Vegetable Cowpea Research Articles

Fine mapping Ruv2, a new rust resistance gene in cowpea (Vigna unguiculata), to a 193-kb region enriched with NBS-type genes.

A new rust resistance gene Ruv2 was fine-mapped in cowpea to a 193-kb region on chromosome 2, which harboured 23 predicted gene models enriched with NBS-type genes. ZN016 is a landrace vegetable cowpea highly resistant to rust. Two previous studies using mixed-spores inoculation suggested different modes of inheritance of rust resistance in ZN016. In this study, we initially developed a detached leaf assay with a purified single-rust isolate (Auv-LS). Using this approach, we assessed the inheritance of rust resistance in a recombinant inbred line (RIL) population and an F2 population, both derived from the cross of "ZN016" and the susceptible cultivar "Zhijiang282." A single dominant gene mode against Auv-LS was revealed in both populations. QTL mapping showed that this gene was coincident with the Ruv2 locus on LG7, one of the three resistance QTLs previously mapped based on mixed-spores inoculation data. Therefore, Ruv2 was considered as specifically against the rust isolate Auv-LS. Through an analysis of the RIL recombinants at Ruv2, we fine-mapped the gene to an ~ 0.45-cM interval between SNP markers 2_09656 and 2_00973, which corresponded to an ~ 193-kb region on chromosome 2 that harboured 23 predicted gene models enriched with NBS-type genes. Re-sequencing of the two parents revealed polymorphisms in four genes predictively to cause substantial protein structural changes, rendering them valuable candidate genes for future validation. Cross-species syntenic analysis indicated that Ruv2 may represent a novel rust resistance gene in food legumes. A cleaved amplified polymorphic sequences marker tightly linked to Ruv2 was developed to facilitate breeding. This work establishes a basis for map-based cloning of Ruv2 and breeding for rust resistance in cowpea and other legume crops.

<i>Bt-</i>Cotton–Vegetable-Based Intercropping Systems as Influenced by Crop Establishment Method And Planting Geometry Of <i>Bt</i>-Cotton In Indo-Gangetic Plains Region

The present study was conducted at ICAR-Indian Agricultural Research Institute, New Delhi in a splitplot design replicated thrice with four main-plot treatments, i.e. four combinations of two cotton establishment methods (CEMs) and two planting geometries (PGMs) [ M 1 – transplanted cotton (90 × 60 cm PGM); M 2 – transplanted cotton (120 × 45 cm PGM); M 3 – direct seeded cotton (DSC; 90 × 60 cm PGM); M 4 – DSC (120 × 45 cm PGM)]; while sub-plot treatments comprised three intercropping systems [S-Ct – sole cotton; Ct + Ok – cotton + okra (1 : 2 row ratio); Ct + Cp – cotton + cowpea (vegetable purpose; 1 : 2 row ratio)]. It can be inferred from the study that transplanted cotton (TPC) with 90 × 60 cm planting geometry in Bt -cotton + vegetable cowpea intercropping system exhibited maximum seed-cotton equivalent yield (SCEY) as well as gross and net returns and other economic indices, followed by Ct + Ok and sole cotton. DSC with 90 × 60 cm PGM in Ct + Ok intercropping system proved superior in terms of SCEY, and gross and net returns besides other economic indices. Based upon yield advantage indices, TPC in 90 × 60 cm PGM under Ct+Cp intercropping system and DSC in 90 × 60 cm PGM under both intercrops were found to be the best options. Crop competition indices also revealed that the inclusion of these intercrops is advantageous because of spatial and temporal complementarity, different rooting pattern and plant architecture to utilize natural resources more efficiently in Bt -cotton-based intercropping systems in the semiarid Indo-Gangetic plains region.

