Dodder (Cuscuta) species are obligate shoot parasites that attach to stems and leaves of plants belonging to diverse families, diverting water, minerals, and metabolites, resulting in suppression of crop plants and yield reduction. Lespedeza dodder has the most diverse and numerous host range among the Cuscuta genus and is a major weed problem in tomato production in certain parts of the world, including California. At present, few resistant varieties of normally susceptible plant species have been developed or identified, and none are available in California. In this study, greenhouse and field studies were conducted to test and characterize the tolerance of commercial hybrid tomato varieties to lespedeza dodder. In greenhouse studies, Heinz varieties ‘9492’, ‘9553’, and ‘9992’ exhibited tolerance to the parasite, compared to the susceptible variety, ‘Halley 3155’. Lespedeza dodder germinated, made contact, twined around tomato stems, and adhered to them, but in most cases, haustoria failed to penetrate into the stem, eventually leading to the death of the parasite. In field studies, lespedeza dodder attachments were 75% less on tolerant varieties, and dodder growth was reduced by more than 70%.

Nomenclature: Lespedeza dodder, Cuscuta pentagona Engelm. CVCPE; tomato, Lycopersicon esculentum L. ‘Heinz 9492’, ‘Heinz 9553’, ‘Heinz 9992’.