Cowpea Seedlings Research Articles

Phenotyping Cowpeas for Adaptation to Drought

Methods for phenotyping cowpeas for adaptation to drought are reviewed. Key factors involve achieving optimal time of flowering and cycle length, and appropriate morphology for different types of cultivars as they relate to their utilization for dry grain, hay, and fresh pea production. Strong resistance to vegetative-stage drought is available and should be incorporated. The extreme ability of extra-early erect cowpea cultivars to escape terminal drought should be exploited in zones with very short rainfall seasons. In zones with the possibility of limited rainfall in the middle of the growing season, resistance to mid-season drought, and the delayed-leaf-senescence trait can be valuable. Breeding for water-use efficiency, deeper rooting, and heat tolerance are discussed. Diseases and pests that influence adaptation to drought are considered. Resistance to the organism causing ashy stem blight disease should be incorporated because this disease can destroy cowpea seedlings under hot, dry soil conditions. The value of varietal intercrops with contrasting types of cowpea cultivars in enhancing adaptation to drought is described. Implications of cowpea/cereal rotations for cowpea breeding are discussed. Breeding strategies for enhancing cowpea adaptation to drought are described.

Origin of hydrogen peroxide during the cowpea- Xanthomonas interaction

To assay hydrogen peroxide (H2O2) production by phytopathogenic bacteria in vivo, cowpea seedlings were inoculated using wild-type Xanthomonas campestris pv. phaseoli and its mutant strain on ahpC (with attenuated H2O2 production). Antibiotic rifampicin (Rif) was used to kill off the Xanthomonas campestris pv. phaseoli in cowpea leaves. The optimal concentration of Rif to eradicate the bacteria was 500 μg mL–1, and duration of the Rif treatment to eradicate the bacteria in the cowpea tissues was 48 h. This level of Rif did not significantly affect chloroplast and mitochondrial function in cowpea leaves. The concentration of H2O2 in cowpea inoculated with wild-type or mutant strain of Xanthomonas campestris pv. phaseoli following Rif treatment was measured. Increased H2O2 accumulation was observed in cowpea leaves respectively inoculated with wild-type and mutant strain. The accumulation of excess H2O2 was significantly decreased by the Rif treatment on cowpea wild-type bacteria systems. However, the level of H2O2 in cowpea leaves inoculated with mutant strains following Rif treatment was at the same level as in plant leaves without Rif treatment. The results demonstrate that the change in H2O2 concentration observed in vivo was caused by wild-type bacteria.

Plant growth promoting potential of Pontibacter niistensis in cowpea ( Vigna unguiculata (L.) Walp.)

During the past couple of decades, understanding of rhizosphere biology has progressed with the discovery of a special group of microorganisms known as plant growth promoting rhizobacteria (PGPR) and its application for sustainable agriculture has increased tremendously in various parts of the world. The search for microorganisms that improve soil fertility and enhance plant nutrition has continued to attract attention due to the increasing cost of fertilizers and some of their negative environmental impacts. In this study we demonstrated, a novel bacterial species Pontibacter niistensis NII-0905 isolated from forest soil in Western ghat forest soil with potential plant growth promoting ability (PGP) such as phosphate solubilization, indole acetic acid (IAA), siderophore and hydrogen cyanide (HCN) production. The activity varies with different growth temperatures, strain solubilize 28.5 ± 0.9, 48.02 ± 1.9 and 65.07 ± 2.1 μg mL −1 at 4, 15 and 30 °C respectively and produced 24.8 μg mL −1 day −1 of indole acetic acid (IAA) in tryptophan amended media. Qualitative detection of siderophore production and HCN were also detected at all temperature tested. At a lower temperature (4 °C) strain NII-0905 retained all the plant growth promotion attributes. A significant increase in the growth of cow pea was recorded with inoculations of strain NII-0905 in pot experiments. Scanning electron microscopic study revealed the root colonization on cow pea seedlings against the untreated one. These results demonstrate that, the isolate NII-0905 has the promising PGPR attributes for both in cold as well as in humid condition. It has potential as a biofertilizer to enhance soil fertility and promote the plant growth.

