Raymond Louie

Differential transmission of isolates of the High Plains virus by different sources of wheat curl mites.

High Plains virus (HPV) isolates from Colorado, Idaho, Kansas, Texas, and Utah were serologically related, had similar relative molecular masses (sodium dodecyl sulfate-polyacrylamide gel electrophoresis) for the 32-kDa diagnostic HPV protein, and were transmissible and maintained free of Wheat streak mosaic virus (WSMV) by vascular puncture inoculation. Collections of wheat curl mites (Aceria tosichella Keifer; WCM) from Kansas, Montana, Nebraska, South Dakota, and Texas differentially transmitted these isolates. For collections from South Dakota and Texas, little or no HPV transmission occurred, whereas WCM from Nebraska and Montana transmitted all five isolates. The collection from Kansas mostly transmitted only one HPV isolate. Aviruliferous or viruliferous WSMV Nebraska WCM transmitted HPV at similar rates and aviruliferous Montana WCM transmitted HPV at lower levels than viruliferous Montana WCM.

Identification of quantitative trait loci controlling resistance to maize chlorotic dwarf virus

Ineffective screening methods and low levels of disease resistance have hampered genetic analysis of maize (Zea mays L.) resistance to disease caused by maize chlorotic dwarf virus (MCDV). Progeny from a cross between the highly resistant maize inbred line Oh1VI and the susceptible inbred line Va35 were evaluated for MCDV symptoms after multiple virus inoculations, using the viral vector Graminella nigrifrons. Symptom severity scores from three rating dates were used to calculate area under the disease progress curve (AUDPC) scores for vein banding, leaf twist and tear, and whorl chlorosis. AUDPC scores for the F2 population indicated that MCDV resistance was quantitatively inherited. Genotypic and phenotypic analyses of 314 F2 individuals were compared using composite interval mapping (CIM) and analysis of variance. CIM identified two major quantitative trait loci (QTL) on chromosomes 3 and 10 and two minor QTL on chromosomes 4 and 6. Resistance was additive, with alleles from Oh1VI at the loci on chromosomes 3 and 10 contributing equally to resistance.

Maize necrotic streak virus, a new maize virus with similarity to species of the family tombusviridae

A new virus was isolated from maize (Zea mays L.) leaves showing mild mosaic symptoms and coinfected with Maize dwarf mosaic virus. The virus was readily transmitted by vascular puncture inoculation (VPI) but not leaf-rub inoculation. Virus symptoms on susceptible maize included pale green, yellow, or cream-colored spots and streaks measuring 1 to 2 mm on emerging leaves 5 to 7 days post-VPI. As leaves developed, the spots and streaks became spindle-shaped, then coalesced into long, chlorotic bands. These bands became translucent and necrotic around the edges. There was a distinctive chlorosis on the stalks that became necrotic. Based on these distinctive symptoms, the new virus was named Maize necrotic streak virus (MNeSV). The virus was not transmitted by Aphis maidis-radicus, Myzus persicae, Macrosiphum euphorbiae, Rhopalosiphum padi, Dalbulus maidis, Graminella nigrifrons, Perigrinus maidis, or Diabrotica virgifera virgifera under persistent or nonpersistent conditions. Both susceptible and resistant maize genotypes were identified following VPI with MNeSV. The isolated virus had isometric (32 nm) virions and a single 29.5-kDa coat protein. MNeSV was serologically distinct from morphologically similar maize viruses. The 4.3-kb single-stranded RNA genome had 25 to 53% sequence identity with species in the family Tombusviridae.

