Submitted to: Plant Pathology
Publication Type: Research notes
Publication Acceptance Date: 2/25/2008
Publication Date: 3/26/2008
Citation: Osiru, M., Adipala, E., Olanya, O.M., Paula, K., Lemaga, B., Kapinga, R. 2008. Leaf Petiole and Stem Blight Disease of Sweet Potato Caused by Alternaria Bataticola in Uganda. Plant Pathology. 7:118-119 Interpretive Summary: Leaves and stems of diseased sweet potato plants were evaluated to identify the pathogen species causing the disease. Diseased samples showed typical and characteristic symptoms of Alternaria leaf and stem blight. All isolates had similar colony morphology, spore characteristics and dimensions. From representative isolates cultured on artificial media, the species was identified as Alternaria bataticola. Pathogen identification is important for diagnosis and effective disease management.
Technical Abstract: Alternaria leaf petiole and stem blight is an important disease of sweet potato (Ipomoea batatus (L.) Lam.) in tropical and sub-tropical regions. In surveys conducted in Uganda from 2001 to 2003, disease incidence ranged from 0-49%. Symptoms of Alternaria leaf and stem blight disease consisted of small, dark grey to black, oval lesions on stems and petioles. Chlorotic and brown circular lesions with concentric rings were also observed on diseased leaves of New Kawogo (CIP 441743) and NASPOT1 (NIS/91/52 cultivars. The pathogen was isolated from vines and leaves exhibiting characteristic symptoms of Alternaria disease and cultured on sweet potato decoction media and potato dextrose agar (PDA). Pathogenicity and Koch’s postulate tests conducted in controlled experiments, on the above cultivar resulted in symptoms typical and characteristic of Alternaria leaf and stem blight disease. Isolates cultured on PDA had similar colony morphology, conidia shape, size and number of septae. Conidia were solitary, pale brown to brown, elongate-obclavate, with two directional septae. The numbers of muriform, transverse and longitudinal septae were 5-8 and 2-4, respectively. Average dimensions of 40 conidia from colony on PDA were 46 x 19 um (34-160 x 15-42 um range). The isolates were identified as Alternaria bataticola, and confirmed by CABI Biosciences Plant Health Clinic. Pathogen species identification is crucial for diagnosis and effective disease management.