First report of black rot of Oxalis tuberosa tubers caused by Lasiodiplodia theobromae.
Tubers of O. tuberosa in different stages of rotting were collected from fields, local markets and storage sites in 3 different localities of the Andes in Peru. Initial infections were small, discoloured, sunken areas on the surface of tubers. As infection progressed, affected tissues enlarged and mummified. A crusty layer of black conidia was observed on decayed tubers. L. theobromae [Botryodiplodia theobromae] 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-diam. plugs cut from the edge of 5-d-old colonies growing on PDA. These were placed in cylindrical wells formed by removing surface tissue 5 mm in diam. and c. 5 mm deep. Inoculated tubers were incubated for 7 d at 28°C in a moist environment. 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. B. theobromae was reisolated from artifically inoculated tubers. Tubers used as controls showed no decay. This is thought to be the first report of B. theobromae causing tuber rot of O. tuberosa.