Screening of cowpea accessions for cowpea aphid resistance

ABSTRACT Cowpea (Vigna unguiculata) genotypes may preserve important characteristics of potential use for the genetic breeding of this species. This study aimed to characterize sources of genetic resistance to the cowpea aphid (Aphis craccivora), among accessions maintained at the cowpea germplasm bank of the Universidade Federal do Ceará (Brazil), in order to suggest crossing options for obtaining superior cultivars. Twenty-one local accessions were assessed together with two genotypes as resistant checks and two others as susceptible checks. A randomized complete block design, with four replications, was used. Counts of live adults and nymphs per plant were used to evaluate the genotypic resistance and, based on the ranking of these data, the effective resistance was estimated. The applied approach showed to be effective to discriminate the genetic variability for cowpea aphid resistance, identifying antibiosis as the probable resistance mechanism. Four genotypic groups were identified: resistant, intermediate, susceptible and highly susceptible. Thus, for a short-time cultivar release strategy, backcrosses are suggested between the BRS Guariba cultivar (recurrent parental, with good agronomic traits) and aphid-resistant accessions, such as Enrica Pobre (CE-36), Das Almas (CE-07), CE-51 (selected within CE-13) and Ritinha (CE-08). However, for a long-term breeding strategy, crossings between the most dissimilar accessions are suggested, using resistant genitors (e.g. BRS Guariba, Enrica Pobre, Das Almas, CE-51 and Ritinha) and others with good commercial and agronomic attributes. RESUMO Triagem de acessos de feijão-caupi quanto à resistência ao pulgão-preto Genótipos de caupi (Vigna unguiculata) podem preservar importantes características de uso potencial para o melhoramento genético dessa espécie. Objetivou-se caracterizar fontes de resistência genética ao pulgão do caupi (Aphis craccivora), entre acessos mantidos no banco de germoplasma de caupi da Universidade Federal do Ceará, buscando sugerir opções de cruzamento para a obtenção de cultivares superiores. Foram avaliados 21 acessos locais, juntamente com dois genótipos como padrões de resistência e outros dois como padrões de suscetibilidade. Utilizou-se delineamento em blocos completos casualizados, com quatro repetições. Contagens de adultos e ninfas vivos por planta foram utilizadas para avaliar a resistência genotípica e, a partir do ordenamento desses dados, foi estimada a resistência efetiva. A