Pathogenic Variability of <i>Colletotrichum</i> Isolates From the Southern Areas of Coffee ( <i>Coffea arabica</i> L.) Producing in Ethiopia

Arabica coffee plays a crucial role in the Ethiopian economy. Unfortunately, the production of this important crop is severely affected by coffee berry disease (CBD), which is caused by the fungus <i>Colletotrichum kahawae</i> Waller and Bridge. Information regarding the pathogenic variability of <i>Colletotrichum</i> isolates in southern Ethiopia is limited. Consequently, this study is aimed at characterizing and assessing the pathogenicity of representative <i>Colletotrichum</i> isolates from various coffee-producing regions in southern Ethiopia. Eighteen representative isolates of <i>Colletotrichum</i> from the study area, along with one isolate from Gera, were obtained from infected green coffee berries. These isolates exhibited significant variations in their cultural and morphological characteristics, as well as differences in incubation periods and pathogenicity. The findings from the cultural and morphological analysis indicated variability in colony color and type, mycelial growth rates, and conidial production and size. The growth rate of mycelia varied significantly (<i>p</i> < 0.001), with measurements ranging from 2.05 to 4.14 mm per 24 h. Additionally, conidial size exhibited notable differences (<i>p</i> < 0.001), with widths varying from 2.31 to 4.41 <i>μ</i>m and lengths spanning from 10.15 to 12.17 <i>μ</i>m. Conidial production also showed considerable variation (<i>p</i> < 0.001), ranging from 157.21 to 418.12 conidia/mL. Among the detected 18 isolates, 13 were pathogenic to the susceptible coffee variety 370, displaying differences in disease reaction percentages that ranged from 75.00% to 100.00%. Furthermore, the incubation period showed substantial variation among isolates, ranging from 5.0 to 7.00 days. In conclusion, the aggressive isolate FG should be utilized for screening purposes when assessing coffee germplasms for resistance to CBD in southern Ethiopia.