Incidence of red rust (alga leaf spot) in cashew orchards in Ghana

Abstract

Cashew (Anacardium occidentale L.) production is under threat in the Dormaa area of the Bono region of Ghana due to a green algae pathogen. The objective of this study was therefore to determine the incidence and severity of red rust disease in cashew orchards in Dormaa Central Municipality. A survey was conducted in the 2019 and 2020 seasons in 30 selected orchards in six cashew-growing communities in Dormaa municipality. The identification of the putative alga was done both in vivo using visual assessment and in vitro using microscopic observation at a magnification of 40x. Koch's postulate was completed to confirm the pathogen’s identity. The result of the test produced symptoms similar to those observed before the test, i.e., circular, raised, or flattened velvety/fuzzy orange-brown or burnt-orange or rust-pigmented or greenish-grey spots with dimensions ranging from specks to spots with average sizes of up to 3mm. The incidence and severity of the disease varied significantly (P < 0.001) according to the community and orchard. Based on the morphological analysis and pathogenicity test, the algal pathogen was identified as Cephaleuros spp.