Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 56-62). Also available via the Internet.

Thesis (M. Sc. Agriculture (Agronomy)) -- University of Limpopo, 2016. / Cowpea (Vigna unguiculata (L.) Walp) is an important annual leguminous crop in semi-arid and tropics, where it is mainly grown for consumption and livestock feeding. The crop has good morphological and biochemical qualities which make it well adapted to the semi-arid and tropics. However, farmers in South Africa currently lack good seed for planting and experience very low cowpea grain yields. The aim of this study was to evaluate 97 newly introduced cowpea germplasm for adaptation and yield parameters. The study was conducted in two locations in Limpopo Province, with each location having two experiments, experiment I consisted of 57 early maturing cowpea germplasm, and experiment II consisted of 40 medium maturing cowpea germplasm, these materials were introduced from IITA, Nigeria and A&M University, Texas, USA. Both with one local check (Glenda). The first location was at Ukulima Farm near Modimolle in the Waterberg district during 2012/13 and the second was at University of Limpopo experimental farm Syferkuil during 2013/14 summer-planting season. The experiments were laid out as an incomplete randomized block design (lattice design), consisting of 3 replications, four rows per plot with intra row spacing of 25 cm and inter row spacing of 75 cm. Each row was 4m long. The following agronomic variables were collected, in both locations; plant height, number of pods per plant, pod length, number of seed per pod, number of branches, hundred seed weight and grain and fodder yield. Data was subjected to ANOVA using statistical software, Statistic 9.2. The variances of the parameters measured were summarized in ANOVA table. The treatments that showed significant difference were separated using Duncan Multiple Range at 5% level of significance. The result showed significant difference (P<0.05) among cowpea varieties for the following yield parameters; plant height, number pods per plant, number of branches, seed weight, pod weight and hundred seed weight. In experiment I the mean plant height, number of branches, mean pod length, total pod weight, weight of seeds per pod, hundred seed weight and number of seed per pod were respectively (100 cm, 21, 23 cm, 1413.4 kg/ha, 1121.62 kg/ha, 28.283g and 16) and were greater than the control Glenda (49 cm, 15, 14 cm, 777.82 kg/ha, 622.87 kg/ha, 13.300 g and 13). In vi experiment II the mean plant height, number of branches, mean pod length, total pod weight, weight of seeds per pod, hundred seed weight and number of seed per pod were respectively (97 cm, 21, 21 cm, 1546.19 kg/ha, 1245.11 kg/ha, 27.363 g and 16) and these were better than the control, Glenda (50 cm, 15, 17 cm, 795.11kg/ha, 661.01 kg/ha, 18.393 g and 13). Weight per 100 seeds showed that 51 and 32 breeding lines had weights higher than Glenda in the early and medium maturity trials, respectively. The evaluated cowpea varieties varied in performance between the two locations. The above results indicate the superiority of the introduced breeding over the local check as well as the potentials of using these promising lines for the development of better adapted germplasm in South Africa. The lines with better agronomic characters and yield performance in the two locations are recommended for seed production to meet the immediate needs of farmers, after due registration with DAFF at Pretoria. Data generated from the studies will contribute useful information to the data-base of the characteristics of these cowpea lines. Key words: Evaluation, Cowpea germplasm, Adaptation, Vigna unguiculata. / AgriLIFE A&M University of Texas USA, National Research Foundation (NRF) and ARC/IITA

No description available.

