Foraging behaviour of the parasitoid Lysiphlebus testaceipes (Hymenoptera: Braconidae) in response to plant volatiles,with reference to biocontrol of aphids in peri-urban vegetable production systems

Foraging behaviour of Lysiphlebus testaceipes was studied in a Y-tube olfactometer. Naïve females responded to the Aphis gossypii/eggplant complex on which they had been reared, but did not show a preference for this aphid/plant complex over an uninfested eggplant, an eggplant that had been damaged by the aphid or an A. gossypii/okra complex. Females that had been allowed to forage on the A. gossypii/eggplant complex before being tested in the olfactometer showed a strong preference for an uninfested eggplant over an uninfested okra plant and for the A. gossypii/eggplant complex over an A. gossypii/okra complex, indicating that they had learned to associate eggplant-derived volatiles with host availability. When females that had been reared on the A. gossypii/eggplant complex were tested after foraging experience on the A. gossypii/okra complex, they did not show a preference for either complex, suggesting that they still retained a memory of the cues associated with the complex on which they had been reared. The efficiency of L. testaceipes as a biological control agent in peri-urban vegetable production, such as the Cuban organoponics system, potentially could be improved by producing and releasing females behaviourally primed to prefer specific host/plant complexes.     

Salt Tolerance in Selected Vegetable Crops

Ensuring adequate food production is a major issue in the context of an increasing human population, limit to the areas of new land that can be cultivated, and loss of existing cultivated lands to abiotic stresses. Of these stresses, salinity consistently has the greatest impact in reducing the area of cultivated land, often due to inappropriate irrigation techniques. To increase food supply, there is a need to produce salt-tolerant crops, which can grow successfully on salt-affected lands. Among crops, vegetables possess a central position in the human diet because of their nutritional value providing vitamins, carbohydrates, proteins, and mineral nutrients. There are many vegetable crops of local importance around the world but others that are very widely cultivated. All of these vegetable crops are affected by salinity more or less severely. Salinity affects every aspect of vegetable crop development including their morphology, physiological function and yield. Although efforts have been made to understand the mechanisms of salt tolerance in vegetable crops, less attention has been paid to these than to the staple crops. Where attempts have been made to improve salt tolerance of vegetables, the strategies have ranged from exogenous application of fertilizers, compatible solutes or plant growth regulators, to use of advanced molecular techniques for genetic modifications. This review focuses on the responses of pea, okra, tomato, eggplant, pepper, carrot, broccoli, cauliflower, and potato to salt stress and the strategies being used to enhance their salt tolerance.     

Genetic and phenotypic variation of Turkish Okra (<Emphasis Type="Italic">Abelmoschus esculentus</Emphasis> L. Moench) accessions and their possible relationship with American,Indian and African germplasms

Okra is an important vegetable crop that provides a significant portion of vitamins and minerals for populations in several countries. Okra has been cultivated in Turkey for centuries, and was likely introduced by the Arabs from Africa in ancient times. In this study, we aimed to clarify the genetic variation within 35 Turkish okra germplasm, by comparing it against 25 different genotypes from India, Africa, and the United States, using 30 morphological characters and 19 sequence-related amplified polymorphism (SRAP) primer combinations. Fruit, leaf, and stem color were the primary characteristics to distinguish the okra accessions. Those features, among 30 individual phenotypic traits, explained 42 % of phenotypic variation in the first three axes of the principal component analysis (PCA) with leaf shape, flower size, cotyledon length, fruit-surface angularity, cotyledon width, and petal color. Phenotypic observation results showed that while 1051 Togo (10.76), Red Wonder (7.99), TR-05-1 (7.2), 1159 Togo (7.17), and Red Balady (7.15) were found to be more divergent accessions, Cajun Queen (5.06), Perkins Spineless (5.09), Jade (5.18), TR-01-1 (5.2), and DLGG (5.32) were the closest okra accessions. According to phenotypic data, Turkish okra accessions were located adjacent to the Indian, American, and African okra accessions in clusters three and four. However, marker data showed that African okra possessed a more distinct form compared to the other okra germplasms. Nineteen SRAP primer combinations produced 92 bands and 29 (31.5 %) of them were found to be polymorphic among okra accessions. 1051 Togo was found to be the most divergent accession in phenotypic observation.     