Aplicação de silício em milho e feijão-de-corda sob estresse salino

Apesar de não ser um nutriente essencial, o silício pode aumentar o potencial produtivo de algumas culturas e tem sido utilizado para atenuar os efeitos tóxicos do estresse salino. Nesse sentido, objetivou-se avaliar o efeito do silicato de sódio aplicado sob dois modos diferentes em plântulas de milho e feijão-de-corda submetidas à salinidade. Em casa de vegetação, as plântulas receberam uma dose de Na2SiO3 a 1 mM, via aplicação foliar ou diretamente na solução nutritiva, e foram cultivadas na presença ou ausência de NaCl a 100 mM, durante 15 dias. Foram avaliados a matéria seca de folhas, caules e raízes, a área foliar e o vazamento de eletrólitos em folhas e raízes. De modo geral, a salinidade reduziu a matéria seca das folhas, caules e raízes e aumentou o vazamento de eletrólitos nas folhas e raízes das plântulas. A aplicação de silício via solução nutritiva promoveu maiores valores em todos os parâmetros de crescimento e reduziu os danos de membrana no milho, mas isso não foi observado em feijão-de-corda. O silício atenuou os efeitos tóxicos do NaCl no crescimento das plântulas de milho, quando aplicado diretamente na solução nutritiva.

Calculated activity of Mn2+ at the outer surface of the root cell plasma membrane governs Mn nutrition of cowpea seedlings

Manganese (Mn) is an essential micronutrient for plant growth but is often toxic in acid or waterlogged soils. Using cowpea (Vigna unguiculata L. Walp.) grown with 0.05–1500 μM Mn in solution, two short-term (48 h) solution culture experiments examined if the effects of cations (Ca, Mg, Na, Al, or H) on Mn nutrition are related to the root cells’ plasma membrane (PM) surface potential, ψ00. When grown in solutions containing levels of Mn that were toxic, both relative root elongation rate (RRER) and root tissue Mn concentration were more closely related to the activity of Mn2+ at the outer surface of the PM, {Mn2+}00 (R2=0.812 and 0.871) than to its activity in the bulk solution, {Mn2+}b (R2=0.673 and 0.769). This was also evident at lower levels of Mn (0.05–10 μM) relevant to studies investigating Mn as an essential micronutrient (R2=0.791 versus 0.590). In addition, changes in the electrical driving force for ion transport across the PM influenced both RRER and the Mn concentration in roots. The {Mn2+}b causing a 50% reduction in root growth was found to be c. 500 to >1000 μM (depending upon solution composition), whilst the corresponding value was 3300 μM when related to {Mn2+}00. Although specific effects such as competition are not precluded, the data emphasize the importance of non-specific electrostatic effects in the Mn nutrition of cowpea seedlings over a 1×105-fold range of Mn concentration in solution.

Compensatory and susceptive responses of cowpea genotypes to infestation by <i>aphis Craccivora</i> koch.

The aim of the study was to estimate yield loss to10 selected genotypes of cowpea as a result of Aphis craccivora infestation during the vegetative phase of the crop. There were two trials with four replications. The first trial serving as the control was sprayed at the seedling, flowering andpodding stages against insect pests with lambda cyhalothrin (PAWA®). The other trial was sprayed only at flowering and podding stages. The cowpea seedlings of the second trial were infested with five four-day-old aphids per seedling two weeks after planting. The aphids were allowed to form colonies and fed on the seedlings until symptoms of damage were observed. When the susceptible seedlings became stunted with distorted leaves and yellowing of leaves at two weeks after infestation (28 days after planting), aphids were controlled. The results showed that aphids’ infestation delayed flowering and maturity of genotypes of cowpea. With the exception of early flowering genotypes all the medium to late flowering genotypes produced higher dry grain yield in infested plots than the control plots. The trend was not different from the production of dry biomass. The results of the present study implies that control of aphids infestation inearly maturing cowpea genotypes should not be delayed up to two weeks after infestation or 28 days after planting. Aphid’s infestation period for studies in susceptive response in medium to late maturing genotypes should go beyond 28 days after planting probably up to 35 days afterplanting.

