A study of the mode of transmission of maize streak virus by Cicadulina mbila using an enzyme-linked immunosorbent assay

Two batches of Cicadulina mbila were given two distinct acquisition access periods (AAP) (3 h and 50 h) on maize plants infected with maize streak virus (MSV). Infectivity assays on susceptible maize were carried out 1, 3, 10, 17, 26 and 35 days after the AAP. Transmission efficiency was significantly higher for C. mbila subjected to the 50-h AAP. At the same time as the infectivity assays, the amount of MSV in each leafhopper was determined by an indirect double antibody sandwich (IDAS) ELISA. There were more ELISA-positive insects after the 50-h AAP than after the 3-h AAP. In the group given a 3-h AAP, only 7% of the insects tested between day 1 and 35 were found to be positive by ELISA. In contrast, after the 50-h AAP, the majority of C. mbila were positive, yet a decrease in ELISA-positive insects was noticed from day 17 onwards. Using a calibration curve obtained with purified virus, as little as 0.15 ng of MSV per insect could be measured by the IDAS-ELISA. A mean value of 0.36 ng of MSV per C. mbila was found 3 days after the 50–h acquisition, whereas 14 days later there was only 0.20 ng of virus per insect. For comparison, when leafhoppers were kept on infected maize, they displayed substantial accumulation of MSV up to an average of 3.83 ng of MSV per insect after 35 days of continuous acquisition. The amount of virus per insect detected in females was usually greater than the amount detected in males. Our results suggest that MSV does not multiply in C. mbila and contribute to the understanding of the persistence of transmission efficiency in the absence of virus multiplication.     

Electrical penetration graphs from Cicadulina mbila on maize, the fine structure of its stylet pathways and consequences for virus transmission efficiency

Five distinct electrical penetration graph waveforms characterising the feeding behaviour of the leafhopper Cicadulina mbila Naudé (Homoptera: Cicadellidae) on maize (Zea mays L.) were obtained using a DC based system. The waveforms were distinguished by spectral features and by statistical analysis of their median voltages, durations and time to first waveform recording. By changing the polarity of the system voltage and the level of the input resistor it was shown that the waveforms are mainly determined by the electromotive force (emf) component. Based on the correlation between waveforms and the fine structure of the stylet pathways observed by transmission electron microscopy, insect's activities have been associated with five waveforms: stylet pathway formation (waveform 1), active ingestion (waveform 2), putative stylet work (waveform 3), salivation (waveform 4) and passive ingestion (waveform 5). Like waveform E1 and E2 of aphids, waveforms 4 and 5 of C. mbila correspond to feeding activities in sieve tubes. However, unlike aphids which probe briefly in non-vascular cells, waveform 2 corresponds to active ingestion in cells, where the cell content is partially ingested and hence the organelles' integrity severely affected. These observations suggest that this specific feeding feature, typical of leafhoppers, determines their ability to acquire geminivirus virions located in the plant cell nucleus.     

Transmission of tomato spotted wilt virus by Frankliniella occidentalism median acquisition and inoculation access period

To quantify the transmission of tomato spotted wilt virus (TSWV) by Frankliniella occidentalis, the median acquisition access period (AAP₅₀) and median inoculation access period (IAP₅₀) were determined. These parameters were established using transmission rates obtained after AAPs and in IAPs which both ranged from 5 to 2560 min. An AAP₅₀ of 106 min was found when larvae acquired virus from TSWV-infected Impatiens plants. IAP₅₀s of 58 or 137 min, respectively, were calculated when petunia or Datura stramonium leaf disks were used to test the inoculation efficiency of viruliferous thrips. The virus could successfully be acquired or inoculated in periods of 5 min. Transmission reached an optimum after an AAP of 21.3 h (AAP_opt) and in an IAP of 42.7 h (IAP_opt). These results show that TSWV can be acquired and transmitted efficiently by F. occidentalis in short feeding periods.     