Recombination Among Begomoviruses on Malvaceous Plants Leads to the Evolution of Okra Enation Leaf Curl Virus in Pakistan

Whitefly transmitted begomoviruses (family Geminiviridae) are the major reason for significant yield losses of dicotyledonous crops in tropics and subtropics. Okra (Abelmoschus esculentus) is one of the important vegetable crops, and leaf curl disease caused by geminiviruses is the most important limiting factor for its production in Pakistan. Here, we report a new species of okra‐infecting begomovirus in south‐eastern region of Pakistan and the name Okra enation leaf curl virus (OELCuV) complex is proposed. This okra enation leaf curl disease complex (OELCuD) in Pakistan is found to be associated with Ageratum conyzoides symptomless alphasatellite (AConSLA). All efforts to clone the betasatellite were unsuccessful. Comprehensive sequence analyses suggest that intermalvaceous recombination between okra and cotton‐infecting begomoviruses resulted in the evolution of the new species. Surprisingly, Bhendi yellow vein mosaic virus (BYVMV) which has not been reported previously from Pakistan is the major parent while Cotton leaf curl Multan virus (CLCuMV) acts as a distant parent of the virus. Comparative recombination analysis also reveals that okra‐infecting begomoviruses from south and north‐western India is causing OELCuD in the Pakistan by recombining with CLCuMV at the Rep (1964–1513 nts). Recombination is common among geminiviruses and recombining of BYVMV and CLCuMV resulted in a new species: OELCuV. To the best of our knowledge, this evolution of a new species of okra‐infecting begomovirus is the first report of intermalvaceous recombination where Rep acts as the target region.     

Increasing the okra salt threshold value with biochar amendments

Soil salinity is a severe worldwide environmental problem that adversely affects soil properties and the crop growth such as okra. We hypothesized that biochar soil amendments could increase the okra salt threshold, alleviate salt stress and improve soil productivity. In this study, a pot experiment was conducted to investigate whether biochar could ameliorate the effects of salinity on okra plants. Three biochar amendment (BA) soil applications (0%, 5% and 10% by mass of soil) were considered for seven irrigation water salinity levels (0.75, 1.0, 2.0, 4.0, 5.0, 6.0 and 7.0?dS?m^?1) in a randomized block design with three replications. The Maas and Hoffman salt tolerance model was used to evaluate the effects of BA on okra plant growth parameters (e.g. yield, biomass) and water use efficiency for each salinity treatment. The results showed that increasing the soil salinity levels caused significant decreases in plant yields and yield components. However, biochar application rates of 5% and 10% increased the okra threshold by 19.7% and 81.2%, respectively, compared to the control (0%). The 10% biochar application rate also resulted in the greatest okra plant growth and increased yield, indicating that the effects of salt stress were ameliorated; moreover, the soil bulk density was decreased, and the water content was increased. Hence, biochar soil amendments could be considered as an important agronomic practice that could potentially overcome the adverse effects of salt stress.     

