Occurrence and Characterization of Bean common mosaic virus Strain NL1 in Iowa.

A legume survey in Story County was conducted to characterize legume viruses present in Iowa and potentially problematic to soybeans. Symptomatic (chlorosis, leaf curl, or vein banding) and non-symptomic leaves were selected from Apios americana, Cyamopsis tetragonolobus, Desmodium spp., Glycine max, Lablab purpureus, Lotus japonicus, Phaseolus coccineus, Phaseolus vulgaris, Vicia faba, Vigna ungulculata, and Chenopodium quinoa (an indicator species), and sent to Agdia Inc. for their Crop Screen: "Bean (Soybean)" tests. Cowpea mosaic virus (in L. purpureus), Southern bean mosaic virus (in A. americana), Soybean dwarf virus (in L. purpureus), and Tobacco streak virus (in Desmodium spp.) were identified. In addition, P. vulgaris was found positive in the serological Potyvirus group test, and was further characterized using reverse transcription (RT)-PCR using total RNA (Qiagen RNeasy extraction kit) from symptomatic leaves. A ~1-kb fragment of virus genome was amplified using degenerate primers, forward: 5' TGYGTNGAYGAYYTYAAYAA 3' (3) and reverse: 5' TCRTARAARTCRAAIGCRTAICKIG 3' (2). The closest GenBank BLAST hits for the sequence were BCMV strain NL1 (GenBank Accession No. AY112735) and BCMV MS1 (EU761198), both at 97% identity. RNA sequencing using an Illumina HiSeq 2500 (100 base paired ends) allowed construction of a nearly complete viral sequence from positions 38 to 10,037 nt (KM023744). This showed 99% similarity to BCMV-NL1 (AY112735) and 98% similarity to BCMV MS1 (EU761198). The BCMV isolate was recovered on the P. vulgaris cv. Taos Red and tested against a panel of Phaseolus, Glycine, and other hosts. Symptomatic hosts (vein-banding, mosaic, stunting, and leaf curl) were P. vulgaris cvs. Starlight, Tohono O'odham vaya Amarillo, Black Valentine Stringless, Sutter Pink, Hidatsa red, Stringless Green Refugee, Burpees Stringless Improved Bush, Princess d'Artois, Princess Double de Holland, and Dubelle Witte. Asymptomatic hosts included P. vulgaris cvs. Sierra, Great Northern Tara, Tara, and Vigna radiata. Non-host plants were P. vulgaris cvs. Michelite 62, Great Northern UI 31, Great Northern UI 123, Pure Gold Wax, Top Crop, Redlands Greanleaf B, Red Mexican UI 34, Imuna, Monroe, Pinto UI 114, Widusa, Othello, Sacramento, Red Kidney, Provider, Black Turtle Soup, Victor, and Witte boon, G. max cv. Williams, Cucumis sativus cv. Straight 8, Solanum lycopericum cv. Reine des Hatives, Vicia faba, Pisum sativum var. macrocarpon, V. unguiculata, and A. americana. The host range of the BCMV isolate on common bean differential species concurred with pathogenicity group I (1) and agreed with assignment as strain NL1. To our knowledge, this is the first complete characterization of a pathotype I strain NL1 of BCMV in the United States, combining biological typing and whole genome sequencing. References: (1) R. E. Klein et al. Plant Dis. 76:1263, 1992. (2) H. Yamamoto et al. J. Gen. Plant Pathol. 74:97, 2008. (3) L. Zheng et al. PLoS One 3:e1586, 2008.

Identification of factors that function in Drosophila salivary gland cell death during development using proteomics.

Proteasome inhibitors induce cell death and are used in cancer therapy, but little is known about the relationship between proteasome impairment and cell death under normal physiological conditions. Here, we investigate the relationship between proteasome function and larval salivary gland cell death during development in Drosophila. Drosophila larval salivary gland cells undergo synchronized programmed cell death requiring both caspases and autophagy (Atg) genes during development. Here, we show that ubiquitin proteasome system (UPS) function is reduced during normal salivary gland cell death, and that ectopic proteasome impairment in salivary gland cells leads to early DNA fragmentation and salivary gland condensation in vivo. Shotgun proteomic analyses of purified dying salivary glands identified the UPS as the top category of proteins enriched, suggesting a possible compensatory induction of these factors to maintain proteolysis during cell death. We compared the proteome following ectopic proteasome impairment to the proteome during developmental cell death in salivary gland cells. Proteins that were enriched in both populations of cells were screened for their function in salivary gland degradation using RNAi knockdown. We identified several factors, including trol, a novel gene CG11880, and the cop9 signalsome component cop9 signalsome 6, as required for Drosophila larval salivary gland degradation.