Effect of dimethoate and UV-B irradiation on the response of antioxidant defense systems in cowpea ( Vigna unguiculata L.) seedlings

To understand the effect of pesticide and UV-B on plant non-enzymatic antioxidant system, Vigna unguiculata was exposed to different concentration of dimethoate and UV-B (30 min) alone and in combination. Negative impact on V. unguiculata due to generation of superoxide radical ( O 2 - ) , hydrogen peroxide (H 2O 2), electrolyte leakage (EC) and lipid peroxidation (MDA) was observed. Combined exposure to UV-B and dimethoate led to further increase in these parameters. The content of non-enzymatic antioxidants such as proline and flavonoids increased whereas the ascorbic acid content showed a decrease. The results suggested the role of proline and flavonoids in scavenging reactive oxygen species generated due to stress.

Chilling-induced changes of vacuolar proton pumps in hypocotyls of Vigna unguiculata

Vigna unguiculata (cowpea) is a legume adapted to high temperatures and is sensitive to low temperatures. Temperature is one of the limiting factors of growth and yield for many crops but its effect on cowpea metabolism is not known. We investigated the effect of chilling on activity of vacuolar proton pumps (V-ATPase and V-PPase) and their protein content in tonoplast vesicles of cowpea hypocotyls. Seedlings grown for 7 days at 10 or 4°C were used for experiments. Chilling treatment at 10 or 4°C markedly suppressed growth of cowpea seedlings. Following chilling at 10 and 4°C, activity of both proton pumps and the relative amount of V-PPase and subunit A of V-ATPase were significantly increased. Both substrate hydrolysis and H+ transport activities of V-PPase remained at relatively high levels during chilling treatment. For V-ATPase, treatment at 10°C for 6 days increased the ATP hydrolysis activity. However, the H+ transport activity of the enzyme was increased when treated for 4 days but was markedly decreased when treated for 6 days. Our results provide evidence for different regulation for these vacuolar proton pumps, indicating that V-PPase is the more stable proton pump throughout chilling stress.

Recovery of cowpea seedling roots from exposure to toxic concentrations of trace metals

Rhizotoxic effects of many trace metals are known, but there is little information on recovery after exposure. Roots of 3-d-old cowpea (Vigna unguiculata (L.) Walp. cv. Caloona) seedlings were grown for 4 or 12 h in solutions of 960 μM Ca and 5 μM B at two concentrations (which reduce growth by 50 or 85%) of nine trace metals that rupture the outer layers of roots. Measured concentrations were 34 or 160 μM Al, 0.6 or 1.6 μM Cu, 2.2 or 8.5 μM Ga, 2.3 or 12 μM Gd, 0.8 or 1.9 μM Hg, 1.0 or 26 μM In, 2.4 or 7.3 μM La, 1.8 or 3.8 μM Ru, and 1.3 or 8.6 μM Sc. Roots were rinsed, transferred to solutions free of trace metals, and regrowth monitored for up to 48 h. Recovery from exposure to Hg occurred within 4 h, but regrowth was delayed for ≥ 12 h with Al, Ga, or Ru. There was poor regrowth after 4 or 12 h exposure to Cu, Gd, In, La, or Sc. Roots recovered after being grown for 12 to 48 h in 170 μM Al, 5.1 μM Ga, 2.0 μM Hg, or 1.4 μM Ru, but the extent of recovery was reduced with longer exposure time. Microscopy showed marked differences in symptoms on roots recovering from exposure to the various trace metals. Differences in (i) concentrations that are toxic, (ii) ability of roots to recover, (iii) time for recovery to occur, and (iv) symptoms that develop, suggest that each trace metal has a unique combination of rhizotoxic effects.