Characterisation of cell wall polysaccharides from okra (Abelmoschus esculentus (L.) Moench)

Okra pods are commonly used in Asia as a vegetable, food ingredient, as well as a traditional medicine for many different purposes; for example, as diuretic agent, for treatment of dental diseases and to reduce/prevent gastric irritations. The healthy properties are suggested to originate from the high polysaccharide content of okra pods, resulting in a highly viscous solution with a slimy appearance when okra is extracted with water. In this study, we present a structural characterisation of all major cell wall polysaccharides originating from okra pods. The sequential extraction of okra cell wall material yielded fractions of soluble solids extractable using hot buffer (HBSS), chelating agent (CHSS), dilute alkaline (DASS) and concentrated alkaline (CASS). The HBSS fraction was shown to be rich in galactose, rhamnose and galacturonic acid in the ratio 1.3:1:1.3. The degree of acetylation is relatively high (DA = 58) while the degree of methyl esterification is relatively low (DM = 24). The CHSS fraction contained much higher levels of methyl esterified galacturonic acid residues (63% galacturonic acid; DM = 48) in addition to minor amounts of rhamnose and galactose. The ratio of galactose to rhamnose to galacturonic acid was 1.3:1.0:1.3 and 4.5:1.0:1.2 for HBSS and CHSS, respectively. These results indicated that the HBSS and CHSS fractions contain rhamnogalacturonan type I next to homogalacturonan, while the latter is more prevailing in CHSS. Also the DASS fraction is characterised by high amounts of rhamnose, galactose, galacturonic acid and some arabinose, indicating that rhamnogalacturonan I elements with longer arabinose- and galactose-rich side chains were part of this fraction. Partial digestion of HBSS and CHSS by pectin methyl esterase and polygalacturonase resulted in a fraction with a lower Mw and lower viscosity in solution. These samples were subjected to NMR analysis, which indicated that, in contrast to known RG I structure, the acetyl groups in HBSS are not located on the galacturonic acid residues, while for CHSS only part of the acetyl groups are located on the RG I galacturonic acid residues. The CASS fraction consisted of XXXG-type xyloglucan and 4-methylglucuronoxylan as shown by their sugar (linkage) composition and enzymatic digestion.     

Effect of the application of selenium on selenium content of soybean and its products

Two experiments were conducted to study the effect of the application of selenium on the selenium content of soybean and its products in two counties with selenium-deficient soil. Selenium-enriched soybean was produced by the application of sodium selenite and Se-enriched fertilizer. The selenium contents of soybeans, soybean protein and okra were determined by hydride-generation atomic fluorescence spectrometry. The results showed that the selenium contents of soybean, soybean protein, and okra were significantly increased by the application of sodium selenite and selenium-enriched fertilizer. Foliar application of selenium provided a higher efficiency for increasing the selenium content of soybean than soil application. Significant differences were found in that soybean cultivars exhibited different accumulation of selenium. There was no remarkable difference in soybean yield, soybean protein, and lipid between selenium and control. The selenium-enriched protein derived from selenium-enriched soybean could be used as a functional ingredient and soybean okra as a selenium-enriched feed for animals for increasing selenium intake.     

Assessment of genetic diversity among okra genotypes using SSR markers

Okra (Abelmoschus esculentus) is an important nutritious vegetable. Despite its high economic and industrial value, very little attention has been paid to assess genetic diversity of okra at molecular level. For effective conservation and proper deployment of germplasm, a study on diversity analysis of okra germplasm was conducted with DNA markers. Microsatellite/Simple sequence repeat (SSR) markers were utilized to evaluate the genetic diversity among 96 accessions of Abelmoschus, of which 92 accessions were of A. esculentus and one accession each of A. tuberculatus, A. moschatus, A. moschatus subspecies tuberosus and A. manihot. A set of 40 SSR primers were tested, of which 30 primers gave reproducible amplification which were used further for diversity analysis. With a mean of 7.1 bands per SSR, DNA amplification with 30 SSRs generated a total 213 bands, of which 60.66 % were recorded polymorphic. Polymorphic information content ranged between 0.11 and 0.80 with an average of 0.52, indicating that the majority of primers were informative. The Jaccard’s coefficient ranged from 0.107 to 0.969. The UPGMA analysis grouped Abelmoschus genotypes into three main clusters at a cut-off of 0.20. Results of present study revealed that sufficient variation exists among the studied accessions and GAO-5 which was found highly diverse can be exploited for okra improvement. The outcome of present research would assist to make use of Ablemoschus germplasm for okra breeding.     