Sequential Cropping Effects of Vegetable Cowpea on Cassava in Cassava-cowpea Intercrop, Umudike, Southeast Nigeria

Sequential Cropping Effects of Vegetable Cowpea on Cassava in Cassava-cowpea Intercrop, Umudike, Southeast Nigeria

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English

SNP marker-based genetic mapping of rust resistance gene in the vegetable cowpea landrace ZN016

Cowpea rust, caused by Uromyces vignae, is one of the most destructive foliar diseases in cowpea [V. unguiculata. (L.) Walp]. Deployment of rust-resistant cultivars is the most environment-friendly and effective way to curb this disease. For this purpose, a fundamental step is to map the rust resistance genes in elite germplasm lines. In the current study, one major and two minor QTLs conferring rust resistance were detected in a 119-line recombinant inbred line (RIL) population derived from a cross between the rust resistant line “ZN016” and a susceptible cultivar “Zhijiang 282”, using the state-of-the-art cowpea iSelect Consortium Array.The major QTL, designated as Ruv1, was mapped to a 12.48 cM interval between the SNP markers 2_01772 and 2_03292 on LG09, which explained 34.8% of the phenotypic variation. The minor QTLs, designated as Ruv2 and Ruv3, were mapped to a 7.01 cM interval on LG7 and a 6.19 cM interval on LG8, which accounted for 13.4% and 11.9% of the phenotypic variation, respectively. This study demonstrates the usefulness of the Consortium SNP Array on complex trait mapping and solidifies the basis for marker-assisted breeding of new cowpea varieties with improved rust resistance.

English

English

Biometrical studies of yield and related traits in advance breeding lines of bush type vegetable cowpea [Vigna unguiculata (L.) Walp.

Sixty-six bush type advance breeding lines of vegetable cowpea developed at ICAR - Indian Institute of Vegetable Research (ICAR-IIVR), Varanasi were evaluated for different horticultural traits for genetic variability, character association, cause-effect analysis and genetic diversity among the genotypes through D2 statistics. High values of genotypic and phenotypic coefficient of variations, heritability (h2B) and genetic advance were recorded for pod yield per plant, number of peduncles and pods per plant, peduncle length, number of primary branches per plant, pod length, pod weight and number of seeds per pod. Pod yield per plant showed strong positive correlation with number of peduncles and pods per plant, pod weight, pod length, number of seeds per pod and number of primary branches per plant, while negative correlation with days to 50% flowering at genotypic and phenotypic levels. The maximum direct positive effect on pod yield per plant was found contributed by number of pods per plant followed by pod weight. Based on degree of divergence the genotypes get grouped into seventeen clusters. The top three characters which contributed most towards the genetic divergence were number of peduncles per plant, peduncle length and pod length. The genotypes of cluster VII showed maximum genetic divergence with genotypes of cluster VIII. Further, cluster VII had the high yielding genotypes, while cluster XVII had early flowering genotypes. Thus, crossing between genotypes of these groups may result in high yielding early genotypes.

Study of biochemical composition of seeds and green beans of vegetable cowpea (Vigna Ung. ssp. Sesquipedalis)

The article presents the results of investigation of the variability of biochemical parameters of seeds and green beans of vegetable cowpea accessions (Vigna unguiculata ssp. sesquipedalis (L.) Verdc.) introduced for use in breeding. Variations of biochemical parameters of seed quality and green beans (such as protein, fat, ash content, fiber, NFES) were established. New data on the fractional composition of proteins (albumins, globulins, prolamins, glutelins) from seeds and green beans were obtained. These data are of great importance for the evaluation of the starting material and the formation of a breeding program and the selection of rational strategies of individual selection from the source populations.

Identifying the markers and tagging a leucine-rich repeat receptor-like kinase gene for resistance to anthracnose disease in vegetable cowpea [Vigna unguiculata (L.) Walp.

ABSTRACTAnthracnose caused by the fungus Colletotrichum lindemuthianum is the most destructive disease of cowpea. Field-type cowpeas show various levels of resistance, whereas pole-type vegetable cowpeas are highly susceptible. Transfer of resistance available in field types to vegetable types is a major breeding objective in cowpea. This paper details the development of an F2 mapping population by crossing field-type cowpea variety Kanakamony (Vigna unguiculata ssp. cylindrica) with pole-type vegetable cowpea variety Sharika (Vigna unguiculata ssp. sesquipedalis), screening this population with artificial inoculation and Bulked Segregant Analysis (BSA) with random marker systems Random Amplified Polymorphic DNA (RAPD) and Inter-Simple Sequence Repeats (ISSR); the objective is to identify the markers linked with major resistance-contributing genes. RAPD primer OPA02 has yielded marker at 850 bp in susceptible genome, whereas ISSR primers UBC810 and UBC811 have yielded markers at 1.4 kb and 1.5 kb respectively in resistant genomes. These markers were reproducible and their linkage with resistance and suitability in marker assisted selection (MAS) were confirmed through co-segregation analysis in F3 population. UBC811 marker was eluted, cloned on pGEM-T, and sequenced. The sequence had shown that this marker is anchored on LRR receptor-like serine/t\\hreonine protein kinase gene which could be involved in the resistance mechanism.

