Abstract
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.
Highlights
Cowpea [Vigna unguiculata (L.) Walp.] is an important food crop and a basic component in the diet of rural and urban populations, in a variety of countries where it is produced by both large and small farmers (FAO 2017)
The TVu 408 P2 and VITA 7 cultivars were introduced from the International Institute of Tropical Agriculture (IITA), in Nigeria; while the BRS Guariba and BR 17 Gurgueia cultivars were developed by the Embrapa, in partnership with other Brazilian agricultural research institutions
The cowpea accessions Enrica Pobre (CE-36), Das Almas (CE-07), CE-51 and Ritinha (CE-08) were statistically similar (p > 0.05) to the resistant genotypes used as check (BRS Guariba and TVu 408 P2), with the lowest numbers of adult insects
Summary
Cowpea [Vigna unguiculata (L.) Walp.] is an important food crop and a basic component in the diet of rural and urban populations, in a variety of countries where it is produced by both large and small farmers (FAO 2017). Most of its production and consumption are concentrated in the African continent, where Nigeria is the main producer, with 3.7 million hectares cultivated and an average. These numbers are considered lower than the actual potential of this crop, since, in other countries with a more technologically intensive agriculture, like the United States, yields exceed 1,500 kg ha-1 (FAO 2017). In Brazil, a similar pattern emerges, when comparing yields from different regions; for example, between the northeast (414 kg ha-1) and midwest (1,152 kg ha-1) of the country (Conab 2018)
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