Analysis of antioxidant activity (AOA) of entries in the 2002 Regional Southernpea Cooperative Trial revealed not only significant differences among entries, but that entries with pigmented (black and red) seed coats were clustered among the highest, cream types were the lowest, while pinkeye and blackeye types were intermediate. Red colored peas were higher in antioxidant activity than black types. These findings provided strong evidence that compounds responsible for pigmentation were involved in AOA. The objectives of the present investigation were to investigate the inheritance of AOA in cowpea and further study the relationship between AOA and seed coat color. Four advanced selections, ARK95-356 (black), ARK98-348 (red), ARK96-918 (cream), and LA92-180 (cream), were crossed in a complete diallel mating design, generating F1, F1', F2, F2', BC1, and BC2 populations. Individual seeds were ground and samples were extracted in methanol and analyzed for AOA using the free radical 2, 2-Diphenyl-1-picrylhydrazyl (DPPH) method. Combining ability tests using Griffing??s Method I Model I indicated presence of highly significant general combining ability (GCA), specific combining ability (SCA), and reciprocal (REC) and maternal (MAT) effects, with pigmented lines exhibiting positive GCA and MAT, while non-pigmented lines exhibited negative GCA and MAT. AOA in the F1 was not significantly different from the maternal parent, with seed coat color also resembling the maternal parent. Segregation for seed coat color was observed in the F2 and F2'. Additive, dominance, and epistatic effects were significant. The broad sense heritability estimate was 0.87. Minimum number of genes responsible for AOA was estimated at about five. Factors governing high AOA appeared to be the same as those responsible for seed coat color, with apparent pleiotropic effects. In conclusion, breeding for high AOA is possible using highly pigmented parental lines.

Analysis of antioxidant activity (AOA) of entries in the 2002 Regional Southernpea Cooperative Trial revealed not only significant differences among entries, but that entries with pigmented (black and red) seed coats were clustered among the highest, cream types were the lowest, while pinkeye and blackeye types were intermediate. Red colored peas were higher in antioxidant activity than black types. These findings provided strong evidence that compounds responsible for pigmentation were involved in AOA. The objectives of the present investigation were to investigate the inheritance of AOA in cowpea and further study the relationship between AOA and seed coat color. Four advanced selections, ARK95-356 (black), ARK98-348 (red), ARK96-918 (cream), and LA92-180 (cream), were crossed in a complete diallel mating design, generating F1, F1', F2, F2', BC1, and BC2 populations. Individual seeds were ground and samples were extracted in methanol and analyzed for AOA using the free radical 2, 2-Diphenyl-1-picrylhydrazyl (DPPH) method. Combining ability tests using Griffing??s Method I Model I indicated presence of highly significant general combining ability (GCA), specific combining ability (SCA), and reciprocal (REC) and maternal (MAT) effects, with pigmented lines exhibiting positive GCA and MAT, while non-pigmented lines exhibited negative GCA and MAT. AOA in the F1 was not significantly different from the maternal parent, with seed coat color also resembling the maternal parent. Segregation for seed coat color was observed in the F2 and F2'. Additive, dominance, and epistatic effects were significant. The broad sense heritability estimate was 0.87. Minimum number of genes responsible for AOA was estimated at about five. Factors governing high AOA appeared to be the same as those responsible for seed coat color, with apparent pleiotropic effects. In conclusion, breeding for high AOA is possible using highly pigmented parental lines.

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Cowpea (Vigna unguiculata. L) is an important African crop. However, it is also an underutilized grain legume. Consequently, there is not enough research data on cowpea seed physiology. Whereas there is evidence of cowpea being a drought tolerant crop, there is no evidence to associate plant drought tolerance with seed quality in response to water stress. This study sought to understand the effect of production site and water stress on cowpea seed quality development with respect to germination capacity and vigour. Patterns of raffinose family of oligosaccharides (RFO) during seed development to mature dry stage were used to physiologically relate seed performance to water stress. The effect of water stress and exogenous ABA on the accumulation of stress LEA proteins (dehydrins) in relation to seed quality development and germination was investigated. RFOs are known for their roles in desiccation sensitivity but no studies have shown their significance in cowpeas. Seeds of six cowpea cultivars were produced at two distinct growth sites characterised by irrigated and dry land conditions. The seeds were assessed during six developmental stages, for water content, dry matter accumulation, and performance. Harvested seeds were then planted in a pot experiment under controlled conditions to examine the effect of water stress