Sources of black aphid resistance in the cowpea

Abstract

For a variety of agronomic reasons, landraces have strategic importance for cowpea Vigna unguiculata (L.) Walp. genetic breeding programs. The aim of the current research was to identify black aphid, Aphis craccivora Koch resistance in cowpea landraces. Twenty-three landraces from different regions of the state of Ceará, Brazil, were compared to four literature-cited standards: BRS Guariba and TVu 408 P2 (resistant); BR 17-Gurguéia and VITA 7 (susceptible). Experiments were conducted in a greenhouse located at Campus do Pici, Universidade Federal do Ceará, in Fortaleza, Ceará state, Brazil. A completely randomized block design was used, with six replicates, each composed of one plant in a 300 mL pot. Plants were individually infested with five six-day-old adult insects. Adults were subsequently evaluated two days after infestation and nymphs at four days. Six landraces were highly resistant (Um-named 1-DIP, Feijão de arrancada, Feijão moitinha, Feijão de moita, Cara preta and Roxim miúdo) to levels compatible to the BRS Guariba standard. Three other landraces (Feijão da Bahia, Cojó and Feijão da Consuelo Rocha) showed moderate resistance, similar to the TVu 408 P2 standard. In addition to the high genetic variability found in the landraces, antibiosis was the main resistance mechanism observed.