Alternaria stem and leaf blight of sweet potato (Ipomoea batatas (t ) Lam ): a new disease in the highlands of Papua New Guinea.

Abstract

A new disease on sweet potato (Ipomoea batatas) (L.) Lam.) causing black lesions on stems and petioles that eventually lead to dieback of vines was reported in the Western Highlands Province of Papua New Guinea in early 1987. Isolations from necrotic lesions on stems and petioles yielded the fungi Alternaria alternata, Phoma exigua, Phomopsis ipomoeae, Fusarium oxysporum, F. solani, F. subglutinans, F. lateritium and the bacteria Bacillus sp. and Pseudomonas cichorii. Pathogenicity tests on isolates of A. alternata, P. ipomoea, F. oxysporum, F. solani, F. subglutinans, F. lateritium and a Colletorichum sp. at Kuk Agricultural Research Station in 1987 and 1988 conformed that A. alternata was the causal agent of stem and leaf blight of sweet potato.