Identification of aesculin-hydrolyzing streptococci, lactococci, aerococci and enterococci from subclinical intramammary infections in dairy cows

Aesculin-hydrolyzing, catalase-negative, gram-positive cocci isolated from subclinical intramammary infections in dairy cows were identified to species level using growth characteristics and biochemical activity. The results indicated that the aesculin-hydrolyzing cocci associated with this type of infection are a very heterogenic group. S. uberis strains, including inulin- or beta-glucuronidase-negative isolates, accounted for only about one-third of the collection, and Enterococcus faecalis strains for one-fifth. Other species of some importance included (in descending order of isolation frequency) Aerococcus viridans, Streptococcus pluranimalium, Lactococcus garvieae, Streptococcus bovis and Streptococcus gallolyticus.     

Paraneoplastic thrombocytosis-induced systemic thromboembolism in a cat

A six-year-old cat presented with clinical signs consistent with distal aortic thromboembolism while clinical signs of cardiovascular disease were absent. Diagnostics, including thoracic radiographs, electrocardiography, and echocardiography revealed no cardiovascular anomalies. Thoracic radiographs revealed multifocal pulmonary lesions consistent with neoplasia. Complete blood cell count demonstrated a marked thrombocytosis, leukopenia, and neutropenia. Histopathology of the pulmonary lesions confirmed multiple bronchoalveolar carcinomas. Myelodysplasia with megakaryocytic hyperplasia and ineffective myelopoiesis was noted on bone-marrow histopathology from multiple sites. The absence of other causes suggested a paraneoplastic thrombocytosis. The diagnosis of paraneoplastic thrombocytosis-induced thromboembolism was made due to the lack of underlying cardiac disease and the presence of a marked thrombocytosis. The presence of thrombocytosis and thromboembolism associated with neoplasia is discussed.     

Studies on the transmission of Theileria annulata to cattle by the tick Hyalomma lusitanicum

The role of the ixodid tick Hyalomma lusitanicum Koch 1844 as a vector of Mediterranean or tropical theileriosis (caused by the protozoan parasite Theileria annulata Dschunkowsky et Luhs 1904) in southern Spain was studied. Hyalomma lusitanicum was the most common tick, and the only species of the genus Hyalomma L., found on T. annulata-infected cattle from the theileriosis enzootic area studied (province of Cádiz, southern Spain). Likewise, we found that all sera of the cattle previously considered as suspected of theileriosis by clinical signs, tested for T. annulata antibodies, were positive and all blood samples of these suspected cattle examined had infected erythrocytes. Partially fed H. lusitanicum adults were collected in the field on T. annulata-infected cattle in this enzootic area and fed on an uninfected calf in an experimental farm free of theileriosis and ticks. At approximately 3 weeks post-tick feeding on the calf, this became positive for T. annulata antibodies and T. annulata merozoites were found in erythrocytes from blood smears. These results show the ability of H. lusitanicum to transmit the protozoan parasite T. annulata to susceptible cattle and indicate that H. lusitanicum is probably an important vector of T. annulata in the enzootic area surveyed.     

Aggregation of sow lactobacilli with diarrhoeagenic Escherichia coli

A total of 20 strains of lactobacilli were isolated from the oesophagus and vagina of 20 sows at the time of partus. Aggregation activity was seen between six homofermentative autoaggregative lactobacilli and three strains of pathogenic Escherichia coli with F4, F5 and F6 fimbriae. The highest aggregation activity was observed between vaginal Lactobacillus acidophilus PV 32 or oesophageal OE 2/1 and E. coli with F4 (K88). The presence of aggregation-promoting factor (APF) was confirmed by polymerase chain reaction (PCR) with primers of a specific fragment the apf gene derived from human L. gasseri 4B2 in one oesophageal L. acidophilus strain OE 2/1. We propose that autoaggregative lactobacilli that aggregate with diarrhoeagenic E. coli can express a class of APF proteins that exhibit the function of an aggregation mediator.     

