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.

Thesis (DTech (Faculty of Applied Sciences)--Cape Peninsula University of Technology, 2009 / A 3-factorial experiment involving two cowpea densities (83,000 and 167,000 plants.ha-1), two cropping systems (i.e. monoculture and mixed culture) and five cowpea genotypes (i.e. three farmer-selected cultivars, Bensogla, Sanzie and Omondaw and two improved varieties, ITH98-46 and TVu1509) was conducted in the field for two consecutive years in 2005 and 2006. The aim was to assess the effect of plant density, cropping system and cowpea genotypes on: (i) chlorophyll and gas-exchange, (ii) rhizosphere mineral concentration and tissue uptake of nutrients, (iii) acid and alkaline phosphatase activities in the rhizosphere, (iv) plant growth and symbiotic performance, and (v) concentration of flavonoids and anthocyanins in seed extracts and plant organs and their effect on pest infestation and diseases. The results showed that high plant density (167,000 plants.ha-1) and mixed culture significantly decreased gas-exchange parameters, leaf chlorophyll content, 13C and %C in both cowpea and sorghum plants compared with low plant density (83,000 plants.ha-1) and monoculture. The data also showed significantly higher 13C and lower %C in ITH98-46 and TVu1509 compared with Bensogla, Omondaw and Sanzie genotypes with a significant correlation between 13C and water-use efficiency. At harvest, grain yield of cowpea and sorghum was significantly decreased by high plant density and mixed culture compared with low plant density and monoculture. Sanzie genotype was generally superior in grain yield (2,550 kg.ha-1) followed by cvs. Omondaw and Bensogla (2,250 and 2,150 kg.ha-1, respectively) compared with the improved cultivars. Sorghum plants in mixture with cv. TVu1509 or cv. ITH98-46 performed better (1,570 and 1,550 kg.ha-1, respectively) compared with those in mixture with other cultivars. The results also showed greater land equivalent ratio (LER = 1.42 to 1.52), suggesting that mixed culture produced greater total yields per unit land area compared with monoculture.

Cowpea (Vigna unguiculata (L.) Walp) is an important protein-rich grain legume of major economic importance. It is widely grown by small-scale farmers in the arid and semi-arid regions of the world where it is cultivated for its leaves, fresh immature pods and dry grains. However, it is also an underutilized grain legume. In sub-Saharan Africa where most of the cowpea is produced, drought stress is one of the major factors limiting its productivity. Despite the inherent capacity to survive drought stress, several cowpea varieties are affected by mid and late season drought. Therefore, varieties with a higher tolerance to drought stress are required to obtain higher and more stable yields. The objectives of this study were: (i) to determine morphological responses of four dual-purpose cowpea landraces to water deficits during vegetative and reproductive stages (ii) to determine physiological responses of four dual-purpose cowpea landraces to water deficits and recovery during the reproductive stage (iii) to determine yield performance of cowpea landraces after recovery from water stress and how this relates to (ii) above. Four cowpea landraces namely; Lebudu, Lehlodi, Sejwaleng and Morathathane collectedfrom Kgohloane and Ga-Mphela villages, Limpopo Province, South Africa were used in the study. Pot experiments were conducted under glasshouse conditions at the Controlled Environment Facility (CEF), University of KwaZulu-Natal. The first pot experiment evaluated the morphological responses of four cowpea landraces to water stress and recovery. The study was conducted as a single factor experiment laid out in randomized complete block design (RCBD). The treatments (four cowpea landraces) were each planted in 40 pots giving a total of 160 experimental units (drained polyethylene pots with a 5 litre capacity). Each plant in each pot was treated as a replicate. Plants were well-watered until the formation of six fully expanded trifoliates, then irrigation was withheld for 28 days to simulate drought stress during the vegetative growth. The imposition of drought stress was terminated by re-watering all plants after 28 days. The cowpea plants were re-watered sufficiently and allowed to grow until the four landraces reached 50% flowering stage. Watering was withheld again at 50% flowering for a two-week period for all the four landraces to simulate drought stress during the reproductive growth. The second experiment was conducted to investigate physiological responses of the four cowpea landraces to water stress during the reproductive stage. The