Experimental adaptation of an RNA virus mimics natural evolution.

Identification of virulence determinants of viruses is of critical importance in virology. In search of such determinants, virologists traditionally utilize comparative genomics between a virulent and an avirulent virus strain and construct chimeras to map their locations. Subsequent comparison reveals sequence differences, and through analyses of site-directed mutants, key residues are identified. In the absence of a naturally occurring virulent strain, an avirulent strain can be functionally converted to a virulent variant via an experimental evolutionary approach. However, the concern remains whether experimentally evolved virulence determinants mimic those that have evolved naturally. To provide a direct comparison, we exploited a plant RNA virus, soybean mosaic virus (SMV), and its natural host, soybean. Through a serial in vivo passage experiment, the molecularly cloned genome of an avirulent SMV strain was converted to virulent variants on functionally immune soybean genotypes harboring resistance factor(s) from the complex Rsv1 locus. Several of the experimentally evolved virulence determinants were identical to those discovered through a comparative genomic approach with a naturally evolved virulent strain. Thus, our observations validate an experimental evolutionary approach to identify relevant virulence determinants of an RNA virus.

Gain of virulence on Rsv1-genotype soybean by an avirulent Soybean mosaic virus requires concurrent mutations in both P3 and HC-Pro.

In soybean, Rsv1, a single dominant resistance gene, invokes extreme resistance (ER) against most Soybean mosaic virus (SMV) strains, including SMV-N, but not SMV-G7, which provokes a virulent lethal systemic hypersensitive response (LSHR). The elicitor functions of the two viruses provoking Rsv1-mediated ER and LSHR have been mapped to the N-terminal 271 amino acids of P3 from SMV-N and SMV-G7, respectively, which differ by nine residues between the two strains. To identify amino acids of P3 from SMV-N provoking Rsv1-mediated ER, the unique residues of SMV-G7 were substituted with those of SMV-N. Of the mutants tested on Rsv1-genotype soybean, only SMV-G7(I788R) and SMV-G7(T948A) lost virulence. However, substitution of amino acids of SMV-N, individually or in combination, with the reciprocal residues from SMV-G7 at these two positions failed to confer virulence to SMV-N. In the search for additional virulence determinants, a series of SMV-N chimeras was generated in which fragments within a region from near the middle of the helper-component proteinase (HC-Pro) cistron to the 5' end of the cytoplasmic inclusion cistron, nucleotides 1,605 to 3,787, were replaced with those of SMV-G7. Only SMV-N-derived chimeras harboring the 3' region of HC-Pro, at least from nucleotide 2,013, and the entire 5' end of P3 (nucleotides 2,430 to 3,237) from SMV-G7 were virulent whereas reciprocal exchanges resulted in loss of SMV-G7 virulence. This region of HC-Pro differs by three amino acids between SMV-N and SMV-G7. Analyses of SMV-G7-derived HC-Pro site-directed mutants showed that only SMV-G7(M683R) lost virulence on Rsv1-genotype soybean; however, SMV-N(R682M) failed to gain virulence. Nevertheless, an SMV-N derived mutant with three concurrent substitutions, R682M+R787I+A947T, gained virulence. The data indicate that both P3 and HC-Pro are involved in virulence of SMV on Rsv1-genotype soybean.

Adaptation of Soybean mosaic virus avirulent chimeras containing P3 sequences from virulent strains to Rsv1-genotype soybeans is mediated by mutations in HC-Pro.