Histological Aspects of a Hypersensitive Response in Poplar to Melampsora larici-populina

ABSTRACT The course of the infection and development of the biotrophic fungus Melampsora larici-populina on leaf tissue from the hybrid poplar Populus deltoides x P. nigra 'Ogy' was monitored at the histological level. Leaf disks were inoculated with one of two rust physiological races (E1 and E2), resulting in interactions that were either incompatible (race E1) or compatible (race E2). In the compatible interaction, the fungus rapidly colonized the leaf without inducing any apparent host response. Symptoms appeared on the leaf several days after inoculation just prior to spore dissemination. The incompatible interaction was characterized by the early collapse and disorganization of cytoplasm of infected cells 17 h after inoculation and within 2 h after the appearance of the first haustoria. Resistance to M. larici-populina was mediated through a hypersensitive response, since it was extremely localized and involved only the few cells that were in the immediate vicinity of each infected cell.     

Recessive Genes for Resistance to Puccinia striiformis f. sp. hordei in Barley

ABSTRACT Barley genotypes Abyssinian 14, BBA 2890, Grannelose Zweizeilige, PI 548708, PI 548734, PI 548747, and Stauffers Obersulzer are resistant to all races of Puccinia striiformis f. sp. hordei identified thus far in North America. Astrix, BBA 809, Bigo, Cambrinus, Emir, Heils Franken, Hiproly, I5, Mazurka, Trumpf, and Varunda have specific resistance to certain races, whereas Topper and Steptoe are susceptible to all races. Seedlings of parents and F(1), F(2), and F(3) progeny from crosses of resistant genotypes with Topper and Steptoe were tested for resistance to North American P. striiformis f. sp. hordei races PSH-1, PSH-4, PSH-10, PSH-13, and PSH-20. When tested with PSH-1, one recessive gene was detected in BBA 809, BBA 2890, Bigo, Hiproly, and Grannelose Zweizeilige; two recessive genes were detected in Emir, I5, PI 548708, PI 548734, PI 548747, Varunda, and Astrix; and one dominant gene and one recessive gene were detected in Abyssinian 14 and Stauffers Obersulzer. In tests with PSH-4, one recessive gene was detected in BBA 809, two recessive genes were detected in Trumpf, and two partially recessive genes were detected in Astrix. In tests with PSH-13, one recessive gene was detected in BBA 2890, Grannelose Zweizeilige, I5, and PI 548708 and two recessive genes were detected in Abyssinian 14, Hiproly, PI 548734, and PI 548747. In tests with PSH-20, one recessive gene was detected in Bigo and a recessive gene and a dominant gene were detected in Heils Franken. A gene in Cambrinus for resistance to PSH-10 and a gene in Mazurka for resistance to PSH-20 were dominant on the basis of the response of the first seedling leaf but recessive on the basis of the response of the second leaf. Four different types of epistasis were detected. Information on the number of genes, mode of inheritance, and nonallelic gene interactions should be useful in understanding the host-pathogen interaction and in breeding barley for resistance to stripe rust.     

Identification, characterization, and relatedness of luteovirus isolates from forage legumes

ABSTRACT Virus isolates from forage legumes collected from eight different states were identified as luteoviruses closely related to soybean dwarf luteovirus dwarfing (SbDV-D) and yellowing (SbDV-Y) described in Japan. All isolates produced reddened leaf margins in subterranean clover and were transmitted in a persistent manner by Acrythosiphon pisum, but not by Aulacorthum solani. Specific monoclonal antibodies raised against SbDV-Y were differentially reactive with endemic isolates. Immunoblots probed with a SbDV-D polyclonal antiserum showed single 26-kDa coat protein bands, confirming close serological relatedness to SbDV. Analyses of genomic and subgenomic double-stranded RNAs and northern blot analyses confirmed genomic relatedness to SbDV. Based on our results, we conclude that the U.S. luteovirus isolates studied comprise a strain or strains of the soybean dwarf virus that have clovers as common hosts and the pea aphid as a common vector.     