Vector and Host-Plant Relationships of the Leafhopper-Borne Maize Yellow Stripe Virus

Maize yellow stripe virus (MYSV), associated with tenuivirus-like filaments, is transmitted in a persistent manner by the leafhopper Cicadulina chinai. In this vector, MYSV acquisition and inoculation threshold times were 30 min each, latent period ranged from 4.5 to 8 days depending on temperature (14-25 °C), and retention periods were as long as 27 days. Up to 26 % of C, chinai collected from maize fields in Giza, Egypt, during September and October 1985 were naturally infective with MYSV. Two symptom-types (fine and coarse stripe) appeared on experimentally infected plants, usually on separate leaves of the same plant. However, these two symptom-types could not be isolated on separate plants through transmission by single C. chinai leafhoppers. MYSV was transmitted by nymphs and adults of C. chinai from maize to maize, wheat and barley, and from wheat to maize plants. Up to 6 % of the wheat plants examined in Naga Hamadi (Southern Egypt) in February 1986, were naturally infected. It is suggested that wheat, barley and possibly graminaceous weeds may serve as winter hosts or reservoirs for MYSV and its leafhopper vector in Egypt.     

Detection of maize streak virus antigens over time in different parts of maize plants of a sensitive and a so-called tolerant cultivar by ELISA

Maize streak virus (MSV) capsid antigens were detected over time in different parts of maize plants of a sensitive (INRA508) and a so-called tolerant (“tolerant”) cultivar (IRAT297) using a direct or an indirect double antibody sandwich ELISA. Based on three types of experiments, it was shown that the antigens were distributed in the plant according to the age of the tissues. When the virus was inoculated on a particular leaf of 18-day old plants with infective Cicadulina mbila, only the young leaves above the inoculated one were positive by ELISA but not the older ones below. The antigens could not be detected in the inoculated leaf. At day 3 after inoculation, the antigens were detected in the sheath and/or in the whorl of the third leaf above the inoculated one but not in the oldest part of the leaf, the unfolded lamina. Plants of the sensitive cultivar were inoculated at 9 days with C. mbila deposited in the whorl. At 23 h after inoculation, the antigens were detected in the sheath but not in the whorl which was found to be positive only at 32 h. On the basis of these results, a hypothesis of the mode of virus infection is proposed. Our results contribute to a better understanding of the relationship between the age of the plant at inoculation and yield loss as well as secondary infection. By transmission tests with C. mbila, it was shown that virus could only be acquired from leaves exhibiting symptoms. Virus concentrations were measured in plant samples by ELISA using a range of dilutions of purified virus. The virus concentrations were higher in the sensitive than in the “tolerant” cultivar, but no difference in antigen distribution was observed between the two cultivars. The “tolerant” cultivar appeared to be resistant to virus multiplication.     

Priming of Production in Maize of Volatile Organic Defence Compounds by the Natural Plant Activator cis-Jasmone

cis-Jasmone (CJ) is a natural plant product that activates defence against herbivores in model and crop plants. In this study, we investigated whether CJ could prime defence in maize, Zea mays, against the leafhopper, Cicadulina storeyi, responsible for the transmission of maize streak virus (MSV). Priming occurs when a pre-treatment, in this case CJ, increases the potency and speed of a defence response upon subsequent attack on the plant. Here, we tested insect responses to plant volatile organic compounds (VOCs) using a Y-tube olfactometer bioassay. Our initial experiments showed that, in this system, there was no significant response of the herbivore to CJ itself and no difference in response to VOCs collected from unexposed plants compared to CJ exposed plants, both without insects. VOCs were then collected from C. storeyi-infested maize seedlings with and without CJ pre-treatment. The bioassay revealed a significant preference by this pest for VOCs from infested seedlings without the CJ pre-treatment. A timed series of VOC collections and bioassays showed that the effect was strongest in the first 22 h of insect infestation, i.e. before the insects had themselves induced a change in VOC emission. Chemical analysis showed that treatment of maize seedlings with CJ, followed by exposure to C. storeyi, led to a significant increase in emission of the defensive sesquiterpenes (E)-(1R,9S)-caryophyllene, (E)-α-bergamotene, (E)-β-farnesene and (E)-4,8-dimethyl-1,3,7-nonatriene, known to act as herbivore repellents. The chemical analysis explains the behavioural effects observed in the olfactometer, as the CJ treatment caused plants to emit a blend of VOCs comprising more of the repellent components in the first 22 h of insect infestation than control plants. The speed and potency of VOC emission was increased by the CJ pre-treatment. This is the first indication that CJ can prime plants for enhanced production of defensive VOCs antagonist towards herbivores.     

