Termites mitigate the effects of drought in tropical rainforest

Termites perform key ecological functions in tropical ecosystems, are strongly affected by variation in rainfall, and respond negatively to habitat disturbance. However, it is not known how the projected increase in frequency and severity of droughts in tropical rainforests will alter termite communities and the maintenance of ecosystem processes. Using a large-scale termite suppression experiment, we found that termite activity and abundance increased during drought in a Bornean forest. This increase resulted in accelerated litter decomposition, elevated soil moisture, greater soil nutrient heterogeneity, and higher seedling survival rates during the extreme El Niño drought of 2015–2016. Our work shows how an invertebrate group enhances ecosystem resistance to drought, providing evidence that the dual stressors of climate change and anthropogenic shifts in biotic communities will have various negative consequences for the maintenance of rainforest ecosystems.

Sources of Klebsiella and Raoultella species on dairy farms: be careful where you walk

Klebsiella spp. are a common cause of mastitis, milk loss, and culling on dairy farms. Control of Klebsiella mastitis is largely based on prevention of exposure of the udder to the pathogen. To identify critical control points for mastitis prevention, potential Klebsiella sources and transmission cycles in the farm environment were investigated, including oro-fecal transmission, transmission via the indoor environment, and transmission via the outdoor environment. A total of 305 samples was collected from 3 dairy farms in upstate New York in the summer of 2007, and included soil, feed crops, feed, water, rumen content, feces, bedding, and manure from alleyways and holding pens. Klebsiella spp. were detected in 100% of rumen samples, 89% of water samples, and approximately 64% of soil, feces, bedding, alleyway, and holding pen samples. Detection of Klebsiella spp. in feed crops and feed was less common. Genotypic identification of species using rpoB sequence data showed that Klebsiella pneumoniae was the most common species in rumen content, feces, and alleyways, whereas Klebsiella oxytoca, Klebsiella variicola, and Raoultella planticola were the most frequent species among isolates from soil and feed crops. Random amplified polymorphic DNA-based strain typing showed heterogeneity of Klebsiella spp. in rumen content and feces, with a median of 4 strains per 5 isolates. Observational and bacteriological data support the existence of an oro-fecal transmission cycle, which is primarily maintained through direct contact with fecal contamination or through ingestion of contaminated drinking water. Fecal shedding of Klebsiella spp. contributes to pathogen loads in the environment, including bedding, alleyways, and holding pens. Hygiene of alleyways and holding pens is an important component of Klebsiella control on dairy farms.

A New Member of the Clover Proliferation Phytoplasma Group (16SrVI) Associated with Elm Yellows in Illinois

A disease with symptoms similar to elm yellows (EY) was noticed in the early 1990s in suburban Chicago, IL. More than 1,000 mature American elms (Ulmus americana) have since died. Infected trees varied in the incidence and severity of canopy yellowing, leaf epinasty, butterscotch discoloration, and wintergreen odor of the phloem, but all developed a sparse and clumpy crown, uniformly necrotic phloem, and died within 2 years of showing canopy symptoms. Because symptoms were expressed irregularly and phytoplasma detection results by a commercial diagnostic company were inconsistent, a study was initiated to determine if EY phytoplasma was the causal agent. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) methods using universal or EY phytoplasma specific primers were employed to detect putative phytoplasma(s) associated with 10 trees of varied disease severity within the outbreak region and 10 asymptomatic trees from an uninfected area (controls). Nested PCR using universal primers revealed that 90% of trees from the outbreak region were positive for phytoplasma while asymptomatic elms from another location (controls) tested negative. Phytoplasma-positive trees ranged in disease severity from 1 (asymptomatic) to 5 (near death). Inner bark samples chiseled from the lower trunk had higher phytoplasma detection rates than foliage or drill shavings. RFLP analyses and DNA sequencing of 16S rDNA indicated that the phytoplasma recovered from dying elms in Arlington Heights is not related to the reference EY phytoplasma (group16SrV). It is most closely related to clover proliferation (CP) phy-toplasma (group 16SrVI), and we have designated it Illinois Elm Yellows (ILEY) phytoplasma, and assigned it to a new taxonomic subgroup (16SrVI-C). EY phytoplasma was not detected in any samples, but two ILEY phytoplasma positive trees also were positive for aster yellows (AY) phytoplasma. ILEY phytoplasma was not detected in local leafhopper populations trapped in elm trees between May and September 2000. This is the first report of a phytoplasma related to CP phytoplasma causing elm yellows disease symptoms.