experiment was laid out as a 4 x 2 factorial treatment structure in randomized complete design (CRD) with the following three factors: cowpea landraces – 4 levels (Lebudu, Lehlodi, Sejwaleng and Morathathane), water regimes – 2 levels (stressed and well-watered) treatment combinations each replicated 20 times (20 pots each containing one plant) giving a total of 160 experimental units (drained polyethylene pots with a 5 litre capacity). Data on morphological responses were collected and included: number of green vs. senesced leaves, visual assessment of leaf greenness, stem, branch greenness and survival percentage. Physiological responses to water stress were determined during the reproductive stage and included: leaf water potential, relative water content, stomatal conductance, proline content, chlorophyll content, carotenoid content, chlorophyll a content, phenolics (free and membrane-bound), total antioxidant capacity and chlorophyll fluorescence parameters (Fv/Fm). Genstat 14th edition (VSN International, UK) was used to perform analyses of variance (ANOVA) and differences between means were determined by the Least Significant Differences (LSD) at the 5% probability level. Landraces showed different morphological responses during both vegetative and reproductive growth stages. Lebudu, Lehlodi and Sejwaleng displayed a strong ability to maintain stem greenness longer as compared to Morathathane during vegetative growth. Lebudu delayed leaf senescence more than other landraces; no differences in survival were observed. All landraces survived for 28 days without water and resumed growth after re-watering. During the reproductive stage, Lebudu displayed a strong ability to maintain leaf, branches and stem greenness longer and showed relatively higher tolerance to drought stress compared to other three landraces. Water stress caused a decline in leaf water potential, relative water content, carotenoid content, chlorophyll content, stomatal conductance and increased proline content, phenolics, chlorophyll a content, total antioxidant capacity and while chlorophyll fluorescence parameter, Fv/Fm, was not affected. All landraces maintained higher relative water content above a critical threshold with Sejwaleng maintaining a significantly higher RWC (69%) than Lehlodi, Lebudu and Morathathane. Morathathane developed a more negative leaf water potential at maximum stress than Lebudu, Lehlodi and Sejwaleng. Stomatal closure was observed in all cowpea landraces during water stress, but re-opened after re-watering. Chlorophyll content was considerably reduced in Morathathane as compared to Lebudu, Lehlodi and Sejwaleng. No significant differences were observed between the cowpea landraces with respect to carotenoid content at maximum stress. Chlorophyll a content increased significantly for Morathathane as compared to Lebudu, Lehlodi and Sejwaleng. High accumulation of proline was observed for Lebudu, Lehlodi and Morathathane as compared to Sejwaleng, which showed a very slow accumulation of proline. Lebudu, Lehlodi and Sejwaleng showed an increase in phenolic compounds while a decline was observed for Morathathane. Total antioxidant capacity (TAOC) was high in all cowpea landraces during water stress. Also, all chlorophyll fluorescence parameters showed that cowpea landraces had efficient photo-protection mechanisms during drought stress. After re-watering, relative water content, leaf water potential, stomatal conductance, chlorophyll content, carotenoids, chlorophyll a, proline content and TAOC recovered and reached the same level as that of well-watered plants. All four landraces were re-watered after the imposition of stress and above ground biomass, pod mass and number and seed yield determined. Although there was a reduction in the total above-ground biomass, pod mass and number in all four landraces under water stress compared to the well–watered treatment; this was not statistically significant (P > 0.05). Furthermore, no significant differences (P > 0.05) were observed between the four landraces with respect to seed yield under stressed and well-watered conditions. This study established that cowpea landraces vary with respect to the various morphological and physiological adaptive mechanisms in response to water deficits. Such adaptive mechanisms probably ensure their survival under severe water stress conditions until the next rainfall and therefore allowing them to produce reasonably relatively higher leaf and seed yield. Detailed knowledge of these mechanisms in the landraces could be useful in the genetic enhancement and breeding for drought tolerance in the existing cowpea germplasm. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.

