Identification of Lasiodiplodia species causing brown leaf spot disease of cassava in Ghana

บทคัดย่อ

Importance of the work: This research connected Lasiodiplodia species to brown leaf spot
(BLS) disease of cassava in Ghana, since there is a lack of published data regarding Lasiodiplodia
theobromae (Pat.) Griffon & Maubl., Lasiodiplodia mediterranea Linald., Deidda & Berraf-Tebbal
and Lasiodiplodia pseudotheobromae A.J.L. Phillips, A. Alves & Crous, as causative agents of BLS
disease in cassava in Ghana.
Objectives: To isolate, identify and describe the fungal pathogens that cause cassava BLS in Ghana.
Materials and Methods: Diseased cassava leaves with BLS symptoms were collected from farms
in five communities, selected from Sunyani Municipality, Sunyani West Municipality and Dormaa
East District, Ghana. Morphological (conidial size and shape, colony diameter, colony growth rate)
characterization was applied in identifying Lasiodiplodia spp. to the genus level, while a multi-locus
study of the internal transcribed spacer (ITS) and β-tubulin (TUB2) regions was used to identify these
pathogens to the species level.
Results: The fungal pathogens L. theobromae, L. mediterranea and L. pseudotheobromae were
identified morphologically and molecularly using their ITS and TUB2 sequences. Together, these three
isolates produced the characteristic BLS symptoms that were seen in farmers’ fields. Conidia widths
were not significantly different, except for the Nsoa community (5.477 µm). The conidia lengths of
the Asua (35.05µm), Asuo (73.90 µm), Kyere (46.20 µm), Nsoa (37.43 µm) and Wam (48.78 µm)
communities were not significantly different, while the D.A (38.22 µm), K.B (36.45 µm), Yaw (27.67 µm)
and Akon (39.38 µm) communities were significantly different from Asuo (73.90 µm). For both the
colony diameter and average mycelial growth rate, all communities were community were significantly
(p < 0.001) different, except for Nsoa (21.1mm, 2.7 mm/day). Pathogenicity testing on healthy plants
produced similar symptoms, validating Koch’s postulates.
Main finding: The present study was the first of its kind implicating L. theobromae, L. mediterranea
and L. pseudotheobromae as causal agents of BLS on cassava in Ghana.