170 research outputs found
Molecular biology and epidemiology of dianthoviruses.
The genus Dianthovirus is one of eight genera in the family Tombusviridae. All the genera have monopartite positive-stranded RNA genomes, except the dianthoviruses which have bipartite genomes. The dianthoviruses are distributed worldwide. Although they share common structural features with the other Tombusviridae viruses in their virions and the terminal structure of the genomic RNAs, the bipartite nature of the dianthovirus genome offers an ideal experimental system with which to study basic issues of virology. The two genomic RNAs seem to use distinct strategies to regulate their translation, transcription, genome replication, genome packaging, and cell-to-cell movement during infection. This review summarizes the current state of our knowledge of the dianthoviruses, with its main emphasis on the molecular biology of the virus, including the viral and host factors required for its infection of host plants. The epidemiology of the virus and the possible viral impacts on agriculture and the environment are also discussed
First identification of the pathogen causing tumor malformations in evergreen oaks in Spain
Candidatus Phytoplasma brasiliense associado ao superbrotamento do hibisco (Hibiscus rosa-sinensis L.) no Estado de SĂŁo Paulo
Survey of Leafhopper Species in Almond Orchards Infected with Almond Witches'-Broom Phytoplasma in Lebanon
Leafhoppers (Hemiptera: Auchenorrhyncha: Cicadellidae) account for more than 80% of all âAuchenorrhynchousâ vectors that transmit phytoplasmas. The leafhopper populations in two almond witches'-broom phytoplasma (AlmWB) infected sites: Tanboureet (south of Lebanon) and Bourj El Yahoudieh (north of Lebanon) were surveyed using yellow sticky traps. The survey revealed that the most abundant species was Asymmetrasca decedens, which represented 82.4% of all the leafhoppers sampled. Potential phytoplasma vectors in members of the subfamilies Aphrodinae, Deltocephalinae, and Megophthalminae were present in very low numbers including: Aphrodes makarovi, Cicadulina bipunctella, Euscelidius mundus, Fieberiella macchiae, Allygus theryi, Circulifer haematoceps, Neoaliturus transversalis, and Megophthalmus scabripennis. Allygus theryi (HorvĂĄth) (Deltocephalinae) was reported for the first time in Lebanon. Nested PCR analysis and sequencing showed that Asymmetrasca decedens, Empoasca decipiens, Fieberiella macchiae, Euscelidius mundus, Thamnottetix seclusis, Balclutha sp., Lylatina inexpectata, Allygus sp., and Annoplotettix danutae were nine potential carriers of AlmWB phytoplasma. Although the detection of phytoplasmas in an insect does not prove a definite vector relationship, the technique is useful in narrowing the search for potential vectors. The importance of this information for management of AlmWB is discussed
Molecular biology and pathogenicity of phytoplasmas
Phytoplasmas are a large group of plant-pathogenic wall-less, non-helical, bacteria
associated with diseases, collectively referred to as yellows diseases, in
more than a thousand plant species worldwide. Many of these diseases are of
great economic importance. Phytoplasmas are difficult to study, in particular
because all attempts at culturing these plant pathogens under axenic conditions
have failed. With the introduction of molecular methods into phytoplasmology
about two decades ago, the genetic diversity of phytoplasmas could
be elucidated and a system for their taxonomic classification based on phylogenetic
traits established. In addition, a wealth of information was generated
on phytoplasma ecology and genomics, phytoplasmaâplant host interactions
and phytoplasmaâinsect vector relationships. Taxonomically, phytoplasmas are
placed in the class Mollicutes, closely related to acholeplasmas, and are currently
classified within the provisional genus âCandidatus Phytoplasmaâ based
primarily on 16S rDNA sequence analysis. Phytoplasmas are characterised by
a small genome. The sizes vary considerably, ranging from 530 to 1350 kilobases
(kb), with overlapping values between the various taxonomic groups and
subgroups, resembling in this respect the culturable mollicutes. The smallest
chromosome, about 530 kb, is known to occur in the Bermuda grass white leaf
agent âCa. Phytoplasma cynodontisâ. This value represents the smallest mollicute
chromosome reported to date. In diseased plants, phytoplasmas reside
almost exclusively in the phloem sieve tube elements and are transmitted from
plant to plant by phloem-feeding homopteran insects, mainly leafhoppers and
planthoppers, and less frequently psyllids. Most of the phytoplasma host plants
are angiosperms in which a wide range of specific and non-specific symptoms
are induced. Phytoplasmas have a unique and complex life cycle that involves
colonisation of different environments, the plant phloem and various organs of
the insect vectors. Furthermore, many phytoplasmas have an extremely wide
plant host range. The dynamic architecture of phytoplasma genomes, due to the
occurrence of repetitive elements of various types, may account for variation in
their genome size and adaptation of phytoplasmas to the diverse environments
of their plant and insect hosts. The availability of five complete phytoplasma
genome sequences has made it possible to identify a considerable number of
genes that are likely to play major roles in phytoplasmaâhost interactions.
Among these, there are genes encoding surface membrane proteins and effector
proteins. Also, it has been shown that phytoplasmas dramatically alter their
gene expression upon switching between plant and insect hosts
The Cost of Male Aggression and Polygyny in California Sea Lions (Zalophus californianus)
In polygynous mating systems, males often increase their fecundity via aggressive defense of mates and/or resources necessary for successful mating. Here we show that both male and female reproductive behavior during the breeding season (JuneâAugust) affect female fecundity, a vital rate that is an important determinant of population growth rate and viability. By using 4 years of data on behavior and demography of California sea lions (Zalophus californianus), we found that male behavior and spatial dynamicsâaggression and territory sizeâare significantly related to female fecundity. Higher rates of male aggression and larger territory sizes were associated with lower estimates of female fecundity within the same year. Female aggression was significantly and positively related to fecundity both within the same year as the behavior was measured and in the following year. These results indicate that while male aggression and defense of territories may increase male fecundity, such interactions may cause a reduction in the overall population growth rate by lowering female fecundity. Females may attempt to offset male-related reductions in female fecundity by increasing their own aggressionâperhaps to defend pups from incidental injury or mortality. Thus in polygynous mating systems, male aggression may increase male fitness at the cost of female fitness and overall population viability
A New Tern (Sterna) Breeding Record for Hawaii
Recent observations of terns, either the Old World Little Tern
(Sterna albifrons) or the New World Least Tern (Sterna antillarum), at Pearl and
Hermes Reef in the Northwestern Hawaiian Islands have documented that one
of these species bred there in 1988 and possibly also in the several preceding
years. Two small Sterna terns were first observed at Pearl and Hermes in 1984,
and the numbers subsequently observed there gradually increased until five birds
were recorded in 1988. In 1988 a nest containing three eggs was found, and at
least one egg produced a nestling. No small Sterna terns were seen during a
2-week visit to the atoll in 1989 or a 2-day visit in 1990. No specimens were
collected, and photographs taken do not permit specific identification of the
birds. We favor S. albifrons sinensis because there are now specimen records of
Asiatic Little Terns from French Frigate Shoals and Midway Atoll and a sight
record from Laysan Island, and because a review of prevailing wind systems in
the Pacific and other vagrant bird records from the Northwestern Hawaiian
Islands suggest that such birds are more likely to arrive from the west than from
the east
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