Adoption of cowpea hermetic storage by women in Nigeria,Niger and Burkina Faso

In this study, 2741 randomly selected rural women were interviewed about their cowpea storage practices in 101 villages in Burkina Faso, Niger and Nigeria in late 2010 and early 2011. The overall objective was to determine their cowpea storage practices and identify the most important factors in choosing Purdue Improved Crop Storage (PICS) triple bag storage. About two thirds of women said they used some type of hermetic storage. The hermetic containers included metal drums, plastic jugs, double bags and triple bags. The weighted percentage of women using PICS triple layer bags is 46%. Quantity of cowpea stored by technology showed similar patterns. Overall the percentage of cowpea in hermetic storage was 64%. The study estimated that women stored 50% of their cowpea in PICS bags. The percentage of cowpea in hermetic storage overall and in PICS bags specifically is higher for women than for men in a parallel 2012 ten-country study of mostly male household heads. In PICS villages, the women cite PICS technicians as the most important source of information. In Non-PICS villages, radio was the most important. Most women say that higher income is the major benefit of PICS. The 2009–2010 three country weighted average of the net cash flow from cowpea storage in PICS bags is $10.81/100 kg bag and $39.27 per respondent. Overall, the women indicated that local unavailability was the primary constraint to use of PICS bags. The LOGIT regression analysis shows that the most important factor influencing use of PICS technology is living in a village where PICS demonstrations occurred. The regression shows that radio and the PICS technicians have key roles as information sources. Being able to attend mixed gender meetings was statistically significant only in Burkina Faso where PICS did not organize many women-only PICS activities.     

Trehalose and proline failed to enhance cold tolerance of the cowpea weevil,Callosobruchus maculatus (F.) (Col.: Bruchidae)

The cowpea weevil, Callosobruchus maculatus (F.) (Col.: Bruchidae) is a cosmopolitan field-to-store pest ranked as the major post-harvest pest of cowpea in tropical regions. The cold tolerance of an insect species can vary as a result of abiotic features including food resources. In this study, C. maculatus larvae were fed with proline and trehalose (10, 20, and 40 mmol) treated cowpea seeds to determine the effects of these potential cryoprotectants on the supercooling (SCP) and cold hardiness of the upcoming adult beetles. The SCPs of the control, proline-fed and trehalose-fed adults non-significantly changed from −18.2 °C for the control to −17.2 °C for trehalose-fed adults. The cold hardiness (24 h at 0, -5.0, −7.5, −10.0, and −12.5 °C) of the adults was almost the same for control and treatments. Median lethal times (LT₅₀; lethal time for 50% mortality) were 6.3, 6.0, and 5.4 h, respectively. Moreover, feeding the larvae with proline and trehalose-treated seeds did not affect the proline and trehalose contents of the adult beetles. Our results showed that C. maculatus could not tolerate subzero temperatures well above their SCP, indicating that this species might be a chill-susceptible insect.     

Genetics of bruchid (Callosobruchus maculatus Fab.) resistance in cowpea (Vigna unguiculata (L.) Walp.)

Bruchid resistance has been measured using a variety of techniques. Mean development period (MDP) and percentage adult emergence (PAE) are two of the more important traits measuring bruchid (Callosobruchus maculatus Fab.) resistance in cowpea. The objective of the study was to evaluate the genetic relationship between MDP and PAE in C. maculatus resistant cowpea. Seventy-two F₂ population plants were developed from the cross between C. maculatus resistant TVu-11953 (with delayed MDP and low PAE) and C. maculatus susceptible Ife Brown (with early MDP and high PAE) which were evaluated for resistance to cowpea C. maculatus. MDP at 45 days after infestation (DAI) and PAE at 60 DAI were taken as analysed measures for resistance to C. maculatus infestation. Data generated were subjected to chi-square analysis. Varied resistant response to C. maculatus infestation was observed among the F₂ generation plants but their responses showed inclination to the susceptible parent. A 15:1 ratio for susceptible to resistant genotypes was observed with MDP among the F₂ genotypes evaluated which is an indication of the presence of two recessive genes that control of MDP. The segregation of PAE also showed a 15:1 ratio goodness of fit (P > 0.05) for susceptible to resistant genotypes. Test of independence between MDP and PAE was not significant (χ² = 2.19, P = 0.19). This study revealed that the recessive genes controlling these two traits (MDP and PAE) were independently assorted and showed no linkage. This was also evident in the observed F₂ genotypes with C. maculatus resistance expressing either delayed MDP or low PAE and not both in the study.     