Detection and Characterization of an Elm Yellows (16SrV) Group Phytoplasma Infecting Virginia Creeper Plants in Southern Florida

The polymerase chain reaction (PCR) employing phytoplasma-specific ribosomal RNA primer pair P1/P7 consistently amplified a product of expected size (1.8 kb) from 29 of 36 symptom-less Virginia creeper (Parthenocissus quinquefolia) plants growing in southern Florida. Restriction fragment length polymorphism analysis of P1/P7-primed PCR products indicated that most phytoplasmas detected in Virginia creeper were similar to phytoplasmas composing the elm yellows (16SrV) group. This relationship was verified by reamplification of P1/P7 products using an elm yellows (EY) group-specific rRNA primer pair fB1/rULWS1. rDNA products (1,571 bp) were generated by group-specific PCR from 28 phytoplasma-positive plants and 1 negatively testing plant identified by earlier P1/P7-primed PCR. Analysis of 16S rDNA sequences determined the Virginia creeper (VC) phytoplasma to be phylogenetically closest to the European alder yellows (ALY) agent, an established 16SrV-C subgroup strain. However, presence or absence of restriction sites for endonucleases AluI, BfaI, MspI, RsaI, and TaqI in the 16S rRNA and 16-23S rRNA intergenic spacer region of the VC phytoplasma collectively differentiated this strain from ALY and other 16SrV group phytoplasmas. Failure to detect the VC phytoplasma by PCR employing nonribosomal primer pair FD9f/FD9r suggests that this newly characterized agent varies from known European grapevine yellows (flavescence dorée) phyto-plasmas previously classified as 16SrV subgroup C or D strains.

Responses of Six Eurasian Ulmus Cultivars to a North American Elm Yellows Phytoplasma

Elms (genus Ulmus) of six clonal cultivars representing Eurasian species and hybrids were grafted when 2 to 3 years old with bark patches from U. rubra infected with an elm yellows phytoplasma or were left untreated as controls. The cultivars were U. glabra × minor 'Pioneer', U. minor × parvifolia 'Frontier', U. parvifolia 'Pathfinder', U. wilsoniana 'Prospector', and the complex hybrids 'Homestead' and 'Patriot'. Trees were evaluated for infection and symptoms 1 or 2 years after inoculation. Infection was detected via the 4',6-diamidino-2-phenylindol e·2HCl (DAPI) fluorescence test in 26 of 86 grafted trees representing five cultivars. Infection of selected trees was confirmed by polymerase chain reaction (PCR) amplification of a fragment of phytoplasmal rDNA, and the phytoplasma was identified by restriction fragment length polymorphism (RFLP) analysis of the amplified DNA using restriction enzymes AluI, RsaI, and TaqI. Elm yellows phytoplasma was also identified by nested PCR and RFLP analysis in two of seven inoculated, healthy-appearing, DAPI-negative trees and one noninoculated control tree. All RFLP profiles were identical to that of reference strain EY1. Phytoplasma-associated symptoms, observed in five cultivars, included suppressed growth, progressive size reduction of apical shoots and leaves, chlorosis, foliar reddening, witches'-brooms, and dieback. Phyto-plasma was not detected in cv. Homestead. Possible resistance of this cultivar to elm yellows phytoplasma was indicated by localized phloem necrosis in stems below inoculum patches.

Responses of 11 Fraxinus Cultivars to Ash Yellows Phytoplasma Strains of Differing Aggressiveness

Five cultivars of Fraxinus americana (white ash) and five of F. pennsylvanica (green ash) were graft-inoculated with three strains of ash yellows phytoplasmas at Ames, IA, and with thrsee other strains at Ithaca, NY. A sixth green ash cultivar was tested only in New York. Trees were allowed to grow in field plots for 3 years. Infection was detected via the DAPI (4', 6-diamidino-2-phenylindole 2HCl) fluorescence test. Incidence of witches'-brooms on infected trees was greater on white ash than green ash and varied significantly among phytoplasma strain treatments at both locations. Volume growth of infected ash, averaged across cultivars over 2 years in Iowa and 3 years in New York, was 49 and 59%, respectively, as great as that of noninfected trees. Foliar greenness was reduced significantly by infection at both locations, and this reduction was positively correlated with growth reduction. Cultivars at each location varied significantly in growth of noninfected trees and in growth of diseased trees relative to that of nonin-fected trees (a measure of phytoplasma tolerance), but cultivar means for these variables in Iowa were not significantly correlated with those in New York. Green ash cvs. Bergeson, Dakota Centennial, and Patmore and white ash cv. Autumn Applause were above average in tolerance at both locations. Phytoplasma strains at each location varied significantly in aggressiveness as indicated by host growth suppression.

Variation in Aggressiveness of Ash Yellows Phytoplasmas

Twelve strains of phytoplasmas belonging to the ash yellows (AshY) group, from across the known range of AshY and representing six host species, were assessed for differences in ability to suppress growth and cause chlorosis in graft-inoculated Fraxinus pennsylvanica (green ash) and Catharanthus roseus (periwinkle). In each of two experiments with ash and one with periwinkle, different strains caused significantly different degrees of growth suppression and loss of foliar greenness. These growth and color impacts were positively and significantly correlated among experiments and between ash and periwinkle, indicating strain variation in aggressiveness. After two strains that differed in aggressiveness were coinoculated to periwinkle plants, polymerase chain reaction/restriction fragment length polymorphism (PCR/RFLP) assays of DNA from leaves remote from the inoculation sites revealed the presence of the aggressive strain sooner and more frequently than that of the less aggressive strain. Thus, aggressiveness was associated with more rapid multiplication and/or movement than was achieved by the less aggressive strain. When either strain was inoculated 11 weeks before the other into the same plant, only the initial strain could be detected after a further 12 weeks of incubation. Thus, the initial strain or its effect on the host may have interfered with multiplication and/or long-distance movement of the second strain. A concept of preemptive dominance is proposed to account for detection by primary PCR of only single phytoplasma strains in plants that may harbor two or more strains.