Rotations with Coastal Bermudagrass and Fallow for Management of Meloidogyne incognita and Soilborne Fungi on Vegetable Crops

The efficacy of fallow and coastal bermudagrass (Cynodon dactylon) as a rotation crop for control of root-knot nematode (Meloidogyne incognita race 1) and soilborne fungi in okra (Hibiscus esculentus cv. Emerald), squash (Cucurbita pepo cv. Dixie Hybrid), and sweet corn (Zea mays cv. Merit) was evaluated in a 3-year field trial. Numbers of M. incognita in the soil and root-gall indices were greater on okra and squash than sweet corn and declined over the years on vegetable crops following fallow and coastal bermudagrass sod. Fusarium oxysporum and Pythium spp. were isolated most frequently from soil and dying okra plants. Numbers of colony-forming units of soilborne fungi generally declined as the number of years in sod increased, but were not affected by coastal bermudagrass sod. Yields of okra following 2-year and 3-year sod and squash following 2-year sod were greater than those following fallow. Yield of sweet corn was not different following fallow and coastal bermudagrass sod.     

Activation of Dry Starter Cultures in Milk

The revitalization of mixed strain dried starter cultures at 22 and 32 C in sterile skim milk was materially accelerated when the substrate was fortified with 0.2% pancreas-extract solids. At 22 C, all cultures grew up satisfactorily in 18 hr, and in unfortified milk none of the cultures reached comparable growth in this period. When the cultures were grown at 32 C, the dried cultures developed adequately in 7.5 hr, but required 9 to 10 hr in plain milk. Culture growth was enhanced in milk containing pancreas extract to the extent that the amount of dried culture required to produce adequate acidity in normal incubation times could be markedly reduced. At 32 C, certain cultures could be reduced to 12.5% of recommended amounts, and at 22 C certain ones could be reduced by 50%. Revitalization of the dried cultures in milk containing pancreas extract did not affect the growth of subcultures in plain milk. Also, when dried cultures initiated growth in fortified milk at 32 C their subsequent growth at 22 C in milk alone was not affected. The faster rate of culture growth in milk containing pancreas extract should permit, with more certainty, the establishment of active mother and bulk starters. Furthermore, economy of dried cultures, as well as of time, could be realized by the use of fortified milk.     

Performance of calves fed on milk replacers containing fish protein hydrolysate

Milk substitutes for calves are based upon dried skim milk and added fats of vegetable or animal origin. Many attempts have been made to replace part of the skim milk in these feeds by cheaper sources of protein.A milk product coagulates in the calf's abomasum and has a high digestibility. Milk replacers based on fish protein hydrolysate (FPH) do not coagulate in the abomasum, but have a high apparent digestibility coefficient (0.92) and the amino acid balance is similar to that of skim milk.Calves were fed on milk replacers prepared from FPH made from various materials. In general, FPH prepared from white fish (cod, blue whiting, white fish offal) was satisfactory although calf performance until weaning was poorer than for calves fed on milk replacers with dried skim milk (SMP). Some ways are suggested by which the quality of the product (FPH) could be maintained. FPH preparations from fatty fish, like sprats and mackerel, were also used. An antioxidant was added in the preparation of sprats and mackerel because of the unsaturated nature of fish fats. Milk replacers containing sprats prepared without an antioxidant and mackerel (31% body fat) with antioxidant were unsatisfactory and further development work is required on FPH materials from fatty fish.FPH from white fish can be dried without any appreciable loss in calf performance. The daily gain to weaning was 0.25 and 0.29 kg per day for calves fed on the dried and undried material, respectively. On the basis of present knowledge it is suggested that FPH can replace one third of skim milk in milk replacers for early weaned calves; the proportion recommended may rapidly increase with further technical development of the product.     

