Identification of fungal pathogens causing leaf and fruit diseases in Robusta coffee (Coffea canephora) from Loei Province

Abstract

Robusta coffee (Coffea canephora) cultivation has expanded significantly in northeastern Thailand, particularly in Loei Province, which currently holds the largest area under Robusta coffee production. This study aimed to investigate and identify fungal pathogens associated with Robusta coffee diseases in Khok Khamin Subdistrict, Wang Saphung District, Loei Province during 2021–2022. Four major diseases were observed: leaf spot, leaf blight, fruit rot, and rust. A total of 103 fungal isolates were obtained from symptomatic leaves and fruits using the tissue transplanting method, including 47 isolates from leaf spot, 16 isolates from leaf blight, and 40 isolates from fruit rot. The result of pathogenicity tests revealed that 68 isolates were capable of causing disease in Robusta coffee. Among these, isolates LS24, LS1, and LS4 caused the most severe leaf spot symptoms, while LB4, LB23, and LB10 produced the largest lesions in leaf blight tests. For fruit rot, isolates FR38, FR40, FR17, and FR34 showed the highest severity. Based on morphological characteristics, the pathogenic isolates were classified into 7 genera: Colletotrichum (39 isolates), Lasiodiplodia (11), Phomopsis (11), Corynespora (3), Fusarium (2), Pestalotiopsis (1), and Curvularia (1). Seven highly virulent isolates were selected for species identification using nucleotide sequence analysis of the ITS, TEF-1α, and TUB2 gene regions compared with GenBank sequences. The results identified Corynespora cassiicola (LS1), Lasiodiplodia pseudotheobromae (LS24 and FR34), and four species of Colletotrichum: C. theobromicola (LB10), C. siamense (FR38), C. fructicola (FR40), and C. aenigma (FR17). This study provides essential information for the diagnosis and management of fungal diseases in Robusta coffee cultivation in Thailand.