Recent studies of fungal pathogens of onion in Puerto Rico

Abstract

First descriptions of fungal pathogens of onions in Puerto Rico were reported by J. A. B. Nolla, J. Matz, R. A.Toro and C.M.Tucker during the 1920s. At that time onions were grown in the northern region of the island and fungal pathogens such as Alternaria allii, Aspergillus niger, Colletotrichum dematium, C. gloeosporioides, Rhizoctonia sp. and Stemphylium botryosum were reported causing important fungal diseases under field conditions. From 1999 to 2000 a broad survey of fungi associated with onion was conducted in the southern region of the island. Pathogenicity tests were conducted with 25 fungal isolates obtained from soil, mature onion bulbs and foliage from fields at Guánica, Juana Díaz, and Santa Isabel, Puerto Rico. The pathogenicity tests were performed on onion tissues of cultivars Excalibur and Nikita under laboratory and greenhouse conditions. Tests showed that A. niger, Phoma sorghina, Phoma sp., Penicillium purpurogenum and Sclerotium rolfsii were pathogenic to mature bulbs; Alternaria alternata, A. tenuissima, Fusarium acuminatum, F. equiseti, F. oxysporum, Stemphylium sp. and S. herbarum to foliage; Phoma sp. and Phoma sorghina, pathogenic to young roots and bulbs. This is the first report of Phoma sorghina, Penicillium purpurogenum and Sclerotium rolfsii causing diseases in onions in Puerto Rico and the Caribbean.