The emergence of okra enation leaf curl virus—an important begomovirus,infecting okra in several states across India

Okra enation leaf curl virus (OELCuV), a begomovirus, is an emerging serious constraint for okra production in India. OELCuV was earlier reported in Haryana, Gujarat and Karnataka. In the current study, a survey was conducted on okra crop in the other predominant okra growing regions of India and identified for the first time, a widespread symptomology of OELCuV. The disease incidence was recorded between 5 and 74% in all the surveyed regions. The diseased samples collected from all the locations were amplified with coat protein specific new primer in PCR. The amplicons were sequenced and deposited to NCBI Gene Bank. The finding could be highly useful in okra breeding programs against OELCuV.     

Modification of commerical and custom-built slab gel electrophoresis units for two-dimensional polyacrylamide gel electrophoresis

Many commercial and custom-built slab gel electrophoresis units can be modified to function as two-dimensional polyacrylamide gel electrophoresis units with the insertion of Plexiglas adapters. These adapters can be made for about $50 a pair and can be used for either temporary or permanent modification of the slab gel units. The physical dimensions of the adapters can be varied to permit great flexibility in the diameter of cylinder gels and the thickness of slab gels that can be run together. For example, proteins from 6-mm cylinder gels can be easily separated on 1-mm slab gels, which can then be dried for autoradiography.     

Efficient genetic transformation of okra (Abelmoschus esculentus (L.) Moench) and generation of insect-resistant transgenic plants expressing the cry1Ac gene

Key message

Agrobacterium -mediated transformation system for okra using embryos was devised and the transgenic Bt plants showed resistance to the target pest, okra shoot, and fruit borer ( Earias vittella ).

Abstract

Okra is an important vegetable crop and progress in genetic improvement via genetic transformation has been impeded by its recalcitrant nature. In this paper, we describe a procedure using embryo explants for Agrobacterium-mediated transformation and tissue culture-based plant regeneration for efficient genetic transformation of okra. Twenty-one transgenic okra lines expressing the Bacillus thuringiensis gene cry1Ac were generated from five transformation experiments. Molecular analysis (PCR and Southern) confirmed the presence of the transgene and double-antibody sandwich ELISA analysis revealed Cry1Ac protein expression in the transgenic plants. All 21 transgenic plants were phenotypically normal and fertile. T₁ generation plants from these lines were used in segregation analysis of the transgene. Ten transgenic lines were selected randomly for Southern hybridization and the results confirmed the presence of transgene integration into the genome. Normal Mendelian inheritance (3:1) of cry1Ac gene was observed in 12 lines out of the 21 T₀ lines. We selected 11 transgenic lines segregating in a 3:1 ratio for the presence of one transgene for insect bioassays using larvae of fruit and shoot borer (Earias vittella). Fruit from seven transgenic lines caused 100 % larval mortality. We demonstrate an efficient transformation system for okra which will accelerate the development of transgenic okra with novel agronomically useful traits.     

Mite pests and their predators on seven vegetable crops (Arachnida: Acari)

During this study the frequency of occurrence and dominance of phytophagous and predatory mites harboring seven vegetable crops in Egypt, namely common bean, cowpea, eggplant, okra, squash, sweet pepper and sweet potato during 2017–2018 were investigated to identify predatory mites that might be useful for the biological control of the phytophagous mites. Three phytophagous and nine predatory mite species were surveyed. The two spotted spider mite Tetranychus urticae Koch of the family Tetranychidae was the dominant pest on these vegetables, while phytoseiids Phytoseiulus persimilis (Athias- Henriot), Typhlodromips swirskii (Athias- Henriot) and Euseius scutalis Chant were the dominant predators. The population of the native or indigenous phytoseiid mite fauna in Egypt such as Phytoseiulus persimilis could be considered as a good biocontrol agent and a part of the Integrated Pest Management (IPM) program in the future. Mite fauna of Egypt especially local populations of Phytoseiulus persimilis can be considered for implementation in future Integrated Pest Management (IPM).     