on seed quality development and data collected during three developmental stages. Harvested seeds from the pot experiment were subsequently analyzed for changes in RFO accumulation during development using gas chromatography. The seeds were also used to investigate the effect of water stress and ABA on the accumulation of stress LEA proteins (dehydrins) in relation to seed quality development in cowpea. In addition, this study evaluated the use of image analysis as a method that can be used to objectively determine seed coat colour variation in cowpea. Statistical variation in individual seed’s solute leakage for cowpea cultivars differing in seed coat colour and produced under different environmental conditions was explored and correlations were done between seed conductivity test with other aspects of seed performance during germination. Furthermore the results of the conductivity test were compared with accelerated aging test, in relation to seed performance. The study provided evidence that cowpea seed lots produced under different environmental, and possibly management conditions may not differ with respect to seed quality as determined by germination capacity and vigour. However, significant differences between sites with respect to seed maturation patterns determined by water content and dry matter accumulation were observed. Adverse maternal environmental effects on the subsequent performance of seeds in a drought tolerant crop may not necessarily lead to poor performance. Cultivar differences in response to simulated drought conditions at the whole plant and tissue level can be considerable and highly variable; however, these differences may not have adverse effects on the germination and vigour of the seeds. Drought avoidance mechanisms at the whole plant level in cowpea are quite efficient in allowing the species to adapt to simulated drought conditions. These mechanisms may allow the cowpea cultivars to maintain metabolism and restore conditions for their continued growth under water stress; and produce few seeds of high germination capacity and vigour. Stachyose was found to be the predominant member of the raffinose family of oligosaccharides in cowpea. It is suggested that stachyose accumulation could be used as an indicator of stress tolerance in cowpea. However, the relationship between RFO concentration and the acquisition of desiccation remained as a matter of speculation in the present study and is still generally inconclusive. There was no evidence to suggest the acquisition of maximum desiccation tolerance is associated with maximum seed vigour. It is suggested in cowpea, which is drought tolerant, that maximum vigour does not necessarily imply the acquisition of maximum desiccation tolerance; rather there is a minimum level of desiccation tolerance that is required for the development of optimal seed vigour. The use of an in vivo approach in the study of LEA function in cowpea enabled the accurate comparison of two different groups of LEA proteins in developing cowpea seeds under conditions of water stress and in relation to germination and vigour. Both group 1 LEA and group 2 LEA (dehydrin) were shown to increase in concentration in response to water stress. In addition group 1 LEA protein was observed to be relatively abundant in cowpea seeds. A maternal influence on LEA protein gene expression under conditions of water stress, which may induce dehydrin accumulation vii during the earlier stages of seed development, was implied by the observation that dehydrin-like proteins were induced after two weeks of development in cowpea plants subjected to stress during the vegetative phase. In addition, the exogenous application of ABA delayed radicle protrusion; this was associated with a delay in the disappearance of LEA proteins and is suggestive of a relationship between LEA protein accumulation and the acquisition of desiccation tolerance. The study has demonstrated that image analysis can objectively discriminate seed coat colour variation in cowpea. Dark coloured seeds in general performed better than light coloured seeds; however seed coat colour was not always associated with better performance. A newly developed Aging Stress Differential Index (ASDI) has been used in this study to demonstrate a link between seed coat colour and sensitivity to water stress. The ASDI correlated well with the observations relating stress tolerance to stachyose accumulation. The skewed distribution patterns in individual electrical conductivity and the presence of extreme values may have implications with respect to the suitability of using standard statistical analyses which compare mean values to evaluate such data. In addition variation in individual electrical conductivity may also be influenced by cultivar differences and the chemical composition of the seed coat. Therefore associations between seed coat colour and electrical conductivity as a measure of performance should be treated with caution. The AA test does reflect changes in seed vigour, however ranked electrical conductivity values after AA did not consistently reflect differences in seed performance between cultivars and sites, and they did not correlate well with other aspects of performance. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2007.