In Rsv1-genotype soybean, Soybean mosaic virus (SMV)-N (an avirulent isolate of strain G2) elicits extreme resistance (ER) whereas strain SMV-G7 provokes a lethal systemic hypersensitive response (LSHR). SMV-G7d, an experimentally evolved variant of SMV-G7, induces systemic mosaic. Thus, for Rsv1-genotype soybean, SMV-N is avirulent whereas SMV-G7 and SMV-G7d are both virulent. Exploiting these differential interactions, we recently mapped the elicitor functions of SMV provoking Rsv1-mediated ER and LSHR to the N-terminal 271 amino acids of P3 from SMV-N and SMV-G7, respectively. The phenotype of both SMV-G7 and SMV-G7d were rendered avirulent on Rsv1-genotype soybean when the part of the genome encoding the N-terminus or the entire P3 cistron was replaced with that from SMV-N; however, reciprocal exchanges did not confer virulence to SMV-N-derived P3 chimeras. Here, we describe virulent SMV-N-derived P3 chimeras containing the full-length or the N-terminal P3 from SMV-G7 or SMV-G7d, with or without additional mutations in P3, that were selected on Rsv1-genotype soybean by sequential transfers on rsv1 and Rsv1-genotype soybean. Sequence analyses of the P3 and helper-component proteinase (HC-Pro) cistrons of progeny recovered from Rsv1-genotype soybean consistently revealed the presence of mutations in HC-Pro. Interestingly, the precise mutations in HC-Pro required for the adaptation varied among the chimeras. No mutation was detected in the HC-Pro of progeny passaged continuously in rsv1-genotype soybean, suggesting that selection is a consequence of pressure imposed by Rsv1. Mutations in HC-Pro alone failed to confer virulence to SMV-N; however, reconstruction of mutations in HC-Pro of the SMV-N-derived P3 chimeras resulted in virulence. Taken together, the data suggest that HC-Pro complementation of P3 is essential for SMV virulence on Rsv1-genotype soybean.

An outbreak of perirenal oedema syndrome in cattle associated with ingestion of pigweed (Amaranthus hybridus L.).

Forty seven of 150, 15-month-old long weaners died of an acute renal disease syndrome following introduction into an old maize field with a heavy stand of Amaranthus spp. The clinical syndrome was characterised by sudden onset neurological disease with ataxia and recumbency. Subcutaneous oedema, ascites and perirenal oedema with urine odour were the major gross necropsy findings. Renal histopathology revealed marked coagulative renal tubular necrosis of the proximal and distal straight tubules with intertubular haemorrhage. Acute renal failure and perirenal oedema has been described in cattle, pigs, horses and sheep associated with the ingestion of A. hybridus L. and A. retroflexus L. This perirenal oedema syndrome has been widely reported in the Americas, while in South Africa intoxication with the amaranths has only previously been associated with nitrate and possibly oxalate poisoning in cattle.

Strain-specific P3 of Soybean mosaic virus elicits Rsv1-mediated extreme resistance, but absence of P3 elicitor function alone is insufficient for virulence on Rsv1-genotype soybean.

When challenged by mechanical inoculation, the Rsv1 gene of soybean invokes extreme resistance (ER) against Soybean mosaic virus (SMV) strain N, but not SMV-G7 and its experimentally evolved variant, SMV-G7d. SMV-G7 provokes a lethal systemic hypersensitive response (LSHR), whereas SMV-G7d induces systemic mosaic. Thus, for Rsv1-genotype soybean, SMV-G7 and SMV-G7d are both virulent virus strains. The elicitor function of SMV-G7 provoking Rsv1-mediated LSHR was recently mapped to P3, and the influence of amino acids 823, 953, and 1112 of the precursor polypeptide of SMV-G7d on evasion of Rsv1-mediated recognition provoking LSHR was demonstrated. We have now extended this study to SMV-N. Initially, amino acids corresponding to those of SMV-G7d at these positions were substituted, individually or in combinations. All the mutants remained replication competent on rsv1-genotype soybean; however, none lost the elicitor function provoking Rsv1-mediated ER. Subsequently, P3 of SMV-N was precisely replaced with P3 of SMV-G7 or SMV-G7d and vice versa. All the chimeras were replication competent on rsv1-genotype soybean, but surprisingly SMV-N/G7P3 and SMV-N/G7dP3 failed to gain virulence on Rsv1-genotype soybeans. However, SMV-G7/NP3 and SMV-G7d/NP3 lost virulence, and this loss of virulence function was mapped to the N-terminus domain of SMV-N P3. The data indicate that SMV strain-specific P3 provokes Rsv1-mediated ER; however, virulence on Rsv1-genotype soybean is not solely a consequence of the absence of the P3 elicitor functions provoking Rsv1-mediated ER and LSHR.

