Evaluation of arabica coffee (Coffea arabica L) germplasm for major coffee diseases with especial emphasis to coffee wilt disease (Gibberella xylarioides) at jimma, Ethiopia

Abstract

Among diseases affecting coffee production, coffee berry disease (Colletotrichum kahawae), coffee wilt disease (Gibberella xylarioides) and coffee leaf rust (Hemileia vastatrix) are the most important ones. In Ethiopia, coffee wilt disease (CWD) is increasingly becoming more important, especially in garden semiforest and plantation coffees. The national incidence and severity of CWD in the country were 29.9 % and 3% respectively, with financial loss of more than 3.7 million USD, justifying all possible control options including use of resistant coffee varieties. This study was, therefore conducted under both laboratory and field conditions at Jimma Agricultural Research Center with objective of evaluating Arabica coffee germplasm and identifying resistant genotypes to coffee wilt disease. The experiment was conducted on one hundred coffee accessions (each 30 seedlings per box) grouped in two batches in a randomized complete block design with three replications. Stem nicking inoculation was employed with 2.3x 106 conidia of G. xylarioides isolate at cotyledon stage of the seedlings. In addition, the tested accessions were further assessed for coffee wilt, coffee berry disease (CBD) and coffee leaf rust (CLR) under field conditions at Jimma. In the seedling test, significant variations were recorded among coffee accessions in reaction to CWD. Mean wilt (dead) percent seedlings varied between 0 - 98.8% and 2.3 - 97.5 % in batch I and II, respectively. Nine accessions from batch I namely 279/71, 226/71, 259/71, 244/71, 120/71, 3/70, 16/70, 245/71, and 30/70; and 10 accessions from batch II 27/77, 12/74, 26/77, B3/06, B2/06, 44/83, 48/83, B1/06, 11/77 and 13/74 showed low percentages of seedling death expressing high to moderate resistance reactions as compared to resistant standard check catimor J-19. however, coffee accessions from batch I 1/70, 18/84, 5/84, 5/72, F-31, Geisha, 54/70,250/71, 4/84 13/79 199/71 and coffee accessions 9/78, 26/84, 20/84, 24/84, 22/84 from batch II were highly susceptible. Correlation between mortality of coffee trees in the field and wilt severity of seedlings in artificial inoculation were not significant, while incubation period and AUDPC was found significant. The clustering patterns of 55 and 51 coffee accessions were generated from means of three CWD parameters grouped coffee accessions into three clusters. In both set of experiments, the first cluster was characterized by grouping all susceptible reaction to CWD, cluster three in batch one express resistant reaction, where as cluster two in batch one and cluster two and three in batch two express moderately resistant reaction to CWD. The disease assessment result indicated that coffee berry disease varied between 0-95.6 and 0-83.1 in batch I and batch II respectively. The mean coffee leaf rust varied from 0-34.4 in batch I and 0-13% in batch II. The results of the study, implicated that there is important diversity in conservation block of Jimma Agricultural Reserch Center in reaction to G. xylarioides infection. However, susceptible reaction was observed in coffee accessions collected from Kaffa, Iluababor, West Gojam and West Wellega. Further evaluation of moderately resistant CWD accessions in different agroecological areas in wilt devastated gardens or farms (sick plot) so as to validate their performance and adaptation to different localities (multilocation trials) are recommended.