Thesis (MScAgric) -- University of Stellenbosch, 2003. / ENGLISH ABSTRACT: Cowpeas are produced under low and irregular rainfall in most of arid and semi-arid areas of sub-Saharan Africa. Growth and yield are therefore reduced due to the occurrence of water stress during the growing season. Knowledge of the responses and adaptive mechanisms of cowpeas to water stress may help to improve the management practices for these areas. Therefore, three glasshouse experiments were conducted at Welgevallen Experimental Farm of the University of Stellenbosch to test the responses of two cowpea cultivars to water stress. In the first experiment, physiological responses were used to identify those physiological parameters, which can be used to distinguish between drought tolerant and susceptible cowpea cultivars. In the second experiment, some of the identified physiological parameters together with some morphological growth responses, yield and grain protein content of the same two cowpea cultivars were used to identify which is the more tolerant cultivar. Tn the third experiment, the hypothesis that increased phosphorus supply may improve the tolerance of cowpea plants to water stress and their ability of recover from the stress was tested. The results showed that water stress affected water relations, morphological growth parameters, yield and grain protein content, but increasing P supply reduced the effect of water stress and promoted more rapid recovery after re-watering. Water relations were affected by water stress because it reduced relative water content, which resulted in reduced water potential and increased leaf diffusive resistance and proline accumulation. Morphological growth responses and yields were affected because water stress reduced the leaf area, which resulted in reduced biomass production and seed yield. Lower leaf area under water stress was the result of the reduced number of leaves and leaf expansion rate, but the number of leaves was the most important parameter. Reduced seed yield was due to reduced number of pods. The responses of the two cultivars tested were different. AB Wit, which performed better under well-watered conditions was more affected by water stress due to its larger leaf area that resulted in excessive water loss by transpiration. ACH14 was more drought tolerant than AB Wit due to a combination of a more rapid stomatal closure and proline accumulation, which induced osmotic adjustment, and which in tum helped to maintain higher water potentials. The increased P supply reduced the effect of the water stress. High-P level plants showed higher root growth, which resulted in more water uptake and larger leaf area during the water stress period, and after re-watering these plants recovered more rapidly. The more rapid recovery from stress was the result of enhanced root growth and leaf expansion rate and most probably due to increased water uptake. High-P level plants also showed more rapid leaf appearance and plant growth at earlier stages compared to the low-P level plants. / AFRIKAANSE OPSOMMING: Akkerbone word onder toestande van lae en wisselvallige reenval in baie ariede en semi-ariede gebiede van Afrika verbou. In hierdie gebiede word groei en produksie dikwels beperk deur water tekorte gedurende die groei seisoen. Kennis van reaksies en aanpassingsmeganismes van akkerbone teenoor water tekorte mag dus help om produksietegnieke in bogenoemde gebiede te verbeter. Om hierdie rede is drie glashuiseksperimente onder gekontroleerde toestande op die Welgevallen Proefplaas van die Universiteit van Stellenbosch uitgevoer. In die eerste eksperiment is fisiologiese reaksies van twee cultivars gebruik om eienskappe te identifiseer wat gebruik kan word om tussen droogteweerstandbiedende en droogte gevoelige cultivars te onderskei. In die tweede eksperiment is sommige van die geidentifiseerde eienskappe asook morfologiese groei, opbrengs en kwaliteitsreaksies van dieselfde twee cultivars gebruik om die meer droogte weerstandbiedende cultivar te identifiseer. In die derde eksperiment is die hipotese dat P-bemesting die droogteweerstandbiedendheid teen en herstelvermoe na droogte kan verbeter, getoets. Die resultate toon dat water tekorte beide plantwaterverhoudings, morfologiese eienskappe asook opbrengs en proteieninhoud beinvloed, maar dat hoe P-peile die invloed van water tekorte verminder en herstelverrnoe na die droogte verbeter. Plant-waterverhoudings is bemvloed omdat water tekorte relatiewe waterinhoud van plante verlaag wat aanleiding gee tot verlaagde plantwaterpotensiale, verhoogde huidmondjie weerstand en 'n toename in prolien inhoud. Morfologiese eienskappe en opbrengs is benadeel weens 'n veri aging in blaaroppervlakte wat fotosintetiese vermoe en gevolglik ook biomassaproduksie en saad opbrengs benadeel. Verlaagde blaaroppervlakte tydens water tekorte was hoofsaaklik die gevolg van 'n vermindering in aantal blare, terwyl verlaagde saadopbrengs grootliks die resultaat van 'n vermindering in aantal peule was. Die cultivar AB Wit wat die hoogste opbrengs onder gunstige groeitoestande gelewer het, is die meeste bemvloed deur water tekorte omdat die welige blaargroei van hierdie cultivar, luukse waterverbruik en groter transpirasie verliese veroorsaak het. Die cultivar ACH 14 daarteenoor het waterverliese beperk deurdat die huidmondjies vinniger gesluit het en verhoogde prolien-inhoude, osmotiese aanpassings veroorsaak het. Dit het gehelp om waterpotensiale instand te hou. Hierdie cultivar was gevolglik meer droogte weerstandbiedend as AB Wit. Hoe vlakke van P-bemesting het die effek van water tekorte verminder weens verbeterde wortelgroei. Dit het wateropname gedurende en na die peri ode van water stremming verbeter sodat plante vinniger herstel het na die droe periode. Plante wat by hoe P-peile gegroei is het ook 'n verhoogde blaarverskyningstempo en 'n toename in groei tydens die vroee ontwikkelingstadiums getoon.