Emulsifying and Foaming Properties of Protein Concentrates Prepared from Cowpea and Bambara Bean Using Different Drying Methods

Effect of cabinet-drying, vacuum-drying, and freeze-drying methods on the surface hydrophobicity, secondary structure, emulsifying, and foaming properties of protein concentrates prepared from different cultivars of cowpea and Bambara bean was investigated. The vacuum-drying method reduced hydrophobicity, while freeze-dried concentrates presented high hydrophobicity. The concentrates prepared by freeze drying presented more β-sheet (40–43%) and less β-turn (19–24%) structures. Bambara bean protein concentrates prepared by freeze-drying presented higher emulsifying activity (56–59%) compared to those by vacuum-drying and cabinet-drying, while emulsifying activity varied significantly among cultivars of cowpea (46–61%). Protein concentrates prepared by cabinet-drying showed the highest foaming ability.     

Biological activity and persistence of four essential oils towards the main pest of stored cowpeas, Callosobruchus maculatus (F.) (Coleoptera: Bruchidae)

The use of essential oils extracted from native aromatic plants is perceived as a promising alternative to protect stored cowpeas in West Africa. However the optimal conditions for their efficiency remain to be determined. A study was therefore carried out to compare the biological activity and temperature-related persistence of four selected essential oils towards Callosobruchus maculatus, the main pest of stored cowpeas. Essential oil extracted from Ocimum americanum proved to be very toxic towards C. maculatus adults (LC₅₀ = 0.23 μl/l) while the oils from Hyptis suaveolens, Hyptis spicigera and Lippia multiflora exhibited higher LC₅₀ values (1.30 μl/l; 5.53 μl/l and 6.44 μl/l respectively). The persistence of the biological activity of the four oils was variable and that from O. americanum was most persistent. Fourteen days post-application, this oil was still as active on C. maculatus adults as it was immediately after its application. Exposure of this oil to a high temperature, close to temperatures occurring during storage in Burkina Faso in the dry season, however, resulted in a rapid decrease in its efficacy. Our results emphasize the need to take into account environmental factors such as temperature to optimize the use of promising essential oils for controlling stored-product pests in West Africa.     

Varietal effects of cowpea, Vigna unguiculata, on tolerance to malathion in Callosobruchus maculatus (Coleoptera: Bruchidae)

The impact of cowpea variety on the response of cowpea bruchid, Callosobruchus maculatus, to malathion was investigated. The interaction of six cowpea varieties (Adamawa Brown, Ife BPC, Ife Brown, Lilongwe, Ntcheu and NCRI-L25) with the geographical strains of C. maculatus (Brazil and Cameroon), temperature (23, 25, 27 °C) and insecticide concentration were considered. Cowpea variety (V) had an unpredictable effect on C. maculatus response to malathion. Bruchid populations produced by Ife BPC were the most susceptible to malathion while those yielded by NCRI-L25 were the most tolerant. Regardless of the cowpea variety, the Brazil strain showed higher tolerance than the Cameroon strain. There was significant effect of temperature (T) and insecticide concentration (C) on malathion tolerance in both strains (S). Likewise, there was significant impact of all two-way interactions on cowpea bruchid tolerance except V x C. Significant three-way interactions on C. maculatus tolerance to malathion was only observed in S × T × V and S × T × C. The predictability of changing one of the factors on the susceptibility of C. maculatus to insecticide was very low. This study suggests a need to take the insecticide tolerance of insect populations produced by novel varieties into account during plant breeding in addition to factors such as yield and resistance to insect and disease attack.     