Characteristics of sugarcane white leaf phytoplasma transmission by the leafhopper Matsumuratettix hiroglyphicus

The leafhopper Matsumuratettix hiroglyphicus (Matsumura) (Hemiptera: Cicadellidae) is the most important vector of sugarcane white leaf (SCWL) phytoplasma that significantly affects the sugarcane crop in Asia. Here, we aimed to study the characteristics of SCWL phytoplasma transmission by M. hiroglyphicus. To this end, the stylet penetration activities performed during the acquisition access period (AAP) and inoculation access period (IAP) were investigated by the direct current electrical penetration graph technique and confirmed by quantitative polymerase chain reaction (qPCR). Additionally, the latent period (LP) of SCWL phytoplasma in the vector was determined by qPCR and localised by fluorescent in situ hybridisation. The results indicated that the acquisition of SCWL phytoplasma occurred during phloem ingestion (waveform D), whereas its inoculation was associated with salivation into the phloem sieve element (waveform C). The minimum AAP was 15 min and the minimum duration of phloem ingestion was 2.35 min. The minimum LP of SCWL phytoplasma in the vector was at least 14 days; then, SCWL phytoplasma moved to the salivary glands of the insect, enabling the transmission of the pathogen to the host plants. The minimum IAP for a successful transmission of SCWL phytoplasma to the host plants was 11–12 min, with a minimum duration of salivation into phloem of 1.35 min. The female vectors had higher SCWL phytoplasma copy numbers than the male vectors, and displayed faster AAP, IAP, and LP. Overall, our findings provide important information related to the feeding behaviour of M. hiroglyphicus and its effect on the transmission of SCWL phytoplasma.     

Intercrops, Cicadulina spp., and maize streak virus disease

Intercrops of bean and finger millet were tested as a possible means of controlling maize streak virus disease (MSVD) in maize by disrupting the mating behaviour of the insect vectors of the maize streak virus, Cicadulina mbila and C. storeyi. A series of three trials were done. In the first, MSVD incidence 2 months after sowing was reduced to 14.9% and 17.4% in millet and bean intercrops compared to 29.5% in the pure maize stand. The number of male Cicadulina spp. caught on sticky pole traps was also significantly reduced relative to the control, but there was little effect on the catch of females. There was no significant yield penalty for the millet intercrop but maize yield was 49% lower in the bean intercrop treatment than in the pure stand. In the second trial, there were two millet and two bean intercrop treatments and a maize only control. Fewer male Cicadulina spp. were caught in the intercrop treatments relative to the control but MSVD incidence was reduced in one millet intercrop treatment only for which the associated maize yield penalty was 89%. In the final trial the bean intercrop was again tested but it had no effect on MSVD incidence. These experiments demonstrated that intercropping maize with bean or millet decreased vector activity and/or vector numbers. Vector catches were predominantly male, and catches of males but not females were reduced in the intercrop treatments compared with pure stands. However the lower vector catch was not consistently associated with a significant reduction in MSVD incidence, and when it was there was often an associated yield penalty in the maize due to the intercrop.     