Biometrical approaches for selection of parents in vegetable cowpea (Vigna unguiculata) breeding programme

Eighty nine genotypes of vegetable cowpea collected from different parts of India were evaluated for yield and yield-attributing traits for genetic variation, character association, cause-effect analysis and genetic diversity among the genotypes through D2 statistics. High values of genotypic and phenotypic coefficient of variations, broad sense heritability and genetic advance were estimated for plant height, pod yield/plant, number of peduncles and pods/plant, pod weight and pod length. Pod yield/plant showed strong positive correlation with pod weight, number of peduncles and pods/plant, pod length and number of seeds/pod, while negative correlation with days to 50% flowering at genotypic and phenotypic levels. The maximum direct positive effect on pod yield/plant was contributed by pod weight followed by number of pods/plant. Based on degree of divergence the genotypes were grouped into twelve clusters. The genotypes of cluster XII showed maximum genetic divergence with cluster X, hence, crossing between genotypes within these groups could produce good recombinants and desirable segregants. Cluster III was found to be the best performing for number of pods/plant, pod weight and pod yield/plant while the cluster IX flowered much earlier. Thus, crossing between genotypes within these groups could produce desirable transgressive segregants for earliness and high yielding genotypes. Plant height contributed highest towards divergence (29.37%) followed by number of peduncles/plant (26.30%), number of pods/plant (18.39%) and pod weight (16.42%) among vegetable cowpea genotypes.

Assessment of yield and economics of vegetables as intercropping system in coconut garden for additional returns

A field experiment was conducted on assessment of yield and economics of vegetables as intercropping system in coconut garden for additional returns at different villages of Tiptur taluk, Tumkur districts of Karnataka during from 2013 to 2015 to study the influence of intercropping system on coconut yield, economics of coconut based intercropping system with vegetables and the soil fertility status of coconut garden. The experiment consisted of three different intercropping systems viz., coconut sole cropping as farmers practice (T 1 ), coconut+vegetable cowpea (T 2 ) and coconut+French bean (T 3 ) with seven replications at farmers field in a 36 year old coconut garden of Tiptur tall variety planted at 9m × 9m spacing. The average three year results of experiments were recorded. The yield of coconut was found to higher nut yield (9594 nuts/ha/year) under french bean as intercrop in coconut garden followed by cowpea as intercrop in coconut garden (9348 nuts/ha/year) during third year. Whereas lowest nut yield was recorded in coconut sole crop in farmers practice. The highest net annual income Rs. 99,720/ha and B:C 3.22 were recorded in coconut+French bean intercropping system with more additional income and market demand of beans followed by coconut+vegetable cowpea (Net annual income Rs. 84,260/ha and B:C 3.10) with less market demand of vegetable cowpea, where as lowest net annual income Rs. 43,107/ha and B:C 2.34 were recorded in coconut sole cropping with no additional income from the farmers practices. The soil fertility status viz ., NPK availability in soil were analyzed before and after the experimental period of three year. Gradually increased N, P and K content of soil in coconut intercropping with beans and cowpea on far with each other, but lowest soil fertility were recorded in coconut as sole cropping system in farmers practices due to high biomass of french bean and cowpea, which fixes atmospheric nitrogen, residue incorporated into soil and suppression of weed growth results in improvement of soil fertility status. Higher net returns and improve the soil fertility by growing the french bean as intercrops in coconut garden is more suitable cropping system to boost economy of farmers.

