A multivariate analysis of growth and development parameters of the legume pad borer, Maruca testulalis, on variably resistant cowpea cultivars

Principal component analysis was employed to study the variation patterns in 18 cowpea cultivars developed for resistance to Maruca testulalis Geyer (Lepidoptera: Pyralidae) based on 7 developmental parameters of the pest on floral buds, flowers and sliced pods. On the whole, three developmental parameters: percentage pupation (V2), percentage emergence (V5) and growth index (V7) were the most important for the grouping of the cultivars with respect to M. testulalis damage. However, out of the three parameters, growth index (V7) had the highest factor score. Using the cluster analysis technique, the cultivars were sorted into five distinct groups for each part. The importance of these findings in the determination of protection periods for particular cultivars and cultural control studies of M. testulalis in cowpea are discussed

Evaluation of cowpea genotypes for field resistance to the legume pod borer, M. testulalis in Nigeria

Eighteen cowpea cultivars were screened for resistance to the legume pod borer, Maruca testulalis under field conditions at two locations (Mokwa and Ibadan) in Nigeria under unprotected and two types of insecticide protection levels. Unprotected plots gave zero yield due to their exposure to the entire cowpea pest complex. Plots that received a mixture of Cypermethrin and dimethoate (as Cymbush Super ED®) treatment were better (P < 0.05) than plots treated with monocrotophos (as Nuvacron 40EC) in all the damage parameters studied. Results showed that larval population per se are not adequate in resistance categorization of cowpea cultivars. For percentage pod damage at both locations, TVu 946, MRx2-84F and MRx109-84F were the best three cultivars while IT82D-716 was the worst. Yield reduction caused by M. testulalis at Ibadan ranged from 3.47% in MRx2-84F to 49.75% in IT82D-716; at Mokwa values ranged from 10.65% for MRx54-84M to 52.23% for MRx15-84F. Based on their yield performance, among other resistance parameters, the following eight cultivars were selected as moderately resistant to M. testulalis: MRx2-84F, MRx49-84M, MRx109-84M, MRx50-84M, MRx54-84M, MRx55-84M, MRx8-84F and MRx48-84M. These cultivars have good plant type and are either white or brown seeded which makes them good candidates that could be used in breeding programme

Cowpea plant architecture in relation to infestation and damage by the legume pod borer, Maruca testulalis Geyer (Lepidoptera: Pyralidae) 1. effect of canopy structure and pod position

The effects of cowpea, Vigna unguiculata (L.) Walp. canopy structure and pod position in relation to infestation and damage by the legume pod borer, Maruca testulalis Geyer were investigated. Defoliated cultivars sustained significantly less infestation and damage (P < 0.05) than those undefoliated. Relative humidity measured under the canopy was lower in defoliated cultivars, while soil and ambient temperatures were higher. Percentage pod damage and larval infestation by M. testulalis in flowers were positively correlated with relative humidity, and negatively correlated with temperature. Both correlations were significant (P < 0.01). Cultivars with pods held within the canopy suffered significantly more damage (P < 0.05) than cultivars whose pods were held in the normal position. Canopy structure and pod position acting together or independently, exerted profound effects on cowpea resistance to M. testulalis. Selection and breeding cowpea cultivars with less dense foliage (= open canopies) and long peduncles holding the reproductive structures above the canopy, should increase cowpea resistance to M. testulalis

Podwall toughness has no effect on cowpea resistance to the legume pod borer

The possibility of the involvement of pod wall toughness in the resistance of cowpea, Vigna unguiculata (L.) Walp., to the legume pod borer, Maruca testulalis was studied. The toughness of non-intact and intact pod wall increased with age, but the rate varied at different growth stages of the pod as well as between cultivars. There was a positive and significant correlation (r = 0.82**) between pod age and pressure required to penetrate pod wall. No significant differences (P > 0.05) were observed in non-intact pod wall toughness between TVu 946 (resistant) and IT82D-716 (susceptible) at all the growth stages tested. However, significant differences (P < 0.05) were observed between these two cultivars for only 6-day-old intact pods where IT82D-716 recorded a higher value than TVu 946. Correlation between pod damage severity by M. testulalis and toughness of non-intact and intact pod wall of these cultivars at different growth stages were not significant. While pod wall toughness would be a desirable trait, it is concluded from this study that pod walls of the cultivars studied did not play any appreciable role on cowpea resistance to the larvae of M. testulalis