Separating multiple, short‐term, deleterious effects of saline solutions on the growth of cowpea seedlings

• Reductions in plant growth as a result of salinity are of global importance in natural and agricultural landscapes. • Short-term (48-h) solution culture experiments studied 404 treatments with seedlings of cowpea (Vigna unguiculata cv Caloona) to examine the multiple deleterious effects of calcium (Ca), magnesium (Mg), sodium (Na) or potassium (K). • Growth was poorly related to the ion activities in the bulk solution, but was closely related to the calculated activities at the outer surface of the plasma membrane, {I(z)}₀°. The addition of Mg, Na or K may induce Ca deficiency in roots by driving {Ca²+}₀° to < 1.6 mM. Shoots were more sensitive than roots to osmolarity. Specific ion toxicities reduced root elongation in the order Ca²+ > Mg²+ > Na+ > K+. The addition of K and, to a lesser extent, Ca alleviated the toxic effects of Na. Thus, Ca is essential but may also be intoxicating or ameliorative. • The data demonstrate that the short-term growth of cowpea seedlings in saline solutions may be limited by Ca deficiency, osmotic effects and specific ion toxicities, and K and Ca alleviate Na toxicity. A multiple regression model related root growth to osmolarity and {I(z)}₀° (R²=0.924), allowing the quantification of their effects.

Isolation and characterization of novel plant growth promoting Micrococcus sp NII-0909 and its interaction with cowpea

A phosphate-solubilizing bacterial strain NII-0909 isolated from the Western ghat forest soil in India was identified as Micrococcus sp on the basis of phenotypic characteristics, carbon source utilization pattern, fatty acid methyl esters analysis, and 16S rRNA gene sequence. The strain exhibited the plant growth-promoting attributes of phosphate solubilization, auxin production, 1-aminocyclopropane-1-carboxylate deaminase activity, and siderophore production. It was able to solubilize (122.4μg of Ca(3)PO(4) ml(-1)), and produce IAA (109μgml(-1)) at 30°C. P-solubilizing activity of the strain NII-0909 was associated with the release of organic acids and a drop in the pH of the NBRIP medium. HPLC analysis detected two organic acids in the course of P-solubilization. A significant increase in the growth of cow pea was recorded for inoculations under controlled conditions. Scanning electron microscopic study revealed the root colonization of strain on cow pea seedlings. These results demonstrate that isolates NII-0909 has the promising PGPR attributes to be develop as a biofertilizer to enhance soil fertility and promote the plant growth.

Rhizotoxic effects of silver in cowpea seedlings

Silver (Ag) is highly toxic to aquatic organisms, including algae, invertebrate animals, and fish, but little information exists on Ag rhizotoxicity in higher plants. In two solution culture experiments with approximately 1,000 microM Ca(NO3)2 and 5 microM H3BO3 (pH 5.4), 20 to 80% of added Ag (< or =2 microM) was lost from solution within approximately 30 min, with a further decrease after 48 h root growth. Using measured Ag concentrations at the start of the experiments, the median effective concentration (EC50) for root elongation rate of cowpea (Vigna unguiculata [L.] Walp. cv. Caloona) was 0.010 microM Ag in the first 4 h of exposure (0.021 microM in the first 8 h). This demonstrates that Ag (as Ag+) is rapidly rhizotoxic to cowpea seedlings at concentrations similar to those that are toxic to freshwater biota. Rupturing of rhizodermal and outer cortical layers was evident after 48 h with 0.13 to 0.57 microM Ag initially in solution, being most severe at 0.13 or 0.25 microM Ag. An additional experiment showed that ruptures were first evident after 20 h exposure to 0.17 microM Ag, with increased severity of rupturing over time. The rhizotoxic effects of Ag are similar to those of some other trace metals (e.g., Cu, Al, La) that bind strongly to hard ligands and weakly to soft ligands. The similarity of rupturing effects, despite the difference in strong binding to soft ligands by Ag and to hard ligands by the other metals, suggests a distinctive metabolic effect of Ag that binds only weakly to hard ligands.