Loss and gain of elicitor function of soybean mosaic virus G7 provoking Rsv1-mediated lethal systemic hypersensitive response maps to P3.

Rsv1, a single dominant resistance gene in soybean PI 96983 (Rsv1), confers extreme resistance against all known American strains of Soybean mosaic virus (SMV), except G7 and G7d. SMV-G7 provokes a lethal systemic hypersensitive response (LSHR), whereas SMV-G7d, an experimentally evolved variant of SMV-G7, induces systemic mosaic. To identify the elicitor of Rsv1-mediated LSHR, chimeras were constructed by exchanging fragments between the molecularly cloned SMV-G7 (pSMV-G7) and SMV-G7d (pSMV-G7d), and their elicitor functions were assessed on PI 96983 (Rsv1). pSMV-G7-derived chimeras containing only P3 of SMV-G7d lost the elicitor function, while the reciprocal chimera of pSMV-G7d gained the function. The P3 regions of the two viruses differ by six nucleotides, of which two are translationally silent. The four amino acid differences are located at positions 823, 915, 953, and 1112 of the precursor polypeptide. Analyses of the site-directed point mutants of both the viruses revealed that nucleotide substitutions leading to translationally silent mutations as well as reciprocal amino acid substitution at position 915 did not influence the loss or gain of the elicitor function. pSMV-G7-derived mutants with amino acid substitutions at any of the other three positions lost the ability to provoke LSHR but induced SHR instead. Two concomitant amino acid substitutions at positions 823 (V to M) and 953 (K to E) abolished pSMV-G7 elicitor function, provoking Rsv1-mediated SHR. Conversely, pSMV-G7d gained the elicitor function of Rsv1-mediated LSHR by a single amino acid substitution at position 823 (M to V), and mutants with amino acid substitutions at position 953 or 1112 induced SHR instead of mosaic. Taken together, the data suggest that strain-specific P3 of SMV is the elicitor of Rsv1-mediated LSHR.

Evolution of Soybean mosaic virus-G7 molecularly cloned genome in Rsv1-genotype soybean results in emergence of a mutant capable of evading Rsv1-mediated recognition.

Plant resistance (R) genes direct recognition of pathogens harboring matching avirluent signals leading to activation of defense responses. It has long been hypothesized that under selection pressure the infidelity of RNA virus replication together with large population size and short generation times results in emergence of mutants capable of evading R-mediated recognition. In this study, the Rsv1/Soybean mosaic virus (SMV) pathosystem was used to investigate this hypothesis. In soybean line PI 96983 (Rsv1), the progeny of molecularly cloned SMV strain G7 (pSMV-G7) provokes a lethal systemic hypersensitive response (LSHR) with up regulation of a defense-associated gene transcript (PR-1). Serial passages of a large population of the progeny in PI 96983 resulted in emergence of a mutant population (vSMV-G7d), incapable of provoking either Rsv1-mediated LSHR or PR-1 protein gene transcript up regulation. An infectious clone of the mutant (pSMV-G7d) was synthesized whose sequences were very similar but not identical to the vSMV-G7d population; however, it displayed a similar phenotype. The genome of pSMV-G7d differs from parental pSMV-G7 by 17 substitutions, of which 10 are translationally silent. The seven amino acid substitutions in deduced sequences of pSMV-G7d differ from that of pSMV-G7 by one each in P1 proteinase, helper component-proteinase, and coat protein, respectively, and by four in P3. To the best of our knowledge, this is the first demonstration in which experimental evolution of a molecularly cloned plant RNA virus resulted in emergence of a mutant capable of evading an R-mediated recognition.

Temporal and Spatial Spread of Soybean mosaic virus (SMV) in Soybeans Transformed with the Coat Protein Gene of SMV.

ABSTRACT Soybean lines transformed with the coat protein (CP) gene of Soybean mosaic virus (SMV) were evaluated for SMV resistance by quantifying the temporal and spatial spread of SMV strain AL-5 released from a point source in the field. The temporal spread of SMV within field plots during 1999 and 2000 was quantified by enzyme-linked immunosorbent assay. The Gompertz model most appropriately described temporal spread. Two SMV CP transformed lines (genotypes) had significantly lower infection rates and significantly lower final SMV incidence values (P

Rsv1-mediated resistance against soybean mosaic virus-N is hypersensitive response-independent at inoculation site, but has the potential to initiate a hypersensitive response-like mechanism.

