Infection process and defense response of two distinct symptoms of Cercospora leaf spot in coffee leaves

Abstract

Cercospora leaf spot, an important disease in coffee caused by the fungus Cercospora coffeicola, can appear as two distinct symptoms on leaves, which are ‘brown eye spot’ (BES) and the ‘black spot’ (BS) in field conditions. However, it was unknown whether these two distinct symptoms could be obtained when plants are inoculated under greenhouse conditions and whether the C. coffeicola strains causing the distinct symptoms would induce defense-related genes in a similar pattern. Thus, this work was performed to address these questions. C. coffeicola strains were isolated from diseased leaves collected from coffee fields. The coffee leaves were inoculated with each of the two strains under greenhouse conditions. Leaf samples were collected from a time-course experiment and the disease progression was analyzed using scanning electron microscopy. The plant defense response was analyzed using qRT-PCR of defense-related genes. Both strains showed very similar germination, colonization, and sporulation patterns in the coffee leaves. The expression analysis showed that both strains were able to induce defense-related genes. Both strains produced symptoms of the typical BES for the conditions used, there might be other factors leading to the development of black spot symptom under field conditions and further investigation is needed.