Impact of soil amendment on phytotoxicity of a 5-month old waste engine oil polluted soil

The present study investigated the effects of soil amendment on the remediation of waste engine oil (WEO) polluted soil, as well as the eventual phytotoxic effects of remediated amended soil on some growth parameters of cowpea. There was significant decrease in heavy metal concentration of the polluted soil more than average, nine months after amendment. There was also total remediation of some PAH compounds (benzo(a)anthracene, benzo(a)pyrene, benzo(b)fluoranthene, benezo(g,h,i)perylene, benzo(k)fluoranthene, chrysene, dibenzo(a,h)anthracene, fluoranthene, fluorene and Indeno(1,2,3-c,d)pyrene). Achromobacter sp, Clostridium sp,Sarcina sp and Micrococcus sp were prevalent bacteria species found in the polluted soils, while prevalent fungi species included Aspergillus niger, Penicillium sp,Geotrichum sp and Trichoderma sp. The actinomycete Nocardia sp was prevalent as well. Ecological risk factor initially posed by the presence of heavy metals in the unamended soil was significantly reduced to safe levels. Phyto assessment of the polluted soil was carried out just before soil was amended with saw dust and results showed that virtually all the cowpea seedlings died within 2 weeks; only those seedlings in unpolluted soils survived. Nine months after soil was amended, all cowpea plants survived up to fruiting. The present study also showed that cowpea was able to bioaccumulate heavy metals into harvestable parts, though bioaccumulation quotients calculated showed that these accumulations were not significant. Key words: Penicillium sp, Geotrichum sp, phytotoxic, fluoranthene, fluorine

Effects of culture ages on the production and activities of polygalacturonase and cellulase (CX) enzymes produced by &lt;i&gt;Pythium aphanidermatum&lt;/i&gt; (Edson Fitzpat.) Isolated from soft stem rot disease of cowpea.

Effect of culture ages was investigated on the production and activities of polygalacturonase (PG) and Cx cellulase enzymes. Pythium aphanidermatum was isolated from cowpea seedlings infected by soft stem rot disease and prepared into pure culture through successive culturing. Two discs (2 mm each) of two-day-old culture of P. aphanidermatum were put into 21 Erlenmeyer flasks containing 50 ml of Reese and Levinson’s solution, consisting of Sodium Polypectate (NaPP) as carbon source, and incubated for 7 days at 38oC. At one-day interval, content of 3 flasks was independently centrifuged at 10,000g for 30 min. The PG enzyme activity was determined viscometrically and expressed as the Relative Viscometric Unit (RVU). Data collected were analysed using analysis of variance (Anova) and the means separated by the Duncan Multiple Range Test. Activity of Cx cellulase enzyme was also evaluated by the same method used for PG enzyme but using, carboxylmethyl cellulose (CMC) as the carbon source. The results showed that there was significant difference in the production and activities of PG and Cx enzymes in the various days of the incubation. The PG and Cx enzymes were produced progressively from the 1st day of incubation and reached their peak on the 5th day for PG (RVU 105) and 4th day for Cx (RVU 49), after which, production and activities of the enzymes started declining. Results suggested that soft stem rot disease in cowpea is a monocyclic disease, whereby any attacked plant that is able to withstand the disease is capable of surviving after the peak of the infection. Key words: Pythium aphanidermatum, polygalacturonase, Cx cellulose,enzymes, viscometric, rot, disease.