Assessment of yield losses as a result of co-infection by maize streak virus and maize stripe virus in Mauritius

The effect of co-infection by maize streak virus (MSV) and maize stripe virus (MStV) on plant growth and grain yield was investigated in a susceptible variety of maize (Zea mays), ZS 5206, in Mauritius. Under natural conditions MSV, transmitted by the leafhopper Cicadulina mbila, was normally established before MStV, which is vectored by the planthopper Peregrinus maidis; as a result, MStV symptoms were often partially or completely masked by those of MSV, making MStV detection by symptomatology very unreliable. MSV and MStV were diagnosed by ELISA and MStV by a novel method of detecting the MStV-coded non-capsid protein. The maize hybrid ZS 5206 was inoculated with either MSV, MStV or both, at two stages in the growth cycle (3–5 or 7–10 leaf stage). A greater reduction in plant growth was observed in plants inoculated singly with MStV (80% and 29% for first and second stage, respectively) than with MSV (50% and 23%, respectively). No cobs were produced by plants singly infected with MStV at the first stage, or co-infected with MSV and MStV at both stages; however, marginal grain production was recorded in plants singly infected with MSV at the first stage (91% reduction), or infected either with MSV or MStV, at the second stage (65% and 80% reduction, respectively). In maize hybrid ZS 5206, MStV is more virulent than MSV; co-infection by both viruses causes greater reductions in plant growth and grain yield than single infection by either virus at a given stage of plant development. In the event of co-infection by MSV and MStV, yield losses can be erroneously attributed to MSV only if the symptoms of MStV are masked by those of the former and if adequate methods for MStV detection are not used.     

Maize streak virus: an old and complex 'emerging' pathogen

Maize streak virus (MSV; Genus Mastrevirus, Family Geminiviridae) occurs throughout Africa, where it causes what is probably the most serious viral crop disease on the continent. It is obligately transmitted by as many as six leafhopper species in the Genus Cicadulina, but mainly by C. mbila Naudé and C. storeyi. In addition to maize, it can infect over 80 other species in the Family Poaceae. Whereas 11 strains of MSV are currently known, only the MSV‐A strain is known to cause economically significant streak disease in maize. Severe maize streak disease (MSD) manifests as pronounced, continuous parallel chlorotic streaks on leaves, with severe stunting of the affected plant and, usuallly, a failure to produce complete cobs or seed. Natural resistance to MSV in maize, and/or maize infections caused by non‐maize‐adapted MSV strains, can result in narrow, interrupted streaks and no obvious yield losses. MSV epidemiology is primarily governed by environmental influences on its vector species, resulting in erratic epidemics every 3–10 years. Even in epidemic years, disease incidences can vary from a few infected plants per field, with little associated yield loss, to 100% infection rates and complete yield loss. Taxonomy: The only virus species known to cause MSD is MSV, the type member of the Genus Mastrevirus in the Family Geminiviridae. In addition to the MSV‐A strain, which causes the most severe form of streak disease in maize, 10 other MSV strains (MSV‐B to MSV‐K) are known to infect barley, wheat, oats, rye, sugarcane, millet and many wild, mostly annual, grass species. Seven other mastrevirus species, many with host and geographical ranges partially overlapping those of MSV, appear to infect primarily perennial grasses. Physical properties: MSV and all related grass mastreviruses have single‐component, circular, single‐stranded DNA genomes of approximately 2700 bases, encapsidated in 22 × 38‐nm geminate particles comprising two incomplete T = 1 icosahedra, with 22 pentameric capsomers composed of a single 32‐kDa capsid protein. Particles are generally stable in buffers of pH 4–8. Disease symptoms: In infected maize plants, streak disease initially manifests as minute, pale, circular spots on the lowest exposed portion of the youngest leaves. The only leaves that develop symptoms are those formed after infection, with older leaves remaining healthy. As the disease progresses, newer leaves emerge containing streaks up to several millimetres in length along the leaf veins, with primary veins being less affected than secondary or tertiary veins. The streaks are often fused laterally, appearing as narrow, broken, chlorotic stripes, which may extend over the entire length of severely affected leaves. Lesion colour generally varies from white to yellow, with some virus strains causing red pigmentation on maize leaves and abnormal shoot and flower bunching in grasses. Reduced photosynthesis and increased respiration usually lead to a reduction in leaf length and plant height; thus, maize plants infected at an early stage become severely stunted, producing undersized, misshapen cobs or giving no yield at all. Yield loss in susceptible maize is directly related to the time of infection: infected seedlings produce no yield or are killed, whereas plants infected at later times are proportionately less affected. Disease control: Disease avoidance can be practised by only planting maize during the early season when viral inoculum loads are lowest. Leafhopper vectors can also be controlled with insecticides such as carbofuran. However, the development and use of streak‐resistant cultivars is probably the most effective and economically viable means of preventing streak epidemics. Naturally occurring tolerance to MSV (meaning that, although plants become systemically infected, they do not suffer serious yield losses) has been found, which has primarily been attributed to a single gene, msv‐1. However, other MSV resistance genes also exist and improved resistance has been achieved by concentrating these within individual maize genotypes. Whereas true MSV immunity (meaning that plants cannot be symptomatically infected by the virus) has been achieved in lines that include multiple small‐effect resistance genes together with msv‐1, it has proven difficult to transfer this immunity into commercial maize genotypes. An alternative resistance strategy using genetic engineering is currently being investigated in South Africa. Useful websites: 〈 http://www.mcb.uct.ac.za/MSV/mastrevirus.htm 〉; 〈 http://www.danforthcenter.org/iltab/geminiviridae/geminiaccess/mastrevirus/Mastrevirus.htm 〉.     