Rsv1, a single dominant gene in soybean PI 96983, confers resistance to most strains of Soybean mosaic virus (SMV), including strain G2. The phenotypic response includes the lack of symptoms and virus recovery from mechanically inoculated leaves. To study the resistance mechanism, SMV-N (an isolate of strain G2) was introduced into PI 96983 by grafting. Hypersensitive response (HR)-like lesions occurred on the stems, petioles, and leaf veins, and virus was recovered from these lesions. The response demonstrated the cytological and histological characteristics of HR as well as elevated transcription of a soybean salicylic acid-inducible, pathogenesis-related (PR-1) protein gene. Mechanical inoculation of PI 96983 primary leaves with a high level of SMV-N virions caused no symptoms or up regulation of the PR-1 protein gene transcript. Furthermore, inoculation with infectious viral RNA did not alter the resistance phenotype. The data suggest that interaction of SMV-N with Rsv1 has the potential to induce an HR-like defense reaction. Rsv1-mediated resistance in the inoculated leaf, however, is HR-independent and operates after virion disassembly.

First Report of Transmission of Soybean mosaic virus and Alfalfa mosaic virus by Aphis glycines in the New World.

The recent discovery of the soybean aphid, Aphis glycines Matsamura, in the North Central region of the United States is significant because it is the first time that a soybean-colonizing aphid has been detected in the New World. Although the aphid has the potential to cause physiological loss of up to 52% on soybeans (4), it can also transmit Soybean mosaic virus (SMV). Transmission of Alfalfa mosaic virus (AMV) has not been reported. SMV, and less commonly AMV, are found in soybeans in the North Central states and are transmitted by numerous aphids in a nonpersistent manner (2; Grau, unpublished). For SMV, potential exists for specificity of transmission between virus strain and aphid species (3). For these reasons, it was important to determine if an endemic isolate of these viruses could be transmitted by this introduced species of aphid in the North Central region. Transmission experiments were conducted as described (3), using 3, 5, and 10 aphids per plant. Ten plants of the soybean cultivar Williams 82 were used for each treatment. To preclude confounding results by possible seed transmission, plants used in all tests were grown from seeds harvested from virus-indexed plants grown in the greenhouse. For experiments involving SMV, the aphid-transmissible field isolate Al5 (GeneBank Accession no. AF242844) and, as a negative control, the non-aphid transmissible isolate N (GeneBank Accession no. D500507) were used. For experiments involving AMV, a field isolate of AMV, confirmed by ELISA and host range, was used. The aphid species Myzus persicae was maintained on broad bean and A. glycines was maintained on virus-free soybean. The protocol for transmission studies of AMV was identical to that used in the SMV study, except only A. glycines was tested. For experiments, plants were periodically observed for symptom development and tested by ELISA 4 to 5 weeks after inoculation access. No transmission of SMV-N occurred in any tests, which together involved 180 aphids each of M. persicae or A. glycines. For the Al5 isolate, transmission efficiencies of 30, 50, and 50% were obtained with 3, 5, and 10 individuals, respectively, of M. persicae per plant. Efficiencies for A. glycines were 30, 40, and 40%. Transmission levels by the two aphid species did not differ significantly (t-test, P = 0.01). For AMV, corresponding transmission efficiencies were 0, 0, and 20%. The data suggest that the introduced A. glycines can be an efficient vector of SMV, but a less efficient vector of AMV, in the North Central region. Transmission of AMV by M. persicae has been documented (1) but was not examined in this study. Transmission of SMV and AMV by A. glycines is of concern because it may increase SMV and AMV incidence. With the recent outbreak of Bean pod mottle virus (BPMV) in the region, the potential for synergism of SMV and BPMV is increased (2). References: (1) M. B. Castillo and G. G. Orlob. Phytopathology 56:1028, 1966. (2) G. L. Hartman et al., eds. 1999. Compendium of Soybean Diseases, 4th Ed. American Phytopathological Society, St. Paul, MN. (3) B. S. Lucas and J. H. Hill. Phytopathol. Z. 99:47, 1980. (4) C. L. Wang et al. Plant Prot. 20:12, 1994.

Intragenic suppression of an active site mutation in the human apurinic/apyrimidinic endonuclease.

