Index (YSI) were used to assess bean yield and organoleptic quality stability performance. Combined analysis of variance for most of the traits showed significant genotype, environment and GEI effects. This indicated that the variations among the genotypes, environment used and inconsistency of genotypic performances across the environments. From the total sum squares of GEI for bean yield, the environment accounted for the largest (42.74%) components of the total variation, whereas genotype and GEI effects accounted for 9.31% and 32.32%, respectively. Although none of the genotypes showed consistently superior performance across environments, genotype L52/2001 followed by L55/2001 and L56/2001 exhibited the highest mean yields across the environments with overall mean yield of 1558.14, 1473.43 and 1464.45 kg/ha, respectively. Moreover, L55/2001 with high bean yield exhibited acceptable quality characters as compare to all the other genotypes. Among the environments, the highest mean yield was recorded at Agaro (1891.5 kg/ha) in 2015/16 cropping season, whereas the lowest mean yield observed at Haro (438.01 kg/ha) in the same season. The first two Interaction Principal Component Axis of AMMI exhibited highly significant and cumulatively contributed about 63.21% of the total GEI sum of squares for bean yield. For the stability analysis, Pi and YSI were found to be strongly correlated with bean yield and identified two high-yielding genotypes such as L52/2001 and L55/2001 as the most stable genotypes. This type of stability parameter is not preferable for resource poor farmers unless and otherwise the farmers are willing to accept higher risk along with high mean yields and the potential for the genotype to respond to agronomic inputs or better environmental conditions. Other stability models such as SSC, IPCA1, W2 i, ASV as well as AMMI2 and GGE on average identified L55/2001 and L63/2001 as the most desirable genotypes. Moreover, GGE biplot grouped the environments into four clusters with five genotypes being the winners in different group of environments. In addition, L55/2001 and E6 (Jimma 2015/16) were identified as an ideal genotype and an ideal environment, respectively. Therefore, it can be concluded that L55/2001 is the most desirable genotype for its high yielding potential, acceptable quality characters and wider adaptability. In general, this study identified stable genotypes, suitable environment for each of the coffee genotype studied and environment similarity based on bean yield and quality traits. However, further research work on other quality attribute such as biochemical composition as well as resistance to disease and insect pest has paramount importance to select improved varieties for future use of coffee genotypes in Limmu coffee growing areas.