The transmission of cocksfoot mottle and phleum mottle viruses by Oulema melanopa and O. lichenis.

Oulema melanopa and O. lichenis both transmit cocksfoot mottle and phleum mottle viruses with similar efficiencies. The viruses were serologically dissimilar and did not cross-protect against each other in barley. Both viruses were acquired after a few minutes feeding, but longer acquisition feeding periods increased both the efficiency of transmission and persistence in the vectors. Acquisition of either virus increased vector mortality whilst acquisition of both together did not. When both viruses were ingested, only one was transmitted. Each virus could be recovered from haemolymph and faeces, but regurgitation was not observed and could only be induced with the greatest difficulty. The results suggest possible circulative transmission of some beetle-borne viruses.     

Transmission features of Mai de Río Cuarto virus in wheat by its planthopper vector Delphacodes kuscheli

Mal de Rio Cuarto virus (MRCV, Fijivirus) infects maize (Zea mays) and other gramineae, producing significant losses in Argentina. Although MRCV mainly affects maize, other cereals, such as wheat, serve as potential virus reservoirs and hosts for the planthopper vector Delphacodes kuscheli. Aspects of the virus‐vector relationships were elucidated by studying the minimum periods of acquisition access (AAP_min), latency (LP_min) and inoculation access (IAP_min) in wheat (Triticum aestivum L.). Trials were conducted under controlled conditions of temperature (24 ± 1°C), photoperiod (12 h light) and humidity (50 ± 5%). The results show that the AAPmin was 5 h, LPmin was 10 days (even though, the median latent period was between 16 and 17 days) and IAPmin was 30 min. Our experiments have demonstrated, for the first time, a persistent manner of virus transmission. No differences were detected in transmission ability between males and females. The implication of these results on virus taxonomy and epidemiology are discussed.     

Biological factors affecting leafhopper transmission of purified maize chlorotic dwarf machlovirus

A helper component from maize chlorotic dwarf machlovirus (MCDV)-infected plants was necessary for insect transmission of purified MCDV. Purified MCDV, WS strain, when acquired by membrane feeding, was transmitted byGraminella nigrifrons (Forbes) (Homoptera: Cicadellidae) which fed first on MCDV (M1 strain)-infected maize. Conversely, feeding on MCDV-WS-infected maize allowed transmission of purified MCDV-M1, indicating that the helper component was not strain specific. ViruliferousG. nigrifrons lost the ability to transmit MCDV-M1 after feeding for 24 h on healthy maize, but retained the ability to acquire and transmit purified MCDV-WS for up to 36 h. Wheng. nigrifrons fed initially on MCDV-infected plants and then on a second strain of purified MCDV, the second strain of MCDV could be transmitted alone, suggesting that the helper component from MCDV-infected plants was something other than the virion itself. Lengthening acquisition feeding ofG. nigrifrons on MCDV-M1-infected maize or purified MCDV-WS did not significantly change the transmission frequency of MCDV-WS.Amblysellus grex (Oman), an experimental vector of MCDV, also transmitted purified MCDV-WS after an initial acquisition feeding on MCDV-M1-infected maize. This suggests that the helper component is not vector species specific.     