The apurinic/apyrimidinic endonucleases (APE) contain several highly conserved sequence motifs. The glutamic acid residue in a consensus motif, LQE96TK98 in human APE (hAPE-1), is crucial because of its role in coordinating Mg2+, an essential cofactor. Random mutagenesis of the inactive E96A mutant cDNA, followed by phenotypic screening in Escherichia coli, led to isolation of an intragenic suppressor with a second site mutation, K98R. Although the Km of the suppressor mutant was about sixfold higher than that of the wild-type enzyme, their kcat values were similar for AP endonuclease activity. These results suggest that the E96A mutation affects only the DNA-binding step, but not the catalytic step of the enzyme. The 3' DNA phosphoesterase activities of the wild-type and the suppressor mutant were also comparable. No global change of the protein conformation is induced by the single or double mutations, but a local perturbation in the structural environment of tryptophan residues may be induced by the K98R mutation. The wild-type and suppressor mutant proteins have similar Mg2+ requirement for activity. These results suggest a minor perturbation in conformation of the suppressor mutant enabling an unidentified Asp or Glu residue to substitute for Glu96 in positioning Mg2+ during catalysis. The possibility that Asp70 is such a residue, based on its observed proximity to the metal-binding site in the wild-type protein, was excluded by site-specific mutation studies. It thus appears that another acidic residue coordinates with Mg2+ in the mutant protein. These results suggest a rather flexible conformation of the region surrounding the metal binding site in hAPE-1 which is not obvious from the X-ray crystallographic structure.

Relationship Between Late-Season Severity of Stewart's Bacterial Wilt and Seed Infection in Maize.

The relationship between the amount of foliar disease on maize plants and seed contamination by the causal bacterium, Pantoea stewartii, was studied by comparing disease severity on adult plants with results from laboratory seed tests. Seventy-seven naturally infected maize lines (25 in 1990 and 52 in 1992) were selected and assigned to one of six disease severity classes based on the percentage of ear leaf tissue killed by Stewart's wilt: trace to 2%, 6 to 14%, 25 to 34%, 35 to 49%, 50 to 74%, and 75 to 100%. Ears were harvested from 10 to 20 plants representative of the disease class for each maize line, and seeds were tested by enzyme-linked immunosorbent assay (ELISA) of bulk-seed samples. Seed infection percentages were estimated from the bulk-test results by using statistical equations for group testing. The accuracy of the bulk-seed method for estimating seed infection was validated by comparison with 300-kernel single-seed tests. Infected seed was detected only from seed of plants with ≥25% disease severity; however, 45 of 63 such seed lots had no infection. Three seed lots had >5% infected seeds, all from plants with >50% disease severity. The results suggest a possible threshold level between 15 and 25% disease severity for Stewart's wilt on leaves before bacteria are detected in seed. This study describes a relatively simple method for estimating the incidence of infected seeds in a seed lot and contributes additional evidence to indicate that the chance of spreading P. stewartii from U.S.-produced maize seeds is low.

Characterization of a monoclonal antibody recognizing a DAG-containing epitope conserved in aphid transmissible potyviruses: evidence that the DAG motif is in a defined conformation.

Two viral proteins, the helper component-protease and the coat protein, are required for the non-persistent aphid transmission of potyviruses. In the potyvirus coat protein, the tripeptide aspartate-alanine-glycine (DAG) has often been shown to be involved. A monoclonal antibody, raised against a synthetic decapeptide containing the DAG tripeptide, reacted with the peptide as well as with isolates of soybean mosaic, tobacco etch and tobacco vein mottling potyviruses. Experiments indicate that the monoclonal antibody recognizes a conformational rather than a sequential epitope. The data support the suggestion that the DAG region plays a structural role to determine a coat protein-helper component-protease conformation that influences aphid transmission.

Seed Transmission of Pantoea stewartii in Field and Sweet Corn.