Yield and Productivity of Eggplant Genotypes Intercropped with Vegetable Cowpea in the Humid Tropics

ABSTRACTIntercropping fruit vegetable crops with legumes may influence performance of component crops and improve residual nitrogen contribution to the cropping system. Eggplant (Solanum spp.) genotypes whose fruit and leaves are a good source of income and provide essential vitamins and minerals for good health were intercropped with vegetable Cowpea (Vigna unguiculata Walp ssp. sesquipedalis) in 2 years. Eggplant was monocropped using genotypes ‘Ex-Lantan’, Solanum macrocarpon L., S. melogena L, S. aethiopicum L. (mikky mikky-Gilo), ‘Nsukka green’, and ‘Nsukka white’. A semiprostrate vegetable cowpea was grown in monocrop and the crops were intercropped. Eggplant fruit yield, pod yield of cowpea, and interrelationships between yield characters, as well as the biological and economic productivity of the system, were studied. Intercropping eggplant with cowpea produced a high degree of complementarity. The mono- and intercropped eggplant genotypes exhibited wide genotypic variation. On average over two cropping seasons, ‘Nsukka green’/cowpea intercrop followed by ‘Nsukka white’/cowpea intercrop had the highest total land equivalent ratio (LER; 1.78) and land equivalent coefficient (0.79) compared to other mixes. The ‘Ex-Lantan’/cowpea intercrop had the highest mean gross monetary and net returns (NR); the S. melogena/cowpea intercrop produced the highest total cost of production (TCP) among intercrops; the highest benefit–cost ratio (BCR) was for monocropped S. macrocarpon. Among intercrops, the BCR of S. macrocarpon/cowpea mix was highest compared to ‘Ex-Lantan’, S. melongena, S. aethiopicum, ‘Nsukka green’, and ‘Nsukka white’, at 0.57%, 21.58%, 33.46%, 26.30%, and 19.89%, respectively. There was a positive but weak linear relationship between LER and NR and between LER and BCR. Intercropping eggplant with cowpea enhances productivity and financial return.

Profitability of Rice based Cropping System by Sequencing Vegetable Cowpea under Various Establishment Techniquesin Periyar-Vaigai Command

Field experiment was conducted during Rabi season, 2013-14 to the study the effect of crop establishment techniques and crop geometries on yield and economics of rice-vegetable cowpea cropping system. Experiment was laid out in strip plot design and treatments were replicated thrice. The sixteen treatment combination consisted of four establishment techniques viz., puddled transplanting (E1 ), puddled direct seeding (E2 ), unpuddled transplanting (E3 ), unpuddled direct seeding (E4 ) and four crop geometries such as 30 x 20 cm (S1 ), 20 x 10 cm (S1 ), 25 x 25 cm (S3 ) and 30 x 30 cm (S4 ). Among the different treatment combinations, square planting of 25 x 25 cm adopted in puddled condition gave higher grain yield of 6963 kg ha-1 and straw yield of 9299 kg ha-1. In case of succeeding vegetable cowpea, higher yield of 8780 kg ha-1 and halum yield (13926 kg ha-1) was obtained in the combination of 30 x 30 cm under unpuddled direct seeded method. Similarly, higher gross return, net return, B:C ratio and lower production cost recorded under same combination. Puddling practice was conducive for rice, unpuddled soil was found to be optimum for succeeding deep rooted crops like vegetable cowpea.

Genetic divergence in vegetable cowpea (Vigna unguiculata L.)

Twenty one genotypes of vegetable cowpea including checks were planted in Randomized Block Design at the experimental farm of Pt.K.L.S.College of Horticulture and Research Station, Rajnandgaon, during 2015-16. The data recorded on twenty one characters were subjected to analysis of variance. The analysis of variance revealed highly significant differences among the genotypes for all the characters studied except pod width. It indicates that sufficient variability exhisted among the genotype for the mentioned characters. The GCV value was higher for plant height, pod yield per plant indicated that these characters exhibited variability among the genotypes. The highest heritability was recorded for the characters plant height (60DAS), days of maturity , fruiting duration, 50 per cent flowering ,pod setting per cent per plant, 100 dry seed weight, 100-green seed weight. The genetic divergence in the present study observed among 21 genotypes of vegetable cowpea, showed low quantum of divergence and was grouped into five clusters On the basis of D 2 analysis. Maximum number of genotypes (9) was accommodated in cluster - II. The average inter and intra cluster divergence (D) values had also been calculated. The intra-cluster distance varied from 0.00 to 5.04. The maximum intra cluster distance was shown by cluster I (5.04) followed by cluster V, cluster II, cluster III and cluster IV. The maximum inter cluster distance was observed in between cluster I and V (5.04). The cluster III showed maximum value for mean green pod yield (146.820g.) followed by cluster IV (146.156g). Crossing between the genotypes of maximum two clusters appeared to be most promising to combine the desirable characters.

