First Report of Black Rot of Oxalis tuberosa tubers Caused by Lasio-diplodin theobromae. T. Icochea, International Potato Center (CIP), Box 1558, Lima, Peru. W. Perez, and H. Torres, International Potato Center (CIP), Box 1558, Lima, Peru. Plant Dis. 79:425. Accepted for publication 21 February 1995. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/PD-79-0425D.
Oxalis tuberosa Molina is widely grown as a food plant in the highlands (3,000-4,000 m altitude) of South America. Its sweet, starchy tubers are consumed both boiled and roasted. Tubers in different stages of rotting were collected from fields, local markets, and storage sites in three different localities of the Peruvian Andes. Initial infections were small, discolored, sunken areas on the surface of tubers. As infection progessed, affected tissues enlarged, turned black in color, and became slightly soft. Tubers finally became mummified. A crusty layer of black conidia was observed on decayed tubers. Lasiodiplodia theobromae (Pat.) Griff, and Maubl. was isolated in pure culture by transferring conidia, which were being discharged from pycnidia, from the surface of infested tubers to petri dishes containing sterile potato-dextrose agar (PDA). Pathogenicity was confirmed by inoculating surface-sterilized tubers with 5-mm-diameter plugs cut from the edge of 5-day-old colonies growing on PDA. These were placed in cylindrical wells formed by removing surface tissue 5 mm in diameter and about 5 mm deep. Inoculated tubers were incu-baled for 7 days at 28 C in a moist enviroment. Controls were similarly treated tubers, except that agar plugs used for inoculation were cut from plates containing sterile PDA with no fungus. A decay similar to that of the original tubers was observed around the inoculated area. Lasiodiplo-dia theobromae was reisolated from artificially inoculated tubers Tubers used as controls showed no decay. This is the first report of L. theobromae causing tuber rot of O. tuberosa.