Phytoplasmas Associated with Elm Yellows: Molecular Variability and Differentiation from Related Organisms

Restriction fragment length polymorphism (RFLP) analyses were performed on polymerase chain reaction (PCR) amplimers of phytoplasmal DNA from eight samples obtained from Ulmus spp. (elms) affected by elm yellows (EY) in Italy and the United States, from Catharanthus roseus infected with strain EY1, and from five other plant species infected with phytoplasmas of the EY group sensu lato (group 16SrV). RFLP profiles obtained with restriction enzyme TaqI from ribosomal DNA amplified with primer pair P1/P7 differentiated elm-associated phytoplasmas from strains originally detected in Apocynum cannabinum, Prunus spp., Rubus fruticosus, Vitis vinifera, and Ziziphus jujuba. RFLP profiles obtained similarly with BfaI differentiated strains from A. cannabinum and V. vinifera from other phytoplasmas of group 16SrV. Elm-associated strains from within the United States had two RFLP patterns in ribosomal DNA based on presence or absence of an RsaI site in the 16S-23S spacer. Elm-associated phytoplasma strains from Italy were distinguished from those of American origin by RFLPs obtained with MseI in the same fragment of non-ribosomal DNA. Strain HD1, which was discovered in A. cannabinum associated with EY-diseased elms in New York State, was unique among the strains studied.

The phytoplasma associated with ash yellows and lilac witches'-broom: 'Candidatus phytoplasma fraxini'

Phytoplasmas associated with the plant diseases ash yellows (AshY, occurring in Fraxinus) and lilac witches'-broom (LWB, occurring in Syringa) represent a putative species-level taxon. Phytoplasmal DNA from 19 ash or lilac sources across the known geographic range of AshY (71-113 degrees W) was examined to determine if AshY and LWB phytoplasmas are a coherent group, if variability exists in both conserved and anonymous DNA, and if variability in 16S rDNA is related to host or geographic origin. The 16S rRNA gene and the 16S-23S spacer were amplified using primer pair P1/P7 and analysed using 15 restriction enzymes. RFLPs were detected in digests obtained with Alul, Hhal or Taql, for a total of four RFLP profile types. Sequencing of the amplimers from strains AshY1T, AshY3, AshY5 and LWB3 (which represent the four 16S rDNA RFLP profile types) revealed only three positions in the 16S rRNA gene and one position in the 16S-23S spacer at which differences occurred; these were single nucleotide substitutions. Sequence homology between any two strains was > 99.8%. A portion of a ribosomal protein operon, amplified with primer pair rpF1/R1 from each of the four strains noted above, was analysed with six restriction enzymes, resulting in the detection of two RFLP profiles with Msel. Southern analysis, utilizing two non-specific probes from other phytoplasma groups, revealed three RFLP profile types in anonymous chromosomal DNA of strains representing the four 16S rDNA genotypes. Two strains, AshY3 and LWB3, had unique combinations of characters in the various assays. On the basis of RFLP profiles, the strains from the other plants sampled comprised two groups. The grouping was not clearly related to host or geographic origin. The genome size of strain AshY3 was estimated from PFGE data to be 645 kbp. Phylogenetic analysis of a 1423 bp 16S rDNA sequence from strains AshY1T, AshY3, AshY5 and LWB3, together with sequences from 14 other mollicutes archived in GenBank, produced a tree on which the AshY and LWB strains clustered as a discrete group, consistent with previous analyses utilizing only type strain AshY1T. Thus, the AshY phytoplasma group is coherent but heterogeneous. The name 'Candidatus Phytoplasma fraxini' is proposed for this group.

Comparisons of Tolerance of Ash Yellows Phytoplasmas in Fraxinus Species and Rootstock-Scion Combinations

Growth responses of different ash (Fraxinus) species and rootstock-scion combinations to ash yellows (AshY) phytoplasmas were compared in greenhouse experiments by expressing each measurement as a proportion of the final average value of the variable in noninoculated, own-rooted control trees. Phytoplasmal infection suppressed shoot growth of white ash (F. americana) and green ash (F. pennsylvanica) beginning when buds opened, but did not suppress velvet ash (F. velutina) until after 60 days of growth. AshY-associated growth losses in height, stem diameter, and root volume, averaged across two experiments, were 80, 93, and 98%, respectively, in white ash; 60, 57, and 79% in green ash; and 23, 0, and 12% in velvet ash. Growth in height, but not in stem diameter or root volume, of diseased white ash on velvet ash rootstock was significantly greater than growth of diseased own-rooted white ash. White ash witches'-brooms grafted onto healthy velvet ash continued to grow but did not produce vigorous, dominant shoots. Growth of diseased velvet ash on white ash roots was severely suppressed in comparison with that of diseased own-rooted velvet ash. Management of AshY through the use of tolerant genotypes may require tolerance in both scions and rootstocks.