Genomic regions, cellular components and gene regulatory basis underlying pod length variations in cowpea (V.unguiculata L. Walp).

SummaryCowpea (V. unguiculata L. Walp) is a climate resilient legume crop important for food security. Cultivated cowpea (V. unguiculata L) generally comprises the bushy, short‐podded grain cowpea dominant in Africa and the climbing, long‐podded vegetable cowpea popular in Asia. How selection has contributed to the diversification of the two types of cowpea remains largely unknown. In the current study, a novel genotyping assay for over 50 000 SNPs was employed to delineate genomic regions governing pod length. Major, minor and epistatic QTLs were identified through QTL mapping. Seventy‐two SNPs associated with pod length were detected by genome‐wide association studies (GWAS). Population stratification analysis revealed subdivision among a cowpea germplasm collection consisting of 299 accessions, which is consistent with pod length groups. Genomic scan for selective signals suggested that domestication of vegetable cowpea was accompanied by selection of multiple traits including pod length, while the further improvement process was featured by selection of pod length primarily. Pod growth kinetics assay demonstrated that more durable cell proliferation rather than cell elongation or enlargement was the main reason for longer pods. Transcriptomic analysis suggested the involvement of sugar, gibberellin and nutritional signalling in regulation of pod length. This study establishes the basis for map‐based cloning of pod length genes in cowpea and for marker‐assisted selection of this trait in breeding programmes.

Genetic interrelationship among cowpea varieties elucidatedthrough morphometric, RAPD and SSR analyses

The genetic interrelationship among all the popular vegetable cowpea varieties cultivated in Kerala was investigated through morphometric, RAPD and SSR analyses. High polymorphism was observed in RAPD (88.0 per cent of bands were polymorphic) and SSR (80.0 per cent of bands were polymorphic) analyses. Dendrogram based on morphological parameters has divided the genotypes into two main clusters which truncated at 68.0 per cent similarity, with purple and green poded varieties segregating into separate clusters. Morphometric analysis was successful to group the varieties with determinate and indeterminate growth habits whereas, RAPD and SSR markers could not make a clear division. However, distinction was apparent between purple poded and green poded types and purple poded varieties viz Vyjayanthi and Varun exhibited high similarity with each other in SSR analysis (80.0 per cent) when compared to RAPD (77.0 per cent). Dendrogram of pooled data of SSR and RAPD analyses has revealed maximum similarity between Vyjayanthi and Varun (77.0 per cent).

Influence of Nutrient Source on Yield, Quality and Economics of Seed Production in Vegetable Cowpea (Vigna unguiculata ssp. sesquipedalis)

Field investigation was carried out to study the influence of different sources of nutrients on seed production in vegetable cowpea (Vigna unguiculata ssp. sesquipedalis) during 2010-11 in Randomized Block Design, with twelve combinations of nutrient sources. Results showed significant variation in seed yield potential in the crop. Highest seed yield (435.97kg ha-1) was recorded in the treatment where recommended NPK dose for the seed crop was applied along with vermicompost at 50 per cent nitrogen substitution. Yield attributes were found non-significant, but had a positive influence on seed yield. Germination percentage and 100-seed weight was significantly higher in treatments receiving a combination of vermicompost and poultry manure. Benefit:Cost analysis revealed that 50 per cent N substitution with vermicompost and 25% N with poultry manure were the most profitable in cowpea seed production.

Adoption of Kerala Agricultural University Recommended Practices of Amaranthus and Vegetable Cowpea

The study was conducted in Thiruvananthapuram district of Kerala. Ninety farmers engaged in commercial cultivation of amaranthus and vegetable cowpea were selected through three stage random sampling procedure. Ten independent variables were selected based on judges’ relevancy rating. Majority of the respondents belonged to medium category with respect to adoption. In the case of amaranthus growers, four variables, namely, contact with extension agency, scientific orientation, innovativeness and mass media exposure were found to be significantly and positively related to adoption. Education, scientific orientation and innovativeness were found to be significantly and positively related to adoption in the case of vegetable cowpea growers.