Influence of Seedling Age at Inoculation and Cultivar on the Pathogenicity of a Virus Causing Yellow Mosaic Disease of Commelina Benghalensis L. on Cowpea

A screenhouse experiment was conducted to evaluate the influence of seedling age at inoculation and cultivar onpathogenicity of the virus causing yellow mosaic disease of Commelina benghalensis L, a broad leaf weed, on cowpea.Three cowpea varieties namely Vita 5, IT84S2246D and Ife Brown were grown in pots and inoculated with sapextracted from leaves of C. benghalensis infected with yellow mosaic disease at 7, 14, and 21 days after germination(DAG). It was found that inoculation of cowpea seedlings at 7 DAG subsequently led to the most severe symptoms,which were manifested by mosaic and yellowing of leaves and eventual poor growth and yield attributes. On the otherhand, plant growth and yield attributes that were comparable to those of the healthy control plants were recorded forplants inoculated at 21 DAG. Specifically, in regards to the interaction effects, cv. Vita 5 that were sap-inoculated at 7DAG had the lowest yield attributes, while cv. IT84S2246D inoculated at 21 DAG had the highest yield attributes. Theresults put together showed that although the yellow mosaic virus of C. benghalensis was sap-transmissible andpathogenic to cowpea causing characteristic yellow mosaic disease symptoms and reduction in yield attributes, severityof the disease is less if infection occurs at older stage of cowpea growth.

Salt-induced changes in antioxidative enzyme activities in root tissues do not account for the differential salt tolerance of two cowpea cultivars

The salt stress effect in root growth and antioxidative response were investigated in two cowpea cultivars which differ in salt tolerance in terms of plant growth and leaf oxidative response. Four-day-old seedlings (establishment stage) were exposed to 100 mM NaCl for two days. The roots of the two cultivars presented distinct response in terms of salt-induced changes in elongation and dry weight. Root dry weight was only decreased in Pérola (sensitive) cultivar while root elongation was mainly hampered in Pitiúba (tolerant). Root relative water content remained unchanged under salinity, but root Na+ content achieved toxic levels as revealed by the K+/Na+ ratio in both cultivars. Then, root growth inhibition might be due to ionic toxicity rather than by salt-induced water deficit. Although electrolyte leakage markedly increased mainly in the Pérola genotype, lipid peroxidation decreased similarly in both salt-stressed cultivars. APX and SOD activities were reduced by salinity in both cultivars reaching similar values despite the decrease in Pitiúba had been higher compared to respective controls. CAT decreased significantly in Pitiúba but did not change in Pérola, while POX increased in both cultivars. The salt-induced decrease in the CAT activity of Pitiúba root is, at principle, incompatible to allow a more effective oxidative protection. Our results support the idea that the activities of SOD, APX, CAT and POX and lipid peroxidation in cowpea seedling roots were not associated with differential salt tolerance as previously characterized in terms of growth rate and oxidative response in plant leaves.

Differential expression of defence-related proteins in Vigna unguiculata (L. Walp.) seedlings after infection with Fusarium oxysporum

This work aimed to study the induction of defence proteins in cowpea seedlings during the first days after infection with the fungi Fusarium oxysporum f. sp. cubenses and F. oxysporum f. sp. phaseoli. Cowpea seeds, after disinfection, were transferred to Petri dishes containing 0.5% agar and, after germination, were infected with a drop of a suspension containing 0.5 × 10 4 spores ml −1. Seedlings were collected at 24, 48, 72 and 96 h after infection and were dissected into leaves, hypocotyls, roots, cotyledons and teguments, which were measured and weighed for morphometric analysis. The agar medium was also analyzed. Enzymatic assays of proteic extracts yielded antimicrobial peptides detected by Western blotting. The cowpea seedlings showed a complex pattern of induction and repression of defence proteins in response to infection by both pathogens. Furthermore, morphometric analysis showed differences between infected and control seedlings. Infected samples did not at any time exhibit chitinase activity, but did exhibit different β-1,3-glucanase and peroxidase activities. Western blotting for lipid transfer protein (LTP) demonstrated its presence in all parts of the infected seedlings. Exuded proteins, also obtained from cowpea seeds in the germination medium, were separated by SDS-PAGE and tricine gel electrophoresis. The analysis showed that some proteins were exuded from moistened cowpea seeds, particularly after F. oxysporum infection.