The Mdm1 Locus and Maize Resistance to Maize dwarf mosaic virus

Previously, Mdm1, a gene controlling resistance to Maize dwarf mosaic virus (MDMV), was identified in the inbred line Pa405. The gene was tightly linked to the restriction fragment length polymorphism marker umc85 on the short arm of chromosome 6. This chromosomal region is also the location of resistance genes to two other viruses in the family Potyviridae, Sugarcane mosaic virus (SCMV) and Wheat streak mosaic virus (WSMV). A diverse collection of 115 maize inbred lines was evaluated for resistance to MDMV and SCMV, and for MDMV resistance loci on chromosome 6S. Forty-six resistant inbred lines were crossed to three MDMVsusceptible inbred lines to develop F2 populations. The F2 populations were inoculated with MDMV and scored for infection and symptom type. Environmental factors influenced both the rate and type of symptom development. Bulked segregant analysis of each F2 population indicated that, in 42 of 43 MDMV-resistant lines, chromosome 6S markers found in the resistant parent also were present in the bulked resistant but not the susceptible tissue. Markers previously associated with resistance to both SCMV and WSMV on chromosome 3 and to WSMV on chromosome 10 were associated with resistance in nine and seven of the F2 populations, respectively. These data suggest that Mdm1 or closely linked genes on chromosome 6S are associated with MDMV resistance in most germplasm, but that other loci also may affect resistance.

Transmission of viral RNA and DNA to maize kernels by vascular puncture inoculation

Vascular puncture inoculation (VPI) is an effective technique for transmission of maize viruses without using arthropods or other biological vectors. It involves using a jewelers engraving tool to push minuten pins through a droplet of virus inoculum toward the major vascular bundle in the scutellum of germinating kernels. Here, VPI is shown to be useful for introducing RNA and DNA viral genomes into maize. Maize dwarf mosaic potyvirus (MDMV) virions, MDMV genomic RNA, foxtail mosaic potexvirus (FoMV) genomic RNA and maize streak geminivirus (MSV) DNA were introduced into kernels by VPI, and infection rates determined. At high concentrations, both MDMV virion and genomic RNA preparations produced 100% infection of susceptible maize. However, MDMV genomic RNA was transmitted with about 100-fold lower efficiency than virions. FoMV genomic RNA and MSV DNA were transmitted at lower efficiency than the MDMV RNA, and the highest transmission rates were about 50%. Ribonuclease A pretreatment prevented genomic MDMV and FoMV RNA transmission, but not MDMV virion transmission indicating the viral RNA was the infectious entity. Proteinase K (ProK) pretreatment reduced transmission of MDMV RNA suggesting that integrity of the viral genomic protein bound covalently to the viral RNA may be important for efficient transmission.

Sugarcane mosaic virus in Kenya.

LOUIE, R. 1980. Sugarcane mosaic virus in Kenya. Plant Disease 64:944-947. Surveys for sugarcane mosaic virus (SCMV) in maize (Zea mays L. subsp. mays) were made in 34 of 41 districts in Kenya. SCMV was found in 20 districts and only in the western plateaus, Central Highlands, and Rift Valley. Provinces with high incidence of SCMV included Nyanza (15.2%), Rift Valley (15.8%), and Western (19.6%). SCMV was not found in Coast or Nairobi provinces. The incidence of SCMV was higher in late-planted maize planted for the April-May rains or the October-November rains than in early plantings. This is the first report of natural infection with SCMV in Cynodon dactylon, C. nlemfunsis, Digitaria nuda, D. abyssinica, Eragrostisexasperata, Paspalum notatum, P. scrobiculatum, Rhynchelytrym repens, and an unknown Tripsacum fasciculatum cross. The distribution of SCMV in maize appeared to be related to the distribution of sources of inoculum, but the periodicity of disease development appeared to be related to vector populations. Maize streak and maize mosaic viruses were most often found in Central (4.5%) and Coast (13.8%) provinces. Additional key words: corn, maize dwarf mosaic virus, weed hosts In 1973, Kulkarni (14) reported sugarcane mosaic virus (SCMV) in sugarcane (interspecific hybrids of Saccharum) and maize (Zea mays L. subsp. mays) in six of 41 districts of Kenya and in Tanzania and Uganda. Because SCMV causes serious losses in maize (14, 16), which is grown in most parts of Kenya (1), more information was needed to delineate the distribution of SCMV and determine its possible overseasoning hosts. We report on the distribution of SCMV in maize in Kenya, the seasonal development of the disease at Muguga and Kitale, and the possible sources of inocula. SCMV includes strains specially adapted to sugarcane, maize, or sorghum (Sorghum spp.) that are difficult to transmit from one grass host to another; for example, maize dwarf mosaic virus strain A is easily transmitted to johnsongrass (S. halepense (L.) Pers.) but not to sugarcane (23). No attempt was made in this paper to identify strains. A preliminary report on weed hosts has been published (18). MATERIALS AND METHODS One-hundred maize plants along an edge row of each field and 100 plants Present address of the author: AR, SEA, USDA, Department of Plant Pathology, Ohio Agricultural Research and Development Center, Wooster, OH

