Host range of Alternaria alternata f.sp. sphenocleae causing leaf blight of Sphenoclea zeylanica

Abstract

Forty-eight plant species in 40 genera representing 20 families were screened for susceptibility to Alternaria alternata (Fr.) Keissler f.sp. sphenocleae, a candidate biological control agent for Sphenoclea zeylanica Gaertner (gooseweed). Gooseweed was the only species susceptible to A. alternata f.sp. sphenocleae when plants were treated with 3.5 × 105 conidia/mL (approximately 107 conidia/m2) in the presence or absence of supplemental dew. All inoculated gooseweed plants were killed when subjected to a 14- to 15-h dew. Lactuca sativa L. (lettuce), Glycine max (L.) Merrill (soybean), Phaesolus vulgaris L. (common bean), Psophocarpus tetragonolobus (L.) DC. (winged bean), Vigna radiata (L.) R. Wilcz. (mung bean), Vigna unguiculata (L.) Walp. (string bean), Musa sapientum L. (banana), and some Oryza sativa L. (rice) cultivars showed highly resistant reactions. Brassica oleracea L. (cabbage), Raphanus sativus L. (radish), and Abelmoschus esculentus (L.) Moench (okra) showed highly resistant to moderately resistant reactions while Gossypium hirsutum L. (cotton) showed moderately resistant to moderately susceptible reactions. Symptoms on cotton were restricted to the cotyledons. Sporulation, however, was observed only on detached excised gooseweed leaves, and no sporulation occurred on any of the other plant species evaluated. Gooseweed was the only compatible host plant of A. alternata f.sp. sphenocleae found in these studies.Key words: Alternaria alternata f.sp. sphenocleae, biological weed control, host specificity, gooseweed, Sphenoclea zeylanica.