Cowpea (Vigna unguiculata L.) is an important legume, especially in the hot, dry tropics and subtropics of sub-Saharan Africa. It has been widely reported to be drought tolerant. Cowpea is a highly nutritious, multi-purpose crop, used as a leafy vegetable and grain legume with potential to contribute to food security in marginal areas. However, the crop is still classified as a neglected underutilised species; legume research focus has been mainly devoted to established legumes such as common bean and soybeans. There is a need to collect empirical information on cowpea which could be used to advise farmers on management strategies. This study evaluated cowpea responses to water stress under controlled and field conditions. Initially, two cowpea varieties (Brown and White birch) were evaluated for seed quality using the standard germination that was laid out in a completely randomised design and each variety was replicated for times. Electrolyte conductivity test was also performed under laboratory conditions. Thereafter, a pot trial was conducted to evaluate cowpea response to water stress imposed at different growth stages under varying growth temperatures. The pot trial comprised three factors: temperature [High (33/27ºC), Optimum (27/21ºC) and Low (21/15ºC)], water regimes (no stress, terminal stress, intermittent stress – vegetative and intermittent stress - flowering) and cowpea varieties. Lastly, a field trial was conducted to evaluate cowpea production as well as the effect of sequential leaf harvesting on yield under irrigated and rainfed conditions. The field trial was laid out as a split-plot design, with water regime (irrigation vs. rainfed) as main factors, cowpea varieties as sub-factor and sequential harvesting (no harvest, harvested once and harvested twice), replicated three times. All treatments were arranged in a randomised complete block design. Results of the initial study showed that germination capacity and vigour of cowpea varieties were significantly different (P < 0.001). White birch had higher electrolyte leakage than Brown birch. Pot trial results showed that cowpea growth (leaf area, leaf number and plant height) was vigorous in the high temperature regime compared with optimum and low temperature regimes. Chlorophyll content index was higher under high temperature relative to optimum and low temperature regimes, respectively. Under low and optimum temperature regimes, cowpea growth was stunted; cowpea failed to flower and form yield. Whereas, under high temperature regime, cowpea growth was vigorous hence flowered and formed yield. Vegetative growth was more sensitive to water stress than flowering stage. Terminal stress and stress imposed during flowering resulted in increased proline accumulation relative to no stress and stress imposed during vegetative growth. Harvest index was lower when water stress was imposed during vegetative relative to flowering stage. Field trial results showed that cowpea growth was sensitive to water stress. Plant height, leaf number, chlorophyll content index and stomatal conductance were lower under rainfed relative to irrigated conditions. Sequential harvesting of leaves had no significant effect on cowpea yield. It is concluded that tropical temperature conditions are most suitable for cowpea production; the controlled environment study showed best crop performance under 33/27ºC. In the context of varieties used for the present study, vegetative growth was the most sensitive stage to water stress. Cowpea performed better under rainfed relative to irrigated conditions with respect to yield formation. Low temperature was found to be more limiting to cowpea growth, development and productivity compared with water stress. Whereas, under high temperature conditions, water stress was more limiting to plant growth and productivity. White birch may be used as a dual purpose crop due to its ability to produce reasonable grain yield regardless of defoliation. / Thesis (M.Sc.Agric)-University of KwaZulu-Natal, Pietermaritzburg, 2012.

No description available.