Soybean Brown Stem Rot, Phytophthora sojae, and Heterodera glycines Affected by Soil Texture and Tillage Relations

ABSTRACT Investigations were conducted to determine whether the effects of tillage practices on the prevalence of brown stem rot of soybean (caused by Phialophora gregata), Heterodera glycines, and Phytophthora sojae were confounded by soil texture in samples collected in the fall of 1995 and 1996. Soil and soybean stem samples, along with tillage information, were collected from 1,462 randomly selected fields in Illinois, Iowa, Minnesota, Missouri, and Ohio in collaboration with the National Agricultural Statistics Service. The incidence of brown stem rot was determined from 20 soybean stem pieces collected from each field in a zigzag pattern. The detection frequency of P. sojae (expressed as percent leaf disks colonized) and population densities of H. glycines were determined from soil cores also collected in a zigzag pattern. The soil samples were grouped into various textural classes, and the effect of soil texture and tillage relations on the activities of each pathogen were determined. Both tillage and soil texture affected the incidence of brown stem rot; however, there was no interaction between tillage and soil texture. Conservation tillage had a greater (P < 0.05) incidence of brown stem rot in clay loam and silty clay loam than did conventional tillage. The detection frequency of P. sojae was not affected by tillage, but a tillage x texture interaction (P = 0.013) indicated that the effect of tillage depended on soil texture. There was a greater (P < 0.05) detection frequency of P. sojae in conservation tillage than in conventional tillage in silt loam and loam soils. However, in sandy loam, the detection frequency of P. sojae was greater (P = 0.0099) in conventional tillage than in conservation tillage. Population densities of H. glycines were significantly affected by both tillage and soil texture, but overall, there was no tillage x texture interaction. There was an inverse relationship between population densities of H. glycines and percent clay (r = -0.81, P = 0.01) in no-till fields, but little or no change in nematode densities was observed with increasing clay content in tilled fields. Population densities of H. glycines were less (P < 0.05) in no-till fields than in tilled fields in silty clay loam and clay soils. There was no difference in H. glycines densities between the tillage categories in soils sandier than silty clay loam or clay. The findings emphasize the need for cautious interpretation of the effects of tillage practices on diseases and pathogens in the absence of information on soil texture.     

trans-Dominant Inhibition of Geminiviral DNA Replication by Bean Golden Mosaic Geminivirus rep Gene Mutants

ABSTRACT Geminiviruses are a group of single-stranded DNA viruses that cause major losses on a number of important crops throughout the world. Bean golden mosaic virus (BGMV) is a typical bipartite, whitefly-transmitted geminivirus that causes a severe disease on beans (Phaseolus vulgaris) in the Western Hemisphere. The lack of natural resistance to geminiviruses has led to attempts to engineer resistance, particularly through the use of pathogen-derived resistance strategies. The rep gene contains several conserved domains including nucleoside triphosphate (NTP)-binding and DNA-nicking domains and is the only geminiviral gene necessary for replication. Previous analysis by our group and others has demonstrated that the NTP-binding and DNA-nicking domains are necessary for geminiviral DNA replication. The ability of the rep gene and rep gene mutants to interfere with geminiviral DNA replication, when expressed in trans, was examined using a transient assay in a tobacco suspension cell culture system. Wild-type (wt) and mutant rep genes were cloned into plasmids under the control of the cauliflower mosaic virus 35S promoter for in planta expression and coinoculated into tobacco cells with infectious clones of various geminiviruses. The wt rep gene from BGMV-GA was able to support replication of BGMV-GA DNA-B. Several different rep gene mutants, with function-abolishing mutations in the NTP-binding or DNA-nicking domains, were potent trans-dominant inhibitors of geminiviral DNA replication.