豇豆涂膜保鲜效果的研究

目的分析大豆分离蛋白与茶多酚对豇豆进行涂膜保鲜的可行性。方法用茶多酚和大豆分离蛋白复合涂膜液处理豇豆,测定低温(7℃)贮藏过程中呼吸强度、细胞膜相对透性、失重率、叶绿素含量、纤维素含量和维生素C含量等各项指标的变化。结果涂膜处理可明显降低豇豆的呼吸速率和失重率,减缓了贮藏期间豇豆维生素C与叶绿素含量的下降,对豇豆的纤维化及细胞膜相对透性的上升有明显的抑制作用,且成膜剂大豆分离蛋白中添加茶多酚可进一步增强涂膜处理的效果,和对照相比,5%的大豆分离蛋白溶液中添加200mg/kg茶多酚制得的涂膜液处理样品可将豇豆的低温保鲜期从6 d延长至12 d。效果显著。结论大豆分离蛋白中添加茶多酚能够明显延长豇豆的保鲜期。     

Natural infection of cowpea (Vigna unguiculata (L.) Walp.) by toxigenic fungi and mycotoxin contamination in Benin, West Africa

Natural infection of cowpea by toxigenic fungi and mycotoxin contamination in Benin, West Africa were studied. Cowpea samples were collected at harvest (T₀) and after three months of storage (T₃) from the four agro-ecological zones of the country. A total of 92 representative samples were analysed for the two periods. About 23 fungal species were identified on cowpea seed samples across zones of which Aspergillus flavus, a fungus that produces aflatoxins, was most frequently encountered. Fusarium species shown to produce fumonisins were not recorded from cowpea seeds. Overall incidence of A. flavus infection was found to increase after storage from 7.6% at T₀ to 28.25% at T₃. In spite of this natural infection of cowpea, very low levels of fumonisin and aflatoxin were detected. Only three out of the 92 cowpea samples, all collected at T₀, were found to be fumonisin B₁ positive with a mean level of 0.03 μg/g. Similarly, only six samples out of the 92, all collected at T₃, were aflatoxin B₁ positive with mean levels of 3.58 μg/kg. Fumonisin (B₂ and B₃) and aflatoxin (B₂, G₁ and G₂) were not detected in any of the samples. Contrary to the situation with maize and groundnut where high levels of toxin are often detected in naturally infected samples, the current results indicate that cowpea is less susceptible to mycotoxin contamination. A low susceptibility could be due to the presence in cowpea of substances that inhibit mycotoxin biosynthesis. Further investigations are underway to confirm this hypothesis.     

Response surface methodology for optimisation of protein concentratepreparation from cowpea [Vigna unguiculata (L.) Walp]

The optimum conditions for the preparation of protein concentrate from cowpea were determined using response surface methodology. A central composite rotatable design, consisting of eight experimental points and five replications at the centre point, was used to investigate the effects of two independent variables, namely pH and NaCl concentration on four responses: protein content (%,), protein yield (%), reactive lysine (g/16 g N) and zinc content (mg/100 g). A second-order polynomial model was used for predicting the responses. Regression analysis indicated that more than 80% of the variation was explained by the fitted models. Experimental results showed that under optimum conditions (pH and NaCl concentration of 9.91 and 0.15 M, respectively) the protein content was 84%, protein yield 87%, reactive lysine 1.175 g/16 g N and zinc content 7.75 mg/100 g. These results were in agreement with those predicted, hence indicating the suitability of the model used.     

Triple-bagging of cowpeas within high density polyethylene bags to control the cowpea beetle Callosobruchus maculatus F. (Coleoptera: Bruchidae)

Laboratory and on-farm trials were carried out to determine the effectiveness of cowpeas triple-bagging with heavy-grade polyethylene to control the cowpea weevil, Callosobruchus maculatus (F.), the main storage pest of cowpea, Vigna unguiculata, Walp, in West Africa. In the laboratory bruchids numbers and seed damage were significantly reduced when storing cowpeas within 2 layers High Density Polyethylene (HDPE) bags of at least 80 μm wall thicknesses. This thickness considerably reduced oxygen concentration in the bag after 5 days of storage and inhibited insect development. However late instar larvae and pupae were less affected by low oxygen concentration. On-farm storage trials with 2 layers HDPE 50 kg capacity bags tightly sealed and placed in an additional woven nylon bag (triple bag) was effective in controlling the bruchids for 7 months. Moreover, seed damage (<7%) and grain germination were not significantly affected (>89%). These findings allow optimizing the triple-bagging technology with readily local manufactured and affordable bags for long duration cowpea storage.