Biological characteristics of grass geminiviruses from eastern Australia

Two serotypes of chloris striate mosaic virus (CSMV), paspalum striate mosaic virus (PSMV) and geminiviruses infecting Bromus catharticus and Digitaria didactyla were investigated. Their field occurrence and experimental hosts are listed. Serial transmission data for CSMV by single Nesoclutha pallida show a minimum latent period of 12–14 h, and regular transmission with occasional breaks for up to 50 days. Cicadulina bimaculata did not transmit any isolates after plant feeding acquisition, but transmitted CSMV inefficiently after insect injection. The vector of PSMV was found to be a specific biotype of N. pallida which bred only on Paspalum spp. The rate of transmission of CSMV with the Chloris biotype of N. pallida and of PSMV with the Paspalum biotype reached c. 50% with single insects, but only when freshly-infected source plants were used. Geminate particles were found in thin sections of leaf tissue infected with all four viruses, and partially purified preparations were made of three of these. In gel diffusion tests, the virus from Microlaena stipoides produced a spur reaction with CSMV, when reacted with CSMV antiserum. The B. catharticus and D. didactyla isolates failed to react serologically with CSMV, maize streak or Vanuatu digitaria streak viruses.     

Leafhopper transmission of a virus causing maize wallaby ear disease

A virus causing maize wallaby ear disease was transmitted experimentally by Cicadulina bimaculata to fourteen species of monocotyledonous plants. It was also transmitted by Nesoclutha pallida, and by grafting. The symptoms obtained resemble closely those reported for maize leaf gall disease in the Philippines and maize rough dwarf virus in Italy and Israel. About 85% of C. bimaculata caught in the field carried maize wallaby ear virus (MWEV), and many of their progeny were viruliferous even when not allowed access to infected plants. The proportion of infective individuals in clones bred for nine generations from selected non-transmitting adults decreased from 85% in the first nymphs to less than 1%; such individuals were difficult to rear, as their fecundity and longevity decreased greatly. N. pallida transmitted MWEV after injection with partially purified extracts of infected plants. Spherical particles c. 85 nm in diameter were found in the salivary glands of viruliferous C. bimaculata, but not in those of non-transmitting individuals. The particles occurred in tubules in the cytoplasm and each had a densely stained core c. 50 nm in diameter. Particles similar in size to the core were found in extracts of infected but not uninfected maize, and in extracts of viruliferous but not in non-viruliferous C. bimaculata and N. pallida.     

Phytohormones Related to Host Plant Manipulation by a Gall-Inducing Leafhopper

The maize orange leafhopper Cicadulina bipunctata (Hemiptera: Cicadellidae) induces galls characterized by growth stunting and severe swelling of leaf veins on various plants of Poaceae. Previous studies revealed that galls are induced not on feeding site but on distant, newly extended leaves during the feeding, and strongly suggested that some chemicals injected by the leafhopper affect at the leaf primordia. To approach the mechanism underlying gall induction by C. bipunctata, we examined physiological response of plants to feeding by the leafhopper. We performed high-throughput and comprehensive plant hormone analyses using LC-ESI-MS/MS. Galled maize leaves contained higher contents of abscisic acid (ABA) and trans-Zeatin (tZ) and lower contents of gibberellins (GA₁ and GA₄) than ungalled maize leaves. Leafhopper treatment significantly increased ABA and tZ contents and decreased GA₁ and GA₄ contents in extending leaves. After the removal of leafhoppers, contents of tZ and gibberellins in extending leaves soon became similar to the control values. ABA content was gradually decreased after the removal of leafhoppers. Such hormonal changes were not observed in leafhopper treatment on leaves of resistant maize variety. Water contents of galled leaves were significantly lower than control leaves, suggesting water stress of galled leaves and possible reason of the increase in ABA content. These results imply that ABA, tZ, and gibberellins are related to gall induction by the leafhopper on susceptible variety of maize.     