Seed transmission of Pantoea stewartii was evaluated by assays of more than 76,000 plants in greenhouse and field grow-out trials. Fourteen P. stewartii-infected seed lots were obtained from two dent corn inbreds and two sweet corn cultivars that were inoculated with either a rifampicin and nalidixic acid-resistant strain (rif-9A) or a wild-type strain (SS104) of P. stewartii. Four additional seed lots were collected from naturally infected inbreds. Percentages of infected kernels ranged from 0.8 to 72%, as determined by agar plating or by individual-kernel enzyme-linked immunosorbent assay (ELISA). Plants grown from this seed were assayed by a stem-printing technique that consisted of cutting and pressing a cross-section of each stem onto agar media. Prints were examined for development of P. stewartii colonies after 24 and 48 h. The transmission rate from seed produced on the inoculated plants was 0.066% (28 of 42,206 plants), based on all seedlings assayed. Transmission was estimated to be 0.14% from infected kernels. The transmission rate from seed produced on naturally infected plants was 0.0029% (1 of 34,924 plants), based on all seedlings, and 0.022% from infected kernels. Seed transmission occurred significantly less often (P = 0.034) from seed produced on naturally infected plants than from seed produced on inoculated plants, probably due to greater kernel damage caused by ear shank inoculation. The rarity of seed transmission of P. stewartii from heavily infected seed lots that would ordinarily be rejected due to poor germination suggests that the likelihood of seed transmission from good quality commercial seed corn is virtually nonexistent.

Quantification of within-field spread of soybean mosaic virus in soybean using strain-specific monoclonal antibodies.

ABSTRACT Strain-specific monoclonal antibodies were used to follow the temporal increase and spatial spread of soybean mosaic virus (SMV) strain G-5 released from a point source. The use of strain-specific monoclonal antibodies allowed discrimination of within-field temporal and spatial spread of SMV strain G-5 from non-G-5 SMV isolates that originated from exogenous field sources. SMV isolates originating from exogenous sources have potential to alter the temporal and spatial pattern of within-field virus spread, which could potentially affect the choice of models used to quantify within-field pathogen spread. Analysis of SMV epidemics in field-plot experiments indicated that the logistic model was the most appropriate model to describe and compare the temporal spread of SMV among years. On the basis of ordinary runs analyses, within-field spread of SMV strain G-5 was random in 1991 and 1994, but was mostly aggregated in 1992 and 1993. Non-G-5 SMV isolates arising from exogenous sources displayed a random spatial pattern over time. This is the first study in which pathogen incidence (detection of SMV using strain-specific monoclonal antibodies) as opposed to disease incidence (based on symptoms) was employed to monitor and model SMV spread in time and space.

Survey of newborn security in British Columbia hospitals. Review Committee on Newborn Security. Provincial Ministry of Health.

The abduction of a newborn from Kelowna General Hospital, Kelowna, BC, in September 1996 resulted in the formation of a newborn security review team by the province's Ministry of Health and the British Columbia Health Association. Part of the duties of the review team was the surveying of 87 hospitals in British Columbia that provide maternity services on current security protocols in each facility. Results of the survey are presented in this article, along with the subsequent recommendations of the review committee.

CO2 enrichment influences yields of 'Florunner,' 'Georgia Red' and 'New Mexico' peanut cultivars.

Three peanut cultivars, 'Florunner,' 'Georgia Red,' and 'New Mexico,' were grown in reach-in chambers to determine response to CO2 enrichment. CO2 treatments were ambient (400 micromol mol-1) and 700 micromol mol-1. Growth chamber conditions included 700 micromol m-2 s-1 photosynthetic photon flux (PPF), 28/22C, 7O% RH, and 12/12 h photoperiod. Growth media consisted of a 1:1 mixture (v/v) of vermiculite and sterilized sand. Six 10 L pots of each cultivar were fertilized three times per week with 250 mL of nutrient solution containing additional Ca (10 mM) and NO3 (25 mM) and watered well. Beginning 21 days after planting (DAP) and every three weeks thereafter up to 84 days, the second leaf from the growing axis (main stem) was detached to determine CO2 effect on leaf area, specific leaf area (SLA) and dry weight. Plants were harvested 97 DAP, at which time total leaf area, leaf number, plant and root weights and pod production data were taken. Numbers of pods per plant, pod fresh and dry weights, fibrous root and plant dry weights were higher for all cultivars grown at 700 micromol mol-1 than at ambient CO2. Also, leaf area for all cultivars was larger with CO2 enrichment than at ambient. SLA tended to decline with time regardless of CO2 treatment. Percentage of total sound mature kernels (%TSMK) was similar for both treatments. Plants grown at 700 micromol mol-1 CO2 had slightly more immature pods and seeds at final harvest.