Evaluation of Selected Cowpea Lines and Cultivars for Inherent Resistance against Cowpea Seed Beetle, Callosobruchus maculatus Fabricius (Coleoptera: Chrysomelidae: Bruchinae)

Abstract

Four cowpea lines (IT99K-494-6, IT97K-390-2, IT84S-2246-4 and IT06K-141) obtained from the Genetic Resources Centre, International Institute of Tropical Agriculture (IITA), Ibadan Nigeria, one cultivar (Ife Brown) obtained from Institute of Agricultural Research and Training (IAR&T), Obafemi Awolowo University, Ibadan and two cultivars (Drum and Oloyin) obtained from Wazobia Market, Ogbomoso, Nigeria were screened for comparative susceptibility to the infestation of cowpea seed bruchid, Callosobruchus maculatus. The number of eggs laid on IT99K-494-6 (20.05) was significantly (p < 0.05) lower than the number laid on all the local cultivars (56.33-78.83). First filial progeny emergence (0.71) observed in IT99K-494-6 was significantly (p < 0.05) lower than 2.06 and 1.65 observed in Ife Brown and Drum cowpea cultivars, respectively. Percentage seed damage for 1T99k-49-6 (10.14) was significantly lower than the value obtained in 1T06K-141 (49.93) and Drum (47.74). Alkaloids content was significantly higher in IT06K–141 (31.67 mg/100 g) than in other lines and cultivars. Oloyin had the highest flavonoid (51.7 mg/100 g), tannins (43.3 mg/100 g) whereas 1T84S-2246-4 had the highest saponins (61.7 mg/100 g) Drum had the highest terpenoid (33.33 mg/100 g). Steroid was highest in Oloyin and 1T84S-2246-4 (11.67 mg/100 g). Reducing sugar was highest in Oloyin (5.33 mg/100 g) followed by 1T84S-2246–4 (4.3 mg/100 g) and IT06K–141 (4.0 mg/100 g). Significant and positive relationship exists between saponins content and the number of grains without exit holes (r = 0.46, p = 0.04), suggesting that high saponins was contributory to cowpea host plant resistance to the cowpea seed bruchid, C. maculatus.

Keywords: cowpea cultivars, Drum, Oloyin, host plant resistance