The occurrence and importance of okra mosaic virus in Nigerian weeds

The Nigerian National Horticultural Research Institute experimental and commercial farm has a long history of okra mosaic virus (OMV) disease. In an attempt to determine possible sources of inoculum, weeds growing within or around the vicinity of the farm were investigated. Several weeds showed virus or virus-like disease symptoms and mechanical inoculation of crude sap from three malvaceous weeds (Abutilon hirtum, Sida acuta, and Malvastrum coromandelianum) and one solanaceous weed (Physalis angulata) induced symptoms of OMV on okra test seedlings; serological tests confirmed the presence of OMV. Beetle vectors caught both from weeds and from okra were infective when confined on healthy okra seedlings for 48 h. Increase in the abundance of beetle vectors was accompanied by an increase in the incidence of OMV disease. The implications of these findings in the epidemiology and control of OMV are discussed.     

Vegetative Compatibility and Virulence Diversity of <i>Verticillium dahliae</i> from Okra (<i>Abelmoschus esculentus</i>) Plantations in Turkey and Evaluation of Okra Landraces for Resistance to <i>V. dahliae</i>

Forty-four V. dahliae isolates were collected from symptomatic vascular tissues of okra plants each from a different field in eight provinces located in the eastern Mediterranean and western Anatolia regions of Turkey during 2006- 2009. Nitrate-nonutilizing (nit) mutants of V. dahliae from okra were used to determine heterokaryosis and genetic relatedness among isolates. All isolates from okra plants were grouped into two vegetative compatibility groups (VCGs) (1 and 2) and three subgroups as 1A (13.6%, 6/44), 2A (20.5%, 9/44) and 2B (65.9%, 29/44) according to international criteria. Pathogenicity tests were performed on a susceptible local okra (A. esculentus) landrace in greenhouse conditions. All isolates from VCG1A and VCG2B induced defoliation (D) and partial defoliation (PD) symptoms, respectively. Other isolates from VCG2A gave rise to typical leaf chlorosis symptoms without defoliation. The obtained data showed that the virulence level of V. dahliae isolates from okra was related to their VCG belongings. Eighteen okra landraces from diverse geographical origins were screened for resistance to VCG2B and VCG1A of V. dahliae. The results indicated that all landraces were more susceptible to highly virulent VCG1A-D pathotype displaying D or PD symptoms depending on their susceptibility levels with a mean disease severity index of 3.52 than to less virulent VCG2B-PD pathotype of V. dahliae displaying PD and ND symptoms with a mean disease severity index of 2.52. Significant differences were observed among the landraces; however, none of them exhibited a level of resistance. Okra landraces; Çorum, Hatay Has and Şanlıurfa displayed the lowest level of susceptibility or little tolerance to both D and PD pathotypes. VCG2B of PD was prevailing in the surveyed areas and VCG1A of D was the most virulent of the VCGs identified. Introduction of resistant genotypes to Turkish okra germplasm from different sources and breeding new resistant okra cultivars are critical for the sustainability of okra production.     

Two methods that facilitate autoradiography of small 32P-labeled DNA fragments following electrophoresis in agarose gels

Two methods which permit detection by autoradiography of small 32P-labeled DNA fragments resolved by agarose gel electrophoresis are described. Agarose gel electrophoresis poses problems for autoradiography as (i) the gels are normally too thick to allow autoradiography without being dried first, and (ii) fragments of DNA of 1000 bp or less in length are readily lost during drying. In this study DNA fragments as small as 121 bp have been retained in agarose gels upon drying. This has been achieved by either (i) first fixing the DNA with the cationic detergent cetyltrimethylammonium bromide, or (ii) drying the agarose gels onto Zeta-Probe charge-modified membranes.