First Report of <i>Curvularia pseudobrachyspora</i> Causing Leaf Spots Disease on Coconut (<i>Cocos nucifera</i> L.) Seedlings in Ghana

Abstract

Coconut (Cocos nucifera L.) is an important oilseed and a multipurpose perennial plantation crop. It is mostly grown in humid and coastal areas of Ghana. In June 2019, leaf spot disease was observed on coconut seedlings in 10 coconut growing Districts in Ghana. The Initial symptoms appeared as elliptical, brown-dark-red lesions, 4 - 6 mm on affected leaves. Lesions reached 2.0 cm and gradually developed into spindly, dark brown spots with a light tan centre. A study including survey and laboratory work was carried out to assess disease prevalence and to identify the causal agent of the disease on coconut seedlings, in order to formulate effective management strategies against it. A total of 250 symptomatic leaves were picked from ten selected Districts for laboratory analysis. Additionally, the ribosomal internal transcribed spacer (ITS) region and glyceraldehyde 3-phosphate dehydrogenase (GAPDH) of the isolated pathogen were amplified using ITS1 and ITS4, gpd1 and gpd2 primers respectively. The disease incidence peaked at 95%. Fungal colonies on PDA grew to 50 - 70 mm in diameter in one week at a temperature of 28°C ± 1°C with an even to undulating, immersed striated, mycelium; aerial mycelium being dark velvety green and sometime woolly-cottony. Acervuli formed on the aerial mycelium and contained black powderish conidial masses. Hyphae characteristics were similar to that of Curvularia pseudobrachyspora. Pathogenicity tests were done following Koch’s postulate. For molecular confirmation, the combined ITS (MT075719) and GAPDH (MT075720) sequences were compared with published sequences of 52 Curvularia isolates and eight Bipolaris isolates using phylogenetic analysis. This is the first report of C. pseudobrachyspora as a causal agent of leaf spot on coconut seedlings in Ghana and possibly Africa but the pathogen has been reported on other crops in China, Florida and India.