Theobroma cacao (chocolate tree) is currently under serious threat from thread blight disease (TBD), which has been attributed to the causal agent Marasmiellus scandens in other regions of the world. TBD in Ghana has similar symptomology but variable signs. This study sought to determine whether TBD in Ghana was caused by a single agent and whether Marasmiellus scandens was a significant agent of TBD. Forty-eight isolates were collected from eight geographical locations in Ghana for morphological and molecular characterization. Disease signs occurred as vegetative rhizomorphs or hyphal aggregates, which were classified into five morphotypes: A, abundant thin, black, “horse hair”-type rhizomorphs; B, scattered brown rhizomorphs; C, whitish to brownish-white; D, faint cream or dull white; and E, aggregates of shiny or silky white hyphae. Sequencing and analyses of three loci—the internal transcribed spacer region of the nuclear ribosomal repeat, nuclear large subunit, and mitochondrial small subunit—detected four species, all members of the Marasmiaceae, causing TBD-like disease. These were identified as Marasmius crinis-equi (morphotype A), Marasmius tenuissimus (morphotypes B and C), Marasmiellus palmivorus (morphotype E), and Marasmiellus scandens (morphotype D). Marasmius tenuissimus, the most frequently isolated TBD fungus in this study, is primarily an Asian fungus and not previously associated with diseases of cacao. Marasmiellus palmivorus, the second most frequently isolated fungus, is a pan-tropical pathogen with a broad host range; this is the first report of the fungus causing TBD on cacao. Marasmius crinis-equi also has a broad pan-tropical distribution and host range and causes thread blight on several tropical tree crops. Surprisingly, Marasmiellus scandens, the most frequently cited agent of TBD in cacao, made up only 8% of the isolates.

Outbreak of anthracnose of cacao (Theobroma cacao L.), covering an estimated total growing area of 248.47 hectares, occurred in parts of Ghana from July to October 2019. Disease samples were collected from the outbreak areas to isolate and identify the pathogen and establish its pathogenicity. Disease symptoms appeared on leaves as dark brown patches with yellow halo margins. Colletotrichum gloeosporioides s.l. was isolated from infected plant tissues and pathogenicity tests confirmed it as the causative agent. The disease was widespread in the Prestea-Huni Valley district of the Western Region, particularly in the Yareyeya community, where a 14.8-hectare farm was seriously affected. Anthracnose has long been known as a sporadic but minor disease of cacao in Ghana. The current shift in status and rapid spread of the disease from infected farms to new farms, though it may or may not be contiguous, cannot be readily explained. Application of copper fungicides, namely Nordox 75 WG (86% cuprous oxide), Champion (77% cupric hydroxide) and Royal Cop 50 WP (77% copper hydroxide) at 75 g, 100 g and 100 g, respectively, each in 15 litres of water, at 2-week intervals for four months, effectively managed the disease.

White thread blight disease (WTBD) is currently emerging as an important foliar disease on cocoa in Ghana. The disease has been known in the country for many years. Yet, the incidence and severity levels on cocoa in the growing regions are not known. Surveys and sampling were conducted between 2011 and 2013 to estimate incidence and severity of WTBD in the six cocoa growing regions (Ashanti, Brong-Ahafo, Central, Eastern, Western and Volta) of Ghana. Diseased samples were assayed for the infecting fungus and its identification. Chi square tests were used to find relationships between age, sanitation practice and the disease severity. Effectiveness of chemical and cultural control methods against the disease were tested. The disease was found in all the cocoa growing regions of Ghana and out of 24,000 trees inspected, 1,281 (5.3%) were infected. The majority of infected trees (74.2%) were moderately affected but 3.2% of the trees were very severely affected and almost dead. A positive correlation (r = 0.889) was found between WTBD incidence and the severity. The most severely affected regions were Ashanti (13.8%), Brong-Ahafo (10.2%) and Western (7.6%) regions. Poor maintenance significantly (p=0.0001) increased the levels of disease occurrence and severity. Older cocoa trees also appeared more susceptible than younger ones. Pruning of affected branches controlled the disease better than fungicides spray. However, Nordox (75% copper (I) oxide) at 5 g/l and Metalm (12% metalaxyl and (60% copper (I) oxide) at 3.3 g/l fungicides were effective in reducing mycelial growth of the Marasmiellus fungus. Therefore, fungicide should be used in situations of severe infection to supplement pruning. Key words: Thread blight, cocoa, Marasmiellus, disease severity.

Thread blight disease (TBD) is a serious emerging threat to global cacao production, causing leaf blight symptoms and necrosis in the canopy of infected trees. Though previously thought to be cause...

Plants are known to possess antimicrobial properties, as such, their extracts remain potential sources of eco‐friendly antimicrobial products. Extracts from sweet orange have been evaluated as potential antimicrobial sources. However, their activity against pathogens of major agricultural crops such as cocoa is unknown. In this study, the essential oil (EO) of the peel of sweet orange was evaluated against Marasmiellus scandens and Erythricium salmonicolor , the pathogens, respectively, responsible for causing white thread blight and pink disease on cocoa. Minimum Inhibitory Concentration (MIC), IC ₅₀ , IC ₉₀ , and IC ₉₅ against mycelial growth of the pathogens were determined by agar plate tests following 7 days of incubation. Mycelial growths of the two pathogens were completely (100%) inhibited at 10% (w/v) of the EO. The MIC, IC ₅₀ , IC ₉₀ , and IC ₉₅ against M. scandens were 0.1%, 0.25%, 1.23%, and 2.11% while those against E. salmonicolor were 0.01%, 0.13%, 0.75%, and 1.35%, respectively. This study shows that EO of sweet orange peel has antifungal activity against the pathogens. Determining the bioactivity of the individual compounds in the EO and field application of effective formulations in future research has potential for the biological control of these fungal diseases of cocoa.