Cowpea yields in Mozambique can be increased through breeding farmers’ accepted cultivars with drought tolerance and stability across environments. A study was conducted in the southern region of Mozambique to: (1) determine farmers perceptions on major constraints limiting cowpea production and identify preferences regarding cultivars and traits, (2) determine the variability of selected cowpea germplasm for drought tolerance, (3) determine the gene action controlling drought tolerance, yield and yield components in cowpea, and (4) assess the genotype × environment interaction and yield stability of cowpea genotypes under drought-stressed and non-stressed conditions. The study on farmers’ perceptions about the major constraints limiting cowpea production and preferences regarding cowpea cultivars and traits established that cowpea was an important crop, cultivated for its grain, leaves and fresh pods for household consumption and the market. The study revealed that cowpea grain and leaves were equally important across the three districts in the study. Differences in accessibility to markets between districts influenced the ranking of grain and leaves among districts. Grain was more important in Bilene and Chibuto districts which are situated far from the major urban centre, Maputo, while leaves were more important in Boane district which is near the major market of Maputo. Fresh pods were important in Bilene district which is situated along the major highway connecting Maputo and other provinces. Drought was the most important production constraint followed by aphids, bruchids and viral diseases. The criteria used by farmers to select cowpea varieties included high grain and leaf yield, large seed size, earliness, smoothness of the testa and potential marketability of the variety. The implication of this study is that different types of varieties need to be developed for different areas. Dual-purpose or grain-type varieties need to be developed for areas situated far away from the major markets while varieties for leaf production need to be bred for areas near major markets. During the breeding process, a selection index needs to be adopted whereby drought tolerance, high grain and leaf yield, large seed size, smooth testa, earliness, aphids and bruchids resistance should be integrated as components of the index. High grain yield should receive high weight for varieties developed for areas located far from major markets while high leaf yield would receive high weight for varieties developed for areas located near major markets. The study on variability of cowpea germplasm collections for drought tolerance revealed wide genotypic variability among the tested germplasm. Biplot displays indicated that the genotypes could be grouped into four categories according to their drought tolerance and yielding ability as indicated below: high yielding-drought tolerant (group A), high yielding-drought susceptible (group B), low yielding-drought tolerant (group C), and low yielding-drought susceptible (group D). Examples of high yielding-drought tolerant genotypes were Sh-50, UC-524B, INIA-24, INIA-120, IT96D-610 and Tete-2. Stress tolerance index was the best criterion for assessing genotypes for variability in drought tolerance because it enabled the identification of high yielding and drought tolerant genotypes (group A). The assessment on gene action controlling drought tolerance (stay-green), yield and components indicated that both additive and non-additive effects were involved in controlling all of these traits. Additive gene action was more important than non-additive gene affects in controlling stay-green, days to flowering, number of pods per plant, number of seeds per pod and hundred seed weight. Under no-stress conditions, additive gene action was more important than non-additive gene action while under drought-stressed conditions, non-additive gene effects were more important than additive gene effects. Stay-green can easily be assessed visually in early segregating populations while yield and yield related traits cannot. Hence, selection for drought tolerance using the stay-green trait would be effective in early segregating generations while selection for yield and number of pods per plant would be effective in late segregating generations. Selection for yield could be conducted directly under no-stress conditions and indirectly using the number of pods per plant under drought stress conditions. Genotype INIA-41 would be the most desirable to use as a parent for drought tolerance and IT93K-503-1 would be the most desirable to use as a parent for drought tolerance and yield. The assessment on genotype × environment interaction and cowpea grain yield stability for forty-eight (48) cowpea genotypes grown under drought-stressed and non-stressed conditions indicated that cross-over genotype × environment interactions were present for yield indicating that genotypes responded differently to varying environmental conditions. Genotypes adapted to specific environmental conditions could be identified. Genotypes IT-18, INIA-51, INIA-51A and Nhavanca were adapted to non-stressed environments that were either drought stressed or non-stressed while VAR-11D was adapted to low yielding, stressful environments. Genotypes INIA-23A, INIA-81D, INIA-24, INIA-25, INIA-16 and INIA-76 were high yielding and stable while genotypes IT-18, INIA-51, INIA-51A, Nhavanca and VAR-11D were high yielding and unstable. Genotypes Bambey-21, INIA-36, INIA-12 and Monteiro were consistently low yielding and stable except INIA-12 that was consistently unstable. Chókwè was a high yielding environment and suitable for identifying high yielding genotypes but not ideal for selection because it was not representative of an average environment while Umbeluzi was low yielding and not ideal for selection. Overall, the study revealed that genetic improvement of drought tolerance and yield would be feasible. Potential parents for genetic improvement for yield and drought tolerance were identified. However, further studies for assessing yield stability of cowpea genotypes are necessary and could be achieved by including more seasons and sites to get a better understanding of the genotype × environment interaction and yield stability of cowpea in Mozambique. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.