Evaluation of F3 generations of the hybrid crosses between vegetable and field cowpeas and their parents for resistance to the cowpea bruchids (Callosobruchus maculatus (F))

An evaluation of crosses between vegetable and field cowpea for resistance to the cowpea Bruchids, [ Callosobruchus maculatus (F)], was carried out at the Enugu State University of Science and Technology, Enugu southeastern Nigeria. There was a significant difference in the field infestation of the cowpea lines by C. maculatus . AD-36-WB had the highest percentage field infestation by the insect pest, whereas, AE—36-C X AN-16-D, and AN-14-D were free from the field infestation by the pest. Vegetable cowpea lines tested had some levels of resistance to the cowpea Bruchid and the gene responsible for the resistance were successfully transferred from vegetable cowpea to the susceptible field cowpea by cross-breeding techniques. No vegetable cowpea tested had complete resistance to the cowpea bruchid, however, they had lower susceptibility than the field cowpea tested. Reduction in the relative susceptibility of the cowpea to C. maculatus was achieved by cross breeding field cowpea with vegetable types. For instance, in crosses between AD-36-W (field cowpea) and AE-36-C (vegetable cowpea), AD-36-WB (field cowpea) and AN-14-D (vegetable cowpea), AD-36-W (field cowpea) and AE-36-F (vegetable cowpea), AD-36-WB (field cowpea) and AE-36-C (vegetable cowpea), AN-14-D and AE-36-F reduced susceptibility of AD-36-W and AD-36-WB to C. maculatus from 63.59% to 51.09%, 68.46% to 59.09%, 63.59% to 47.38% and 68.48% to 38.84% respectively. Also, gene responsible for susceptibility to the storage insect pest were successfully transferred from field cowpea to the vegetable cowpea through cross-breeding techniques. A cross between two vegetable types namely; AE-36-C and AN16-D had the least susceptibility level of 24.32%. There was a significant difference in mean number of eggs laid per cowpea line with AD-36-WB recording the highest mean number of 134.75 eggs and AE-36-F recording the least mean number of 4.75 eggs. There was also a significant difference in the percentage adults emergence per cowpea line with AD-36WB having the highest percentage of 68.46% adults, and AE-36-C X AN-16-D having the least percentage of 24.32% adults. The result of the experiment also showed a significant difference in mean longevity of female adults reared from cowpea lines with those reared from AD-36WB X An-14-D, and AE-36-C having the highest mean longevity of 14 days each whereas those from AD-36WXAE-36-C had the least mean longevity of 5.6 days. Also, there was a significant difference in mean testa thickness of the seeds tested with AE-36-C having the highest mean testa thickness of 0.20mm, whereas AD-36-WB had the least mean testa thickness of 0.02mm. However, there was no correlation between either testa thickness or moisture content and levels of infestation by the storage insect pest. Again, there was a significant difference between mean weight loss of seeds tested after infestation by C. maculatus , with AD-36WB recording the highest mean weight loss of 0.38g, whereas AE-36-C and AE-36-F, had the least mean weight loss of 0.07g. There was a positive correlation between the weight loss of the adult C. maculatus and the weight (g) of the seeds from which the insect pest was reared (r = 0.03). Key words: Cowpea lines, cross-breeding, Callosobruchus maculatus , resistance, susceptibility

Discriminant function method of selection in Vegetable Cowpea [Vigna unguiculata (L.) Walp.

Sixty diverse genotypes of vegetable cowpea were evaluated for twelve characters in order to construct selection indices. The characters, which had desirable correlation as well as moderate to high direct effect on green pod yield per plant were considered as selection index criterion. The green pod yield per plant (X 1 ) along with its three components viz ., number of pods per plant (X 2 ), pod length (X 3 ) and ten pod weight (X 4 ) were utilized for the construction of selection indices. The discriminant function had higher genetic gain and relative efficiency over straight selection for green pod yield per plant alone. The relative efficiencies of selection indices constructed in combinations of two or more characters were ranged from 3.99 to 136.46%, while genetic advance ranged from 3.99 to 136.28g. There was an increase in genetic gain and relative efficiency with inclusion of an additional trait in the character combination. A selection index involving green pod yield per plant, number of pods per plant, pod length and ten pod weight (X 1 .X 2 .X 3 .X 4 ) followed by green pod yield per plant, number of pods per plant and ten pod weight (X 1 .X 2 .X 4 ) or green pod yield per plant, pod length and ten pod weight (X 1 .X 3 .X 4 ) could be advantageously exploited in the vegetable cowpea breeding programmes.