Biological and Molecular Variability Among High Plains virus Isolates

The High Plains virus (HPV), vectored by the wheat curl mite (WCM) (Aceria tosichella), causes a severe disease of maize (Zea mays) in the U. S. High Plains. In the present study, five HPV isolates from five states were separated from co-infecting Wheat streak mosaic virus and their molecular and biological variability studied. Molecular studies involved time-of-flight mass spectrometry (TOFMS) to determine amino acid sequence variability of the 32-kDa nucleoprotein (32 np) of the isolates. Biological studies involved testing the ability of the five HPV isolates to infect a maize line previously shown to have resistance. Inoculations of the HPV isolates were conducted using vascular puncture inoculation (VPI) and viruliferous WCM. TOFMS analyses demonstrated an 18-amino acid sequence in the isolates at the N-terminus of the 32 np, the presence of amino acid sequence differences among the isolates, and variability among amino acid sequences of the 32 np of some isolates. Three of the five HPV isolates infected the resistant maize inbred, B73, using VPI, and two of the same three HPV isolates infected this line using WCM inoculation, albeit low numbers of plants were infected by each technique.

Spread of maize dwarf mosaic virus from johnsongrass to corn

. plants to the east and west of these Knoke, J. K., Louie, R., Madden, L. V., and Gordon, D. T. 1983. Spread of maize dwarf mosaic mares in eah row were surveye virus from johnsongrass to corn. Plant Disease 67:367-370. resulting in 200 10-plant samples per plot. Spread of maize dwarf mosaic virus (MDMV) from introduced virus-infected johnsongrass to Disease incidence was recorded as the adjacent susceptible corn in experimental plots was evaluated during 1979 and 1980. The proportion of plants in each sample that relationship between MDM incidence in corn and distance from the source was adequately showed disease symptoms. Straight-line described by the model Y = a(exp(-bD)), where Y is disease incidence at distance D from the distances from the johnsongrass to the source, b is the spread coefficient, and a is the scaling factor. In both years, b was significantly center of each 10-plant sample were greater than zero, demonstrating that MDMV spread to the corn test plots. In control plots with no calculated. For regression analysis, intentionally placed virus source, b values and disease incidence were lower than in test plots. For a incidence data in each plot were grouped single planting in 1979, the steepness of the gradient of disease incidence from the source (quantified in 1-m intervals, eg, all observations by b) decreased with time as fewer plants remained uninfected. For two successive plantings in 1980, no significant difference in b values was observed. MDMV spread also was not related to 20-21 m from johnsongrass were prevalent wind direction. No spread of maize chlorotic dwarf virus (MCDV) to corn was observed averaged to calculate incidence at 20.5 m. by symptomatology even though 90 and 50% of the johnsongrass plants were infected in 1979 and In 1980, PAG 246006 and Agway 1980, respectively, as indicated by enzyme-linked immunosorbent assay. The leafhopper vector of XP708 were each machine-planted in MCDV, Graminella nigrifrons, was also present during both years. The presence of MDMV in the four plots on 11 June, 15 July, 8 August, control plots indicates that there were virus sources other thanjohnsongrass or that MDMV moved and 4 September. The sweet corn hybrid more than 400 m from johnsongrass to the control plots. Agway XP708 is susceptible to MDMV and MCDV, whereas the dent corn

Maize white line mosaic virus transmission to maize seedlings in hydroponic culture

A hydroponic culture system and the effects of nonchemical and chemical treatments of root inoculum on transmission of maize white line mosaic virus (MWLMV) were evaluated. Root pieces (0.2 g) from 8- to 10-wk-old infected Seneca Chief sweet corn (Zea mays var. saccharata) plants were used as inoculum to transmit MWLMV to roots of sweet corn test seedlings. MWLMV was transmitted consistently to seedling roots (>90%) as shown by enzyme-linked immunosorbent assays (ELISA). The ELISA values (absorbances at 405 nm) of root inocula and inoculated roots were not significantly correlated (.)