Aphid retention of maize dwarf mosaic virus (potyvirus): epidemiological implications

In total, 17 589 aphids were assayed for rate of loss of inoculativity and maximum retention times of maize dwarf mosaic (MDMV). The Standard-treatment, involved acquisition access to MDMV-infected tissue followed by confinement of active aphids in Petri dishes. In addition various aphid immobilisation treatments were used to prevent probing on solid surfaces after acquisition access to simulate conditions experienced by wind-borne aphids when aloft. Immobilisation treatments, using nitrogen or argon gases at 25°C, or cold treatments at 6°C after acquisition access greatly increased the efficiency of MDMV transmission by greenbugs, Schizaphis graminum, in an experimental design where insects were individually assayed for transmission over a 7 h period. Further tests in which groups of greenbugs were assayed for MDMV transmission revealed that MDMV strains may be retained for over 21 h, regardless of post-acquisition access treatment. Experiments with other aphid vectors of MDMV (Dactynotus ambrosiae, Macrosiphum euphorbiae, Rhopalosiphum maidis and Myzus persicae) also demonstrated MDMV retention times exceeding 18 h. These results show that the rate at which aphids lose MDMV inoculativity is lower when solid surface probing behaviour is denied, and that MDMV retention times are longer than those previously published. The findings are discussed in relation to the epidemiology of nonpersistent viruses and their dispersal over great distances.     

Inoculation and acquisition of maize bushy stunt mycoplasma by its leafhopper vector Dalbulus maidis

Maize bushy stunt mycoplasma (MBSM), a mycoplasma-like organism, is transmitted in a persistent manner by the corn leafhopper, Dalbulus maidis, to maize (Zea mays). The influence of the duration of acquisition access and inoculation access periods on the transmission of MBSM by D. maidis was investigated. The proportion of plants infected by D. maidis increased significantly from 0 to 0.51 as the inoculation access time to a plant increased from 10 min to 72 h (X²= 101.5, P < 0.001). Likewise, the proportion of insects acquiring MBSM from infected plants increased from 0 to 0.19 as the acquisition access time to the source plant increased from 10 min to 72 h (X²= 53.2, P < 0.001). The data were fitted to a loglinear regression model. No significant association was found between the sex of the insects and vector ability.     

Comparison and characterization of maize stripe and maize line viruses

Two morphologically similar viruses isolated from maize in East Africa induced two distinct symptom types in maize. One, designated maize stripe virus (MSV), showed broad yellow stripes or a yellowing of the entire leaf, acute bending of the shoot apex and severe stunting. The second, maize line virus (MLV), induced continuous, narrow yellow lines along the leaf veins and did not cause apical bending or stunting. MSV and MLV were both transmitted by Peregrinus maidis (Delphacidae), but not by Cicadulina mbila (Jassidae) or by sap inoculation. Both viruses were purified by extracting systemically infected leaves in 0–5 M sodium citrate buffer and clarifying with 7 ml n-butanol/100 ml extract, followed by differential, and finally sucrose density gradient, centrifugation. Partially purified preparations of both viruses contained isometric viruslike particles of two sizes: MSV particles were 35 and 40 nm in diameter with sedimentation coefficients (so₂o, w) ^I09 ^anI0o respectively; MLV particles were 28 and 34 nm in diameter. Antisera prepared against MSV and MLV had dilution end points of 1/128 and 1/64 respectively in agar-gel diffusion tests. In tests with low-titre antisera, MSV did not react with MLV antiserum and MLV did not react with MSV antisreum; in the presence of antiserum containing antibodies to both MSV and MLV, the two viruses formed precipitin bands which crossed in the pattern of non-identity. Maize streak virus and maize mottle virus showed no serological relationship with MSV or MLV. On the basis of particle size and serology MSV and MLV are shown to be two distinct and possibly unrelated viruses. MSV and MLV apparently are dissimilar from any characterized viruses of the Gramineae.