Stability of Sources of Resistance to Cowpea Aphid (Aphis craccivoraKoch, Hemiptera: Aphididae) across Major Cowpea Production Zones in Ghana

Abstract

Aphids (Aphis craccivora Koch) are an important vegetative stage pest of cowpea in Africa. The use of resistant cultivars is among the best management option for this pest, but the success of this strategy is influenced by the stability of the resistant genotype to the cowpea aphid biotypes present in the major cowpea growing areas in a country. This work, therefore, aimed at identifying cultivars/genotypes with stable resistance to aphid infestation across different cowpea growing ecologies in Ghana and estimating yield loss due to aphid infestation at the seedling stage. To ascertain the stability of aphid-resistant cultivars/genotypes, four cultivars/genotypes (SARC1-57-2, SARC1-91-1, IT97K-499-35, and Zaayura) and a susceptible check (Apagbaala) were tested across 18 locations in Ghana. An on-station experiment was used to quantify yield losses due to aphid attack at the seedling stage in the five cultivars/genotypes mentioned above together with 5 additional cultivars/genotypes [i.e., IT99K-573-3-2-1, IT99K-573-1-1, Padituya, Resistant BC4F3 (Zaayura//(Zaayura × SARC1-57-2)), and Susceptible BC4F3 (Zaayura//(Zaayura × SARC1-57-2))]. The results showed that SARC1-57-2 was stable in all ecologies, in terms of its resistance to aphids; it had high vigour score (3.8 ± 0.03) and low plant mortality (3.7 ± 0.22%) compared to the susceptible genotypes. The number of days to flowering and maturity were significantly higher in aphid-infested plants than in the uninfested ones. Grain yield loss was estimated to range between 3.8 and 32.8%. Except for SARC1-57-2, Resistant BC4F3, and Padituya, the remaining cultivars/genotypes sustained significant yield losses under aphid infestation. Thus, the aphid-resistance gene in SARC1-57-2 is stable against aphids. This resistance genotype can be incorporated into cowpea improvement programmes to breed for aphid-resistant cultivars. Also, the cultivation of such improved cultivars will reduce pesticide usage in cowpea production.

Pyramiding aphid resistance genes into the elite cowpea variety, Zaayura, using marker-assisted backcrossing

“… Breeding line in CSIR-SARI. Resistant to aphids [ 7 , 14 , 16 ] CSIR-SARI, Ghana IT97K-556-6 A breeding line from IITA, Ibadan, Nigeria. Resistant to aphids [ 10 , 17 ] IITA, Nigeria Zaayura Marfo-Tuya/UCR 01-15-127-2 Aphid susceptible released in 2008 [ 16 ] CSIR-SARI, Ghana Zaayura Pali Zaayura/SARC 1-57-2 Aphid resistant released in Ghana in 2016 [ 14 ] CSIR-SARI, Ghana …”

“…The pyramided lines, Zaayura, SARC 1-57-2, IT97K-556-6 and Apagbaala were evaluated using the seedling-stage aphid-screening method [ 16 ]. IT97K-556-6 and SARC 1-57-2 served as resistant checks while Zaayura (recurrent parent) and Apagbaala served as susceptible checks.…”

“…To develop cowpea cultivars with durable resistance to aphids, it is imperative to pyramid multiple resistance genes that are non-allelic into a single cultivar. The cowpea breeding line SARC 1-57-2 was found to have stable resistance to aphids in all the cowpea growing regions in Ghana [ 16 ]. The resistance in this genotype is conditioned by a single dominant gene [ 14 ].…”

Cowpea Constraints and Breeding in Europe

“…However, finding genotypes with resistance to pests in most cases has proved fruitless [ 49 ], as it is difficult to find resistant genotypes, and usually their resistance relies on a dominant gene which can be easily overcome [ 172 ]. For example, the aphid resistance of the improved line IT97K-499-35 appears to have been overcome by aphid populations in Ghana [ 243 ].…”

“…A plethora of aphid-resistant improved lines, genotypes and commercial varieties have been identified worldwide [ 243 , 244 , 245 , 246 , 247 , 248 ], while aphids did not prefer resistant cowpea genotypes and fed significantly less on them [ 249 ]. Among the screened genotypes, some landraces and wild cowpea accessions presented resistance to aphids ( Table 5 ).…”