Occurrence of latent virus infection in visually-rated cowpea (Vigna unguiculata L. Walp) seedlings

The presence of latent infections was studied in five cowpeas varieties. Seeds of the varieties were planted and the seedlings inoculated with antigens from Cucumber mosaic virus (CMV) genus Cucumovirus, Bean common mosaic virus (BCMV) genus Potyvirus (Blackeye cowpea mosaic virus strain), Southern bean mosaic virus (SBMV) genus Sobemovirus and Cowpea mottle virus (CPMoV) genus Carmovirus seven days after planting. Seedlings expressing symptoms were rouged at two weeks after inoculation, while asymptomatic ones were subjected to serological indexing to detect the presence/absence of latent infection. Protein A-sandwich enzyme-linked immunosorbent assay (PAS ELISA) was employed for the serological detection of CMV, SBMV and CPMoV, while antigen-coated plate (ACP) ELISA was used to detect BCMV in the asymptomatic plants. Cowpea seedlings without virus symptoms but with positive serological reactions were considered as being latently infected. All of the inoculated TVu 1272 and SuVita-2 plants showed symptoms consistent with CMV and CPMoV infections, respectively. The rate of CMV latent infection was high in TVu 1179 (14.5%), low in SuVita-2 (1.3%) but not recorded in TVu 1272.

Influence of Cowpea Planting Date on Tobacco Thrips (Thysanoptera: Thripidae) Abundance, Within Plant Distribution, and Foliar Injury1

The tobacco thrips, Frankliniella fusca (Hinds) (Thysanoptera: Thripidae), is generally the most common insect pest of seedling cowpea, Vigna unguiculata (L.), in the south-central USA. Tobacco thrips damage cowpea by puncturing and feeding on the cells of leaves, thereby causing the leaves to curl and yellow. In 2007 field studies, a mean of 0.82 F. fusca were detected per plant and few significant differences in thrips abundance were detected among the planting dates. Emergent (folded) leaves held significantly more immature and adult F. fusca than more-developed and open leaves. In 2008 samples, mean total thrips numbers were 2.28 per plant. Cowpea planted in May and early June held significantly more adult, immature, and total F. fusca per plant than did cowpea planted in late June, July, or August. Again in 2008, new emergent (folded) leaves held significantly more adult and immature F. fusca than either unifoliate or unfolded trifoliate leaves. Unifoliate leaves exhibited little feeding injury from F. fusca; injury to 1st and 2nd trifoliate leaves was greater. Although foliar injury ratings varied greatly, cowpea seedlings from the latest plantings generally sustained less injury than was observed on earlier plantings.

A simple technique for separation of Cowpea chlorotic mottle virus from Cucumber mosaic virus in natural mixed infections

A simple technique was developed to separate Cowpea chlorotic mottle virus (CCMV) from Cucumber mosaic virus (CMV) in natural mixed infections. Sap from cowpea leaves infected naturally with a mixture of CCMV and CMV was inoculated mechanically on the first tri-foliolate leaf of cowpea seedlings. Both inoculated and non-inoculated upper leaves were sampled 3 or 8 days post-inoculation and tested by reverse transcription polymerase chain reaction (RT-PCR) using primers specific to CCMV and CMV. RT-PCR analysis showed the presence of only CCMV in the inoculated leaf and both viruses in the non-inoculated systemically infected upper leaves. Total RNA from the inoculated leaves positive to CCMV only was further confirmed upon re-inoculation to cowpea seedlings. Typical CCMV symptoms were produced within 1 week and RT-PCR analysis showed only the presence of CCMV in both inoculated and non-inoculated systemically infected upper leaves. Systemically infected upper leaves of the same plants were used for CCMV purification. RT-PCR analysis of the purified virion and RNA extracted from the virion further confirmed the absence of CMV contamination. To our knowledge, this is the first report of a method separating CCMV directly from mixed infections with CMV in cowpea.